Category: Instrumentation

Posted on by

Practical Guide to ABB EL3020 Gas Analyzer: Negative CO Readings and Zero/Span Calibration

1. Introduction

In industrial emission monitoring, combustion control, and process analysis, gas analyzers play a critical role in ensuring safety, efficiency, and compliance with environmental standards. The ABB EL3020 is a widely used multi-component gas analyzer based on infrared optical measurement principles. It is designed to continuously monitor gases such as CO, CO₂, NO, and SO₂ in various industrial applications.

However, during long-term operation, users may sometimes encounter abnormal readings, the most common of which is negative CO concentration values. Such readings do not imply the physical existence of “negative carbon monoxide,” but instead reflect calibration drift, background interference, or hardware-related issues.

This article provides a detailed explanation of the EL3020’s measurement principle, analyzes the possible causes of negative CO readings, and presents practical zero calibration and span calibration procedures. The aim is to help engineers and operators quickly identify the root cause, restore measurement accuracy, and ensure stable operation of the analyzer.

EL3120

2. Operating Principle of ABB EL3020

2.1 Infrared Absorption Principle

The EL3020 operates on the principle of non-dispersive infrared absorption (NDIR).

  • Each gas molecule has a unique absorption band in the infrared spectrum.
  • When an infrared beam passes through a sample gas containing CO, the CO molecules absorb energy at specific wavelengths.
  • The detector measures the reduction in light intensity, which is directly proportional to the gas concentration.
  • By comparing the reference and measurement channels, the analyzer calculates the gas concentration.

2.2 Zero and Span Definitions

  • Zero Point: The output signal when no target gas is present (pure zero gas condition). Ideally, the instrument should display 0 ppm.
  • Span Point: The output when a known concentration of calibration gas is introduced. Span calibration adjusts the slope factor to ensure linear accuracy.
CO shows a negative value

3. Causes of Negative CO Readings

3.1 Zero Drift

Over time, detector electronics and optical components may drift due to temperature variations and aging. If the zero point is not recalibrated, the baseline may shift below zero, producing negative values.

3.2 Background Interference

If the sampled gas contains almost no CO while the instrument’s baseline is incorrectly set too high, the computed result may fall below zero. Excess oxygen, water vapor, or other gases can also disturb the optical path.

3.3 Optical Contamination or Aging

Dust, condensation, or weakened infrared sources reduce the signal strength at the detector, leading to baseline shifts.

3.4 Hardware or Circuit Faults

Faults in the analog acquisition board, A/D converters, or signal amplifiers can also cause abnormal negative readings. If only the CO channel is affected while NO and O₂ are stable, the issue likely lies in the CO detection unit.

4. Zero Calibration Procedure

Zero calibration eliminates baseline drift and resets the analyzer output to zero under clean gas conditions.

4.1 Preparation

  1. Use high-purity nitrogen (99.999%) or certified zero air as the zero gas.
  2. Verify gas purity and set regulator output pressure to ~2 bar.
  3. Check sample lines for leakage or condensation.
  4. Power on the analyzer for at least 30 minutes to stabilize.

4.2 Step-by-Step Process

  1. On the panel, navigate: OK → Menu → Calibration → Zero Calibration.
  2. Select the CO channel.
  3. Switch the sample inlet to zero gas and flush for 3–5 minutes until stable.
  4. Execute Start Zero Calibration.
  5. After completion, the CO value should display close to 0 ppm (±2 ppm acceptable).

4.3 Evaluation

  • If “Zero OK” appears and the reading stabilizes, calibration is successful.
  • If negative values persist, further action such as span calibration or hardware inspection may be required.

5. Span Calibration Procedure

Span calibration corrects the proportionality factor (slope) to align measured values with certified standard gas concentrations.

5.1 Preparation

  1. Use certified CO span gas, preferably at 60–90% of the measurement range (e.g., 100 ppm CO in N₂).
  2. Check cylinder, pressure regulator, and tubing for leaks.
  3. Perform zero calibration before span calibration for best results.

5.2 Step-by-Step Process

  1. On the panel, navigate: OK → Menu → Calibration → Span Calibration.
  2. Select the CO channel.
  3. Switch the sample inlet to the standard gas and flush for 5–10 minutes until stable.
  4. Enter the certified gas concentration (e.g., 100 ppm).
  5. Execute Start Span Calibration.
  6. The analyzer adjusts the slope factor and confirms with Span OK.

5.3 Evaluation

  • If the analyzer output matches the certified value (within ±2%), span calibration is successful.
  • Large deviations indicate optical degradation or electronic faults that may require service intervention.

6. Maintenance and Troubleshooting Recommendations

  1. Regular Calibration
    • Perform zero calibration monthly and span calibration every 1–3 months.
  2. Optical Cleaning
    • Inspect and clean optical windows and gas cells regularly. Prevent dust and moisture accumulation.
  3. Sample Line Maintenance
    • Avoid condensation and leaks in tubing. Use filters and dryers where necessary.
  4. Validation with Reference Gas
    • Periodically validate with independent standard gas to ensure accuracy.
  5. Hardware Inspection
    • If calibration fails, check the infrared source, detectors, and analog boards. Replace if necessary.

7. Case Study: Negative CO Reading Restored by Calibration

In a steel plant, operators observed the EL3020 CO channel consistently showing -5 ppm.

  1. Zero calibration with nitrogen reduced the offset, but the value remained at -3 ppm.
  2. A span calibration using 100 ppm CO gas showed the analyzer reading 95 ppm.
  3. After span adjustment, the zero point stabilized near 0 ppm and span response matched 100 ppm.

The issue was traced to slope drift in the CO channel, which was successfully corrected through calibration without requiring hardware replacement.

8. Conclusion

The ABB EL3020 is a reliable and accurate gas analyzer for continuous industrial monitoring. Negative CO readings are typically not measurement of “negative concentration” but symptoms of baseline drift or span factor deviation. Proper and regular zero calibration and span calibration are essential to maintain measurement accuracy.

For persistent negative values that cannot be corrected through calibration, optical contamination, component aging, or hardware malfunction should be considered. Timely maintenance and service support are key to ensuring the long-term stability of the analyzer.

By following standardized calibration procedures and maintenance practices, operators can keep the EL3020 functioning accurately and extend its service life in demanding industrial environments.

Posted on by

Hach Amtax SC Ammonia Nitrogen Analyzer User Guide

I. Instrument Principle and Features

The Hach Amtax SC Ammonia Nitrogen Analyzer is an online analytical device specifically designed for continuous monitoring of ammonium ion concentration in water bodies. It is widely used in wastewater treatment plants, waterworks, surface water monitoring, and industrial process control. Its core measurement principle is the Gas Sensitive Electrode (GSE) method, where a selective electrode reacts with ammonium ions in the sample, and the concentration value is ultimately output in the form of NH₄–N on the controller (sc1000).

Key Technical Features:

  • Wide Measurement Range: Covers three intervals: 0.05–20 mg/L, 1–100 mg/L, and 10–1000 mg/L, allowing flexible application in both low-concentration surface water and high-concentration wastewater scenarios.
  • Fast Response: 90% response time of less than 5 minutes, suitable for real-time monitoring of dynamic water quality.
  • High Precision and Reproducibility: Measurement error is less than ±3% or ±0.05 mg/L (for low ranges), ensuring reliable data.
  • Automation Capabilities: Features automatic calibration, automatic cleaning, and diagnostic functions, significantly reducing manual intervention.
  • Robust Design: Enclosure with an IP55 protection rating and made of UV-resistant ASA/PC material, suitable for harsh outdoor environments.
  • Modular Expandability: Enables data transmission and remote monitoring through the sc1000 controller, supporting single-channel or dual-channel modes.
    Thus, the Amtax SC combines high precision, low maintenance, and strong adaptability, making it a mainstream choice in the field of ammonia nitrogen online monitoring.

II. Installation and Calibration

1. Mechanical Installation

  • Mounting Options: Supports wall mounting, rail mounting, or vertical installation, with wall mounting being the most common. Choose a sturdy, load-bearing wall and ensure smooth routing of surrounding pipes and cables.
  • Weight and Load Requirements: The instrument weighs approximately 31 kg, and the bracket must support a load of ≥160 kg.
  • Installation Environment: Avoid strong vibrations, strong magnetic fields, and direct sunlight. Maintain an ambient temperature range of –20 to 45°C.

2. Electrical Installation

  • Must be performed by qualified personnel to ensure proper grounding and the installation of a residual current device (30 mA RCD).
  • Power is supplied by the sc1000 controller, with voltages of 115V or 230V. The use of 24V controller models is prohibited.
  • All piping and reagent installations must be completed before powering on.

3. Reagent and Electrode Installation

  • Reagent Preparation: Select standard solutions and reagents according to the measurement range. For example, use 1 mg/L and 10 mg/L standard solutions for low ranges, and 50 mg/L and 500 mg/L for high ranges.
  • Electrode Installation: Fill with electrolyte (approximately 11 mL), ensuring no air bubbles remain, and correctly insert the electrode into the electrolysis cell. Replace the membrane cap and electrolyte every 2–3 months.
  • Humidity Sensor: Must be correctly wired to prevent alarms triggered by condensation or liquid leakage.

4. Calibration Procedure

  • Calibration modes include automatic calibration and manually triggered calibration.
  • Set the calibration interval (typically once per day or shorter), and the system will automatically switch standard solutions for electrode correction.
  • After calibration, the system records key parameters such as slope, zero point, and standard solution potential to ensure long-term stable operation.

III. Startup and Operation

1. Startup Steps

  • Ensure all installations (piping, electrical, reagents, electrodes) are complete.
  • Connect the analyzer to the sc1000 controller and power on.
  • Initialize the system: Register the Amtax SC and sampling probe in the controller, execute the “Prepump All” function to fill the piping.
  • Allow a warm-up time of approximately 1 hour for the instrument, reagents, and electrodes to reach operating temperature.
  • Enter the sensor setup menu to confirm the measurement range, output units (mg/L or ppm), and measurement interval.

2. Normal Operation

  • LED Indicators: Green indicates normal operation, orange indicates a warning, and red indicates an error.
  • Measurement Interval: Adjustable from 5 to 120 minutes, depending on application requirements.
  • Data Viewing: The sc1000 controller displays real-time values, historical trends, and alarm status, and can upload data to a monitoring system via a bus interface.
  • Cleaning Function: Set up timed automatic cleaning to ensure the photometer, piping, and electrodes remain clean.

IV. Troubleshooting and Maintenance

1. Routine Maintenance

  • Appearance Inspection: Regularly check for damage to pipes and cables, and confirm the absence of leaks or corrosion.
  • Fan Filter: Clean or replace every 6–12 months to ensure proper heat dissipation.
  • Reagents and Electrodes: Replace reagents every 2–3 months, electrode membrane caps and electrolyte every 2–3 months, and electrodes every 1–2 years, as recommended in Table 5.
  • Cleaning Cycle: Depends on water hardness; typically perform automatic cleaning every 1–8 hours.

2. Common Faults and Solutions

  • Low/High Temperature: If the internal temperature falls below 4°C or rises above 57°C, the system enters service mode. Check the heating or cooling fan.
  • Humidity Alarm: Liquid detected in the collection tray; locate and repair the leak source.
  • Abnormal Electrode Slope: Check the membrane and electrolyte, replace the standard solution; if the issue persists, replace the electrode.
  • Weak Photometer Signal: Trigger cleaning; if unresolved, manually clean or contact a service technician.

3. Long-Term Shutdown and Storage

  • Flush the instrument with distilled water in a circulation mode to empty the pipes and reagent bottles.
  • Remove the electrode, clean it, and reinstall it in the electrolysis cell, keeping it moist during storage.
  • Install transport locks and store in a dry, frost-free environment.

4. Professional Repairs

  • Certain components (such as pumps, compressors, and main circuit boards) must be replaced by the manufacturer or authorized service personnel. Typical service lives: pumps 1–2 years, compressors 2 years, all covered under warranty.

V. Conclusion

The Hach Amtax SC Ammonia Nitrogen Analyzer is a stable and highly automated online monitoring device. It features a scientific principle, clear installation requirements, a straightforward operation process, and comprehensive maintenance methods. By strictly adhering to the user manual and this guide, users can ensure the long-term stable operation of the device, providing reliable data support for water quality monitoring and wastewater treatment process control. Correct installation, regular calibration, and maintenance are key to ensuring the instrument’s long-term stable operation. Users should strictly follow the safety specifications in the operation manual, regularly replace reagents and electrodes, and promptly address fault alarms to ensure measurement accuracy and extend the instrument’s service life.

Posted on by

Troubleshooting Guide for Raycus RFL-P50QB Fiber Laser

1. Introduction

Raycus is one of the leading manufacturers of fiber lasers in China. Its RFL-P series pulsed fiber lasers are widely used in metal marking, welding, cutting, and surface cleaning.

From the nameplate you provided:

  • Model: RFL-P50QB
  • Output Power: 500W
  • Power Supply: 24VDC / Max. 14A
  • Structure: Main laser unit + fiber delivery cable + laser output head

In practice, common problems with this equipment are mainly related to power supply, fiber, cooling system, control signals, and the laser module.

2. Common Fault Symptoms

  1. No laser output at all
    • Fans running, but no laser beam emitted.
  2. Significant power drop
    • Originally 500W, now only 100–200W, insufficient for welding or cutting.
  3. Unstable output
    • Power fluctuates, beam spot unstable.
  4. Alarm indicators or error codes
    • Typical errors: over-temperature, fiber fault, module error.
  5. Output head contamination or damage
    • Lens blackened, spot distorted or doubled.

3. Troubleshooting Process

Step 1: Power Supply Check

  • Measure the input voltage:
    • Rated requirement: 24VDC, max 14A.
    • Use a multimeter; voltage must remain within 23.5–24.5V.
    • If voltage is too low, the laser cannot start or will output weak power.
  • Check power source:
    • Ensure power supply capacity is sufficient.
    • Tighten loose wiring to avoid overheating.

👉 Key point: Low voltage → no output; ripple noise → unstable laser.

Step 2: Control Signal Check

  • Enable signal:
    • The laser requires an enable signal from external control (CNC / PLC / marking card).
    • Verify connectors are not loose or oxidized.
  • PWM / analog signal:
    • Power control is typically via PWM or 0–10V input.
    • Use oscilloscope or multimeter to confirm correct waveforms.

👉 Key point: Missing signals → no laser; noisy signals → unstable output.

Step 3: Cooling System Check

  • Water chiller:
    • RFL-P50QB requires water cooling.
    • Confirm chiller is running, water temperature at 25 ±1 °C.
    • Ensure no bubbles in the pipeline.
  • Fans:
    • From your photo, the fan intake is dusty. Clean it.
    • Weak airflow → overheating alarm.

👉 Key point: Poor cooling → overheating shutdown.

Step 4: Fiber & Output Head Check

  • Fiber condition:
    • Look for bends, dents, or crushing.
    • Severe bending increases loss or causes permanent damage.
  • Output head (QBH collimator):
    • Inspect lens for black marks or burn spots.
    • Clean with isopropyl alcohol (IPA) and lint-free wipes.
  • Coupling condition:
    • Loose coupling → spot distortion.

👉 Key point: Dirty fiber head → reduced power; damaged fiber → no beam.

Step 5: Laser Module Check

  • Drive current:
    • If power is normal but no light, module failure is possible.
    • Requires factory repair.
  • Power measurement:
    • Use a power meter to test actual output.
    • If significantly lower than rated, the module is aging.

👉 Key point: Aged module → weak power; burnt module → no laser.

4. Common Faults & Solutions

SymptomLikely CauseSolution
No outputPower supply fault / no enable signalCheck 24V supply, verify control input
Power dropDirty fiber head / module agingClean fiber, replace module
Unstable beamPower ripple / cooling issueReplace power source, fix chiller
AlarmOverheat / fiber alarmCheck cooling system, fiber endface
Distorted spotBurnt output lensReplace or repair output head

5. Maintenance Guidelines

  1. Keep air vents clean – blow dust with compressed air.
  2. Replace cooling water regularly – use deionized water or dedicated coolant, change every 3 months.
  3. Clean fiber connectors – use 99% IPA alcohol and lint-free swabs.
  4. Avoid frequent plugging/unplugging of fiber heads.
  5. Stable power supply – use a UPS or voltage stabilizer.

6. Conclusion

The Raycus RFL-P50QB fiber laser is a robust industrial device, but it depends on stable power, proper cooling, clean fiber optics, and correct control signals to function.

From your photos and video, the most likely issues are:

  • Dust-clogged fan → overheating
  • Dirty or burnt fiber output head → power drop
  • Cooling water issues → overheat alarms

👉 Recommended sequence:

  1. Check power input.
  2. Verify cooling system.
  3. Clean fan and fiber head.
  4. Measure output with power meter.
  5. If still faulty → send to manufacturer.
Posted on by

Why Laurell Spin Coater Shows “Need Vacuum” Even When the Sample is Held Securely – A Complete Troubleshooting Guide

1. Introduction

Spin coaters are critical tools in microfabrication, material science, and semiconductor laboratories. They rely on high-speed rotation to uniformly spread photoresists or other coating materials onto wafers, glass slides, or substrates. One of the most commonly used systems in this category is the Laurell Technologies spin coater series.

A built-in safety interlock system ensures that the sample does not fly off during rotation. This is achieved by using a vacuum chuck, which secures the wafer or substrate via suction. If the machine does not detect a valid vacuum signal, it will refuse to start the spin cycle and display the warning message:

“Need Vacuum”

This safety feature prevents dangerous accidents and sample loss. However, in some situations, operators may encounter a scenario where:

  • The sample is firmly held by the vacuum chuck, indicating that the vacuum suction is working.
  • But the controller display still shows “Need Vacuum”, and the motor will not rotate.

This contradiction is exactly the case observed by the customer in South Africa, as shown in the photos and video evidence provided.

In this article, we will thoroughly analyze the issue, explain why it happens, and provide a structured troubleshooting guide for engineers, technicians, and laboratory users.

2. How the Vacuum Interlock Works in Laurell Spin Coaters

To understand the problem, one must first understand the design of the vacuum interlock system:

  1. Vacuum Source
    • Usually provided by an external vacuum pump.
    • In some labs, a central vacuum line is available.
    • The pump draws negative pressure through tubing connected to the spin coater chuck.
  2. Vacuum Chuck
    • A flat plate with small holes that holds the sample by suction.
    • When the pump is active, the wafer is tightly fixed to the chuck surface.
  3. Vacuum Sensor or Switch
    • Located inside the spin coater.
    • Detects whether the vacuum level is sufficient for safe operation.
    • Sends a signal (ON/OFF or analog voltage) to the controller board.
  4. Controller Logic
    • If the vacuum sensor indicates “No Vacuum,” the motor remains locked.
    • If vacuum is detected, the program is allowed to start spinning.

Thus, the machine requires both physical vacuum suction AND a valid signal from the sensor.

3. Symptom Observed by the Customer

From the photos and video provided, the following facts were established:

  • The sample (a square substrate) is securely attached to the chuck during vacuum operation.
  • The vacuum pump and tubing system are operational, as suction is clearly holding the substrate.
  • Despite this, the Laurell controller display shows “Need Vacuum” and the spin motor does not activate.
  • The operator is stuck at Step 00 in the spin program, unable to proceed further.

This mismatch between actual vacuum state and controller feedback is the root cause of the complaint.

4. Possible Causes of the Problem

4.1 Vacuum Sensor Malfunction

  • The vacuum sensor inside the coater may have failed.
  • Even though negative pressure exists, the sensor does not detect or report it.
  • Sensors can fail due to aging, contamination, or internal electrical faults.

4.2 Wiring or Connection Issues

  • The electrical signal from the sensor to the main control board may be interrupted.
  • Loose connectors, broken wires, or corrosion can cause signal loss.
  • A perfectly working vacuum will not be recognized if the signal path is broken.

4.3 Blocked or Misrouted Sensor Line

  • In some Laurell models, the sensor has its own dedicated small tubing.
  • If this line is blocked, pinched, or not connected to the correct port, the sensor will not see the vacuum.
  • Meanwhile, the chuck still holds the wafer properly.

4.4 Controller I/O Board Failure

  • The sensor might be functional, but the control board input channel is defective.
  • The vacuum detection signal never registers in the system.

4.5 Incorrect Parameter or Setup Configuration

  • Laurell systems allow configuration of Vacuum Interlock settings.
  • If the interlock is mistakenly disabled or misconfigured, the machine logic can behave unexpectedly.
  • For example, the controller might be waiting for a different signal threshold than what the sensor provides.

5. Evidence from the Video

The customer’s video shows:

  • At the beginning, the wafer is firmly attached to the vacuum chuck.
  • The operator gently touches or shakes it, and it stays in place.
  • This proves that vacuum suction is indeed active.
  • However, the spin coater does not proceed with rotation, confirming that the problem lies in signal recognition, not actual suction.

This video evidence eliminates issues like:

  • Faulty vacuum pump.
  • Leaking tubing.
  • Improper wafer placement.

Therefore, the focus must shift to detection, feedback, and controller logic.

6. Step-by-Step Troubleshooting Guide

Step 1: Confirm Vacuum Pump Operation

  • Ensure the pump is turned on.
  • Measure vacuum level at the pump output with a gauge (should meet Laurell’s specifications).

Step 2: Verify Chuck Suction

  • Place a sample or even a flat piece of glass.
  • If it is firmly held, the vacuum path from pump → tubing → chuck is confirmed.

Step 3: Inspect Sensor Tubing (if applicable)

  • Some models use a separate small tube leading to the vacuum sensor.
  • Make sure it is not disconnected, clogged, or leaking.

Step 4: Check Sensor Signal

  • Disconnect the electrical connector from the sensor.
  • Measure output with a multimeter when vacuum is applied.
  • If the signal does not change, the sensor is defective.

Step 5: Test Wiring Integrity

  • Use continuity testing on the wiring harness from sensor to controller.
  • Repair or replace cables if broken.

Step 6: Bypass/Short Test (For Verification Only)

  • Short the sensor signal input to simulate “vacuum present.”
  • If the machine starts spinning, the controller is fine but the sensor or wiring is faulty.

Step 7: Check Controller Settings

  • Access the system configuration menu.
  • Verify that Vacuum Interlock is enabled and thresholds are correct.
  • If necessary, temporarily disable interlock for diagnostic purposes (not recommended for normal operation).

Step 8: Controller Board Diagnosis

  • If sensor and wiring are confirmed good, the controller input board may be defective.
  • Replacement or repair of the I/O board is required.

7. Practical Recommendations

  • Replace the vacuum sensor if it shows no electrical response under suction.
  • Check and secure wiring connectors to eliminate intermittent signals.
  • Clean the sensor line to remove possible blockages.
  • Review the configuration in the Laurell menu to ensure interlock is properly set.
  • Contact Laurell service if controller hardware is suspected faulty.

8. Why This Problem Matters

This situation highlights an important principle in equipment maintenance:

  • Mechanical performance does not guarantee electrical recognition.
  • Even though the vacuum holds the wafer physically, the safety system relies on an independent electrical or pneumatic feedback mechanism.
  • If the feedback loop is broken, the machine assumes unsafe conditions and refuses to operate.

Such protective interlocks are common in high-speed rotating machinery, where user safety must always be prioritized.

9. Conclusion

The South African customer’s Laurell spin coater issue is a textbook case where vacuum is physically present, but the system still displays “Need Vacuum.”

  • The video clearly shows that the wafer is tightly held, ruling out pump or chuck problems.
  • Therefore, the most probable causes are vacuum sensor failure, wiring disconnection, or controller input malfunction.
  • A systematic troubleshooting procedure should start from confirming sensor response, checking wiring, and reviewing interlock settings, before finally suspecting controller board faults.

Ultimately, the problem is not the vacuum itself, but the failure of the machine to recognize and accept the vacuum signal.

By following the structured troubleshooting flowcharts and step-by-step guide, laboratory staff can isolate the fault, repair it effectively, and restore the spin coater to full working condition.

Posted on by

Causes of Poor Repeatability in Bingham Viscosity Measurements of Automotive PVC Sealing Adhesives and Troubleshooting Strategies for Rheometers

Introduction

In the automotive industry, PVC sealing adhesives are widely used for seam sealing, underbody protection, and surface finishing. Their typical formulation includes polyvinyl chloride (PVC), plasticizers such as diisononyl phthalate (DINP), inorganic fillers like nano calcium carbonate, and thixotropic agents such as fumed silica. These materials exhibit strong thixotropy and yield stress behavior, which are critical for application performance: they must flow easily during application but quickly recover structure to maintain thickness and stability afterward.

anton paar mcr 52

Rheological testing, particularly the determination of Bingham parameters (yield stress τ₀ and plastic viscosity ηp), is a key method for evaluating flowability and stability of such adhesives. However, in practice, it is common to encounter the problem that repeated tests on the same PVC adhesive sample yield very different Bingham viscosity values. In some cases, customers suspect that the rheometer itself may be faulty.

This article systematically analyzes the main causes of poor repeatability, including sample-related issues, operator and method-related factors, and potential instrument malfunctions. Based on the Anton Paar MCR 52 rheometer, it also provides a structured diagnostic and troubleshooting framework.

I. Bingham Viscosity and Its Testing Features

1. The Bingham Model

The Bingham plastic model is a classical rheological model used to describe fluids with yield stress: τ=τ0+ηp⋅γ˙\tau = \tau_0 + \eta_p \cdot \dot{\gamma}

where:

  • τ = shear stress
  • τ₀ = yield stress
  • ηp = Bingham (plastic) viscosity
  • γ̇ = shear rate

The model assumes that materials will not flow until shear stress exceeds τ₀, and above this threshold the flow curve is approximately linear. For PVC adhesives, this model is widely applied to describe their application-stage viscosity and yield properties.

2. Testing Considerations

  • Only the linear region of the flow curve should be used for regression.
  • Pre-shear and rest conditions must be standardized to ensure consistent structural history.
  • Strict temperature control and evaporation prevention are required for repeatability.

II. Common Causes of Poor Repeatability in Bingham Viscosity

The variability of results can arise from four categories: sample, operator, method, and instrument.

1. Sample-Related Issues

  • Formulation inhomogeneity: uneven dispersion of fillers or thixotropic agents between batches.
  • Bubbles and inclusions: entrapped air leads to noisy stress responses.
  • Evaporation and skin formation: solvents volatilize during testing, increasing viscosity over time.
  • Thixotropic rebuilding: variations in rest time cause different recovery levels of structure.

2. Operator-Related Issues

  • Loading technique: inconsistent trimming or sample coverage affects shear field.
  • Geometry handling: inaccurate gap, nonzero normal force, or loose clamping.
  • Temperature equilibration: insufficient time before testing.
  • Pre-shear conditions: inconsistent shear strength or rest period.

3. Methodological Issues

  • Regression region: including nonlinear low-shear regions distorts ηp.
  • Mode differences: mixing CSR (controlled shear rate) and CSS (controlled shear stress) methods.
  • Wall slip: smooth plates cause the sample to slip at the surface, lowering viscosity readings and increasing scatter.

4. Instrument-Related Issues

  • Torque transducer drift: unstable baseline, noisy low-shear data.
  • Air-bearing or gas supply issues: unstable rotation, periodic noise.
  • Temperature control errors: set vs. actual sample temperature mismatch, viscosity drifts with time.
  • Normal force sensor faults: incorrect gap and shear field.
  • Mechanical eccentricity: loose or misaligned geometries.
  • Software compensation disabled: compliance/inertia corrections not applied.

III. Challenges Specific to PVC Adhesives

PVC adhesives for automotive applications present several specific difficulties:

  1. Strong thixotropy: rapid breakdown under shear and fast structural recovery on rest, highly sensitive to pre-shear and rest history.
  2. Wall slip tendency: filler- and silica-rich pastes often slip on smooth plates, producing low and inconsistent viscosity readings.
  3. Evaporation and skinning: solvent/plasticizer volatilization leads to viscosity increase during tests.
  4. Wide nonlinear region: low-shear region dominated by rebuilding effects, unsuitable for Bingham regression.
anton paar mcr 52

IV. Recommended SOP for PVC Adhesive Testing

To achieve consistent Bingham viscosity results, the following SOP is recommended:

1. Geometry

  • Prefer vane-in-cup (V-20 + CC27) or serrated parallel plates (PP25/SR) to reduce wall slip.

2. Temperature Control

  • Test at 23.0 ± 0.1 °C or as specified.
  • Allow 8–10 min equilibration after loading.
  • Use solvent trap/evaporation ring; seal edges with petroleum jelly.

3. Sample Loading & Pre-Shear

  • Load slowly, avoid entrapping bubbles, trim consistently.
  • Pre-shear: 50 s⁻¹ × 60 s → rest 180 s under solvent trap.

4. Measurement Program

  • CSR loop: 0.1 → 100 → 0.1 s⁻¹ (logarithmic stepping).
  • Dwell: 20–30 s per point or steady-state criterion.
  • Discard first loop; fit second loop linear region (10–100 s⁻¹).

5. Data Processing

  • Report τ₀ and ηp with R² ≥ 0.98.
  • Document regression range and hysteresis.

6. Quality Control

  • Target repeatability: CV ≤ 5% for ηp (≤8% for highly thixotropic samples).
  • Use standard oils or internal control samples daily.

V. How to Verify If the Instrument Is Faulty

When customers suspect a rheometer malfunction, simple tests with Newtonian fluids can clarify:

  1. Zero-drift check
  • Run empty for 10–15 min; torque baseline should remain stable.
  1. Standard oil repeatability
  • Load the same Newtonian oil three times independently.
  • Target: viscosity CV ≤ 2%, R² ≥ 0.99.
  1. Temperature step test
  • Measure at 23 °C and 25 °C; viscosity should change smoothly and predictably.
  1. Geometry swap
  • Compare results using PP25/SR and CC27; Newtonian viscosity should agree within ±2%.
  1. Air supply check
  • Confirm correct pressure, dryness, and filter condition for the air bearing.

If the standard oil also shows poor repeatability, then instrument malfunction is likely. Probable causes include:

  • Torque transducer failure/drift.
  • Air-bearing instability.
  • Temperature control faults.
  • Normal force or gap detection errors.
  • Disabled compliance/inertia compensation.

VI. Communication Guidelines with Customers

  1. Eliminate sample and method factors first: the thixotropy, volatility, and wall slip of PVC adhesives are usually the dominant causes of poor repeatability.
  2. Verify instrument health with standard oils: if oil results are consistent, the instrument is healthy and SOP must be optimized; if not, escalate to service.
  3. Provide an evidence package: standard oil data, zero-point stability logs, temperature records, air supply parameters, geometry and gap information, and compensation settings.

Conclusion

Automotive PVC sealing adhesives are complex materials with strong thixotropic and yield stress behavior. In rheological testing, poor repeatability of Bingham viscosity can be attributed to sample properties, operator inconsistencies, methodological flaws, or instrument faults.

By applying a standardized SOP—including vane or serrated geometry, strict temperature control, controlled pre-shear and rest times, and regression limited to the linear region—repeatability can be significantly improved.

To determine whether the instrument is at fault, repeatability checks with Newtonian standard oils provide the most objective method. If results remain unstable with standard oils, instrument issues such as torque transducer drift, air-bearing instability, or temperature control errors should be suspected.

Ultimately, distinguishing between sample/method effects and instrument faults is essential for efficient troubleshooting and effective communication with customers.

Posted on by

The Role of Micro Bead Filling in Explosion-Proof Displays and Options for Substitution

Introduction

In hazardous environments such as coal mines, petrochemical plants, chemical processing facilities, and oil & gas fields, conventional electronic displays cannot be directly applied. This is because LCD panels and their driver circuits may generate sparks, arcs, or heat during operation, which could ignite surrounding flammable gases or dust. Therefore, specialized explosion-proof displays compliant with ATEX / IECEx standards must be used. These devices feature special designs in their housings, sealing methods, heat dissipation, and internal structures.

During the repair of a customer’s explosion-proof display, the author discovered something unusual: apart from the LCD module and driver board, the interior was filled with a large quantity of uniform, tiny plastic beads—enough to collect half a bowl after disassembly. At first, the purpose of these beads was unclear, and some speculated that they might be desiccants. However, further investigation revealed that these microbeads play a crucial role in the explosion-proof design. This article explores their functional mechanism, possible material types, and alternative options.

I. Basic Requirements of Explosion-Proof Displays

1. Explosion-Proof Standards

According to the IEC 60079 series of international standards, explosion-proof electrical equipment must prevent the following hazards:

  • Arc and spark leakage: Switching elements, relays, or LCD driver ICs may generate sparks.
  • Hot surfaces: LED backlight drivers or power modules may heat up.
  • Internal explosions: If components burn or fail, flames must not propagate outside the enclosure.

Common protection methods include Flameproof (Ex d), Intrinsic Safety (Ex i), Increased Safety (Ex e), and Powder Filling (Ex q)—the method most relevant to this discussion.

2. The Principle of Ex q Powder Filling

Ex q protection involves filling the enclosure with fine particles or powder so that no free air cavities remain inside. Any arcs, sparks, or flames are effectively blocked from propagation. Typical fillers include quartz sand, glass microbeads, or flame-retardant polymer beads.

Advantages include:

  • Friction between particles dissipates energy and prevents flame spread.
  • The filler provides thermal insulation, slowing heat transfer.
  • Properly selected materials are non-flammable and ensure safety.

II. Observations During Repair

Upon disassembly, it was noted that all housing seams were sealed with adhesive. Inside, the cavity was densely packed with white, spherical beads of about 0.5–1 mm diameter, lightweight and smooth.

Initial suspicion that these might be silica gel desiccants was soon dismissed:

  • The sheer volume was far beyond what moisture control would require.
  • Desiccant beads are typically porous and often color-indicating (blue/orange).
  • Their primary purpose is moisture absorption, not shock absorption or flame suppression.

Thus, these were confirmed not to be desiccants but rather specialized filler beads for explosion-proof applications.

III. Likely Material Types

By comparing common industrial fillers, the beads are most likely one of the following:

1. EPS / EPE Foam Beads

  • Appearance: White, lightweight, uniform diameter.
  • Advantages: Excellent energy absorption, cushioning, and vibration damping; inexpensive.
  • Limitations: Low heat resistance unless treated with flame retardants.

2. Hollow Glass Microspheres

  • Appearance: Transparent or white, smooth spherical particles, 100–500 μm typical size.
  • Advantages: High-temperature resistance, non-flammable, chemically stable.
  • Limitations: More expensive, fragile.

3. Expanded Perlite Granules (Glassy Beads)

  • Appearance: Irregular, porous mineral-based particles.
  • Advantages: Fireproof, high-temperature resistant, widely used in construction insulation.
  • Limitations: Dust generation, irregular shapes, not suitable for close contact with electronics.

Based on their smooth spherical shape, uniform size, and dense packing, the filler in this display is more consistent with flame-retardant EPS/EPE beads or hollow glass microspheres, rather than perlite-based construction materials.

IV. Functional Mechanism of Beads in Explosion-Proof Displays

1. Energy Absorption

In the event of arcs, short circuits, or small internal explosions, the beads absorb shock energy through inter-particle friction, preventing flame penetration.

2. Elimination of Cavities

By filling every space inside the enclosure, no free air volume remains, reducing the risk of flammable gases accumulating.

3. Thermal Insulation and Flame Retardancy

The filler layer weakens heat conduction. Even if some circuits generate heat, it is not quickly transferred to the housing. Flame-retardant treated beads will not sustain burning.

4. Shock and Vibration Damping

Explosion-proof displays are often installed in environments subject to mechanical vibration. The filler beads protect LCD panels and circuits by cushioning against long-term vibration.

V. Can “Glassy Perlite Beads” Be Used as a Substitute?

Products such as glassy perlite beads (expanded perlite) are commonly sold for construction insulation. While fireproof, they are not suitable substitutes in this context because:

  • Irregular shapes make them pack poorly, leaving gaps.
  • High dust levels may contaminate electronic boards.
  • Low mechanical resilience means they crumble under vibration and do not cushion effectively.

Thus, glassy perlite beads are not recommended as replacements for the original filler.

VI. Suitable Substitutes and Purchasing Advice

1. Flame-Retardant EPS Beads

  • Recommended size: 1–3 mm diameter.
  • Advantages: Lightweight, easy to fill, cost-effective.
  • Requirement: Must meet certified flame-retardant grades (e.g., UL94 V-0 or B1).

2. Hollow Glass Microspheres

  • Recommended size: 100–500 μm diameter.
  • Advantages: High-temperature resistance, non-flammable, smooth surface.
  • Suitable for higher-spec safety environments.

3. Procurement Channels

  • Chinese e-commerce: Search for “阻燃EPS微珠” or “中空玻璃微珠”
  • International suppliers: Brands such as Storopack and SpexLite offer filler beads with technical documentation.
  • Explosion-proof equipment distributors: Some suppliers provide certified filler material specifically for Ex q applications.

VII. Conclusion

The beads observed inside the explosion-proof display are not desiccants but specialized filler materials that comply with the Ex q powder filling principle (IEC 60079-5). Their functions include absorbing energy, eliminating cavities, insulating against heat, and damping vibration.

Based on observed characteristics, they are most likely flame-retardant EPS/EPE foam beads or hollow glass microspheres, not perlite-based construction fillers. For repairs or replacement, it is critical to choose certified, flame-retardant, low-dust spherical beads, typically 1–3 mm in diameter, to ensure compliance with explosion-proof safety standards.

This choice directly affects not only the reliability of the equipment but also intrinsic safety in hazardous environments. Therefore, service personnel must reference relevant standards and confirm flame-retardant certification when selecting replacement materials.

Posted on by

ABB EL3020 (Uras26) CO₂ Analyzer: Calibration Principles, Common Failures, and On-site Troubleshooting

1. Introduction

The ABB EL3020 (equipped with the Uras26 infrared module) is a high-precision, multi-component gas analyzer widely used in chemical, metallurgy, power, and environmental sectors for continuous CO₂, CO, CH₄, and other gas measurements.
To ensure measurement accuracy and long-term stability, Zero Point Calibration and Span Calibration must be performed regularly. However, during field calibration, engineers often encounter “Calibration Rejected,” “Half Span Shift,” or complete lockout after a failed attempt, preventing further calibration and impacting operation.

This article explains the calibration principle, common causes of failure, error phenomena, troubleshooting steps, and recovery methods. It is based on real field cases, providing engineers with actionable, field-ready solutions.

2. Calibration Principles of the EL3020 (Uras26)

2.1 Zero Point Calibration

The purpose of zero point calibration is to eliminate background interference signals from the optical system and sensors when no target gas is present, aligning the measurement curve to zero.

  • Condition: Introduce zero gas without the target component (e.g., high-purity nitrogen or zero air).
  • Requirement: Gas purity must be adequate (CO₂ < 0.1 ppm for a 0–5 ppm range), the sampling path fully flushed, and readings stable.

2.2 Span Calibration

Span calibration adjusts the analyzer’s sensitivity near the full scale so that the measured value matches the standard gas concentration.

  • Condition: Introduce certified calibration gas with a known concentration (e.g., 3 ppm CO₂).
  • Requirement: Gas concentration must be accurate and stable, and match the value configured in the analyzer.

2.3 Calibration Protection Mechanism

To prevent operator errors from causing measurement drift:

  • If the current reading deviates too far from the expected zero/span value, the analyzer will display a “Span Shift” or “Half Span Error” warning.
  • In some firmware versions, a failed calibration triggers an automatic calibration lock, requiring reset/unlock before retrying.

3. Common Calibration Issues and Root Causes

3.1 “Half Span Error” Warning

Causes:

  1. Incorrect calibration gas concentration (zero gas contains CO₂ or span gas concentration mismatch).
  2. Residual sample gas in the line or insufficient flushing time.
  3. Abnormal flow rate (too low/high or unstable).
  4. Analyzer not stabilized (insufficient warm-up or optical drift).

Recommendations:

  • Verify calibration gas concentration and label match.
  • Flush for ≥5–10 minutes before calibration.
  • Adjust flow rate to recommended value (e.g., 60 L/h).
  • Warm up for ≥30 minutes before calibration.

3.2 Zero Calibration Rejection

Causes:

  • Current reading outside acceptable zero range (e.g., <0.1 ppm for a 0–5 ppm range).
  • Calibration lock active after a failed attempt.
  • Menu access restricted (requires service password).

Recommendations:

  1. Confirm zero gas purity (CO₂ < 0.1 ppm).
  2. Extend flushing until reading stabilizes.
  3. Check service menu for Calibration Reset option.
  4. If locked, perform unlock/reset before retrying.

3.3 Lockout After One Failed Calibration

Causes:

  • Firmware protection: Logs the failure and blocks further calibration until cleared.
  • Data integrity protection: Prevents repeated incorrect calibrations from accumulating drift.

Unlock Methods:

  • Menu Reset: Service → Calibration Reset.
  • Power cycle + Zero gas flush.
  • Factory Calibration Restore (use with caution – overwrites all current calibration data).
  • Serial Command Unlock via ABB EL3020 Service Tool (CALRESET command).

4. Field Troubleshooting and Operating Steps

4.1 Pre-Calibration Checklist

  1. Gas Verification
    • Confirm gas label matches instrument settings.
    • Use ≥99.999% high-purity nitrogen or equivalent zero gas.
  2. Flow and Gas Path
    • Check flowmeter reading matches recommended spec.
    • Inspect for leaks and verify valve positions.
  3. Warm-up and Stability
    • Warm up for 30–60 minutes.
    • Flush for 5–10 minutes after switching gases.

4.2 Calibration Execution

  1. Press the wrench icon on the right-hand side of the display to enter Maintenance Menu.
  2. Select Manual Calibration.
  3. Choose Zero Point or Span depending on the operation.
  4. Wait for the reading to stabilize before pressing OK.
  5. Verify reading changes after calibration completes.

4.3 After Calibration Failure

  1. Verify gas source → Flush → Retry.
  2. If still failing → Service Menu → Calibration Reset.
  3. If no reset option → Power cycle with zero gas flushing.
  4. If lock persists → Use service software via serial port to send CALRESET.

5. Case Study: CO₂ Zero Point Calibration Failure

Scenario:

  • Instrument: ABB EL3020 (0–5 ppm CO₂ range).
  • Zero gas: 99.999% high-purity nitrogen.
  • Flow rate: 60 L/h.
  • Issue: Zero point calibration triggers “Half Span Error,” lockout after failure.

Investigation:

  1. Gas purity verified.
  2. Found flushing time was only 2 minutes – insufficient for stability.
  3. Extended flushing to 10 minutes → Reading dropped from 0.35 ppm to 0.05 ppm.
  4. Performed Calibration Reset → Zero point calibration succeeded.

Takeaway:

  • Insufficient flushing time is a common cause.
  • First step after failure: reset/unlock before retry.

6. Button & Icon Functions

  • Left Icon (Envelope/File)
    Data logging and viewing functions. Opens historical records and calibration logs.
  • Right Icon (Wrench)
    Maintenance and calibration access: zero point, span calibration, gas path test, sensor status.

7. Preventive Maintenance Tips

  1. Regularly verify calibration gas purity to avoid contamination.
  2. Flush sampling lines thoroughly before calibration.
  3. Perform zero and span calibration according to manufacturer’s recommended cycle.
  4. Train operators to follow correct calibration procedures to minimize errors.

8. Conclusion

The ABB EL3020 (Uras26) offers stable, reliable high-precision gas analysis when paired with proper gas path management and calibration. Understanding the calibration principle, protection mechanism, and common failure modes enables operators to troubleshoot effectively and reduce downtime.
When calibration fails or lockout occurs, follow the outlined troubleshooting steps—starting from gas source and flow checks to warm-up, flushing, and finally reset/unlock procedures—to quickly restore normal operation.

Posted on by

Maintenance Analysis Report on YT‑3300 Smart Positioner Showing “TEST / FULL OUT 7535” Status

I. Overview and Equipment Background

This report addresses the status display of the Rotork YTC YT-3300 RDn 5201S smart valve positioner. The front panel shows the following:

TEST  
FULL OUT  
7535

The YT-3300 series smart positioner is produced by YTC (Young Tech Co., Ltd.), often labeled under the Rotork brand. It is designed for precise valve actuator control using a 4–20 mA input signal. The unit supports automatic calibration, self-diagnostics, manual testing, and performance optimization.

TEST FULL OUT

II. Interpretation of Display Information

1. TEST Mode

The “TEST” message indicates the unit is currently in self-test or calibration mode. This occurs typically during initial power-up, after parameter reset, or when manually triggered.

2. FULL OUT

“FULL OUT” means the actuator has moved to the end of its travel range—either fully open or fully closed—depending on the configured logic.

3. 7535

The number “7535” is not an error code. It usually represents the raw feedback signal from the internal position sensor, such as a potentiometer or encoder, scaled between 0–9999. This value gives the current travel position.

III. Possible Root Causes

The following table summarizes possible causes for this status:

No.Possible CauseDescription
1Power-on self-testAfter powering up or parameter loss, the device automatically initiates self-calibration.
2Manual test triggeredThe test mode may have been manually entered via front-panel buttons.
3Feedback sensor issueA stuck or damaged position sensor can cause the value (7535) to freeze or become invalid.
4Air pressure problemInsufficient or unstable air pressure may prevent the actuator from completing movement.
5Mainboard faultMalfunction of internal controller or microprocessor may lock the unit in test mode.
YT-3300 RDn 5201S

IV. Recommended Inspection and Repair Steps

1. Safety and Initial Checks

  • Disconnect the actuator from live control and ensure safe access.
  • Ensure that air pressure is fully vented to prevent unintended valve motion.
  • Confirm the unit is grounded properly (ground resistance <100 ohms).

2. Check Air Supply

  • Verify pressure gauges show clean, dry air within 0.14–0.7 MPa (1.4–7 bar).
  • Check for blocked air tubing or clogged filters.

3. Exit TEST Mode

  • Press the ESC button repeatedly to try returning to the RUN display.
  • If that fails, power cycle the unit and enter Auto Calibration mode via the front panel.

4. Execute Auto Calibration

  • Set the A/M switch to AUTO.
  • Use the keypad to navigate to “AUTO CAL” or “AUTO2 CAL” and execute.
  • The actuator will automatically stroke to both ends and calibrate zero and full travel points.
  • After successful calibration, the display should return to RUN mode.

5. Verify Position Feedback

If the value “7535” remains static or fails to reflect position changes:

  • Open the lower cover and check wiring to the potentiometer (typically yellow, white, blue wires).
  • Measure the feedback voltage (should range from ~0.5 to 4.5V DC).
  • If no variation is detected with actuator movement, the potentiometer or sensor board may need replacement.

6. Diagnostics and Alarm Monitoring

  • Enter the DIAGNOSTIC menu to check for alarm codes or travel deviation alerts.
  • If high or low limit alarms (e.g., HH ALRM or LL ALRM) are detected, reset as per standard procedures.

7. Functional Test and Tuning

  • After restoring to RUN mode, input varying mA signals and observe feedback value (PV) changes accordingly.
  • If actuator motion is slow or unstable, adjust Dead-Zone, Gain, or Filter settings to fine-tune performance.
  • Conduct partial stroke tests (PST) if available to verify control reliability.
TEST FULL OUT

V. Evaluation and Conclusion

Depending on the inspection and action taken, the following scenarios are possible:

  • If Auto Calibration completes successfully and feedback changes smoothly: No hardware failure is present. The unit was simply in test mode after reset.
  • If TEST mode persists and feedback value remains frozen: The position feedback sensor or its circuit is likely faulty and needs replacement.
  • If actuator fails to move despite calibration attempts: Check for blocked pneumatic valves, damaged tubing, or insufficient pressure.
  • If diagnostic menu shows active alarms: Follow alarm-specific reset instructions.

VI. Summary and Recommendations

  1. Preliminary Conclusion: The current “TEST / FULL OUT 7535” status likely indicates a post-reset auto-test, not a malfunction. However, persistent status or failed calibration points to feedback or hardware problems.
  2. Recommended Actions:
    • First attempt to complete auto calibration;
    • Check wiring, feedback sensor, and air supply;
    • Monitor diagnostic menu for error indicators;
    • Replace faulty components if auto-calibration cannot be completed.
  3. Follow-up Advice:
    • Acquire the official user manual for this specific model;
    • Record all air pressures, input/output values, alarms, and parameter settings during troubleshooting for future analysis;
    • If manual steps do not resolve the issue, contact the manufacturer or authorized support for further diagnostics or part replacement.

Posted on by

High-Precision Spin Coater Design: For Nanometer-Scale PLGA Film Deposition on Top of Micropillar Arrays in PDMS Chips

I. Background and Application Needs

In the fields of cell engineering, biomaterials, and drug delivery systems, high-throughput microstructured chip platforms are becoming a key research tool. Especially platforms combining PDMS micropillar array chips with controlled biodegradable thin films (e.g., PLGA) are widely used in:

  1. Single-cell drug delivery and sensitivity evaluation;
  2. Cell-material interface interaction studies (adhesion, migration, differentiation);
  3. Multi-factor high-throughput screening and biomimetic microenvironment construction;
  4. Precise control of nanoscale drug release behavior.
spin coater

These applications often require construction of highly uniform, nanometer-scale (100–300 nm) functional film layers specifically on the tops of the pillars, with PLGA (poly(lactic-co-glycolic acid)) as the typical material due to its biocompatibility, biodegradability, and tunable release properties.

However, traditional planar spin coaters with vacuum suction platforms are not suitable for achieving uniform nanoscale coatings on non-planar structures like micropillars, especially when coating only the pillar tops. This presents a demand for a specially designed spin coater to meet these challenges.

II. Spin Coating Principle Overview

Spin coating is a widely used technique in microelectronics, optics, and biomaterials for the rapid formation of uniform thin films. The basic steps include:

  1. Dropping solution onto a substrate;
  2. Rapid rotation creates centrifugal force spreading the liquid evenly;
  3. Simultaneous solvent evaporation leads to film formation within seconds.

Based on simplified Meyerhofer’s model, film thickness “h” relates to:

h ∝ (c * μ) / ω^{1/2}

Where:

  • c = solution concentration;
  • μ = viscosity;
  • ω = rotation speed (rpm);

By adjusting these parameters, film thicknesses from tens to hundreds of nanometers can be reliably achieved. For pillar-top coating, this must be combined with specialized jigs, non-vacuum mechanisms, and multi-stage programmatic rotation control.

III. Functional Requirements for the Spin Coater

To satisfy the target application, the spin coater must meet the following specifications:

1. Microstructure-Compatible Platform

  • Substrate size: 55 mm × 55 mm PDMS chip;
  • Non-vacuum clamping to prevent microstructure collapse;
  • Compatible with curved/non-planar substrates for optimal pillar-top coating.

2. Precision Rotational Control

  • Speed range: 100–10,000 rpm;
  • Speed resolution: 1 rpm;
  • Acceleration range: 100–10,000 rpm/s;
  • Multi-stage programmable control (min. 10 segments);
  • Each stage must set: speed, time, acceleration.

3. Nanofilm Thickness Control Module

  • Automated dispensing system (micro syringe pump):
    • Volume range: 0.1–10 μL;
    • Precision: ±0.01 μL;
  • Optional heating lid (to improve uniform solvent evaporation);
  • Environmental sealing (for use inside glovebox);
  • Gas inlet for nitrogen or controlled airflow.

4. Software and Feedback Control

  • Color LCD touchscreen for programming and monitoring;
  • Real-time display of speed, time, temp, steps;
  • At least 20 custom program sets storage;
  • USB export of spin data logs;
  • External sensor interfaces (e.g., ellipsometer, IR monitor).
High-precision spin coater in use.

IV. Key Innovation Highlights

  1. Non-vacuum clamping system:
    • Avoids PDMS micropillar collapse;
    • PTFE precision slot clamp secures the chip without central blockage.
  2. Pillar-top coating optimization:
    • Multi-stage program: pre-spread (low speed), main spin (high speed), dry-out (moderate speed);
    • Sample protocol: 300 rpm (10s) → 2000 rpm (30s) → 1000 rpm (20s).
  3. Micro-volume drop dispensing system:
    • Controlled center-drop of PLGA solution (2–5 wt% in DCM);
    • Precision stage and optional laser alignment.
  4. Anti-edge-thickening logic:
    • Delay spin or pre-wet stage to prevent solution migrating to chip edges.
  5. Open programming interface:
    • Supports MATLAB / Python SDK;
    • Integration with AI or bioassay automation platforms.

V. Workflow Example

  1. Deposit 0.5–2 μL PLGA solution at the center of PDMS chip;
  2. Spin program:
    • Step 1: 300 rpm for 10 s (pre-spread);
    • Step 2: 2000 rpm for 30 s (uniform coating);
    • Step 3: 1000 rpm for 20 s (controlled dry);
  3. Optional: N2 gas flow to assist solvent removal;
  4. Post-process: film thickness validated by ellipsometry or AFM.

VI. Implementation and Materials

  • Control system: STM32/ESP32 + encoder + BLDC driver;
  • Syringe pump: stepper-driven microinjection with replaceable tips;
  • Heating lid: PTFE shell + PTC film heater + PID temp control;
  • Housing: CNC-machined aluminum frame + acrylic protective cover;
  • Chip holder: laser-cut PTFE tray, supporting 3–4 mm thick PDMS chips.

VII. Market Benchmarks and Outlook

Comparison with existing devices:

  • Ossila Advanced Spin Coater (UK);
  • Laurell WS-650 series (USA);
  • MTI VTC-100PA (China);

Our design focuses on the niche need for micropillar-top nanofilm coating in biological applications, filling a gap in existing commercial equipment that primarily supports flat wafer processing.

Future development roadmap includes:

  • Multi-solution switching module (e.g., for combinatorial screening);
  • Vision-assisted chip alignment and coating path planning;
  • Closed-loop AI control based on film thickness feedback.

VIII. Conclusion

This design addresses the unmet need for high-precision nanocoating on micropillar arrays in PDMS chips—especially relevant in single-cell drug screening and cell-material interface studies. By integrating multi-stage programmable spin control, non-vacuum platform, microfluidic injection, and programmable environment conditioning, this spin coater provides a complete solution for researchers working on nanoscale PLGA film deposition in structured biological interfaces.

It is expected to contribute significantly to advanced biomedical research, high-throughput drug screening, and future bioMEMS development.

Posted on by

Comprehensive User Guide for the ParticleTrack™ G400 Laser Particle Characterization System

The ParticleTrack G400 from Mettler‑Toledo is an advanced in situ particle analysis system based on Focused Beam Reflectance Measurement (FBRM®) technology. It enables real-time, direct measurements of particle size and count in full-concentration processes without the need for sampling or dilution. This comprehensive guide explains the working principle, installation, configuration, calibration, operation, maintenance, troubleshooting, and advanced integration options of the ParticleTrack G400 system. It is designed to support users from first-time setup to expert-level deployment in laboratory or process environments.

ParticleTrack G400

1. Working Principle and Key Advantages

The ParticleTrack G400 uses a rotating 780 nm laser beam focused just beyond the sapphire window of the probe. When the beam intersects a particle or droplet, it reflects back to the detector. The duration of this reflection is converted into a “chord length”, allowing the system to calculate particle size distributions in real time.

Key advantages include:

  • True in-situ analysis without the need for sample extraction or dilution.
  • Wide dynamic range measuring particles from 0.5 µm to 2 000 µm.
  • Real-time monitoring, with updates as frequently as every second.
  • Modular probe design, including interchangeable tips for different reactor volumes.
  • Process-resilient construction, handling temperatures from –80 °C to +90 °C and pressures up to 100 bar.

2. System Components and Safety Considerations

ComponentDescriptionKey Specifications
Base UnitHouses laser, motor, signal processing hardware100–240 VAC, USB, 3.25 kg
FBRM ProbeSensor head for immersion in process streamAvailable in 14 mm / 19 mm diameters
Software (iC FBRM)Interface for configuration, data capture, analyticsWindows-based, OPC UA/DCS compatible

Safety Notes:

  • The system is classified as a Class 1 laser product and is safe under normal operating conditions.
  • Only trained personnel should handle system components.
  • The internal laser module and electronics are not user-serviceable.
  • Always ensure the system is properly grounded and installed indoors.

3. Installation and Probe Positioning

Installation steps:

  1. Hardware setup:
    • Connect the AC power supply and USB cable to the computer.
    • Confirm the “Power” and “HW-Status” LEDs are illuminated steadily.
  2. Process positioning:
    • Install the probe in a location where flow is continuous and representative.
    • The sapphire window should face the flow direction at a 30°–60° angle, ideally 45°, to maximize measurement accuracy and reduce buildup.
  3. Optional air purge:
    • In cold or humid environments, connect clean, dry instrument air at 1 barg during start-up, then reduce to 0.15 SLPM to avoid condensation.

4. Software Operation (iC FBRM 4.4)

4.1 Experiment Setup

  • Open iC FBRM.
  • Select New Experiment.
  • Enter a name, define the data storage path, set the total run duration, and choose a measurement interval (e.g., 1s, 5s, 30s).

4.2 Real-Time Monitoring

  • Color-coded status indicator:
    • Green: Running
    • Yellow: Paused
    • Red: Error
    • Blue: Stopped
  • You can annotate events (e.g., reagent addition) directly onto live trends.

4.3 Data Review & Reporting

  • Use Trend Viewer to monitor D50, counts/sec, and chord counts over time.
  • Distribution Viewer displays real-time and historical chord length distributions.
  • Statistics Viewer shows mean, mode, and percentile summaries.
  • Export data to Word, Excel, PDF, or CSV for documentation or analysis.

5. Calibration and Validation

TaskFrequencyPurpose
Calibration ValidationEvery 3–6 months or after a fallVerifies scan geometry and optical alignment
Chord Selection ModelBefore each new experimentOptimize detection for fine/coarse particles

Validation procedure:

  • Use the Calibration Validation Wizard in iC FBRM.
  • Mount a standard PVC reference sample in a fixed beaker stand.
  • Run validation and compare results to reference data.
  • Acceptable deviation: less than 5%; if more than 10%, clean or inspect optics.
ParticleTrack G400

6. Maintenance and Cleaning

Routine practices:

  • Window cleaning:
    • Wipe using Kimwipes moistened with distilled water, ethanol, or acetone.
    • For stubborn residue, use a fine (0.3 µm) alumina polishing compound.
  • Air purge maintenance:
    • Maintain steady 0.15 SLPM during operation.
    • Shut off only after cool-down to prevent condensation.
  • Preventive Maintenance (PM):
    • Replace probe tip or rotary bearings every 1–2 years depending on use.
    • Keep software updated to enable PM alerts and tracking.
  • Storage:
    • After use, store the probe upright and dry in a protective case.

7. Troubleshooting

IssuePossible CauseAction
Scan Speed Too LowWorn bearings or incorrect configurationReplace bearings; verify probe type in software
No CountsWindow fouled or probe not immersedClean window; check immersion depth
Signal Intensity Too HighReflective particles causing saturationSwitch to Macro CSM or dilute sample
Data Acquisition ErrorUSB or PC performance issueReconnect cable; adjust interval or upgrade PC
Tach Pulse MissingFaulty motor or encoderContact technical support

Note: The internal electronics are not user-repairable. For serious hardware faults, contact Mettler-Toledo for Return Material Authorization (RMA).

8. Extended Capabilities

  • Dual System Operation:
    • You may connect two G400 units to a single computer for simultaneous monitoring.
    • Configure each instrument separately in the software.
  • OPC UA / Modbus Integration:
    • Allows real-time data output to SCADA or DCS systems.
    • Enables feedback control loops for crystallization and particle formation processes.
  • Data Archiving:
    • Integrate with iC Data Center for secure storage of all measurement records in GMP-compliant formats.

9. Best Practices

  • Pre-warm the probe 30 minutes before use.
  • Choose appropriate measurement intervals:
    • 1–5 s during fast transitions (e.g., seeding),
    • 30–60 s during stable phases to reduce file size.
  • Avoid installing probes parallel to vessel walls or facing baffles.
  • Always validate the system before starting critical experiments.
  • Participate in Mettler-Toledo AutoChem training webinars for advanced topics.

10. Conclusion

The ParticleTrack G400 is a powerful and precise tool for monitoring particle dynamics in real time, directly within your process. By following the installation, calibration, and maintenance recommendations provided in this guide, users can achieve high-quality, reproducible measurements that enhance process understanding, control, and optimization. Whether you’re conducting crystallization research, scaling up emulsions, or controlling flocculation, the G400 provides data you can trust.