1. Description of the problem and scope of application
This manual is intended for diagnosis and troubleshooting related to deviations in the readings of flow meters (electromagnetic, Coriolis, ultrasonic) in industrial processes. This document covers the following symptoms: unstable readings, zero point drift, constant offset and complete loss of signal.
Equipment: technological pipelines (liquids, gases, steam) at industrial facilities. Severity classification: Critical (if the flowmeter is used in a control loop or commercial metering).
2. Safety measures
CAUTION: Lockout/Tagout (LOTO) must be performed for power and pressure sources before starting diagnostics. The use of PPE (safety glasses, gloves, overalls) is mandatory. Work with pressure gauges and aggressive media is carried out only after excess pressure has been released and the system has been drained.
3. Necessary diagnostic tools
| Tool | Specification/Model | Range | Purpose |
|---|---|---|---|
| Multimeter | Digital, True RMS | 0.1 mV – 1000 V, 1 μA – 10 A | Checking the power supply, output signal 4-20 mA |
| Oscilloscope | Portable, 2 channels | DC - 20 MHz | Signal noise analysis, interference diagnostics |
| Thermal imager | Industrial | -20 – 500 °C | Detection of local overheating or leaks |
| Ultrasonic thickness gauge | For metals | 1 – 200 mm | Assessment of the internal condition of the pipeline (corrosion) |
| Calibrator of technological signals | For current loops | 0 - 24 mA | Simulation of the output signal for testing secondary devices |
4. Initial assessment checklist
| Verification | action | norm |
|---|---|---|
| History of accidents | Check the event log for the last week | Absence of cyclical errors |
| Process parameters | Record current pressure, temperature and viscosity | Sensor specification compliance |
| Changes in the system | Check for pipeline or configuration changes | No changes since the last check |
| Visual inspection | Inspect the condition of the cables, housing and flanges | Insulation integrity, no leaks |
5. Systematic diagram of diagnostics
Diagnostics is based on the principle of cut-off: from external factors to internal defects of the device.
- Checking the electrical circuit and power supply stability:
- If there is no signal: check the power supply voltage at the device terminals.
- If the voltage is normal: check the integrity of the output circuit (4-20 mA) using an ammeter.
- Analysis of process conditions:
- If readings are unstable: check for air bubbles or cavitation (pipeline noise).
- If the readings are off: check that the current temperature/pressure matches the calibration.
- Assembly check:
- Are straight sections observed (minimum 10D before and 5D after the flow meter)?
- Are there any pipeline vibrations greater than 2 mm/s (RMS)?
- Diagnostics of the condition of the internal part:
- If contamination is suspected: inspect the flow part when the process is stopped.
6. Matrix of symptoms and causes
| Symptom | Probable cause | Diagnostic test | Expected result |
|---|---|---|---|
| Unstable signal (noise) | Cavitation / Gas bubbles | Analysis of pressure in the system | Pressure < vapor saturation pressure |
| Constant displacement | Dirt/scale on the sensor | Checking the resistance of the electrodes | Resistance > 10 MΩ (for magnetic) |
| Drift over time | Calibration drift | Comparison with the standard | Deviation > 1.5% |
| Zero shift | Pipeline vibration | Vibration analysis (mm/s) | Vibration > 3 mm/s |
7. Root cause analysis
Fouling and scaling: Occurs during long-term use with fluids prone to precipitation. The accumulation of a layer of dielectric on the electrodes of the electromagnetic flowmeter leads to the opening of the measuring circuit or distortion of the potential. Confirmed by visual inspection.
Calibration drift: Occurs due to aging of electronic components or mechanical wear of the measuring sensor (for example, abrasion of the lining). Reduces accounting accuracy, critical for commercial operations.
Incorrect installation: Lack of stabilized flow (turbulence) due to the proximity of taps or shut-off fittings. Creates a non-uniform velocity profile, which leads to systematic error.
8. Step-by-step troubleshooting procedure
- Cleaning of electrodes (for magnetic devices):
- Drain the pipeline.
- Use mild solvents (non-abrasive) so as not to damage the coating.
- Check the integrity of the seals during reverse installation.
- Adjustment of settings (Zero Calibration):
- Stop the flow, ensure that the pipe is completely filled.
- Activate the "Zero Trim" function in the converter menu.
- Installation change:
- If turbulence is detected, add flow straighteners or change the installation location.
9. Preventive measures
| The reason | Strategy | Monitoring method | Interval |
|---|---|---|---|
| Pollution | Periodic washing | Electrode resistance control | 6 months |
| drift | Scheduled verification | Comparison with the standard | 12 months |
| Mechanical wear | Vibration analysis | Vibration sensors | Constantly |
10. Spare parts and components
| Description | Specification | When to replace | UNITEC-D category |
|---|---|---|---|
| A set of seals | PTFE/EPDM | Each time the sensor is removed | Consumables |
| Electronic module | According to the model range | In case of RAM failure/error | Electronics |
| Installation kit | Flanges/Bolts | In case of corrosion | Fastening |
A complete range of spare parts and new devices is available in our catalog: https://www.unitecd.com/e-catalog/
11. Links
- ISO 4064: Water meters for cold drinking water and hot water.
- DSTU EN 60770: Converters used in industrial control systems.
- Technical manuals of manufacturers (OEM manual for your model of flow meter).
