1. Description of the problem and scope
This guide is dedicated to diagnosing temperature measurement inaccuracies caused by incorrect sensor selection, thermal delay, wire resistance, and incorrect transmitter settings. The problem can occur in industrial equipment such as production plants, heating elements, temperature control systems, as well as in the production of food products, chemical liquids and energy equipment. The severity of a problem can be defined as critical if it results in incorrect production or hazards to personnel.
2. Security
Use protective clothing (PPE) and additional protective equipment (PPE) to avoid contact with electrical and thermal elements. Perform a lockout/tagout (LOTO) procedure to shut off power and remove stored energy prior to diagnosis.
When measuring temperature in systems with a high level of energy (for example, in installations with gas or electric drive), be sure to follow safety measures. Provide direct access to equipment and use tools with a high level of stability and accuracy.
3. Necessary diagnostic tools
| Tool | Model/Spec | Measuring range | Purpose |
|---|---|---|---|
| Multimeter | Fluke 87V | 0–2000 Ω, 0–20 mA, 0–200 V | Measurement of wire resistance, current and voltage |
| Thermograph | FLIR T1020 | -20°C to 550°C | Determination of temperature deviations on the surface |
| Vibration analyzer | BBB VIBRA-700 | 0–10000 Hz | Detecting the effect of vibration on the sensor |
| Temperature sensor | PT100, K-type | –200°C to 850°C | Confirmation of compliance of the sensor with the requirements |
4. Initial assessment
| Item | Description |
|---|---|
| 1 | Check the current operating conditions of the equipment (temperature, humidity, load). |
| 2 | Record the history of alarms and errors in the system. |
| 3 | Check for changes in the structure of equipment or measurement systems in the last 24 hours. |
| 4 | Determine whether the parameters of the measured quantities have changed in comparison with the previous data. |
| 5 | Check that sensors and transmitters are configured accordingly. |
5. Systematic diagnostic scheme
- Symptom: Temperature measurement inaccuracy.
- Confirm: Measure the temperature with a thermograph.
- Result: The temperature on the surface does not correspond to the readings of the sensor.
- Conclusion: There is a thermal delay or incorrect installation of the sensor.
- Result: The temperature on the surface corresponds to the readings of the sensor.
- Conclusion: Check the resistance of the wires and the settings of the transmitter.
- Result: The temperature on the surface does not correspond to the readings of the sensor.
- Confirm: Measure the temperature with a thermograph.
- Symptom: Discrepancy between measured data and real values.
- Confirm: Measure the resistance of the sensor wires.
- Result: The resistance of the wires is higher than 100 Ω.
- Conclusion: Wrong sensor or worn wire.
- Result: The resistance of the wires is within 0–100 Ω.
- Conclusion: Check transmitter settings and connection diagram.
- Result: The resistance of the wires is higher than 100 Ω.
- Confirm: Measure the resistance of the sensor wires.
- Symptom: Incorrect correspondence of the measured temperature values to the real state of the equipment.
- Confirm: Measure system vibration.
- Result: Vibration above 5 mm/s.
- Conclusion: Vibration affects the accuracy of the sensor.
- Result: Vibration within 0–5 mm/s.
- Conclusion: Check for thermal delay or incorrect sensor selection.
- Result: Vibration above 5 mm/s.
- Confirm: Measure system vibration.
6. Matrix of causes of deviations
| Symptom | Reasons | Diagnostic testing | Expected result |
|---|---|---|---|
| Inaccuracy of temperature measurement | 1. Incorrect choice of sensor 2. Thermal delay 3. High wire resistance 4. Incorrect transmitter settings |
Measure the resistance of the wires, measure the vibration using a thermograph | Wire resistance >100 Ω, vibration >5 mm/s, temperature differs from the actual value |
| Discrepancy between measured data and real values | 1. Incorrect transmitter settings 2. Incorrect connection scheme 3. Worn sensor |
Check the settings of the transmitter, measure the resistance of the wires, measure the temperature with a thermograph | Incorrect settings, deviation from standard values, worn sensor |
| Effect of vibration on sensor accuracy | 1. High vibration 2. Improper capture of the sensor |
Measure the vibration, check the fixation of the sensor | Vibration >5 mm/s, the sensor is not fixed |
7. Analysis of root causes
7.1 Incorrect selection of the sensor
Sensor selection plays a critical role in measurement accuracy. Sensors have different temperature ranges, compliance with standards (DSTU, EN, ISO) and compliance with operating conditions. The wrong choice can lead to significant deviations in the readings.
Confirmation: Check sensor specifications and compare with system requirements. Use a thermograph to determine deviations.
Side effects: An incorrect sensor can cause incorrect production, explosions or equipment destruction.
7.2 Thermal delay
Thermal delay occurs due to incorrect location or lack of thermal insulation. This results in the sensor not responding to temperature changes in real time.
Confirmation: Use a thermograph to determine deviations in surface temperature. Check the location of the sensor.
Side Effects: Incorrect readings can lead to system mismanagement, resulting in loss of performance or energy.
7.3 High resistance of wires
High wire resistance can lead to signal distortion or decrease in measurement accuracy. This is especially critical for sensors with a high level of stability.
Confirmation: Measure the resistance of the wires with a multimeter. If the resistance is higher than 100 Ω, it indicates a worn wire or a bad connection.
Side effects: Incorrect readings of the measuring system can lead to explosions, leaks or equipment failures.
7.4 Incorrect transmitter settings
The transmitter is responsible for transmitting the signal from the sensor to the control system. Incorrect settings may result in incorrect readings or system failure.
Confirmation: Check transmitter settings and compare with technical documentation. Use a multimeter to measure voltage and current.
Side effects: Incorrect settings can lead to loss of system control, causing hardware failure.
8. Step-by-step correction procedures
8.1 Choosing the right sensor
- Determine the required temperature range according to the system requirements.
- Check the compliance of the sensor with the standards (DSTU, EN, ISO).
- Install the sensor in a suitable place, taking into account thermal insulation.
- Use a thermograph to confirm compliance.
8.2 Correction of thermal delay
- Check sensor location and compliance with standards.
- Apply thermal insulation if necessary.
- Use a thermograph to determine deviations.
- Check the operating temperature of the system.
8.3 Correction of high wire resistance
- Measure the resistance of the wires with a multimeter.
- Replace the wire if the resistance is greater than 100 Ω.
- Check the connections for corrosion or wear.
- Use a thermograph to determine deviations.
8.4 Correcting incorrect transmitter settings
- Check the transmitter settings and compare with the technical documentation.
- Change the settings if they differ from the default.
- Use a multimeter to measure voltage and current.
- Check transmitter compliance with standards.
9. Preventive measures
| The root cause | Prevention | Monitoring | Periodicity |
|---|---|---|---|
| Incorrect sensor selection | Use sensors appropriate to the standards and operating conditions | Periodic temperature measurement | Weekly |
| Thermal delay | Application of thermal insulation, correct location of the sensor | Thermograph measurement | Every month |
| High wire resistance | Periodic inspection of connections, use of stable wires | Measurement of wire resistance | Weekly |
| Incorrect transmitter settings | Setting up the transmitter according to the standards | Measurement of voltage and current | Every month |
10. Replacement parts and components
| Component description | Specification | When to replace | UNITEC-D category |
|---|---|---|---|
| Temperature sensor PT100 | -200°C to 850°C | After wear or after measuring high resistance | UNITEC-D 12345 |
| Wire from the temperature sensor | Minimum resistance, 0–100 Ω | After detecting high resistance or wear | UNITEC-D 67890 |
| Temperature transmitter | Compliance with EN, ISO standards | After detecting incorrect settings | UNITEC-D 54321 |
| Thermograph | -20°C to 550°C | After use or wear and tear | UNITEC-D 98765 |
Please refer to our e-catalog for detailed information on replacement components: https://www.unitecd.com/e-catalog/
11. Links
- Standards: DSTU, EN 60584, ISO 60584
- Manufacturer's technical documentation
- The UNITEC-D series of guides for equipment
- UNITEC-D digital e-catalogue
This guide is compiled in accordance with the requirements of industry standards and production processes. It is designed for effective diagnosis and correction of temperature measurement inaccuracies in industrial systems.
