Guide to Detection and Correction of Temperature Measurement Errors: Sensor Selection, Thermal Lag, Conductor Resistance and Transmitter Setup

1. Problem Description and Area of Application

Symptoms

During the execution of temperature measurements in industrial systems in production, the following symptoms may be observed:

• Unstable or varying temperature indications;
• Deviation of indications from the real value by 2–5 %;
• Mismatch with data from other measurement sources;
• Increased measurement frequency of differences when temperature changes;
• Failures in the function of temperature control systems.

Area of application

This guide is intended for production systems where thermocouples and temperature transmitters are used, including:

• Machinery;
• Thermal systems;
• Chemical production;
• Energy;
• Food industry.

Severity Classification

Critical

If temperature measurements are used for the safety control or operation of critical equipment, deviations may lead to emergency shutdown or hazardous situations.

Major overhaul

If measurements are used for product quality control or process efficiency, deviations may reduce productivity or require additional control.

Minor

If there is no impact on safety or product quality, measurement deviations may be deferred for resolution.

2. Safety

Requirements for the use of protective clothing

During the execution of temperature sensor and transmitter diagnostics, it is necessary to use:

• Gloves;
• Goggles;
• Working form;
• Appropriate protective clothing.

Power Off Warning

Before opening the equipment and diagnostics, the lockout/tagout procedure must be performed in accordance with the standards EN 308 and ISO 12100.

Energy Storage Warning

In the case of absence of electrical energy in the equipment, it is necessary to check the presence of energy in the circuit or perform electrical disconnection according to the standards EN 50110.

High Temperature Warning

During temperature measurement in high-temperature systems, it is necessary to avoid contact with surfaces to prevent burns.

3. Required Tools

Tools	Model/Specification	Measurement range	Purpose
Multimeter	Fluke 434 II	0–2000 Ω, 0–20 mA, 0–600 V	Measurement of electrical parameters
Thermal camera	FLIR T1030sc	–20°C to 1200°C	Surface Temperature Definition
Vibration Analyzer	Keysight 35670A	0–100 kHz	Vibration measurement and temperature sensing
Digital thermometer	Testo 825	–20°C to 1000°C	Thermocouple Measurement Check
Electrical Connection Support	Fluke 117	0–200 V	Electrical connections check

4. Primary Assessment

Criterion	Action
Operating Conditions	Record ambient temperature, humidity, pressure, and electrical parameters.
Changes in the system	Check whether the sensors, cables, or transmitter settings have been changed.
Alarm History	Check alarm logs and error logs.
Physical condition of the equipment	Check for mechanical damage, leaks, and absence of air connections.

5. Systematic Diagnosis

Diagnostic schematic

1. System Check:
   • Measure the temperature using a thermometer and thermal camera.
   • Compare the readings with measuring instruments.
   • If the deviation exceeds 2 %, perform the next step.
2. Sensor type check:
   • Determine whether a thermocouple, thermistor or resistance temperature detector is used.
   • Check whether the sensor type meets the requirements of the production process.
   • If the type meets the requirements, proceed to the next step.
3. Thermal lag check:
   • Measure the temperature compliance according to changes in the process.
   • Check for a delay of 5 to 10 seconds.
   • If the delay exceeds 10 seconds, perform the next step.
4. Resistance Check:
   • Measure the sensor conductor resistance.
   • If the resistance is more than 500 Ohms, perform the next step.
5. Transmitter settings check:
   • Check if the transmitter parameters are correctly set.
   • If the parameters match, proceed to the next step.

6. Matrix of Root Causes

Symptom	Likely Causes	Diagnostic Testing	Expected result
Unstable indications	Inadequate sensor type Thermal delay High Resistance Conductors Incorrect transmitter settings	Measure the temperature with a thermometer and a thermal camera. Check the sensor type. Measure the thermal delay. Measure the resistance of the conductors. Check the transmitter settings.	Deviation from the actual value. Sensor type mismatch. Deviation from thermal delay. Resistance of conductors more than 500 Ohm. Incorrect transmitter settings.
Deviation from the actual value	Inadequate sensor type High resistance of conductors Thermal delay Incorrect transmitter settings	Measure the temperature with a thermometer and a thermal camera. Check the sensor type. Measure the thermal delay. Measure the resistance of the conductors. Check the transmitter settings.	Deviation from the actual value. Mismatch of sensor type. Deviation from thermal delay. Resistance of conductors more than 500 Ohm. Incorrect transmitter settings.

7. Root Cause Analysis

1. Incorrect sensor type selection

Cause: Using the wrong type of sensor (thermocouple, thermistor, resistance temperature detector) for a specific process may lead to inaccurate temperature measurements.

Confirmation: Sensor type check and comparison with process requirements.

Influence: Measurement inaccuracies may lead to inefficient process control, loss of product quality or hazardous situations.

2. High resistance conductors

Cause: High resistance conductors may lead to incorrect temperature measurement due to energy loss.

Confirmation: Measuring conductor resistance with a multimeter.

Influence: High resistance may lead to a decrease in measurement accuracy, which may affect the process efficiency.

3. Thermal Delay

Cause: Thermal delay occurs due to the sensor's lack of rapid response to temperature changes.

Confirmation: Sensor response time measurement.

Influence: Delay may lead to incorrect measurements, which may affect the product quality or process efficiency.

4. Incorrect transmitter settings

Cause: Incorrect transmitter settings may lead to inaccurate temperature display.

Confirmation: Transmitter settings check.

Impact: Incorrect settings may lead to incorrect data, which may affect the process efficiency.

8. Steps to Resolve

1. Choosing the right type of sensor

1. Determine which type of sensor meets the process requirements.
2. Replace the sensor with the corresponding type.
3. Check whether the sensor meets the requirements.

2. Reduction of conductor resistance

1. Measure the resistance of the conductors.
2. Replace conductors with high resistance.
3. Check the resistance of the conductors.

3. Reduction of thermal delay

1. Measure the response time of the sensor.
2. Replace the sensor with a faster response sensor.
3. Check response time.

4. Transmitter Settings Adjustment

1. Check the transmitter settings.
2. Change settings according to requirements.
3. Check settings.

9. Preventive Measures

Root Cause	Preventive strategy	Control Method	Recommended interval
Incorrect sensor selection	Use of the appropriate type of sensor	Sensor type check	Annually
High resistance of conductors	Periodic replacement of conductors	Resistance Measurement of Conductors	Every 6 months
Thermal delay	Use of fast response sensors	Response Time Measurement	Annually
Incorrect transmitter settings	Periodic check of settings	Transmitter Settings Check	Monthly

10. Production Components

Component Description	Specification	When to replace	Category UNITEC-D
Thermocouple	Thermocouple, thermistor, resistance temperature detector	When measurements deviate	03.02.05
Conductors	Minimum resistance 500 Ohm	At high resistance	03.02.06
Temperature transmitter	Configured parameters	When incorrectly set up	03.02.07

Contact UNITEC-D for the appropriate components:
https://www.unitecd.com/e-catalog/

11. References

• EN 60584 — Temperature Sensors
• ISO 16034 — Temperature Transmitters
• DSTU 3013 — Requirements for Temperature Control
• Manufacturer's Maintenance Manuals
• Technical documents UNITEC-D

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