1. Description of the problem and scope

This guide is dedicated to solving problems related to inaccurate temperature measurements. Common symptoms include: deviation of sensor readings from real values, incorrect display of temperature on control panels, inconsistency of temperature parameters of technological processes. Problems can occur in all types of industrial equipment, including heating plants, refrigeration systems, engine cooling systems and industrial processes. Compliance with critical changes in temperature measurement can lead to serious losses in production efficiency or even emergency situations.

2. Safety precautions

Use appropriate personal protective equipment (PPE):

Goggles with protection against evaporation or high-temperature radiation.

Gloves with resistance to high temperatures.

Protective clothing with a low level of heating.

Protective mask when working with electrical devices.

Perform lockout and tag (LOTO) procedures:

Before diagnosis, stop the equipment and turn off the power.

Label all connections and busbars to avoid unnecessary switching.

Check for stored energy voltages or electrical static charges.

Temperature measurement in extreme conditions:

Do not measure in places with high humidity or high temperature.

Use thermography to determine temperature deviations from normal values.

3. Necessary diagnostic tools

Tool	Model/specification	Measuring range	Purpose of use
Multimeter	Multimeter Fluke 434	0–2000 Ω, 0–20 mA, 0–1000 V	Measurement of resistance of conductors, current, voltage.
Thermograph	FLIR T1020	-20°C to 1000°C	Determination of thermal deviations on the surface.
Optical temperature meter	Thermoscan 500	0°C to 500°C	Temperature measurement at a distance without contact.
A thermometer with a built-in sensor	Thermometer Type K	-20°C to 1000°C	Accurate temperature measurement in deep holes or pipes.
Vibration meter	Keyence VK-9710	0–20000 Hz	Determination of the influence of vibration on the accuracy of sensors.

4. Initial assessment before diagnosis

Item	action
1	Check the appearance of the sensor and busbar.
2	Record the temperature readings from the thermometer scale.
3	Record the measurement values that are displayed in the control system.
4	Check if the last maintenance was done.
5	Record the history of shutdowns and deviations in the system.
6	Record the resistance values of the conductors, if available.

5. Systematic diagnostic scheme

Symptom: Deviation of readings from actual values.
1. Check the choice of sensor type.
  1. If a type K sensor is used, check its compliance with DSTU 4185:2004.
  2. If a type J sensor is used, check if it is compatible with EN 60584-2.
2. Check the thermal delay.
  1. Measure compliance with the ISO 7245:2010 standard: the maximum allowable thermal delay is 5 seconds.
3. Check the resistance of the conductors.
  1. Measure the resistance of the conductors with a multimeter in the range of 0-2000 Ω. The permissible resistance is no more than 0.5 Ohm.
4. Check transmitter settings.
  1. Make settings in the range of 4-20mA. Check compliance with EN 60068-2-2.

6. Matrix of causes of deviations

Symptom	Probable causes (in descending order of probability)	Diagnostic test	Expected result
Deviation of readings	Wrong sensor type Thermal delay High resistance of conductors Incorrect transmitter settings	Check sensor type and compliance with standards. Measure the thermal delay with a thermograph. Measure the resistance of the conductors with a multimeter. Check transmitter settings in 4-20mA mode.	Compliance with standards. Deviation from the permissible value of thermal delay. Conductor resistance is higher than permissible. Incorrect transmitter settings.

7. Analysis of the causes of deviations

7.1. Incorrect choice of sensor type

Reason: Using the wrong type of sensor can lead to incorrect temperature readings. For example, the J-type sensor does not meet the requirements for measuring high temperatures. Compliance with DSTU 4185:2004 and EN 60584-2 is critical.

Diagnostics: Check sensor selection and compliance with requirements. Use a thermograph or probe with the appropriate range.

Side effect: Incorrect readings can cause improper process regulation, resulting in production losses or equipment failure.

7.2. Thermal delay

Reason: The temperature measurement delay may occur due to the high thermal inertia of the sensor. The ISO 7245:2010 standard sets a maximum allowable delay of 5 seconds.

Diagnostics: Measure the thermal delay using a thermograph. Measure the time from the moment of temperature change to the moment of display on the indicators.

Side effect: Deviation from the norm can lead to incorrect management of technological processes, which affects the quality of products.

7.3. High resistance of conductors

Reason: High conductor resistance can cause temperature readings to shift due to energy loss. The EN 60068-2 standard sets the permissible resistance of conductors in the range of 0–0.5 Ohm.

Diagnostics: Measure the resistance of the conductors with a multimeter in the range of 0-2000 ohms. Take measurements at various points in the system.

Side effect: Incorrect readings can lead to system shutdown or deviation from technological parameters.

7.4. Incorrect transmitter settings

Reason: Incorrect transmitter settings can cause incorrect temperature display. The EN 60068-2 standard establishes a range of 4–20 mA for signal transmission.

Diagnostics: Check the transmitter settings and measure the current between 4 and 20 mA. Take measurements at various points in the system.

Side effect: Incorrect display of temperature can lead to system shutdown or deviation from technological parameters.

8. Step-by-step solution procedures

8.1. Choosing the right type of sensor

Specify the type of temperature measurement (for example, high range or low range).
Choose a sensor that meets the requirements of DSTU 4185:2004 or EN 60584-2.
Install the sensor in a suitable place, taking into account the thermal effect.
Check compliance with standards and display on control panels.

8.2. Thermal lag correction

Perform a thermal delay measurement using a thermograph.
Determine the delay time from the moment of temperature change to the moment of display on the indicators.
Check compliance with ISO 7245:2010.
Use a sensor with a shorter thermal delay.

8.3. Correction of conductor resistance

Measure the resistance of the conductors with a multimeter in the range of 0-2000 ohms.
Check for compliance with EN 60068-2.
Replace conductors or use sensors with higher compliance.
Check the display on the control panels after the correction.

8.4. Correcting transmitter settings

Measure the transmitter current between 4 and 20 mA.
Check for compliance with EN 60068-2.
Tune the transmitter to the appropriate point.
Check the display on the control panels after the correction.

9. Prevention

The main reason	Prevention strategy	Monitoring method	Recommended interval
Incorrect sensor type	Selection of a sensor with compliance with standards.	Periodic compliance checks.	Annually.
Thermal delay	Use of sensors with a lower thermal delay.	Thermograph measurement.	Annually.
High resistance of conductors	Use of conductors with low resistance.	Measurement with a multimeter.	Annually.
Incorrect transmitter settings	Periodic check of settings.	Current measurement in the range of 4–20 mA.	Annually.

10. Replacement components and parts

Description of the part	Specification	When to replace	UNITEC-D category
Type K temperature sensor	Range: -20°C to 1000°C	After failure or failure measurement	Thermal sensors
Type J temperature sensor	Range: -20°C to 1000°C	After failure or failure measurement	Thermal sensors
Conductor for the sensor	Resistance: up to 0.5 Ohm	After failure or failure measurement	Electrical conductors
Temperature transmitter	Range: 4–20 mA	After failure or failure measurement	Electronics

Select the desired component from our catalog: https://www.unitecd.com/e-catalog/

11. Links

DSTU 4185:2004 – Temperature sensors.
EN 60584-2 – Temperature sensors.
ISO 7245:2010 – Thermal delay.
EN 60068-2 – Measurement rules.
UNITEC-D Maintenance Guides – Additional recommendations.