What types of temperature sensors are there?
Broadly, we distinguish two groups: sensors for continuous measurement with an electrical output signal (thermocouples, RTDs, thermistors, IR sensors) and switching elements for simple on/off control (thermostats). The right choice depends on measuring range, accuracy, response time, process conditions and the desired interface with your control system.
Thermocouple
Fast-responding and compact, with a wide measuring range from -200 °C to +2000 °C. Common types are K (NiCr–Ni) for general industrial use and J (Fe–CuNi) for lower temperatures. Use this type when the process reaches extreme temperatures or a fast response is required.
RTD – Resistance temperature detector (Pt100 / Pt1000)
High accuracy and excellent linearity in the range of -200 °C to +600 °C. Choose an RTD when signal quality and long-term stability are paramount, for example in laboratories or the process industry. The Pt1000 is less sensitive to cable resistance and therefore suited for longer cable runs.
Thermistor
NTC for very fast response at low temperatures (-50 °C to +150 °C), used in HVAC and cooling installations. PTC for protection circuits where resistance increases sharply when a threshold temperature is exceeded.
Thermostat
Electromechanical switch with bimetal element. No continuous signal, but direct on/off switching at a settable point. Used in boiler and HVAC installations where simple control is sufficient.
Non-contact IR sensor
Measures surface temperature via infrared radiation without physical contact. Use this type when the medium is moving, hazardous or when contact is technically not possible.
Comparison: which type of temperature sensor suits your application?
| Type |
Measuring range |
Accuracy |
Response time |
Application |
| Thermocouple |
-200 to +2000 °C |
Moderate |
Fast |
High temperatures, metal industry |
| RTD (Pt100/Pt1000) |
-200 to +600 °C |
High |
Average |
Process industry, laboratories |
| Thermistor (NTC) |
-50 to +150 °C |
Very high (narrow range) |
Very fast |
HVAC, cooling installations |
| Thermostat |
Settable point |
Switching |
Slow |
Boilers, simple control |
| IR sensor |
Depending on type |
Moderate |
Very fast |
Surface measurement, moving parts |
How do you install a temperature sensor?
Contact types (thermocouple, RTD) are installed in a protection tube or thermowell in the pipework, with sufficient insertion length for a representative measurement. If the insertion length is too short, ambient temperature influences the measurement result through conduction losses along the protection tube.
Points to consider during selection and installation:
- Choose the insertion length based on pipe diameter and flow velocity
- Use vibration-resistant mounting under mechanical load
- Ensure correct sealing under overpressure or with aggressive media
- For panel or machine construction, M12 mounting is standard
IR sensors are installed in line of sight with the correct spot size, at a distance according to the D:S ratio of the optics. Compensate for the emissivity of the surface being measured and avoid steam or dust in the measurement path.
Temperature sensors in the process industry
In the process industry, temperature sensors are used for monitoring reactors, heat exchangers, steam lines and cooling installations. RTDs are combined with transmitters that deliver a 4–20 mA or IO-Link signal to the PLC system. In complex installations,
turbidity sensors are additionally used for quality monitoring of liquids alongside temperature and pressure measurements — enabling integrated process instrumentation where deviations are detected immediately.
Select your temperature sensor based on measuring range, process connection and signal type (Pt100, Pt1000, 4–20 mA, IO-Link) or request a quote directly. Unsure which type is right for your application? Our process instrumentation specialists advise on type, range and housing — schedule a free consultation today.
Frequently asked questions about temperature sensors
What is the function of a temperature sensor?
A temperature sensor converts temperature differences into an electrical signal that your control system or logger reads. This allows you to regulate processes stably, set alarms and detect quality deviations in time. Reliable temperature measurement prevents overheating, energy waste and unnecessary downtime.
When do I choose a thermocouple instead of an RTD?
Choose a thermocouple when your process temperature exceeds +600 °C, when a fast response time is required or when a compact design is needed. An RTD (Pt100/Pt1000) is the better choice when high accuracy and long-term signal stability are decisive within a range of -200 °C to +600 °C.
How do I know if my temperature sensor is faulty?
Symptoms include an absent or deviating signal. With an RTD or thermistor, an illogical ohm value indicates an open or short circuit. With a thermocouple, a missing or unrealistic millivolt output points to a fault. Compare the reading with a certified reference thermometer or use a calibrator. Also check connectors, terminals and cable breaks — many transmitters automatically display a fault message or error code.
What is the D:S ratio of an IR sensor?
The D:S ratio (distance-to-spot) indicates the size of the measurement spot at a given distance. A D:S of 10:1 means the sensor measures a spot of 1 cm diameter at 10 cm distance. The higher the ratio, the smaller the spot at greater distance — enabling more accurate measurement of smaller objects.
Where do I install a temperature sensor in my system?
Install contact sensors in a thermowell or immersion socket in the pipework, with sufficient insertion length and flow for a representative measurement. IR sensors are mounted in line of sight at the correct distance according to the optics, free from steam or dust. For panel or machine construction, M12 mounting is standard.
