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Key points to consider when choosing a temperature sensor
The most suitable temperature sensor depends on the object to be measured, the temperature range, the required accuracy, the response speed, and the installation environment. Both thermocouples and resistance thermometer are commonly used for contact-type temperature measurement, but they excel in different conditions.
- Thermocouples: They are easy to use for measurements over a wide temperature range and at high temperatures, and are a good option when responsiveness is important.
- resistance thermometer: Suitable for relatively high accuracy and stable measurements, and are used in quality control and research development.
- Installation and wiring: Insertion depth, thermal contact, noise, lead resistance, and ambient environment affect the measurement results.
- Inspection and Calibration: In process where the reliability of measurement values is required, regular inspection, calibration, and record keeping are important.
1. What is a temperature sensor?
An entry point for treating temperature as an electrical signal.
A temperature sensor is a general term for devices and elements that detect the temperature of objects, air, liquids, equipment, etc., and convert it into a signal that can be used for display, recording, monitoring, and control. In factories and research facilities, it is important not only to measure temperature, but also to record the measured values, monitor for anomalies, and use that information for control and calibration as needed.
The difference between contact and non-contact.
This page focuses on contact-type temperature measurement, where the sensor is placed in contact with the object being measured to determine its temperature. Non-contact methods, such as radiation thermometer and thermal imaging cameras, are options when you want to determine the surface temperature of an object without touching it.
| Method | Typical example | Suitable uses | Points to note |
|---|---|---|---|
| Contact type | Thermocouples, resistance thermometer, thermistors | Liquids, gases, piping, inside furnaces, inside tanks, inside equipment | It is affected by the mounting condition, insertion depth, thermal contact, and wiring. |
| Non-contact type | radiation thermometer, thermal imaging camera | High-temperature objects, moving objects, surface temperature, objects that are difficult to touch. | It is affected by emissivity, distance, field of view, reflection, and the surrounding environment. |
2. Differences between thermocouples and resistance thermometer
Thermocouples and resistance thermometer are both contact-type temperature sensors, but they differ in their principles of temperature detection. This difference affects their temperature range, accuracy, response, wiring, and calibration considerations.
| Item | Thermocouple | Resistance thermometer |
|---|---|---|
| Detection principle | This method utilizes the thermoelectric power generated at contact between different metals. | This method utilizes the property of materials like platinum, where electrical resistance changes with temperature. |
| Strengths | Measurements that require high temperatures, a wide temperature range, and responsiveness. | A measurement method that prioritizes relatively high accuracy and stability. |
| Points to consider when wiring | Compensation wires, polarity, cold contact compensation, noise countermeasures. | 2-wire, 3-wire, 4-wire, lead resistance, current measurement. |
| Points to note | Degradation, drift, incorrect connection of compensation wires, and the effects of cold contact compensation. | Lead resistance, self-heating, and insulation degradation due to vibration and dew condensation. |
Rather than simply deciding "thermocouples are always used for high temperatures" or "resistance thermometer are always used for high accuracy," it is important to consider the measurement target, temperature range, installation environment, and recording, control, and calibration requirements together.
3. Basics of Thermocouples
Thermocouples measure temperature using thermoelectric power.
Thermocouples utilize the property that a small voltage is generated when a temperature difference occurs at the contact of two different metals. This phenomenon is called the Seebeck effect, and the temperature at the measurement point can be determined from the generated thermoelectric voltage and the temperature of the reference contact.
Typical types and how to use them
Thermocouples come in various types, including K, J, T, E, N, R, S, and B. K thermocouples are commonly used for general purposes, T thermocouples are suitable for low-temperature applications or situations requiring humidity resistance, and R, S, and B thermocouples are suitable for high-temperature furnaces. In actual selection, not only the temperature range but also the atmosphere, protective tube, response speed, and durability should be considered.
ground surface/non-ground surface/exposed type
ground type
While this can lead to faster response times, it can also be susceptible to electrical noise.
Non-ground surface
Compared to ground types, it is less susceptible to noise and has structure that is easy to use in industrial applications.
exposed type
While the response time is fast, the level of protection is low, so the usage environment should be carefully considered.
4. Fundamentals of resistance thermometer
resistance thermometer measures temperature by measuring the change in resistance.
resistance thermometer utilize the property that the electrical resistance of a metal changes with temperature. Typical examples include platinum-based Pt100 and Pt1000, which are suitable for relatively high accuracy and stable measurements. They are suitable for applications in quality control, research and development, equipment monitoring, and calibration.
Differences between 2-wire, 3-wire, and 4-wire systems
| wire system | Features | Main Applications |
|---|---|---|
| 2 wire system | Although it involves minimal wiring, this method is susceptible to the effects of lead resistance. | Short-distance or simple measurements. |
| 3 wire system | This method is commonly used in industrial applications and easily compensates for the effects of lead resistance. | General equipment measurement, monitoring, and control. |
| 4-wire | This method makes it easier to minimize the effect of lead resistance. | Research, calibration, and high accuracy measurements. |
Also be careful of self-induced fever.
Because resistance thermometer read resistance values by passing a measurement current through them, the element itself may generate a small amount of heat under certain conditions, which can lead to measurement errors. It is important to check the measurement current, mounting condition, and thermal coupling with the object being measured.
5. Errors that occur during installation and wiring, and countermeasures
The measurement value of a temperature sensor is not determined solely by the type of sensor. Thermal contact with the object, mounting location, protective tubing, wiring, and the surrounding environment all affect the measurement result.
| Check items | Common problems | Direction of review |
|---|---|---|
| Mounting location | The location you want to measure and the actual measurement point are misaligned. | We will check the representative point, insertion depth, fluid flow, and contact with the surface. |
| heat escape | Heat may escape to the protective tube or wiring, causing the reading to appear lower than it actually is. | We will review the insulation, insertion length, thermal conductive grease, and protective tube configuration. |
| noise | display values fluctuate, and the recording becomes unstable. | Check shield, twisting, wiring route, ground, and input filter. |
| Lead resistance | Wiring resistance can cause errors in resistance thermometer. | We will consider using 3-wire and 4-wire systems, low-resistance cables, and converters. |
| Environmental impact | vibration, moisture, corrosive gases, and dew condensation can cause disconnection and insulation degradation. | We will check the protective tubes, terminal boxes, moisture-proof structure, and vibration-resistant/corrosion-resistant specifications. |
6. How to choose a temperature sensor based on its application
When choosing a temperature sensor, you shouldn't simply decide whether to use a thermocouple or resistance thermometer; you should also consider the object being measured, the temperature range, the response speed, the environment, and the calibration requirements.
| Prioritized conditions | Methods that are likely to be candidates | Things I want to confirm |
|---|---|---|
| High temperature and wide temperature range | Thermocouple | Type, protective tube, atmosphere, durability, susceptibility to deterioration. |
| high accuracy and stability | Resistance thermometer | Line type, accuracy class, input device, calibration conditions, installation status. |
| response speed | Small-diameter thermocouples, thin and compact resistance thermometer | Size of the temperature-sensing element, protective tube, thermal coupling with the object, and flow rate. |
| vibration and shock | structure designed with seismic resistance in mind. | Protective tube diameter, fixing method, cable routing, and measures to prevent disconnection. |
| Corrosion, moisture, dew condensation | Sensors that prioritize protective structure | Materials, moisture resistance, terminal box, cable gland, and operating environment. |
| Auditing and Quality Assurance | Easy-to-calibrate configuration | Calibration cycle, calibration points, certificates, traceability, and record-keeping methods. |
7. Inspection and Calibration Approach
Inspection and calibration have different purposes.
Inspection is the process of verifying whether sensors and measuring instruments are functioning properly. Calibration is the process of comparing it to a reliable standard to determine how much difference there is. For critical process, it may be necessary to check not only the sensor itself but also the display, recorder, converter, and wiring.
Calibration cycle varies depending on working conditions
In environments with high temperatures, vibration, corrosive atmospheres, frequent attachment/detachment, and audited process, it is crucial to regularly check for sensor degradation and misalignment. Calibration cycles are determined based on internal standards, specification requirements, past calibration results, and the operating environment.
When using calibration results for quality assurance or audits, it is important to record the calibration date, calibration point, reference instrument, measurement results, judgment, and next calibration schedule. Calibration scope and conditions vary depending on the equipment configuration, so please check the latest information when installing or updating equipment.
8. Checklist before selecting a temperature sensor
Before choosing a temperature sensor, organizing the following points will make product selection and consultation easier.
| Item | Content to organize |
|---|---|
| What to measure | Air, liquids, solids, piping, inside furnaces, inside tanks, surfaces, interiors, etc. |
| Temperature range | Operating temperature, maximum and minimum temperatures, and short-term peak temperature. |
| Required accuracy | Control range, tolerance, calibration requirements, and display /recording resolution. |
| response speed | How quickly do you want to track temperature changes? |
| Installation environment | vibration, moisture, corrosive gases, dust, dew condensation, electrical noise, radiant heat. |
| Operation method | Whether display, recording, monitoring, alarms, control, and remote verification are required. |
| Maintenance/calibration | Replacement frequency, inspection method, calibration cycle, and whether a certificate is required. |
9. Chino temperature sensors and related information
Chino offers a range of products and services related to temperature measurement, including thermocouples, resistance thermometer, application-specific temperature sensors, temperature calibration equipment, and calibration services. When selecting a temperature sensor, considering not only the measurement point but also recording, monitoring, control, and calibration will help you create configuration that suits your specific needs.
Related Products and Services
Related basic knowledge
Are you having trouble selecting or calibrating temperature sensors?
We can consider the appropriate temperature sensor and peripheral equipment configuration based on the measurement target, temperature range, required accuracy, installation environment, and recording, control, and calibration requirements.
Frequently asked questions
Select the question you want to know about, and you will be taken to the answer below. You can check the basics of thermocouples and resistance thermometer thermometers, wiring and troubleshooting, and maintenance and inspection.
FAQ List
If you would like to review the questions first, please click the link below to go to the appropriate answer.
Basics/Selection
- What is the difference between a thermocouple and resistance thermometer?
- Which is better suited for high-temperature measurements?
- Which is better suited for high accuracy temperature measurement?
- How do you choose between a 2-wire, 3-wire, or 4-wire resistance thermometer?
- Does the temperature sensor need to be calibrated?
- What should I check before choosing a temperature sensor?
- What is the response time of a sensor?
Wiring and troubleshooting
- What settings do I need to configure on the temperature display and recorder?
- How should I choose an extension cord?
- What is cold contact compensation (CJC)?
- What happens if you connect a thermocouple with the wrong polarity?
- What is the difference between compensatory conductors and extension conductors?
- Will thermocouples drift or degrade?
- What should you check if the thermocouple reading is lower than expected?
resistance thermometer and maintenance
- What is the difference between Pt100 and Pt1000?
- How can the self-heating of resistance thermometer be suppressed?
- Are there any points to be aware of regarding the color order or terminal connections for a 3-wire system?
- What measures are necessary for long-distance wiring?
- Can humidity or dew condensation cause the readings of resistance thermometer to be affected?
- What do you check when display is unstable or unresponsive?
- Should I set up disconnection detection and anomaly detection?
- What do you check during a simple on-site inspection?
FAQ text
Q. What is the difference between a thermocouple and resistance thermometer?
Thermocouples utilize the thermoelectric force generated at contact of different metals and are suitable for measurements over a wide temperature range and at high temperatures. resistance thermometer utilize the change resistance of materials such as platinum and are suitable for relatively high accuracy and stable measurements.
Q. Which is better suited for high-temperature measurements: a thermocouple or resistance thermometer?
Thermocouples are generally more convenient for high temperatures or wide temperature ranges. However, the appropriate configuration will vary depending on the atmosphere, protective tube, response speed, and required accuracy.
Q. Which is better suited for high accuracy temperature measurement?
When relatively high accuracy and stable measurements are required, resistance thermometer are a suitable option. In practice, the decision should be made considering not only the sensor itself, but also the wiring, input devices, installation conditions, and calibration conditions.
Q. How do you choose between a 2-wire, 3-wire, or 4-wire resistance thermometer?
When using resistance thermometer, the effect of wiring resistance must be considered. Three-wire systems are commonly used in industrial applications, while four-wire systems are a viable option for high accuracy measurement and calibration applications.
Q. Does the temperature sensor need to be calibrated?
Regular calibration and inspection are crucial when the reliability of measurement values is required for quality control, research and development, audit compliance, and compliance with standards.
Q. What should I check before choosing a temperature sensor?
Organizing the measurement target, temperature range, required accuracy, response speed, installation environment, wiring distance, whether recording or control is necessary, and calibration requirements will make the evaluation easier.
Q. What is the response time of the sensor?
Response time is a measure of how quickly the sensor indicated value approaches the new temperature when the temperature changes suddenly. The smaller the temperature-sensing element, the better the thermal contact with the object, and the smaller the heat capacity of the protective tube and surrounding area, the faster the response tends to be.
Q. What settings do I need to configure on the temperature display and recorder?
Check the thermocouple type, resistance thermometer element/wire configuration, unit, input range, filter, alarm, scaling, etc. If the sensor type or wire configuration does not match the settings on the measuring instrument, it will lead to discrepancies in display value or abnormal display.
Q. How should I choose an extension cord?
For thermocouples, use appropriate compensating or extension wires, paying attention to polarity and connection material. For resistance thermometer, consider the wire type, wire diameter, wiring distance, and the use of a converter to minimize the effect of lead resistance.
Q. What is cold contact compensation (CJC)?
Cold contact compensation is a mechanism that corrects the temperature at the measuring instrument terminal where the thermocouple is connected, converts it to a reference temperature, and determines the temperature at the measurement point. This is often done automatically in loggers and transmitters, but in case of malfunction, the temperature environment and settings of terminal should also be checked.
Q. What happens if you connect a thermocouple with the wrong polarity?
Thermocouples have polarity, so connecting them incorrectly can result in an inaccurate reading of the temperature change direction and unnatural display. Check the plug, jack, terminal symbols, and color coding, and connect them according to the specifications and instruction manual.
Q. What is the difference between compensatory conductors and extension conductors?
Compensation wires are made from materials with thermoelectric characteristic similar to those of the thermocouple, while extension wires are made from materials equivalent to those of the thermocouple. Mixing different types of wires can cause errors, so choose a wire that matches the type of thermocouple.
Q. Do thermocouples experience drift or degradation?
Thermocouple characteristic can change due to high-temperature environments, oxidizing/reducing atmospheres, corrosive gases, and repeated use. Regular inspections, calibration, management of replacement timing, and selection of protective tubes can mitigate these risks.
Q. What should I check if the thermocouple reading is lower than expected?
Possible causes include heat escaping from the measurement point to the protective tube or wiring, insufficient insertion length, weak thermal contact with the object, or influence from ambient temperature. Check the mounting position, insertion depth, insulation, and use of thermal conductive grease.
Q. What is the difference between Pt100 and Pt1000?
Pt100 is a platinum resistance thermometer with a nominal resistance value of 100 Ω at 0°C, while Pt1000 has a nominal value of 1000 Ω. Because Pt1000 has a higher resistance value, it may be relatively less susceptible to the effects of lead resistance under certain conditions. Please verify which sensor type is supported by your equipment.
Q. How can the self-heating of resistance thermometer be suppressed?
resistance thermometer may generate a slight amount of heat depending on the measurement current. To minimize errors, avoid using excessively high measurement current, ensure good thermal contact with the object being measured, and check the installation conditions and input device specifications.
Q. Are there any points to be aware of regarding the color order or terminal connections for a 3-wire system?
In a 3-wire system, you need to correctly connect the two lead wires on the same side and the one on the opposite side to terminal. terminal symbols and color identification may vary depending on the equipment and standard, so check the notation such as A, B, B in the instruction manual.
Q. What measures are necessary for long-distance wiring?
For long-distance wiring, noise, lead resistance, contact resistance, and the impact of the wiring route become significant. Consider using twisted, shield, low-resistance cables, converters for 4-20mA signal conversion, or digital transmission.
Q. Can humidity or dew condensation cause the readings of resistance thermometer to be affected?
When insulation deteriorates due to moisture or dew condensation, measurement values may become inaccurate or fluctuate. Check the moisture-proof structure, terminal box, cable gland, seals, and installation location, and revise the protective structure as needed.
Q. What do you look at when display is unstable or slow to respond?
Check the mounting condition, the size of the temperature sensing element, the protective tube, the thermal contact with the object, filter settings of the measuring instrument, and the wiring noise. It is important to distinguish between whether the temperature change itself is slow or whether the response of the sensor or display is slow.
Q. Should I set up disconnection detection or anomaly detection?
For critical monitoring and control applications, it is effective to set up anomaly detection such as sensor disconnection, out-of-range, and higher limit / lower limit alarms. The concept of fail mechanisms, which operate on the safe side in the event of an anomaly, should also be reviewed according to the equipment and process.
Q. What do you check during a simple on-site inspection?
Use freezing point, boiling point, constant temperature bath, dry block, reference sensor, reference resistance, etc., to check for deviations in the measurement system, including display and recorder. For critical process, in addition to simple checks, also verify the necessary calibration certificates and traceability.
Reference information
- For detailed information regarding thermocouples, resistance thermometer, and calibration, please refer to specifications, instruction manuals, applicable standards, and internal company standards for each product.
- This page utilizes AI assistance for configuration planning and some image creation. The content is based on publicly available information and CHINO Corporation 's product and service information. Product specifications, calibration scope, and support conditions may change, so please check the latest product and service information when considering implementation.
