Temperature Sensors – Thermistors Vs Thermocouples
Temperature measurement is a crucial factor in most industrial applications. Temperature sensors help determine the temperature of the given object or system, depending upon their type. This is important because most systems and processes require maintaining a certain temperature for proper functioning. An alarm is raised if the temperature range exceeds or falls beyond the defined limits. Hence, noting this temperature on a regular basis mitigates the risk of system damage and safeguards the personnel from any probable mishaps. Depending upon the requirement, there are various types of temperature sensors and probes such as thermocouple temperature sensors, thermistors, tubular thermistor probes, and so on. This post offers a comparative account of thermistors and thermocouples as temperature sensors, and how to choose the right one based on your application.
Thermocouples vs Thermistors: A Comparative Account
This section concentrates on two types of temperature sensors and their suitability in various applications— thermocouples and thermistors. Let’s see some details of these two types of temperature sensors and the difference between them:
1. Thermistors: These are heat-sensitive resistors, and they offer accurate and stable temperature sensing for various applications. There are positive and negative temperature coefficient (PTC and NTC) thermistors. They display a huge change in resistance in proportion to even a small change in temperature. Usually, NTCs are more widely used as they reflect the minutest changes in temperature. NTCs show a considerable decrease in resistance as the temperature increases; so, here the resistance and temperature are inversely proportional to each other.
Here are some important features of thermistors:
- They are mainly used in industrial applications rather than domestic for temperature measurement and control applications.
- Thermistors are made of metals such as cobalt, manganese, nickel or any semiconductor material, and are usually coated or encapsulated with epoxies, Teflon, or glass.
- They have a very fast repose time of less than a second. Usually, it ranges from 0.2 to 10 seconds.
- They have a linear characteristic curve.
- They can withstand temperature ranges from -200 to +1200 degree Celsius.
- They sense temperature changes based on resistance; so, it is the main parameter.
Here are some of their application areas:
- Oil & gas temperature monitoring systems
- Coolants in automotive products
- Incubator temperature maintenance systems
- Digital thermostats
- 3D printing
2. Thermocouple Temperature Sensors: Thermocouples are temperature sensors comprising two wires connected at two different points. These wires are made of two different metals. These connected wires form two junctions— hot and cold. While hot is the actual temperature measuring junction, cold serves as the reference junction. The temperature difference in these two junctions leads to the production of thermos-electric voltage, which is a low DC voltage. Based on this voltage, the temperature can be detected and resistance is measured.
Here are some important features of thermocouple temperature sensors:
- These are used for thermal conductivity, as well as in temperature measurement and control applications.
- They are usually made of iron, copper, or alloys of nickel, chromium, tungsten, iridium, and more. Most of them have mineral insulation, and can be customized based on bending, calibrating, and other features.
- They have a fast response time ranging from 0.1 to 10 seconds.
- They can withstand temperature ranges from -50 to +500 degree Celsius.
- Their characteristic curve is non-linear.
- They measure the temperature changes based on the voltage at the junction.
Thermocouples are used in industrial systems and processes, as well as domestic appliances. Here are some application areas of thermocouple temperature sensors:
- Temperature measurement and control in kilns, boiling systems, and furnaces
- Steel and iron industrial units
- Gas-powered turbines
- Fire alarm systems
How to Choose the Right One Based on Your Application?
While the above points may serve as a guideline when selecting the right temperature sensor for your application, here are a few parameters which may prove useful when making a decision:
- Stability of the temperature sensor: This largely depends upon the quality of materials used in making the thermistor or thermocouple. When selecting, check for coating and encapsulation materials as they increase the stability of the sensor.
- Accuracy: This is a crucial aspect of any process or tool. You need to determine the level of accuracy you require. When checking the accuracy of the temperature sensor, consider the temperature range they can withstand, and following that check the smallest temperature difference they can determine.
- Resistance to noise: Check if the sensors are resistant to electrical noise when switching on. Also, check for lead resistance.
- Packaging: Check for coatings such as epoxies and glass. Again, this depends upon the environment the temperature sensor will be subjected to. Coatings and housings are essential in harsh environments.
If you are looking for high-quality temperature sensors which give accurate readings, ensure you source them from a known manufacturer and supplier. Also, ensure you get them customized to suit your requirements. Therm-x manufactures high-quality temperature sensors, controllers, and offers end-to-end solutions on temperature-related process control.