The two main types of temperature sensors are Thermocouples and Resistance Temperature Detectors (RTDs), also known as resistance thermometers.
Thermocouples are very popular temperature sensors because of their low cost, versatility and ruggedness. They consist of two different metals joined together, making a continuous circuit. When there is a temperature difference between any two points in the circuit, an electromotive force (voltage) occurs. There are several types of thermocouples, constructed from different metals and with differing temperature ranges and accuracies.
The main advantages of thermocouples include:
- High temperature operating range: can be used in applications with temperatures as high as 1700°C
- Versatility: can be formed to fit a particular application
- Durability in high vibration or mechanical shock applications
- Low cost
- Generally smaller than RTDs
Resistance Temperature Detectors (RTDs)
Resistance Temperature Detectors, also known as RTDs and resistance thermometers, are temperature-sensing devices that changes resistance at a predetermined rate in response to changes in temperature. They are circuit elements whose resistance increases with increasing temperature in a predictable manner.
Pyrosales’ RTDs are specially designed to ensure precise and repeatable temperature versus resistance characteristics. The sensors are constructed in a unique strain-free manner, and use only high quality RTD elements. Ceramic wire-wound elements, flat film technology elements or military spec anti-vibration elements are used as per customer’s requirement to ensure the most suitable specification is supplied.
The main advantages of RTDs include:
- High accuracy/precise measurement
- High signal-to-noise output, which increases the accuracy of data transmission and permits greater distances between the sensor and the measuring equipment
- Physical and chemical stability over a wide temperature range
- Standardisation (elements are available to meet or exceed the requirements of various standardisation agencies)
- Wide temperature operating range
- High temperature operating range
- Linear over wide operating range
- Interchangeability over wide range
- Repeatability even after long exposure to temperatures within the operating range
Thermocouple or RTD – Which is Right for My Application?
Both thermocouples and RTDs are useful sensors for determining process temperature.
Thermocouples are generally less expensive than RTDs. They are more durable in high vibration or mechanical shock applications and are usable to higher temperatures. Thermocouples can be made smaller in size than most RTDs and they can be formed to fit a particular application. It is best to use thermocouples when:
- Point, rather than area sensing, improves control
- The element will be used in applications with temperatures in excess of 650°C
- The element will be used in high vibration or mechanical shock applications
- Cost is an issue
RTDs provide higher accuracy than thermocouples in their temperature range because platinum is a more stable material than most thermocouple materials. RTDs also use standard instrumentation wire to connect to the measurement or control equipment, which has the ability to decrease the overall installation cost. It is best to RTDs when:
- Accuracy and stability are requirements of the customer’s specification
- Accuracy must extend over a wide temperature range
- Area, rather than point sensing, improves control
- A high degree of standardisation is desirable
When choosing a sensor, it is always best to seek technical advice to ensure that you select the best sensor for your unique needs. Contact our experienced sales team for assistance in finding the right sensor for your application.