Temperature transmitters have found increasing applications in industrial sectors such as petroleum, chemical industries, synthetic fiber, textiles, rubber, construction materials, power, metallurgy, pharmaceuticals, and food processing, particularly in the field of process control. Among these transmitters, those using resistance temperature detectors (RTDs) and thermocouples are the most common.
These transmitters use RTDs or thermocouples as temperature-sensing elements. The signal output from the sensing element is sent to the transmitter module, where it undergoes several processes including voltage regulation, signal filtering, operational amplification, non-linear correction, V/I conversion, constant current control, and reverse protection.
Ultimately, the transmitter converts the temperature signal into a standardized 4–20mA current signal that is linear with respect to temperature.
This allows for the conversion of the temperature variable into a transmissible signal, ensuring the transmission of the standard constant-current loop signal to receiving devices in a continuous manner.
RTD Temperature Transmitters
RTDs employed in temperature transmitters are often made of semiconductor materials, most of which have a negative temperature coefficient (NTC), meaning their resistance decreases as temperature increases. Due to the significant change in resistance with temperature, RTDs are considered the most sensitive type of temperature transmitter.
Some key characteristics of RTD temperature transmitters include:
- Fast Response: The small size of RTDs allows for quick responses to temperature changes.
- High Sensitivity: RTDs provide large changes in resistance for relatively small changes in temperature, making them ideal for applications requiring precise measurements.
- Electrical Requirements: RTDs need to be powered by a current source, which can introduce self-heating errors due to their small size.
Despite these challenges, RTDs provide high accuracy, making them suitable for applications where quick and sensitive temperature measurements are required, such as in current control systems.
Despite these challenges, RTDs provide high accuracy, making them suitable for applications where quick and sensitive temperature measurements are required, such as in current control systems.
However, thermocouples are generally less accurate compared to RTDs and are not ideal for applications requiring high precision. Nevertheless, their simplicity and affordability make them widely used in industrial temperature measurement applications.