A temperature transmitter is a type of measurement transducer - a device that processes measurement signals.
Temperature transmitters can be stand-alone devices, or they can work in conjunction with temperature sensors.
Temperature transmitters amplify the signal from a temperature sensor (e.g. resistance temperature sensor pt100, thermocouple), ensure its linearisation and conversion into a voltage signal (e.g. 0-10 V) or a current signal (e.g. 4-20mA, 0-20mA) . They are the heart of the measurement system, as they convert the physical values into a measurement signal that is comprehensible to the controller (e.g. PLC, controller, rejstrator).
For example, a transmitter with a thermocouple input draws a current of 4 mA from the power supply when measuring the lowest temperature.
Then, as the temperature increases, the transmitter draws a proportionally higher current until it reaches 20 mA, the maximum temperature sensed by the sensor.
In other words, 4 and 20 mA correspond to the lowest and highest temperature of the sensor respectively. For example, if the temperature range of the sensor is 0-100℃, a 4mA signal would indicate 0℃. In the same way, 20mA would indicate 100℃.
The main task of temperature transmitters is to convert the analogue signal from the primary measuring element into a standardised output signal. Sometimes, this analog signal is converted to a digital signal.
However, modern temperature transmitters with digital transmission technology have much more to offer: they offer significant improvements in measurement accuracy, versatility, safety and cost savings.
In summary, the advantages of using transmitters in the temperature measurement process are:
the temperature sensor signal is more resistant to interference present in industrial environments, even over long distances
they provide galvanic isolation (isolation between the functional blocks of an electrical system, which prevents direct current flow from one block to another) between the Pt100 circuit and the input signal
allow the use of ordinary transmission cable instead of compensation cables
temperature converters for thermoelectric sensors compensate for cold end temperatures
simpler maintenance and greater diagnostic capability
output signal is compatible with many standard devices
The most noticeable difference is that a temperature sensors, like resistance temperature detectors, are devices that measures or senses physical temperature and converts it into measurable units of electrical current, including voltage or resistance.
A temperature transmitter, on the other hand, is a device connected to a sensor that works to convert the measured temperature into a signal so that it can be seen, recorded and maintained.
Although they are different devices, both temperature sensor and temperature transmitter work together and play a key role in ensuring that the temperature is accurately measured and transmitted so that it can be controlled.
With regard to the signal, a distinction is made between :
analog output temperature transmitters
temperature transmitter 4 20ma - the most commonly used, as most industrial devices are designed to communicate in this temperature range.
0-10V temperature transmitter
digital temperature transmitters
With regard to the mounting location, we divide temperature transmitters into:
head temperature transmitters - designed for direct mounting in head temperature sensors
DIN rail mounted temperature transmitters for panel mounting
field transmitters for installation in process plants
The temperature transmitter can have additional sensors integrated, e.g. humidity or pressure. You can also choose between, for example, a version with or without a display.
humidity and temperature transmitter - integrated humidity sensor
pressure and temperature transmitter - integrated pressure sensor
temperature transmitter with lcd display
Some demanding applications, such as hazardous areas, require specially adapted transmitters.