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Nowadays transducers are essential in both automation and control systems. Transducers are needed when physical quantities are used for a process control. The reason is that it is necessary to record a large number of quantities. In addition to the most common quantities as temperature or pressure, there are other parameters such as pressure, gas content or flow. For electronics to receive a readable signal, transducers must convert the physical quantity into the electrical signal. To ensure flexibility, normalized signals can be read by many meters.
Here you can see the Transducers functioning:
The use of an analogue normalized signal allows transducersto be connected to the same analogue input of a digital display. The digital display should only be scaled, this means that digital display should indicate the value from transducers as an electrical quantity corresponding to a physical quantity value. The next image shows the assignment of 4-20mA output signal to a temperature range of 0 - 100 ºC:
Some transducers have a flexible scale which allows the users to adjust the measurement range according to their needs. Apart form its flexible use, the normalized signal of 4-20 mA has other advantages such as: connection cables from one device to another can be very long, it is possible to add diverse units of analysis to the same circuit, so a current signal from the transducer can be used in different places. As even with the lowest measurement value current flows, users can use the 4 mA to feed sensors. Current below 4mA indicates that there is something wrong with the analysis units. In order to read the measurement value in situ, some transducers have a display. Other transducer models have relays which make a contact when limit values are exceeded.