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Is it possible to electrically isolate HART transmitters?

Yes, when using the HART DC 52500, a 2-wire measuring transducer can be fed and operated by means of HART communication. The 4 - 20 mA measured value with the modulated HART signal is conveyed smoothly over the isolating distance; HART communication is bi-directional, i.e. it is transported in both directions across the electrical isolation.

What is meant by HART Communication?

Hart Communication is a standardized method of additionally transferring bi-directional communication on an analog measuring value. The modulation and the data log are defined exactly in the specifications of the HART Communication Foundation (

This is an FSK signal which is modulated in the measuring transducer to the measuring value, 4 - 20 mA output current of the transmitter. A HART modem is installed in the process controller; it transports the transmitted digital data to a process computer.

The great advantage of this concept is that the analog measured value can be evaluated conventionally. Furthermore, but without any additional cabling work, all kinds of information such as measured values, configuration data or set parameters can be made available to the user in digital form.

HART Communication across the isolation distance

In addition to the analog 4…. 20 mA current signal, many 2-wire transmitters permit digital communication, which is modulated on the output current. A popular protocol is the Hart Communication of the HART Communication Foundation (

It is the function of an appropriate transmitter-repeater amplifier to also transmit the modulated frequency in unadulterated form across the isolation distance. In view of the fact that HART Communication must function in both directions, the HART transmitter repeater has a return channel which transmits the digital queries from the master to the slave (field device, transmitter) against the normal analog data flow.

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