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Use of 250ohm resistance in HART Communication?
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Use of 250ohm resistance in HART Communication?
Why is it necessary to use a 250ohm resistance in HART communication?
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Jonas Berge
16 Dec 2014 11:50 AM
It doesn't have to be exactly 250 ohm. Anything from 230 - 1100 ohm will do
The reason it is required is that the HART signal is transmitted as a current and received as a voltage. The resistor works as a shunt that converts the transmitted current to a voltage the other device receives. The second reason it is required is because a DC power supply will short circuit the AC HART signal. The resistor prevents this from happening.
Note that this resistor is only required for transmitters. It is not required for positioners.