Why ues 250 ohms Resistor during hart type instruments
calibration with hart protocol in details ?
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Answer Posted / carl_ellis
My friend Dan has an article on why HART needs a minimum
resistance in the loop to work.
http://blog.lesman.com/2011/10/06/add250-ohm-resistors-to-
make-hart-work/#more-68
Anzal, above, is on the right path. The loop power supply
is a low pass filter. The 1200Hz HART signal needs a
minimum resistance to develop a signal that the HART
receiver can 'see'.
Tell Dan Carl sent you.
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