Answer / s.k.bakshi

The 250 ohm resiatance is necessary to support the communication between transmitter and HART because it equalizes
1. loop resistance
2. barrier resistance
3.wire resistance
4. receivers resistance

Answer / anzal

WHILE USING COMMUNICATOR ITS NEED 250 OHM IN BETWEEN THE TRANSMITTER AND POWER SUPPLY......
THE COMMUNICATOR INJECT HIGH FREQUENCY IN LOOP FOR COMMUNICATING PURPOSE............
IN POWER SUPPLY USING LOW PASS FILTER...
LOW PASS FILTER ALOVE ONLY LOW FREQUENCY..HIGH FREQUENCY IT WILL BLOCK..........
THAT'S WHY IN BETWEEN 250 OHMS NEED...OTHERWISE IT WILL BLOCK THE HIGH FREQUENCY...IF HIGH FREQUENCY BLOCK IT CANNOT COMMUNICATE WITH TRANSMITTER..........

Answer / g.venkat

Because hart portocol need proper loop resistance

Answer / j shinde

For impedence matching.

Answer / 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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