Should I always have a 250-ohm resistor to use the handheld communicator with a HART device?
Expert’s answer: How to use a handheld and HART together
OK, using a handheld and HART together… As you know, HART communication sends digital data on an analog signal. To do that, the HART reads the frequency of 1200 hertz as “1” and 2200 as “0.”
For the handheld to read the HART signal on the loop, you need to have a minimum impedance. Most of the time, the control system has an internal 250-ohm resistor in each channel, but not always.
The HART Foundation suggests a minimum loop resistance of 230 ohms. However, the 250 is standard, so you can easily find such devices on the market.
If you try to communicate with a handheld and it fails, then you may need to insert the handheld in series with the loop.
These companies provide HART networks:
Handhelds available on the market:
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