Problems with operating the hart475 handheld controller
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I just installed a 475 unit, and according to the instructions I’m unable to connect to the Rosment3051C transmitter no matter what. I would appreciate it if experts could help me figure out why this is happening.
First, it was done directly on the + and - power terminals of the transmitter; later, a 250-ohm resistor was connected in series with the + terminal (provided by a signal generator).
First, it was done directly on the + and - power terminals of the transmitter; later, a 250-ohm resistor was connected in series with the + terminal (provided by a signal generator).
There are two connection methods, and the series connection method is incorrect.
Generally, HART communication requires a matching impedance of 200–600 ohms in the circuit. Since the signal generator provides the power, which can be considered a stable power source, a 250-ohm resistor is connected in series with the positive terminal of the signal generator and to the positive terminal of the instrument; the negative terminal of the instrument is connected directly to the negative terminal of the signal generator. The hand controller is connected in parallel to the positive and negative terminals of the instrument. Some people use series resistors as well, but it doesn’t seem reliable~! !
I don’t need to connect resistors on the Rosemount side; when the battery current of the signal generator is insufficient, it often stays off all night long
Is your HART475 a Rosemount brand or a copy?
Most of the modules available these days come with a 250Ω resistor built in, so there is no need to add one externally. Be careful not to plug it into the FF port.