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Re: Multidropping hart devices.

Message posted by Romilly ( : 81.35.213.163) on 22 February 2008 at 11:10:21.

in reply to: Multidropping hart devices. posted by Andrew on 21 February 2008 at 12:34:10.

I think this is fine.

There is no particular spec for the parking current in devices used in multidrop mode. Manufacturers usually make it as small as they can. For loop-powered devices, 4mA is common, enough to provide power to the electronics, but it could be less or more. For active-source devices with their separate power supply, it could even be zero, but I expect the manufacturer has chosen 0.8mA, to allow the HART signal to be added without actually going into negative current (so simplifying the electronics).




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