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Sink vs Source in relation to 4-20mA loop versus

September 16, 2013 at 3:51 PM

When you talk about digital components, like proximity switches, a "source" component supplies power on its terminals and responds to the change in the load, while a "sink" component does not supply power to its terminals and responds to changes in the voltage or current impressed upon it as measured on those terminals.

In 4-20 ma loop parlance, I could understand a "source" component as one which supplies the loop power such as a powered 4-20 ma output card in a PLC rack or a 4 wire pressure transmitter that provides the loop power from its internal power supply.

Likewise, I could understand a "sink" component as a passive receiver instrument such as a 4-20ma input card on a PLC or one of the gazillion 1/4 or 1/8 DIN panel meters on millions of pieces of equipment in factories.

But that leaves a gap for a couple of pieces. In loops which have a 24VDC loop power supply rather than having power supplied by the transmitter, I certainly wouldn't think of that as "source" instrument despite the fact that the PS is obviously supplying the EMF. Likewise, for a loop powered 4-20 ma pressure transmitter you couldn't call it a "source" instrument if the criteria is that it should supply loop power, since it doesn't supply the power. However, i also wouldn't call it a "sink" instrument, since it isn't a receiving instrument.

SOURCE: http://www.control.com/thread/1026233000

Tags: downhole instrumentation engineering 40mA Loop Oil and Gas Production Downhole Drilling
Category: Technology

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