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24V Loop Power

March 23, 2017

When shopping for an electrical measurement device, customers know what they want to measure, and they know what the output needs to be. In the case of the popular 4-20mAdc analog output, there are different ways that it can be provided. The first option for 4-20mAdc is to provide it as a “Loop Power”, 2 wire output.

Loop refers to the actual current path of the output and consists of the internal “transmitter” circuit that produces the 4-20mAdc signal, the DC power supply that is connected in series, and finally the receiver or receiving circuit (RL on many transducer diagrams). RL may be shown as a resistor and represents many types of optional equipment such as a PLC, Logger, Display, etc.

The second option for a 4-20mAdc analog output is a 4-20mAdc output that does not require a 24Vdc power supply in series with the output loop. RL is still in play, but the series power supply is no longer there. The instrument power applied to the transmitter circuit is connected separately and in a 4-wire configuration.

This method allows for more options for the power voltage such as 120Vac or 48Vdc.

A third option is also available for providing a 4-20mAdc output in a “3 wire” configuration where there is a common point for the power supply negative pole and the output negative pole.

Further questions about loop power or want to buy a loop-powered transducer?
Call the Ohio Semitronics' office at 614-777-1005
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