When selecting a signal indicator, “loop powered” is a phrase that you may come across often. While extremely useful, it’s not always clear to our customers what, exactly, this technology consists of – and how it can help them. This is a very basic explanation of the theory behind, and the purpose of, loop powered indicators.
The most important thing to understand about loop power (or “current loop”), is that it helps maintain the accuracy of signal readings when the distance between a sensor and the monitor is very long. This is because, traditionally, a sensor will transmit information as electrical voltage. Voltage can be lost due to resistance during transmission, resulting in an inaccurately low reading by the monitor. Loop powered indicators solve this problem by converting voltage to electrical current, which is, by definition, the movement of electrons from one point to another. Electrons are much less likely to be lost in transmission than voltage.
So, a loop powered indicator converts a unit reading to a voltage, which is in turn converted to a proportional current figure between 4mA and 20mA (the meaning of the typical 4-20mA current loop). This is converted back to a voltage on the monitor device, either appearing as a display or being processed as a data reading.
For greater detail on the current loop process, see Current Loop.
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