Current Loop Translator ManufacturersMany types of programmable logic controllers (PLCs) only have current loop inputs, and are incompatible with voltage output sensors. Current loops are useful because extremely long cables can be used with no signal degradation. Cable lengths exceeding 1 kilometer can be run with no degradation or scaling to the signal. Compare this to a voltage output sensor where the resistance of the cable forms a voltage divider and scales down the voltage as the cable length increases. Current loops provide a sensor output current that is proportional to the sensor's reading. The standard for most current loops is 4mA to 20mA. So the sensor's minimum value corresponds to 4mA and the maximum value corresponds to 20mA. Because the loop never outputs less than 4mA, broken wires or defective sensors can easily be detected. (If the the current is less than 4mA then there is an error.)
- Vegetronix - Vegetronix specializes in low cost soil moisture sensor probes, grow lights, data logers, and SDI-12 protocol translators, and irrigation systems and solutions. Their moisture sensor probes are sensitive and accurate enough to be used in research grade instrumentation, but because of their extreme low cost they can be deployed on a massive scale in irrigation systems.