Volts to 4-20mA Sensor Converter

The current loop converter/translator V-a-4-20CONV turns any analog voltage output sensor into a 4 to 20mA current loop sensor.

Many 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.)

The translator can directly power sensors that consume under 4mA.  For higher power sensors, an isolated external power supply is needed. The translator has 2 solderable holes that can be connected to external isolated power.  The translator has a jumper which can switch between loop power, and external isolated power. 

The current loop translators are factory calibrated with two trim potentiometers, which adjust the 4mA and 20mA limits, respectively.  If desired, these can be re-calibrated in the field with a simple calibration procedure which is described below.
The current loop can read voltages up to 3.0V. This input voltage can be customized by changing a single resistor on the board.

The current loop translator can directly loop power the following Vegetronix sensors:VG400
VG400-LV
THERM200
Since the VH400 consumes more than 4mA it must be powered from an external isolated supply.   
Voltage to 4 - 20mA Current Loop Translator

Applications
Interface voltage sensors to PLCs.
Remote placement of sensors with long cables. 
Interface Vegetronix soil moisture sensors to programmable logic controllers.

Features
Low Cost.
Low Power.
Screwless terminal blocks for quick connect. 
Factory calibrated limits, which can be re-calibrated in the field with 2 trim pots. 
Interfaces with nearly any voltage output sensor.

Can power sensors from loop current if the sensor consumes less than 4mA.
Accepts isolated voltage supply for sensors that consume more than 4mA.

4 mounting holes in each corner.