The AB Electronics UK Knowledge Base provides support solutions, tutorials and troubleshooting guides.
We often receive enquiries about how to use commercial sensors with a 4-20mA output with the Raspberry Pi.
As many of the commercial sensors operate from a 24-volt supply and need to be isolated from the Raspberry Pi, it wouldn’t be possible to measure the output current across a load resistor directly on the ADC input as there would be the potential for the input voltage offset to be too high and damage the Raspberry Pi and ADC chips.
To resolve this, we found many commercial modules that convert the 4 to 20mA signals to a 0 to 5V output, which can then be read using the ADC Pi boards.
The conversion modules are often marketed on sites such as eBay called Current to Voltage Transmitter Signal Module 4-20MA to 0-5V Linear Conversion or similar and only cost a few pounds.
The photo below shows an example of one of the modules we purchased to test with the ADC Pi boards.
We also purchased a PT100 Temperature Sensor Transmitter, which outputs a 4-20mA signal from the PT100 sensor, and we connected this to the signal converter. The module uses a 24-volt supply, allowing us to test for the voltage conversion.
The output from the current-to-voltage module is then connected to one of the ADC Pi inputs, and you could use up to 8 of these current-to-voltage modules with a single ADC Pi.
We do not have any affiliation with the eBay sellers on the above links; these are just examples of the modules available.
