“4-20mA generators are available on ebay, but I for one love the DIY part of things and using parts I have laying around.
I wanted to test our PLC’s analog inputs to verify our scada readings and to test the output of 4-20mA instruments. There are loads of current to voltage converters and voltage to current converters for arduino on ebay, they need calibration though. I can use this to calibrate any of those converters found on ebay and the likes.
I decided that I will DIY a generator and tester. At this point in time it is still a work in progress and a prototype.
I had an old 2.1 sound system that was not being used (small speakers). So I used one of the speaker boxes as an enclosure. I also had an amplifier that died because of lightning, I removed the speaker terminal from that amplifier to make connecting up a breeze. I intend to make a PCB in the future and a better enclosure.
LCD // 20x4 (adapt code if yours is smaller)
LM7808 // 8volt regulator
LED // Any type or size
Resistor for LED // Appropriate for the LED type and 8volt
100 ohm resistor + 47 ohm resistor in series // Will be used as shunt resistor
10K resistor // Arduino analog in protection against high voltage
22K resistor // To stop A0 from floating
Trimpot 100 ohm + 47 ohm resistor in series // PT100 simulator
35 volt capacitor // I used 470uF, just to keep supply voltage fluctuations down
RTD (PT100 transducer) //Span does not matter (range)
DIODE (for polarity protection)