i am working on MKM14 series microcontroller for 4-20mA application using Sigma Delta ADC in Single Ended mode

[harish_gode]

I have designed circuit using 2 channels for 4-20mA Analog input circuit. The loop is powered by another meter with two 4-20mA output with 24V Supply. The Budern = 16.6 ohm is scaled to MKM14 microcontroller = 20mA * 16.6 ohm = 332 mV ( Max) to ADC pin of Microcontroller. The two channels are connected to Signal Delta ADC in single ended mode. when i connect two 4-20 mA channels from a Two Analog output ( 4-20mA) to two 4-20mA ( two Analog input) for MKM14 microcontroller the reading is correct . But if i open one terminal of Analog input channel the voltage at other channel of ADC changes from 332 mV to 1.74V DC. The other channel in which the loop is closed reads 332 mV only. What is the root cause of it

[Alexis_A]

Hi harish gode,

I don't understand very well your application, to provide a better answer, could you share your schematic?

Also I have a concern about your implementation, the highest current the MCU supports is 25mA (the sum of all pins) if you supply the MCU with 20 mA in a single pin, is highly possible to break it. Be careful with this.

Best Regards,

Alexis Andalon