XBee Analog Adapter 4 - 20mA mode

I’m using an XBee adapter in 4 - 20mA mode.

The documentation for the adapter (http://ftp1.digi.com/support/documentation/90000891_E.pdf) states that it “measures amperage on a scale of 4 to 20 mA, and translates it into a 10-bit scale from 0 to 1023 as possible values.” So I’m assuming that 4mA input = 0 and 20mA input = 1023.

But a little future down in the document is says that full scale input is 23.5mA. So does this mean that 4mA input = 0 and 23.5mA input = 1023?

Can someone clarify this for me? Thank!

This has been a headache for me too … there is few and spear documentation … after some research I have concluded:

It seems you will never get 1023 when reading 4-20mA device. Zigbee will report 1023 when it reads 23.5 mA ( never in a 4-20mA device ).

so transform is:

mA = value*(23.5/1023)

so, if you are reading from a device ie. temperature sensor from 0 to 50ºC, with 4-20mA output, full transform should be:

C = (value*(23.5/1023)-4)*(50/16.0)


value*(23.5/1023) reports readed mA.

As device scale reports 4mA at 0, substract 4 from mA.

Then, you have that from 4 to 20 mA, scale goes from 0 to 50ºC so every mA you have 50/(20-4) ºC

so If you multiply mAs * 50/16 you have phisical ºC value.