How to design a 2 channel 4-20mA transmitter?

xtr117 problem

Hi all,

Having some problem designing multiple channel of 4-20mA transmitter. We would like to design a card that will provide 3 channels of 4-20mA transmitter that are independent of each other using XTR117. But based on the equivalent diagram provided by the datasheet, we notice that the current of different channels within the same card will be affecting each other, since all the XTR117 shares a common ground.

Are there any two or three channels 4-20mA transmitter within the same chip?

Thanks!

Best rgds,
klpang

XTR117 is a two-wire (loop powered) transmitter. It unusual to have multi-channel two-wire transmitters to my opinion, for several reasons. It could be necessary to define the application exactly to check, if a solution is possible.

One reason is the unclear common connection. Two-wire transmitters are expected to have neither common positive nor negative terminal with others, they have to be floating (or isolated) current sources (respectively sinks).

It would be easier to design a multi-channel two wire transmitter for a known analog input module or PLC, which has e. g. a common positive terminal. But it couldn't be used for any application unconditionally und would be of limited value.

A multiple channel "4-wire" (self powered) analog transmitter with common ground can be operated with nearly any analog input module without particular precautions.

hi

Thank you all for the reply. Will take note and decide on the relevant changes in design. Have been having issues accessing edaboard these few days...

Anyway, temporary, we are studying on using XTR111. This chip seems to be more suitable for multichannel transmitter.

Thank you.

Best rgds,
Pang