1-Ch. 4-20mA Current Loop Transmitter I2C - has it isolated output?

Hardware
1

We have " 1-Channel 4-20mA Current Loop Transmitter I2C Mini Module" and can measure that the output is not galvanically isolated from the input.
We have a resistor of 10ohm over the terminal but the potential on the either side of the resistor is at about 16V, and the common mode impedance is few ohms so shorting to input GND shorts the system supply.

Is this function

  1. by design or
  2. have we misconfigured or misuse the device or
  3. can it be broken?

The datasheet is not very specific at this point so we need clarification.
Thanks

2

This IC provides the signal isolation

and this one does power isolation

Thanks

3

Many thanks,
The parts information is very clear.
I am looking for the module specs. Can I derive from your information that the module is designed to isolate the output from the input (within these limits of x hundred of volts). I.e. the rest of the circuit is made to support this isolation?

I ask this seemingly superfluous question, because

a) The module specs do not specify that it is isolated - it only specifies that the digital data are isolated which strictly is not necessarily the same as stating that the output is isolated.

b) We are in possession of 4 modules and they all do not have isolated output - as I describe. The current into a floating load does however follows the commanded values. So can they all be broken with respect to the isolation? They have not been exposed to any common mode voltage of serious amplitude (basically just laying on the desk)

Thanks for any suggestions.

4

Any ideas about this question?
I notice that the modules we have, look different from the one pictured in the webshop of same name. Ours have more components in the end with the screw terminal. Are there different models? Can this explain what we see?
thanks for considering this.

5

You might have the one which provides a loop power supply.

6

The module is definitely able to drive current through the attached load resistor without any additional power supplies. I.e. a voltmeter (floating) across this load resistor shows the correct current corresponding to the commanded value.
So it is an active source of current.

We assumed that we had this version: https://store.ncd.io/product/1-channel-4-20ma-current-loop-transmitter-i2c-mini-module/ which is quoted as a transmitter but looks different to the picture as I mentioned.

Do you have a link to the version “the one which provides a loop power supply.” which you suspect it is then?
Would that explain that it appears to be not isolated?
Thanks
The module is marked: PR33-49 on wire side and P_4-20mATx Rev. A on component side.

7

We have decided to abandon use of this module. If we can’t get documentation and function to match-up then it is not reliable for our use.