XTR117: XTR117

Hi Hen,

There are a few things you need to be certain of in your setup:

1) Most importantly, the input voltage to the XTR117 must not have any connection to the ground of your loop supply. The IRET terminal must be allowed to float relative to the loop supply ground and the input circuitry must float with it. With your use of AGND, it seems like you have accounted for this, but I am not exactly sure what your "CleanPower" source is referenced to.

2) If connecting the scope ground to the output resistor fixes the problem then this leads me to believe that your supply is not properly grounded and the loop is finding its path to ground through your scope probe. You may want to double check your supply connections.

3) Something else to be aware of is the possibility of flux contamination. Solder flux can create parasitic paths for current flow between pins if your boards have not been properly cleaned. Since the XTR works with such low level current inputs, it doesn't take much to cause erratic behavior. This usually couples in through the adjacent reference pin or supply pins. Be sure you have thoroughly cleaned your board to eliminate any impact this may have.

Hi Hen,

what do you connect to pin 3 of R13? This should be the minus pole of Power-In1 supply.

Take care, there are many different GND potentials in your circuit and many additional supply voltages. This is not really the way the XTR117 is intended to be used. Have a look at figure 1, 4 and 5 of datasheet of XTR117 to see how additional circuitry is usually powered.

Kai

Hi,

 

Thanks for your help,

 

I will try to answer your question,

 

We have 2 power supplies: 

 

1st one for the RTB board "CleanPower" that support anther board that the 2 analog 1-5v come from.

A RTB board GND and The AGND just separate with a ferrite Bead from the GND, 

I all ready test it with one GND.

 

The analog from the controller pass thru U5 one stage Opamp for amplifying the signal.

I think I have a good analog 1-5v input to XTR117.

 

2nd 24vdc power supply just connect to the XTR117 U6 thru Power_In1 (+) and return R13 Iout_4_20ma_1 (-), I use a resistor of 270 Ohm between the power supply (-) to this line.

I use 2 potentiometer for calibration, R12 input voltage 1-5vdc and the R13 for the output resistant. 

 

To do:  I will clean the board from Flux and test it again.

 

Can it be that the transistor Q1 not good, or the Bridge diode? 

Hi,

Thanks for your help,

I will try to answer your question,

We have 2 power supplies:

1st one for the RTB board "CleanPower" that support anther board that the 2 analog 1-5v come from.
A RTB board GND and The AGND just separate with a ferrite Bead from the GND,
I all ready test it with one GND.

The analog from the controller pass thru U5 one stage Opamp for amplifying the signal.
I think I have a good analog 1-5v input to XTR117.

2nd 24vdc power supply just connect to the XTR117 U6 thru Power_In1 (+) and return R13 Iout_4_20ma_1 (-), I use a resistor of 270 Ohm between the power supply (-) to this line.
I use 2 potentiometer for calibration, R12 input voltage 1-5vdc and the R13 for the output resistant.

To do: I will clean the board from Flux and test it again.

Can it be that the transistor Q1 not good, or the Bridge diode?

Hi Hen,

It is not likely that this is a transistor or diode issue.

As I mentioned the IRET pin of the XTR117 needs to be allowed to float relative to the loop supply ground, and all of your input circuitry must float with it. Additionally, everything on your input side that is referenced to IRET must consume a total current less than 4mA. Since IRET is effectively your input ground, all of your input circuitry current will flow through it and become a part of your output current, you cannot output a current less than the total of what your input consumes.

Here is a presentation that I think you will find useful. Take a look and let me know if this helps you resolve your issue.

3312.4-20mA_Basics.pdf