XTR117: XTR117

The XTR117 is designed for a 2-wire loop, where the measurement circuit is powered from the loop, and floating. Is this the case in your application, or do you have a separate power supply?

Where does that 20 V signal come from, and what are its characteristics? The XTR117 has a built-in 5 V LDO; if you need a higher voltage, you can connect your own regulator between V+ and I_RET. Alternatively, divide down the input signal so that it can be handled with a 5 V circuit.

The 20v signal comes from an electric motor sensor output, it is supposed to connect to the PLC, so the PLC has 4-20mA input, while the motor measurement is 0-20v, there is no any separate power supply at the motor side. I have a schematic, but I don't know how to upload it.

So the motor and the PLC use the same supplies (or at least the same GND)? And there is a 24 V supply available for your circuit? The XTR111 would be a better choice. (Its input should be below 12 V, so you should divide down the signal.)

To upload the schematic, make a screenshot, save it to a file, and use the "Insert" / "Image" menu below the text box. If the entire schematic can be put on a public forum, you can insert the .pdf directly.

No, they don't share ground

4_20mA is the field signal at barrier, barrier then communicate with PLC through MODBUS

Signal and power are on the same line

I have attached the pictures below. R2=150k,R1=125k,R3=250.

HI Faisal,

The XTR117 is a 2-wire current transmitter.

The sensor and driving circuit producing the signal driving the XTR117 must be referred to the local current transmitter GND (IRET) and IRET needs to be allowed to float and isolated from the 4-20mA loop supply GND.  Also, the overall current consumption of the XTR117 current transmitter + driving circuitry must not exceed 4mA.  

If your 0-20V signal source is referred to the loop GND and it is not isolated, this will not work with the 2-wire current transmitter. 

The figure below shows the 2-wire transmitter (XTR116) with I_RET incorrectly shorted to V_LOOP GND.

The figure below shows the 2-wire transmitter (XTR116) with I_RET correctly connected, where IRET is allowed to float with respect to V_LOOP GND.

This is explained in detail on the blog series below:

https://e2e.ti.com/blogs_/archives/b/precisionhub/posts/two-wire-4-20-ma-transmitters-background-and-common-issues

https://e2e.ti.com/blogs_/archives/b/precisionhub/posts/part-2-two-wire-4-20-ma-transmitters-background-and-common-issues

Your schematic shows IRET connected to GND.  If your signal source is not isolated from the loop supply, please consider instead the XTR111 which is a 3-wire current transmitter.  On 3-wire current transmitter, the sensor and driver circuit of the XTR111 can be referred to the 4-20mA loop supply GND without issues.

Please also refer to the links below for more information on 2-wire and 3-wire current transmitters.

[FAQ] What is a 2-wire 4-20mA current transmitter?

[FAQ] What is a 3-wire 4-20mA current transmitter?

Best Regards,

Luis

Hi Luis,

I have isolated the IRET. But I will first test the design with a desktop power supply and DMM.