3-wire 4-20mA using XTR115

TI007100

Other Parts Discussed in Thread: XTR115, XTR111, XTR110, XTR117

I am thinking to use XTR115 for a 3-wire 4-20mA system as follow, will it be all right?

I prefer XTR115 over XTR111 since it requires much less external components.

over 9 years ago

0 Collin Wells over 9 years ago

TI__Guru 62935 points

Hi Joshua,

You can't use the XTR115 as a three wire transmitter, it simply will not work. Consider the XTR110 or XTR111 when designing three-wire 4-20mA transmitters.

I wrote a blog about the issue this will cause which you can read here:

http://e2e.ti.com/blogs_/b/precisionhub/archive/2014/12/09/part-2-two-wire-4-20-ma-transmitters-background-and-common-issues

Here's parts 1 and 3 if you're interested in further reading:

http://e2e.ti.com/blogs_/b/precisionhub/archive/2014/11/04/two-wire-4-20-ma-transmitters-background-and-common-issues

http://e2e.ti.com/blogs_/b/precisionhub/archive/2015/01/13/two-wire-4-20ma-transmitters-background-and-common-issues-part-3

0 TI007100 over 9 years ago in reply to Collin Wells

Intellectual 300 points

Hi Collin,

Thank you for your reply.

Surprisingly I manage to get it work! Let me explain how it works.

First of all, I did not short IRET to IO as you mentioned in the article. The pin is left floating. Other pins that left floating are VREG and VREF.

I tested the circuit with Arduino. For V+ I use unregulated 12V from an adapter, powering both Arduino and XTR115. I get the analog voltage using Arduino PWM output, and the current is injected into Iin through a 22k resistor.

Then I measured the current between IO and GND, and I can see the current swinging from 0mA to 22mA.

0 TI007100 over 9 years ago

Intellectual 300 points

Here is a TI reference design using XTR117 in a 3-wire current loop. Wondering if XTR115 can do the same?

www.ti.com/.../tidr225.pdf

0 Collin Wells over 9 years ago in reply to TI007100

TI__Guru 62935 points

Hello Joshua,

The schematic you've attached clearly shows that the XTR117 is used as a two-wire transmitter. The two connections to the transmitter are Loop+ and Loop-. The XTR115 would work in place of the XTR117 is the schematic you've attached.

0 TI007100 over 9 years ago in reply to Collin Wells

Intellectual 300 points

Thanks.

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3-wire 4-20mA using XTR115