XTR115: XTR115

Hi Amruta,

 If I interpreted the post correctly, the variable resistor (330-Ohm to 470-Ohm) is connected to an IC 7555 to generate a PWM.  The PWM signal is fed through and RC filter, generating an analog voltage of 0.82V to 1.8V.  You intend to use this 0.82-1.82 analog voltage as input of the XTR115 to generate the 4-20mA signal.  Is my understanding correct?  Can you please provide a schematic of the PWM circuit with the XTR115?

Please keep in mind the XTR115 is a 2-wire transmitter, where the 2-wire transmitter and the sensor circuitry is powered from the loop supply (no local power supply) and the current consumption of the complete circuit should be less than ~4mA or you minimum scale current will be limited to the current consumption of the circuit.  What is the current consumed by the PWM (IC 555 circuit)?

Please find below a couple a links to blogs related to 2-Wire transmitters that you may find useful.  Particularly, the blog below discusses an externally powered MCU producing a PWM signal through an RC filter, controlling the 2-wire transmitter:

https://e2e.ti.com/blogs_/b/precisionhub/archive/2015/02/24/two-wire-4-20ma-transmitters-background-and-common-issues-part-4

Also, below find other blogs discussing general 2-wire transmitter topics that you may find useful.

Thank you,

Best Regards,

Luis

1. 2-Wire 4-20mA Sensor Transmitters: Background + Compliance Voltage
   https://e2e.ti.com/blogs_/b/precisionhub/archive/2014/11/04/two-wire-4-20-ma-transmitters-background-and-common-issues

2. 2-Wire 4-20mA – IRET Can’t connect to Vloop GND
   https://e2e.ti.com/blogs_/b/precisionhub/archive/2014/12/09/part-2-two-wire-4-20-ma-transmitters-background-and-common-issues

3. 2-Wire 4-20mA – IRET < 4mA
   https://e2e.ti.com/blogs_/b/precisionhub/archive/2015/01/13/two-wire-4-20ma-transmitters-background-and-common-issues-part-3

4. 2-Wire 4-20mA – Controlling 2-Wire Transmitters with Externally Powered Sources
   https://e2e.ti.com/blogs_/b/precisionhub/archive/2015/02/24/two-wire-4-20ma-transmitters-background-and-common-issues-part-4

5. 2-Wire 4-20mA – Input Isolated Sensor Transmitter
   https://e2e.ti.com/blogs_/b/precisionhub/archive/2015/03/10/2-wire-4-20ma-sensor-transmitters-background-and-common-issues-part-5

6. 2-Wire 4-20mA – Increasing Sensor Power
   https://e2e.ti.com/blogs_/b/precisionhub/archive/2015/04/14/2-wire-4-20ma-sensor-transmitters-background-and-common-issues-part-6
   
   

    

 

Hi Luis,

You interpreted post correctly, I had check current flow through IRET pin of XTR115 and current flow through IRET greater than 4 mA so XTR 115 not work properly in my application.

I had design 4-20 mA transmitter using PWM. PWM generated from controller then PWM signal fed to RC filter and then to XTR115 to generate 4-20mA.This circuit gave good result and this is in production now.

In this application major issue was resistance change is very less it is only 130E,because of that I did not get large range in Duty cycle. Is there any other way to generate PWM as variable resistance is input or I had attach schematic please review it and suggest any changes so I will use XTR115 in my application. XTR115_Rev1.1 - Project.pdf

 

Hi Amruta,

One possible way to connect the variable resistor to the XTR115 is a circuit similar to the one shown below.

It uses the REF200 (Dual 100uA Current source) and a instrumentation amplifier such as the INA326 (or similar); producing an input voltage that can be connected to the XTR115 through a resistor RIN.  This circuit should consume less than 4mA.  Please see below preliminary simplified schematic.

Is this something that could work in your application, instead of using the PWM generator?

Many Thanks,

Luis

Hi Luis,
Thank you for guidance , I have one concern about INA i.e it has large temperature drift. Application that I will design it will install at field site and there is lot of temperature change. Is there solution without instrumentation OP-AMP.

Hi,XTR115_Rev1.2 - Project.pdf

I had attached schematic in attachment. I have some doubt mention below.

1.In this application I am using INA332.I will set gain 165 for INA332.I am not able to understand how to use Reference pin and shutdown pin.

2.Also please review schematic and suggest any changes.

Hi Amruta,

why not using TINA-TI and running some simulations?

Kai

Hi,

The simulation model given in the examples of TINA-TI for current loop transmitter xtr116 in not functioning as specified.

I have tested it on TINA-TI.

It Current in the output loop was not changing when the input Voltage is changed from 0.1 to 1 Volts and it is not working according to the datasheet.

Can any TI source give me a working simulation model?



Thank You sir.

Regards,
Amruta

Hi,

The simulation model given in the examples of TINA-TI for current loop transmitter xtr116 in not functioning as specified.

I have tested it on TINA-TI .

It Current in the output loop was not changing when the input Voltage is changed from 0.1 to 1 Volts and it is not working according to the datasheet.

Can any TI source give me a working simulation model?



Thank You sir.

Regards,
Amruta

Hi Amruta,

but you can check the INA322 section of your circuit by the help of TINA-TI.

Kai