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Respected Sir/Madam.
While testing the 4-20mA current transmitter after doing the connections as per the data sheet I could not get the variation in the current at the output, I was receiving a constant current on series with the Load Resistor.
Please provide a basic testing circuit with component values.
Thank You,
Koustubh.
Hi Koustubh,
Kai has pointed many references over the E2E forum on the XTR117 or 2-wire 4-20mA transmitter topics and application.
Enclosed is a simulation in Tina-TI. The input is 0-5Vdc and a linear V-to-I conversion is directly proportional to the output current from 4-20mA, and at the output with R_load of 250Ω, it converts 4-20mA current loop back to 1-5 Voutput in voltage (4mA * 250Ω to 20mA*250Ω ).
XTR117 0-5V 4-20mA 02232022.TSC
If you need further assistant, please let us know.
Best,
Raymond
Hi Koustubh,
at VREG and V_i2V where I should get 6.1V and 1V respectively ...
Please get a new XTR117 and replace the existing XTR117. The VREG node should get 5Vdc. Please start with 7.5-10Vdc from the power source, instead of 24Vdc. Once it is working, you can crank the input voltage. The XTR117's internal regulator has to work at 5Vdc.
(simulation has to use V1 = 10Vdc or higher with all the connection).
If you break the input after Rset or 31.25k, you should get 4mA constant current out. The internal current gain of the circuit is 100, where 40uA*100 = 4mA should be sourced at the output Iout or pin4.
Instead of break the input connection, it will be easier to remove the power source from the input, see the image below.
The following input is very important. Vin is the input power source, 0-5Vdc power source has to be floating. 0-5Vin voltage source has to be measured with respect to Pin3 or IRET node. It won't work if Vin is referenced to ground. As it is simulated, the ground is on the Vloop power source side or 8Vdc in this case.
The current as simulated is increased to 120uA (40uA + 80uA), with the current gain of 100, the pin3 should source 12mA.
Please try this out and see if it works better now.
Here are two 4-20mA application notes and bench testing results in case that you are interested.
Best,
Raymond
Hi Koustubh,
As Kai indicated, something in the setup is gone wrong. Here is what I'd like you to do, in addition to post the complete schematic and setup photo and/or layout.
Please make sure Ros = 125kΩ and Rset = 31.25kΩ. If you do not have these, please find two of 250kΩ and 62.5kΩ, and parallel these resistors to make up these values. Or you can place two resistors in series and make up these values.
Setup 1:
1. Without input voltage Vin = 0 or short the input Vin or disconnect the Vin.
2 . Vp = 6.1Vdc and V_i2V = 1.0V over 250Ω load, where Iout = 1.0V/250Ω = 4.0mA.
3. I_sum = 5V/125kΩ = 40uA, where IRET pin or Pin3 should read approx. 1.1Vdc.
Setup 2:
1. With input voltage Vin = 1.57Vdc with a brand new dry cell battery (AA, AAA or others) and input is floating.
(note: not all brand new dry cell will read 1.57Vdc, but it is not important, I just want to the data from the Vin figure, please record battery's Vin value).
2 . Vp = 7.48Vdc and V_i2V = 2.26V over 250Ω load, where Iout = 2.26V/250Ω = 9.04mA approximately.
3. I_sum = 40uA + 50.24uA = 90.2uA where IRET pin should read approx. 2.48Vdc.
Please let me know what you measured from your setup. The data you provided may mix up with different input conditions. I can not interrupt it properly.
Best,
Raymond
