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Good day! I would like to ask regarding my project, I'm using V350 35 R22 and having a modulating valve as a controlled instrument using plc analog output.

My problem is that I can't control the valve on below 50% openning (below ~11mA output) however, I can actuate the valve or command on 50% - 100% opening (12mA - 20mA output).

I've tried to isolate the plc output to verify the output current and it seems fine (4mA - 20mA)

Also, I've tried to insert a ammeter to check the loop current while the plc's injecting current to instrument,

12mA-20mA was OK but when the plc's inject below ~11mA plc output command the ammeter readout dropped to ~0.98mA...  


Is there something i missed out on configuration??

Can anyone please help me with this matter? Thanks in advance. 


Furthermore, I'm using Samson i/p converter type 6116 as my field instrument...



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What is a valve model?

Some 4-20 mA current loop devices have dynamic internal impedance.

At a time the impedance is more than 500 ohm, current loop will not work.

*500 ohm is an impedance limit for Unitronics current loop outputs..

You can measure V and I on current loop output to calculate impedance.

Change I(current) by step of 1 mA.


If there is a case - you have to use current loop conditioner, which will wotk with specific valve.


You can contact valve manufacturer for information about recommended, or tested, or used in manufacturing process current loop devices/conditioners.

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I also use Unitronics and Samson devices. In some cases for SAMSON devices  you need a current loop converter. I use MCR-C-I-I-00-DC (281408 form Phoenix contact). That works fine.


Technically theese Samson devices need 5V for the internal electronics (above 10 mA they work with Unitronics...). So they have as AlexUT wrote dinamycal Impedance.



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  • 4 years later...

I didn't get MCR-C-I-I-00-DC (2814508 -Phoenix Contact) which is 4-20mA input to 4-20mA output in the market, so I bought MCR-C-U-I- 4-DC - (2814537- Phoenix contact) which is 0-10V input to 4-20mA. I changed my Analog Output to 0-10V in the Hardware Configuration,  I connected the 0-10V as the input to 2814537 and connected the output from it which is 4-20mA to my I/P Transducer, it worked well. Thanks to everyone.

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