Als

4-20mA applied to 500 ohm resistor.

7 posts in this topic

I am building up an Allen Bradley ML1400 PLC training kit for myself.

Now can I apply 4-20mA from my Process Fluke Multimeter to a 500 ohm resistor to obtain 1-10 VDC and use that as my Analogue Voltage Input into the module?

thank you,

Share this post


Link to post
Share on other sites

That sounds fine other than 4 mA into 500 Ω will give you 2 V and not 1 V.

Share this post


Link to post
Share on other sites

Thanks so much Transistor for affirmation.

Will try it out and see how it goes.

Share this post


Link to post
Share on other sites

You may want to consider using a 250 ohm resistor which would give you 1-5VDC.  Many analog devices have a maximum impedance of 500 ohms so you will be on the edge of what they are capable of driving with a 500 ohm resistor.  See the bottom of this article  in the section titled "Measuring a 4-20ma Input With a Voltage Input Device" for more details

https://www.theautomationstore.com/analog-circuits-voltage-0-10vdc-current-source-and-current-loop-4-20ma/

Share this post


Link to post
Share on other sites

This brings more light now. Thank you so much, TWControls. I would very much like to use 250 Ohms resistor to take 1-5 VDC into my voltage analgue input module, but my problem is that ML1400 has a built-in 0-10VDC analgue input module that I am now trying to use. Can I stil use 250 ohm resistor to take 1-5VDC into the PLC?

Share this post


Link to post
Share on other sites

Yes, there is nothing that says you have to use the full range of an analog input.  Look at the SCP instruction to scale it into a real world value that you can understand.

Share this post


Link to post
Share on other sites

This is it! TWControls, you are now lighting up my PLC pathway. Thank you for resolving my problem.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now