Antialias (Customer) asked a question.
Hi
This is my first PLC programming project and I feel like I am doing circles in the documentation without an answer. I am attempting to control LED lighting on a 0-10V module, through a part that will convert 4-20mA to 0-10V. Unfortunately the Vout only goes 0-5V or I would have used that to control the LED dimmer. (Side question: what is the use of 0-5V signal? I have never seen a device that uses that before...)
I have a Click CO-02DD2-D module. I can see on the monitor screen and in the program as I scale DF4 that the PLC thinks it is outputting 4-20mA through output DA2-I . However, my field device refuses to function and when I put my meter on it, I read 0.4 MICRO amps. So, essentially nothing. Scaling the value up and down does nothing to change the value that my meter is reading. There is no voltage at the terminals, either.
I have found a part of the documentation that indicates a 250 ohm resistor is needed for the current module, (with a max 1200ohms for a 30V load power supply) for the current output. Can anybody here please expand on that a little bit? Do I need an inline resistor? The conversion module I have, appears to only have a 100 ohm resistor on it. My meter will have no resistor. However, at 4mA or 20 mA there is no voltage present at the terminals of DA2-I and A-COM. What difference will a resistor make if there is no voltage present?
My field device is powered by 24v - the same power supply that powers the device, powers my PLC. Is the relatively small current sampling resistor on the device (100 ohms) stopping the whole process from working?
I can scale the 0-5V just fine on outputs DA1V and DA2V and see the corresponding values on my multimeter as expected. I should also mention that I have literally 0 more room inside this panel... So buying a 0-10V output module is unfortunately not an option for me
Any help or a direction to look in would be greatly appreciated
The resistor you are talking about just represents whatever load / device you are wiring to. I've never really thought about there being a min resistance. You could always stick a resistor inline to test the theory.
There are a few things we can check first.
Does your wiring go:
ACOM ---- (-) Power supply (+) --- (+) Device (-) --- DA2 I
Are you setting the channel to current in the "CPU Built-In I/O Setup" under Setup?
While many (possibly most?) 4-20mA output circuits actually do literally output current, that model of CLICK does Not, it is a current sink. The current needs to be supplied by an external power supply, the CLCIK only modulates the current, it does not supply it..
I didn't know a sinking 4-20mA was a thing. I can't say I've seen that before.
Oh man, the answer was right in the manual screenshot I posted. You are correct that this is a sinking current module. I feel sheepish for missing this small but vital piece of information. Every device I have ever hooked up has always been a 4-20mA source, and I incorrectly assumed that it just always was. I simply glossed over that and caused myself a larger headache than needed. Thanks for your help here, guys.
Happens to all of us. Our brains like to make presumptions for us.