4-20 mA woes

Hi all, I'm not sure if I have selected incorrectly when setting this up, if I have something hooked up wrong, or if I'm missing something on the PLC side.

I have a humidity sensor : https://www.omega.com/temperature/pdf/HX71.pdf (HX71-MA)
Power Supply: https://www.automationdirect.com/ad...VDC,_12VDC,_48VDC,_DIN_Rail_Mount/PSB12-015-P
and Analog Input card: https://www.google.com/url?sa=t&rct...al.pdf&usg=AFQjCNH-6bGA75rJ462p3KyWDxOgGu4Zqg



I'm going from the positive terminal of the power supply, to the red wire on the humidity sensor, then the black wire from the humidity sensor to the positive terminal on the PLC, then the negative terminal on the PLC to the negative of the power supply. When looking at the logic in the PLC my digital value is 4000 (100%), which reading looked like on 4-20mA it shouldn't have gone over 2000. I started to think maybe I had the dip switches set wrong and that it was operating 0-10v, which would have made sense giving full voltage at the tail end of a 4-20ma device, but this wasn't the case. Next, I tried putting a meter between the black wire and the positive terminal of the PLC and checking my mA which reads 1.21 mA. This is the only thing going to this PLC card, the rest of the analog is 24vDC and seem to work, but I can't find anything in the literature that says the analog card won't work with 12vDC. Any ideas on where I may have gone wrong?

5000 uses 1/1000 units, so 4000 would be 4 (0%) on a 4-20mA scale if I'm not mistaken. That is, if you're using 5000?

No, its a MITSUBISHI Melsec A. Nice and old. I gave a link to the user manual for the card, but should have mentioned the brand in my initial description. I'll edit it.

EDIT, can't edit original post. Have exceeded my time limit.

Sorry I get AB tunnel vision

You need to initialise that card and start the reading from software. There is a step sequence to follow.

I am not sure which Mitsubishi analogue module you are using but most of the ones I recall need you to link the +ve current input terminal to the +ve voltage input terminal. You also need to set some things such as resolution and filtering up in the PLC programme.

Sorry - Just noticed the link to the manual. You just need the DIP switches set correctly on your module.

spaderkung said:

You need to initialise that card and start the reading from software. There is a step sequence to follow.

Click to expand...

I used the initialization that is working for the card prior to it. Below is how it's done (I'm not strong with Mitsubishi, I came from AB and have been basically getting by).

https://imgur.com/a/WneFN

I can unplug the return from the humidity sensor and my reading goes to 0, then plug it back in and the reading "jumps" to 4000 (it'll flash somewhere inbetween depending on the scan), so it looks like I have the correct slot/input (learning to access buffer memory after being pampered with address tables was interesting). As mentioned, this is the same settings used for other cards in the same rack.

Andybr said:

I am not sure which Mitsubishi analogue module you are using but most of the ones I recall need you to link the +ve current input terminal to the +ve voltage input terminal. You also need to set some things such as resolution and filtering up in the PLC programme.

Sorry - Just noticed the link to the manual. You just need the DIP switches set correctly on your module.

Click to expand...

By the book it looks like my dip switches are correct though, SW1-8, SW2-8, and SW3-8 are all turned on which shows as being 4-20mA if I'm reading correctly?

I appreciate all responses, I love learning and I know there are many knowledgeable people on this site! Let me know if more information is needed, or other things to try (or if something I've mentioned is flat wrong).

Check wiring.
- You say you have 1.21 mA - that's not possible for a healthy 4-20mA device. Disconnect from PLC and measure again.
- Your description of wiring seems otherwise ok.
Terminals on the cards are confusing, zig zag, double check.

You suspected if 12VDC was ok for your card. Irrelevant - the device outputs a current to the PLC.

Compare with working channel - switches, wires, program. What channels are working and are they for 4-20?
You should use FROMP, not FROM, just because it's that way in the example on p5-4.
You write, TOP, to buffer mem K20 - but this is the analog reading for CH7. Why write? You may need to look over your whole code.

I assume your card is in position A0 because you configure a new channel on an existing card?

I share your view of the interesting in buffer memories. Card slot adressing is nice too. I did the exact same card a year ago and although the manual says the ad conversion bits are on by default - they were not. EDIT: Maybe similar card Q64AD. But I definately remember this manual, specifically the error Mitsi made in the buffer table using the same name for Channel and Channel Filter.