Contrologix AO not AO'ing

tomalbright · Nov 10, 2006

I was finally able to put some PID controls in service. Unfortunately, I am not having much success.

I have an active PID with the control variable assigned to an AO point. Everything is scaled, the PID function ramps the output accordingly. It seems.

I have no actual change on my control variable, even though the PID is at 100%, the AO variable is 0, and 4 mA.

I feel I am probably missing something very basic here.

(A 1756-L61 and an OF8, BTW)

curlyandshemp · Nov 10, 2006

tomalbright said:
I was finally able to put some PID controls in service. Unfortunately, I am not having much success.

I have an active PID with the control variable assigned to an AO point. Everything is scaled, the PID function ramps the output accordingly. It seems.

I have no actual change on my control variable, even though the PID is at 100%, the AO variable is 0, and 4 mA.

I feel I am probably missing something very basic here.

(A 1756-L61 and an OF8, BTW)

Can you post a screen capture of how your PID control variable is being outputted to the analog output channel.

Also, you have configured the output of the OF8 channel to be 0 - 20ma and scaled accordingly ?

Ian

tomalbright · Nov 10, 2006

Yes, my output card configuration looks exactly like that.

Here's my PID:

tomalbright · Nov 10, 2006

HAH!

err... I found it. In the PID configuration the CV high value wasn't set. The question of why the default is "0" rather than "100" is odd, but since the contrologix allows so much user scaling, I guess I can see why. That's one more thing I need to check, I guess.

Too many years on the earlier PLCs, wasn't looking for that one!

curlyandshemp · Nov 10, 2006

Your control variable is being outputted to the Input image of the analog output

tomalbright · Nov 10, 2006

Yes, it sure is, isn't it.

I am so embarrassed. Well, a little. I used the alias to the IO, but didn't noticed where the default was set in the base tag.

Thanks.

tomalbright · Nov 10, 2006

Hm. I recieved this project with the IO already assigned. Actually, that was ALL that was done, and I never noticed this. Unfortunately, it is online.

curlyandshemp · Nov 10, 2006

tomalbright said:
Hm. I recieved this project with the IO already assigned. Actually, that was ALL that was done, and I never noticed this. Unfortunately, it is online.

Chances are the digital logic was tested via simulation then handed over to you. Things such as PIDs and analigs can only really be field tested.

Before I ship out a panel, I always test the analog outputs by forcing a value to the PLC tag that is outputted to the analog channel and use a Fluke meter to measure the 4-20ma

Ian

tomalbright · Nov 10, 2006

Yes, I prefer to have a little more done when installing a project.

I was handed the chassis I/O configuration, a box of PLC parts, a do-it yourself hoffman box, and about 3000 feet of wire. Offshore. All the construction, programming, and testing was in-place.

Not one of my proudest or neatest jobs. All "hurry up! we're coming on line any time!" for 6 months. It was a replacement for a PLC that got destroyed by Katrina, no program files, no documentation, nothing. I had to re-engineer how the platform had to work based on what the untagged spliced wires I was hooking up actually went to.

Fun, eh?

curlyandshemp · Nov 12, 2006

tomalbright said:
Yes, I prefer to have a little more done when installing a project.

I was handed the chassis I/O configuration, a box of PLC parts, a do-it yourself hoffman box, and about 3000 feet of wire. Offshore. All the construction, programming, and testing was in-place.

Not one of my proudest or neatest jobs. All "hurry up! we're coming on line any time!" for 6 months. It was a replacement for a PLC that got destroyed by Katrina, no program files, no documentation, nothing. I had to re-engineer how the platform had to work based on what the untagged spliced wires I was hooking up actually went to.

Fun, eh?

Wow,

that must be a tough situation to be in.

Contrologix AO not AO'ing

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