PID may be dead... and I need some guidance, please!

[dmankin]

I have a Bunn ES-1A (rotary/E-61/HX), with a PID installed.  Although I installed the thermocouple, SSR & PID myself, it was done with the precise directions from Tex.  He actually gathered all the parts for me, programmed the PID (Cal 3200), bundled the wires… basically handed me a PID kit, and following his directions, I was able to do the installation.

Over the years, while mechanical things had their cranky times, the electronics of the PID system was faithful… until recently.  On one occasion, while turning the machine on and watching the temp rise on the PID display, I noticed that it stopped heating, and began to fall back toward room temperature.  I replaced the SSR, thinking that it was the culprit.  Well, the machine came up to temp as usual, but reached and surpassed my temp setpoint.  I shut it down, and tried a few more times – not sure why… but it behaved identically.  With a few SSRs sitting around, I tried yet a third one, and it behaved exactly like the last one – when the setpoint was reached, it kept on going.

I strongly suspect the PID as being faulty at this point.  Having only followed Tex’s directions with his kit, I don’t know anything about programming a PID, or how to approach the replacement & programming of a new PID.  I am aware of units that have an auto-tune feature, and I am wondering if I can hook a new PID up, set a desired target temp, and let the auto-program do its thing… or am I foolishly oversimplifying the process in my head?  I remember downloading a manual for my CAL-3200 and glazing over due to its complexity, and my inability to comprehend the thing.

Tex is out of commission for now (although we have spoken on the phone, and I may call him regarding this issue), and I’m looking for advice and guidance as to how to test if my PID is bad, and how to replace it if needed.  Any words of wisdom would be very much appreciated.

Thanks,

David

[milowebailey]

What you describe suggests the PID is faulty, but I've not had one fail.  I assume it would totally stop working, but strange things can happen.  Does it read the correct temperature?  It could be your thermocouple died... I would check that before replacing the PID, but it could also be the PID.  Test the thermocouple (ice water and boiling water). 

Tex could walk you through re-programming a new CAL PID over the phone, I'm sure.  I use fuji PIDs, and could probably figure out the CAL, but Tex would be a better source for CALs and tell you what settings he uses for BUNNs... I also don't know BUNNS...

Check youtube.... somebody might have a video on how to program the CAL

[dmankin]

Thanks for your reply.

1. Thermocouple seems to be doing its job as far as giving me what I believe to be good boiler temp readouts, so I am suspecting it is functioning properly.

2.  Not mentioned previously - there is a small green LED that flashes on the face of the CAL 3200 as the unit "thinks".  It ceases to flash as I approach the target temp range, and the temp just sails past the setpoint (as if the PID has stopped monitoring the process).

3. YouTube.. yep, I bet you're right.

Thanks, Milowebailey

[peter]

That Milo...       he's not just another pretty face.

[sea330]

Bad thermocouple would be my first guess, very rarely have I seen a controller go bad, but they can. 25 years in the process control world 90 % of the time with what you are describing seems to me a flaky TC or operator error to the point that even auto tune won't fix.. If replacing the TC don't fix it I would call the manufacture and get things back to factory defaults. Firmware can get corrupt. Good luck.

Open TC=  temp runaway. Bad weld at the junction can mean things will go crazy when it gets hot, but it works ok at lower temps. Make sure you have the right TC for your controller.

[dmankin]

I do plan on turning the machine on once more, just to observe both the LED on the PID and the SSR as it goes from room temp to setpoint (and beyond, sadly).  In any case, I just pulled the trigger on a replacement thermocouple - the identical Omega model that Tex had in the kit.  With the holiday, I don't expect to see it until next week - at the earliest.

Thanks for all the guidance and opinions.  I'll post my LED observations once I have a chance to fire it up & take notes on the findings.

David

[sea330]

If you were close by I have a TC simulator to loan. If you mess with this stuff allot maybe good idea to get one, there not that expensive. I have seen them on ebay for around 40 bucks used, new run a little over a hundred. I don't use mine very often but when I do sure makes it easy to identify issues. Just a thought

[dmankin]

With a 90% chance of the TC being bad, I bought an exact replacement (Omega) thermocouple online, and am expecting it within a few days.  I'll replace the original and report back the results. 

Thanks again for everyone's input.

Dave

[dmankin]

OK - I spoke with Tex the other day regarding this PID/Thermocouple issue.  I received my new thermocouple the other day as well.  When I removed the original one, I found a 'barb' or 'ferrule' attached firmly to the TC.  Tex tells me that this attaches itself in the compression fitting tightening, and is not removable.  He mentioned that they are a 30-cent item... but he couldn't think of what they are called!  I'm not even sure that I would have a hardware store nearby that would carry this, but once I find out what this thing is called, I can call Google into action to locate one.

Can anyone identify this item? <assuming I can figure out how to insert an image here!>


Thanks,

David

[peter]

It looks like a ferrule you'd see in a compression plumbing fitting.

[dmankin]

Ah - thanks!  Robert couldn't remember what it was called... but he did remember that it's 1/8".  I'll put the original in my pocket and bring it with me  once I locate a reasonable hardware store!

[paultflorida]

Any lowes. Home depot. Ace etc hardwRe store should carry them. But yes bring it along

[Ascholten]

It's called a ferrule, and if it is a swagelok fitting then it has a backing ring that needs to be on top of it too.   You can use brass or stainless,  Id recommend stainless for durability over time.  Not to mention the thermocouple is probably stainless.  You will need something as least as hard as the metal you are putting it on (the tc) or it will not swage / seal properly.   Also the dissimilar metals of brass can give you a chance at galvanic corrosion as well which is not good.

When you tighten it, do NOT go over 7 'sides' on the nut, in other words one complete turn and then one 'side' to snug it.  Over tightening can cause problems and actually in extreme instances cut into the thermocouple shell and cause even more bad issues.

Aaron

[dmankin]

Thanks to all for the great input!  There's even a nice animation on the page showing how to install the ferrule!  This is what I found online, and seems to be the right part:

http://www.swagelok.com/search/find_products_home.aspx?part=SS-200-SET

I'll see if the local Lowes/Home Depot carry such a piece. 

Cheers,

David

[dmankin]

OK!  None of my local big-name hardware stores had the pieces I needed, so good-ol' Amazon saves the day once again!  I now have an exact replacement Thermocouple and two pieces of the compression ferrule (Parker).  I'll  read up on the the conventional wisdom regarding how many turns is proper for this brand ferrule. I'm in a very busy season, so I'm not exactly sure when I will put wrench to fitting on this, but I hope to get to it soon.

Thanks for all your input(s) on this issue.  I am systematically replacing the entire PID system, and after this, the only thing left is the PID itself... and I'm hoping to not need to go down that road!

David