New guy PID controller question

[partsproduction]

Hi,

Please help a new guy with his stupid question. 

I bought a cheap 240V electric muffle furnace off ebay. The furnace seemed to work well when I first got it, but since the first firing to about 300C I'm unable to even turn the elements on, much less program it. I've been able to get it to the point where indicator lights show it's under load but it doesn't heat up at all.

The controller is an i-Therm AI 7891. Scrolling through youtube it seems that while many commands are universal some are unique to their brands. I downloaded the "Manual" which seems very opaque to me, I can hardly make heads  or tails of it.

 So, my question is this, does anyone here have an i-Therm 7481,7781, 7791, 7681 or 7881 controller who is willing to help me figure out how to program it or even to simply bring it to temperature?  Is it possible for the controller to show itself under load without actually getting hot? If it's not a rule violation I can show the pdf of what's called a manual, or just google i-Therm AI 7891 and you'll see a pdf of the sheet. Should I just choose a controller with a better manual and wire it in?

Thanks for reading this, and thanks for any constructive responses.

 

[Frosty]

Contact the manufacturer is my suggestion.  I wonder why a good muffle furnace would end up on E bay? 

Frosty The Lucky.

[Irondragon Forge ClayWorks]

 

[partsproduction]

"  I wonder why a good muffle furnace would end up on E bay? "

This was a new furnace, but bood, I don't know. I may just be havinf trouble breaking the secret handshake code. I messed with it a while ago and the timer is counting up. No heat yet though.

[Frosty]

Do you have the manual? Are you giving it time to heat up? The muffle furnaces where I used to work took maybe 5 minutes before you could feel heat at all. They weren't in my area of work so I didn't spend any time with them but the guys doing ash corrections used to turn them on an hour or two before checking the temp let alone putting a sample in. 

There aren't any secrets not in the manual if it's not broken. 

Frosty The Lucky.

[partsproduction]

I've left it sit for 30 minutes at a time, checking for life after various inputs. The "manuals" for these pid controllers made in India hardly deserve the name, I've learned a great deal more about them in youtube. I'm hoping for a description using an i-Therm PID controller of what buttons are pushed step by step inputting a simple program. Let's say start at 20C for 5 minutes, ramp up to 300C, hold 300C for 1/2 hour, then ramp up to 815C over 30 minutes, then hold 815C for 30 minutes, then shut off. The one i-Therm pid video I found is done by an Indian with heavily accented English and very fast too, so also very hard to follow. BTW, there is no toggle for Fahrenheit, and that's according to the manufacturer.

 At this point I'm considering starting with a controller I can afford AND which has a manual (and or a good video) that's more clear, then buy that and wire it in place of the i-Therm.

[Frosty]

I mean manual for the furnace itself. Manufacturers often buy components from the lowest bidder and the controller may not be the problem. I'm pretty much out of ideas other than going to the manufacturers manuals and website for help.

Frosty The Lucky.

[timgunn1962]

Pictures would probably/possibly help. A link to the manual would certainly help: google is not helping me much.

As you are asking the question, it's probably fair to assume that you are not comfortable messing with electrics. 

The first thing I'd be looking to do is to narrow down the likely cause of the problem.

It is always better to fault-find in a logical manner. As a rule, it is better to start with the cheap/easy (either the things that are cheap/easy to fix if it turns out they are the problem, or the things that are cheap/easy to eliminate) and work up to the more difficult/expensive ones. 

The "obvious" problem is that your oven is apparently not heating.

Unless you've done a whole bunch of stuff that you've not mentioned already, and definitively narrowed the problem down to the PID controller, it would seem that you've picked the most difficult component to fault-find and/or fix and decided to start there.

Assuming you have checked for certain that it is not actually heating, you will have already eliminated the possibility that there is a fault with the temperature measurement that results in the controller displaying ambient temperature all the time (the most likely cause of this would be a thermocouple wiring fault: probably a short-circuit between the "legs" ), there would seem to be 2 likely causes:

First is that power is being fed to the element(s), but the element(s) have a break that does not allow current to flow. It is pretty easy to check for electrical continuity through the elements with a multimeter on the Ohms setting. This can be done with the equipment unplugged and completely isolated from the power supply, so with no danger of electrocution. It does need a multimeter and some familiarity with it.

Second is that power is not reaching the element, in which case you would be best served by tracing through the wiring to find the open point. It may be a fuse or breaker or it may be the relay/contactor/SSR that is driven by the PID controller output. This can usually be traced through, again using the multimeter, with the equipment completely isolated. With the power off completely, the relay/contactor/SSR will be an open point in the power circuit, but in most cases, it should be the only one if everything else is normal.

If you can reach the point where you are sure the only open point in the power circuit is the relay/contactor/SSR, you can then start to look for the presence/absence of a control input to it, which may well take you to the controller. 

If the output indicator on the controller is telling you that you are getting an output, you can check for it with a multimeter, but need to know what it is that you are looking for: either a DC output to drive an SSR or a relay output to trigger a bigger relay or contactor. 

 

 

 

[partsproduction]

Thanks very much for the responses. This thing has been driving me nuts. It looks like it won't get me kicked out to show the controller's manual URL.

https://webmail.centurylink.net/service/home/~/?auth=co&loc=en_US&id=95428&part=2

To be painfully honest manuals for other controller brands seem similar, that is, written as if a prize is awarded for brevity and obscurity. It's possible too that I'm far more stupid than most folks I suppose, though I've written many hundreds of CNC programs. I admit I also find FANUC manuals are also hard to understand.

Today I looked into buying another brand of controller, but it's not as easy as it seems, there are many variations and possibly only one correct choice, and, as I said, the manuals look about the same. One thing that would be worth a lot would be the ability to change to Fahrenheit. It doesn't seem like much but it's irritating having to do the math every time swapping C for F. 

 

 American and European controllers run in the $500+ price range, so some accommodation might be worth the price difference.

[timgunn1962]

I'm getting a 404 error when I click on the link.

I have built several HT ovens and tend to use either the Omega CN7823 or the Automation Direct Solo SL4848VR ramp/soak controllers. They are the same controller with different badges, as far as I can tell. They are much less than $500.

I buy whichever is cheapest at the time. If your system does not use an SSR, there are other variants with relay outputs.

Both Omega and AD have excellent (worldwide) support and their manuals appear to be written in English by people who write manuals for a living. 

In the US, Auber Instruments seem to be highly rated as well. They have a ramp/soak controler at reasonable cost. They do not have a UK presence so I have not tried them.

With any industrial controller, you are likely to find that the main setup parameters are available from the same access level as the ramp/soak programming. If it's only going to be you that uses it, no problem. One of the guys with an oven I'd built managed to change the thermocouple type when setting a ramp/soak profile. He changed it from type N to type S, so it was pretty obvious and was easily rectified with a phone call, but it does mean that I have to explain the potential for lousing things up when I hand an oven over. 

Dedicated kiln controllers usually keep the operator well away from the configuration settings with password protection.

[Irondragon Forge ClayWorks]

If we knew where in the world you are located, there may be an electronics expert close to you that could hands on diagnose the problem.

[partsproduction]

I'm in oregon USA on the far left coast.

But good news! I emailed the company in Mumbai India asking if a technician who speaks fluent English could talk me through the "secret handshake" of the i-Therm AI 7981 controller. They are very happy to help I find, which is good. They sent a phone number and tonight at 9PM I'll call, as that should be 9:30 AM there.

 Being a technophobe I often ask my brother to open up the secrets of technical interaction with devices, even so he also could make no workable sense of the manual. And as I said earlier , mostly  the manuals I've seen appear to be similar. But I'm excusing myself.

 I know that someone familiar with this brand and model controller can tell me over the phone what I can't make out in the manual,  and so far I've found no one in the USA who has one. It's highly likely that there are many such i-Therm controllers in use, I just don't know how to find anyone to talk with me about this, it does seem that entry procedures are different for different brands..

Thanks very much guys for your help,

parts

New message from India this morning; "Please send message by whatsapp instead of call. Because our technical team will not available at call."

 

Always some secret handshake! I've never heard of whatsapp before today.

[Irondragon Forge ClayWorks]

1 hour ago, partsproduction said:

I'm in oregon USA on the far left coast.

We won't remember this after leaving this post, hence the suggestion to edit your profile to show your location with every post.

[partsproduction]

Here is a video sent from India showing how to program it;

Guys is it necessary to program parameters  to get it to turn on? It appears he is running through them after setting the temperature.

[John in Oly, WA]

I'm learning to run an Auber brand ramp/soak PID with the little burnout oven I just built. The manual is barely decipherable to me, but I think I managed to program it with several steps for burning out my flasks for metal casting. I had to get into the parameters section to set the type of thermocouple and change the temperature read from C to F, and a few other things I can't remember now without the manual in front of me. But once the parameters are set, it looks like I shouldn't have to go back into that section again, so if yours worked once, I wouldn't think you'd have to mess with the parameters. Just the programming.

But none of the PIDs I have (3) are as easy to program and run as the Bartlett V6-CF kiln controller. It's just a bit harder to wire up in the first place.

[partsproduction]

Thanks John. Communications with those in India (who are very willing to help) leaves much to be desired. In fact I've given up for now. Having spent quite a bit of money I'm thinking to replace the SSR first, and if that doesn't help I hope to change the controller. This time I'll investigate the choices with great care.

 With the Auber what steps are involved in simply starting the controller and setting a desired temperature? I ask because I did start this furnace at first but nothing I have done since has raised the temperature at all, and I'm thinking some break has happened. The only fuse appears to be on the controller's power on side, not between it and the elements.

[John in Oly, WA]

Well, with the Auber, I had to set the type of thermocouple in the parameters. The default is a K-type; I have an S-type. Then I set the display to Fahrenheit. Then to just get it started, you set a temp and it takes off. If you want to set a more complicated program of ramps and soaks, it takes some deciphering of the manual. What I've learned so far is it has 30 programmable steps and every change is a step. Each step has a start temp, a time, and a finish temp. So to ramp the temp up, you might set start temp=0, time=50(minutes), end temp=400. If you want it to stay at 400 for a soak period of, say 3 hours, the second step would be start temp=400, time=180, end temp=400. If you look up the Auber website, they have all their PID manuals for download (bottom left corner of their home page), so you could check it out before ever buying one. I bought the SYL-2352P model. It was the cheapest one I could find that has ramp/soak capability.

For the controller/furnace you have, I'd just check all the electrical connections. Make sure you have continuity through the circuit. Don't know how to check the SSR, but they're pretty cheap on eBay. Also check the element for breaks. That happens sometimes. If you have a break in the element, and it's the coil type, you can just overlap the coils to make a connection and test it again. If that does it, you can make a more permanent connection with a high temp butt connector.

[partsproduction]

  Thanks guys. A friend came and checked resistance of the element and found it open. I took the back off and found where it burned up. So I guess I need to replace the element, the wire where it connects to the connector is .062", but the wires going to them throughout the bottom and up to the controller are 18 gage, but where they go from the SSR they are doubled, there and to the incoming power. Next project is determine the coiled length of the element wire and buy some. The break came right where the element goes from inside to outside, is it possible to make a connector?

 Or is the better course to determine the length  needed coiled and do the coiling myself on the lathe? That way there would be no connectors anywhere except where the copper wires connect to the element. Remember, I don't know yet what I'm doing, but I can wind a spring so this shouldn't be much difference.

Thanks,

parts

[John in Oly, WA]

They do make high temp connectors for kiln elements. They're make of stainless steel, I think. A good crimper, like one of those electrical wire stripper/cutter plier-like tools and you're set. That's what I'd do, but I'm cheap. It'd be the simpler solution too. Save you from having to measure the length of the wire, determine resistance and all that.