Thermocouple wiring to GPIO board?

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diztroy
Posts: 5
Joined: Thu Apr 05, 2012 7:19 am

Thermocouple wiring to GPIO board?

Post by diztroy » Mon Apr 09, 2012 10:02 am

Question: What are the various connectors to properly wire thermocouples (EGTs) to the GPIO case/board?

Background/Discussion:
I intend to use the 4 dedicated EGT circuits on the GPIO. I understand the importance of properly wiring thermouples to avoid adding additional junctions to the circuit as explained in the manual, http://www.msgpio.com/manuals/egt.htm , specficially,
The thermocouple leads must continue all the way to the PCB pads on the GPIO main board. "a" on the GPIO EGTx circuits board for alumel, "c" is for chromel. The thermocouple leads should be silver soldered to those locations. You can use connectors (to allow the thermocouple to be detached from the GPIO), but these should be dedicated thermocouple connectors (which are made of alumel and chromel) otherwise you will introduce a second junction, and the readings will be inaccurate
.

As I understand it, running the thermocouple leads through the AMPSEAL connection would be undesirable because it would add additional junctions. The ideal situation would be to have the thermocouples soldered directly to the board which could make installation and EGT sensor replacement/troubleshooting difficult. Also it could be difficult to properly seal the wiring.

For my installation I would like to use thermocouple connectors so the thermocouples are easily removable. I have come up with two solutions.

The first is to use a bulkhead (or panel mount or panel jack) connector that could be installed on the opposite end of the GPIO case as the AMPSEAL. As an example I think the Omega MPJ-K-F may work well (http://www.omega.com/Temperature/pdf/MPJ.pdf). However I'm not familiar enough with these to know how well they seal.

The second is to use a high density wiring feed-through to pass the extension wire through the GPIO case on the opposite end of the AMPSEAL and then use a standard thermocouple connector outside of the GPIO. I'm sure there are several manufactures, but I'm most familiar with Conax. Something like their high density multiple wire feedthrough comes to mind, as shown in the second photo down on page 37 here, (http://www.conaxtechnologies.com/produc ... _5001C.pdf ) where the left side would be the inside of the GPIO case and the right side with the connectors would be outside the GPIO.

I think I prefer the bulkhead connector personally as it would avoid having dangling wires coming from the case, but would like to get other opinions on the matter.

-Troy

Bernard Fife
Posts: 1696
Joined: Fri Apr 04, 2008 1:28 pm

Re: Thermocouple wiring to GPIO board?

Post by Bernard Fife » Mon Apr 09, 2012 1:34 pm

Troy,

I have nothing to add, really. You have identified the issues and solutions, and like you, I personally would prefer a thermocouple bulkhead connector. The one you have identified looks good to me, but I couldn't vouch for how well it seals.

Lance.
"Never wrestle with pigs. You both get dirty and the pig likes it." - George Bernard Shaw

diztroy
Posts: 5
Joined: Thu Apr 05, 2012 7:19 am

Re: Thermocouple wiring to GPIO board?

Post by diztroy » Mon Apr 09, 2012 2:53 pm

Lance,

Thanks for your comments. I am typically a victim of "you don't know what you don't know" so I was wondering if anyone else had other solutions. I like to think out loud (online) and bounce ideas off people.

I think any thermocouple wiring that relies on those non-water resistant connectors could always be troublesome in a wet environment, so mostly I just don't want to damage the GPIO board if it receives moisture through the EGT connections somehow.

Also I was discussing thermocouple wiring through the AMPSEAL with a co-worker that has more experience with thermocouple interconnects. He mentioned that as long as the new "junctions" in the AMPSEAL are at near the same temperature as each other and the thermocouple IC with a short run to the pads on the circuit board the voltage (and thus temperature) offset should be minimal. I'm not sure if thats a realistic operating condition or not? As I see it, it would depend on how the GPIO is configured.

After thinking about this more and more, I personally don't want to hard-wire the thermocouples so I can easily swap or remove thermocouples for calibrations, cross-referencing and troubleshooting as necessary.

I will do some more searching for other bulkhead connectors that may fit better and will report back when I get a setup installed on the GPIO.

-Troy

Bernard Fife
Posts: 1696
Joined: Fri Apr 04, 2008 1:28 pm

Re: Thermocouple wiring to GPIO board?

Post by Bernard Fife » Mon Apr 09, 2012 4:21 pm

Troy,

Yes, one person's 'minimal offset' is totally unacceptable to another person. The chips, and nearby pads on the PCB, do tend to run hotter than the Ampseal connector, just by virtue of being 'powered up'. So using the Ampseal connections depends on the level of accuracy you need, and it's hard to estimate this accuracy beforehand.

For the GPIO board, water itself isn't going to hurt it (we submerse them in hot water to wash them off after assembly after all), but I am sure you are referring to shorting the components on the board with water while it is powered up. That is unlikely in an automotive environment (the GPIO is supposed to be mounted inside the cabin - the electronic components aren't rated for under-hood temperatures). Under those conditions, it's hard to see how enough moisture could come through a connector to be a problem. The best thing to do is to make sure ALL of the residual soldering flux has been removed after assembly by washing/scrubbing thoroughly with 99% isopropyl alcohol, then rinsing with hot water, and letting it dry completely (as recommended in the manual).

If you are mounting this on a personal water craft, or the outside of a submarine(!?!) then I suspect there will be problems without careful consideration of water ingress issues.

Lance.
"Never wrestle with pigs. You both get dirty and the pig likes it." - George Bernard Shaw

diztroy
Posts: 5
Joined: Thu Apr 05, 2012 7:19 am

Re: Thermocouple wiring to GPIO board?

Post by diztroy » Mon Apr 09, 2012 8:27 pm

Lance,

Thanks for the good points and additional info about the circuit and wiring. I agree, best to design the wiring and interconnects as trouble free and accurate as possible.

You are correct, my concern is moisture getting in the case while powered up. I intend to initially mount the GPIO in a coupe so it shouldn't be an issue there, but it will eventually find its way to a roadster project (no top ever) so there is a greater chance of it seeing some rainwater at some point (although still unlikely as it will be mounted under the dash or seat). Sorry no GPIO submarines. :-)

On a side note, I'm really excited to get started with GPIO for setting up sequential with MS3X!

-Troy

ruirito
Posts: 6
Joined: Sat Jan 09, 2010 1:37 pm

Re: Thermocouple wiring to GPIO board?

Post by ruirito » Mon Jul 16, 2012 3:44 pm

Hello Troy.

I also have a GPIO running and my next step is to connect the 4 EGT. I really like the bulkhead connector idea and I think I will use that one. And what about the soldering? Where you able to find the silver solder?

Thanks,

Rui Rito

ruirito
Posts: 6
Joined: Sat Jan 09, 2010 1:37 pm

Re: Thermocouple wiring to GPIO board?

Post by ruirito » Sun Aug 05, 2012 11:47 am

Hello,
I'm still wondering about the silver solder. Is it really silver solder or is it a technique named silver soldering?

Best Regards,

Rui Rito

Matt Cramer
Posts: 55
Joined: Thu Apr 17, 2008 5:19 am

Re: Thermocouple wiring to GPIO board?

Post by Matt Cramer » Mon Aug 06, 2012 4:38 am

Silver solder is the material used as solder, not the technique.

ruirito
Posts: 6
Joined: Sat Jan 09, 2010 1:37 pm

Re: Thermocouple wiring to GPIO board?

Post by ruirito » Mon Aug 06, 2012 6:14 am

Thanks Matt and ok... seems logic. But why is so difficult to find? Is it 100% pure silver?
Maybe if I use this http://www.labfacility.com/pcb-mounting ... -p168-pg71 I don't need to solder?! I will check for dimensions compatibility.

Matt Cramer
Posts: 55
Joined: Thu Apr 17, 2008 5:19 am

Re: Thermocouple wiring to GPIO board?

Post by Matt Cramer » Tue Aug 07, 2012 5:01 am

It's not pure silver - actually, there's only a small percentage of silver in silver solder. This one, for example:

http://www.digikey.com/product-detail/e ... ND/2177056

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