pyro reading pre/post

[BRayls]

been doing some thinking ,and research. I have found,I think, a way to hook 2 thermocouples to one gauge with a switch to toggle back and forth between the 2 for pre-post turbo readings. one of the guys that does calibration,and builds our probes for the funaces at work,has told me he has the switches to do the job on k type thermo applications. do you think it will work? anyone else interested in this or just me?

 

[Gary - K7GLD]

Several here are alredy running what you describe, not necessarily 3rd genny trucks, but other Cummins...

 

[SRadke]

If you have a switch that is made for it, it will work. Many people try to do it with a generic elecrical switch and their readings get thrown off.



-Scott

 

[rbattelle]

Originally posted by SRadke

If you have a switch that is made for it, it will work. Many people try to do it with a generic elecrical switch and their readings get thrown off.



-Scott

The key is to not introduce any metals in the switch that are not exactly the same as the wire in the thermocouple (I think K-type is Chromel-Alumel... Chromium and Aluminum?).

 

[BRayls]

Originally posted by rbattelle

The key is to not introduce any metals in the switch that are not exactly the same as the wire in the thermocouple (I think K-type is Chromel-Alumel... Chromium and Aluminum?).

I don't know what it is. but I know that you are correct,on that it needs to be the same material. I talked with b-d and will be calling again tommorrow to find out what kind of resistance I can add without throwing the gauge off to much. I know the switch I am getting is made for this application,so thats not an issue. any pics of these others here? thanks Barry

 

[y-knot]

I think way to much is being made about this subject. Everyone is trying to make it out too be more then it is, the truth is is makes very little difference what kind of switch you use. There is no need to over engineer it, It is a simple operation that requires no special attention. I have several probes that share a common gage, they work and read just as accurate. I also have the two EGT probes with each having it's own gage. Last fall when I decided to rip out all my old gages and start completely new with all Auto Meter ultra lite gages. I had several that were going to share a gage, I bought relays and a assortment of several quality switches and experimented a little before they were all installed. I too wanted to make sure the switches did not compromise the readings of the gages, after all why install top rated gages if there readings might not be accurate? I measured both Ohms and degree or pressure, on the Auto Meter gages and senders. For comparison standards, I used 10 feet of # 14 copper wire on all electric sender to gage readings. Then I would take a Ohms reading at the gage , then introduce several different switches and two different relays, all of various quality and construction, the readings were negligible, and not worth noting. I also check the accuracy of the senders, both pressure and temperature. For the temp probes, I heated water to two different temperatures I used 160 and 200 degrees. I checked the gages at both temperatures against a cooking thermometer to see if there was any discretion. And for the pressure senders, I used air pressure for the test, and used 40psi, and 75psi as the standards. For accurate air pressure readings I checked my readings against a 4" wide sweep gage I purchased. This might sound drawn-out and complex but it really wasn't. I had all the gages right there and the whole thing only took about an hour, I used break-out box and had all the switches and relays pre wired and it was just a matter of switching from one terminal to the other.

The conclusion was there was almost no difference between any of the switches I had or the relays. All the auto meter gages were very , very close to each other and to my testing standard. I had expected to find more of a difference, but it just wasn't there. Same goes for the EGT probes, I used there supplied probe wires and ran them through the same switches. Only difference was the gage for the EGT's started at 100 degrees so I just boiled the water and ran the testing standard at 212, this was the only way I could keep the temperature the same. No difference. For fun though, I tried some aluminum wire I had, and then even mixed the two types of wires and that did produce some errors in readings.

So from what I gathered out of all of this is switches and relays don't affect the accuracy of the readings, as long as the switch changed states and held it position firmly there was no effect on the readings. But having different lengths of wires, or combining different types of wires together, did effect the readings. By length of wires, I don't mean the wires that go from sender to switch, it the ones that go from switch to gage, they must both be the same length, and type of wire. This was just my small experiment, and was only done to suit my curiosity and take time out of the day, bored I guess? I think the results were valid, and I tried to keep accurate readings. If you ever have some time on your hands and nothing to do, see what you can come up with, I would be interested in hearing about your results.