2 gauges off of 1 thermocouple?

[NNethers]

Anyone know if I can use one thermocouple to run two EGT gauges? One would be a dipricol EGT gauge and the other would be the EGT function on my TST R49AP. The thermocouple I’d be using would be the one that came with the dipricol gauge but I could swap it out for the TST thermocouple if necessary. Both thermocouples have yellow and red wires so my guess is they should be close to the same with calibration.



I only want the TST EGT gauge for the defueling and turbo cool down features.



Any help would be appreciated.



And before anyone asks "why" I wanted to do this I had planned on installing the TST EGT after the turbo (the dipricol EGT is in the manifold) in the port that's in the cast elbow of the pac-brake but it's rusted in there and I can't get it out and I don't want to (read "too lazy") pull the pacbrake out and get it on the bench to either drill a new hole or ez out the rusted in plug. So... running two pyro's off the one thermo is my next best bet.

 

[Red_Rattler]

Won't read correctly, start drilling lol

 

[NNethers]

Why won't it read correctly? Different thermocouple calibration for each gauge? Or because I'd have two gauges off of one thermocouple?

 

[Rams-n-Hogs]

I've been running mine that way for a couple of years. For a while, I ran two probes. Either way, they have always been within about 50* of each other.

 

[Turbo_Bob]

A thermocouple generates DC voltage, (millivolts). A red/yellow thermocouple will produce 33 millivolts at 1500 F. So if you are using one probe to run two gauges, it might throw off the calibration of the gauges ?

 

[Red_Rattler]

Correct, the thermocouple puts out a very small voltage (<50mv). Each device connected to it has a little resistance to add, effectively reducing the signal to the gauge/device. When your resolution is based on very small voltages, ANY change will make a marked difference in the reading. Each device (gauge or TST) has a built in thermocouple amplifier, which will amplify this voltage and therefore, amplify the difference between real temp and displayed temp based on those changes. The difference between a reading of 1300*F vs. 1400*F is only 2. 3mv



But if your ok with that it can be done.

 

[Scrappy]

Anyone know if I can use one thermocouple to run two EGT gauges? One would be a dipricol EGT gauge and the other would be the EGT function on my TST R49AP. The thermocouple I’d be using would be the one that came with the dipricol gauge but I could swap it out for the TST thermocouple if necessary. Both thermocouples have yellow and red wires so my guess is they should be close to the same with calibration.



I only want the TST EGT gauge for the defueling and turbo cool down features.



Any help would be appreciated.



And before anyone asks "why" I wanted to do this I had planned on installing the TST EGT after the turbo (the dipricol EGT is in the manifold) in the port that's in the cast elbow of the pac-brake but it's rusted in there and I can't get it out and I don't want to (read "too lazy") pull the pacbrake out and get it on the bench to either drill a new hole or ez out the rusted in plug. So... running two pyro's off the one thermo is my next best bet.

I did this exact setup in mine and it worked fine, there was very little error in the gauges readings. I just like you did not want to turn my manifold into a porcupine.

 

[GRoutzahn]

Same here. I spliced mine and didn't have any problems.

 

[sweeda]

temp. disable one of the gauges and drive than reconnect with the other disabled and drive check acc. (note the numbers b-4 disable) that should at least tell you what the difference is. try to do on the same day and the same run as close as possible with the same load and you can. Then you can compensate if there is a diffenence. just keep it close to the highest one and set the TST to that to defuel and all will be fine.

 

[JBonpua]

I believe there will be interferance if you "gang" more than one gauge for each type K thermocouple.

 

[biggy238]

I BELIEVE... well, know there will be interferance. . These guys pretty much outlined why and what will happened if you give the voltage two different routes.



You can find the tables for K type thermocouples (and many others) if you google around a while.



Even the resistance from another connection AT the thermocouple could cost you

50-75* of gauge accuracy.



You could build a repeater but that would make things complicated.

 

[AH64ID]

It will read, but like it has already been said you may not read as accuratly. . But there is an easy way to tell. .

Have just the pricol hooked up, do a WOT run and pay attention to EGT's... Hook the other one up on the side of the road and repeat the WOT run. . if they are close you will be fine, but if they are very far off I would start drilling.

 

[SBall]

Sounds like both gauges are calibrated for type K if the wires are yellow/red. Most modern gauges have such a high input impedance that two devices shouldn't impact the reading from one low-impedance thermocouple. In fact, it is quite common in industrial applications to have more than one instrument measuring the signal from a single thermocouple. Just make sure you don't cross the yellow/red wires at any point as you connect the gauges in parallel as you might confuse the cold junction compensation.

 

[Steve St.Laurent]

I have two gauges wired to one thermocouple pre turbo on my truck - one is my dipricol analog gauge and the other is my TST PM3. I ran two seperate sets of leads to the thermocouple - which is what TST said to do. I tested it by removing each set of leads from the thermocouple individually while the truck was on a load dyno and saw no difference at all.

FYI though - for shutdown purposes you want to be reading the temp after the turbo. I have another thermocouple after the turbo and use a turbo temp monitor to monitor it for shutdown and my pre turbo gauge will be under 300 sometime for a long time before the post turbo goes under 300.

 

[Mhannink]

i dont know what you have done for getting the plug out but a thought i have is the plug is pipe and they wedge in and get stuck i have found that with any pipe plug old or new is to hit it really hard. the other thing i like to do is soak the plug in penetrating oil. between the 2 you should be able to get it out. then you wont have any problems with how the guages might read.

 

[Scrappy]

FYI though - for shutdown purposes you want to be reading the temp after the turbo. I have another thermocouple after the turbo and use a turbo temp monitor to monitor it for shutdown and my pre turbo gauge will be under 300 sometime for a long time before the post turbo goes under 300.

I have seen this too.

 

[NNethers]

Well, I'm going to do as some of you have suggested and do side by side runs to see what if any temp difference the gauges read with both of them connected to thermo. If it's substantial... . I'll have to go to plan "B".



As far as getting the pipe plug out of the pacbrake cast elbow... that's probably not going to happen without removing the unit from the truck and getting it on the work bench. I've already broken two sockets trying to get it out and started to strip the pipe plug. I'll try and hit it again with a 1/2" impact but doubt it'll do anything. If i can't get it out AND the temp difference is substantial (as stated above) I'm either going to remove it and work on it or see if I can drill in a new port on the bottom of the elbow for the TST thermo.



Probably won't do anything on it till next weekend... I'll update then.



THanks for all the info guys... .

 

[wlowe]

I have two gauges wired to one thermocouple pre turbo on my truck - one is my dipricol analog gauge and the other is my TST PM3. I ran two seperate sets of leads to the thermocouple - which is what TST said to do. I tested it by removing each set of leads from the thermocouple individually while the truck was on a load dyno and saw no difference at all.

That is what I did on mine. I have an Isspro EGT guage and an Edge juice/attitude. I run them both off the Edge thermocouple. I did a lot of testing and found that the edge is about 80 degrees cooler than the Isspro at 1000 degrees. This difference is the same whether I'm running one guage or two so it's not based on running two guages off one thermocoupler, there's just a built in difference in the accuracy of the guages.



To sum it up I found no difference in readings running two pyro's off one thermocouple, but I did find a difference in the inherent accuracy of the quages. To be safe, I just set the alerts/fuel down on the Edge based on the Isspro readings.

 

[AABEN]

Why take a chance?? Spend a little money that could save you BIG money.