Attention Nowell!!

[R Anestis]

I talked to you on the phone today about spa guages. You said that they don't have a dual pressure guage yet but they are supposed to come out with one. I was wondering: could you do what Steve St. Laurent did with his manual guage? I mean is it possible to install two senders and a toggle switch to go from one to the other or would that cause problems with the guage?

I would have called you back but the phone was tied up here and I had to go to work. Thanks for any help.

-Ron

 

[HVAC]

Yes you can.

You can monitor two pressures using two transducers and a switch. You will need a bit more wiring for the second transducer. It's cheaper then a second gauge by a long shot.



Also, you can monitor pre and post turbo temps by switching between two separate thermocouples.



Thanks for your interest in the SPA's

 

[TXRam]

I think I can answer this. It shouldn't cause any problems as long as you make good connections. You will need an extra sensor as well as an extra cable.

 

[SLang]

On the thermocouple you will introduce some error by placing a switch in line. This is definitely not enough to worry about with the analog gauge I have, but you may see some change on the digital. It shouldn't be more then 20-30F and it will be a fairly constant offset depending on ambient temperature.

 

[HVAC]

Dual EGT

When hooking up a switch for dual EGT readings we always switch the signal downstream of the amplifier. I believe this works best and would develop less error then prior to the amp where the signal is maybe 25 millivolts.

 

[SLang]

The SPA gauges have an external amp for the T/C signal? That's strange. I deal with a lot of digital T/C gauges and have never seen an external amp for the T/C. Is this strickly an amp, meaning what ever the T/C puts in it puts out 10 times more? Or is the actual digital chip used to determine the T/C reading and then puts out a standard output to the gauge (i. e. 4-20 mA, 0-10 Vdc, etc)?

 

[John]

HVAC, I was thinking of adding a switch plus another amplifier and thermocouple to my SPA pyrometer (to monitor POST EGT) however, I figured the switch would be best placed between the gauge and the amplifier thus, allowing less chance for error in the low level signal (i. e. , the percentage error would be magnified as it was processed through the amplifier). Any comments?

 

[HVAC]

SPA Amp For Pyro Operation

Regarding the use of the SPA for pyro operation, it may help to know that the SPA gauge can be run on two different scales. The diff is that for low temps to about 300* we use a sensor (thermister?). This has a 12v supply which is used to trigger the gauge. Now when monitoring EGT's we don't use the sensor, we use the thermocouple and the amp. I'm betting the amp is necessary to increase the signal from say 20mv the tc would provide to something similiar(signal strength) to what the sensor/thermistor would return to the gauge.



Well last night I met with a highly respected team of engineers (ram runners meeting), and I sacrificed the amp on my truck for the cause. Well we scrutinized and scanned and probed etc And in summary, the team of widely renouned experts found that there was in fact an amp on the tiny board. However, the brilliant team of engineering minds also found another lil' suspicious device lurking on the same board with the amp. I'll cut and paste how the team leader surmised this in his official report submitted late last night while the rest of the free world slept.



Quoting team leader now-



"The LT1025 is a thermocouple compensator which

essentially takes out the "non-linearities" of the thermocouple. "



So you see, there are two gizmos in the amp housing that massage and tune the mal nourished signal from the K-style tc and then it goes up the conveyor belt to the gauge which happily flashes and flickers EGT's that always seem to be a bit hotter then you might like

 

[SLang]

Thanks for the info Nowel. Sorry you had to sacrifice your "converter" (what you call an amp) to the curiousity gods.



But hey it was for a good cause... the quest for knowledge.

 

[dresslered]

John-

Your reasoning is absolutely correct on the location of the switch. Look for a switch that has an extremely low contact resistance (preferably gold) and you might even consider a low dc contact resistance relay instead. I used a DPDT switch (paralleling up the contacts thus reducing the resistance) for my dual oil temperature set-up. At very worse, you will offset the reading slightly.