TheSamba.com :: View topic - Any accurate NON digital readout cylinder head temp gauges?

Wed Oct 28, 2020 8:30 am

I have been using Westach gauges in several ACVW's for well over 20 years.
No Westach gauges are cold junction compensated, but the argument for cold junction compensation is a little bit like arguing about religion.

Having the cold junction inside the engine compartment is certainly a bad idea, due to the wild variation of ambient temperature in there. However, a thermocouple with 48" leads can easily be routed from the #3 spark plug to inside the cabin, under the rear seat bench where the ambient temperature is relatively stable; let's say a 30º spread. With the cold junction there, the temperature rarely varies more than 25º from the calibration temp of 75º (at least once the engine has warmed up).
When it's 100º inside the cabin of your car, you'll notice it. Same thing with 50º, so it's pretty simple arithmetic to add or subtract 25º to/from the gauge reading.

For me, it the cabin temperature in my VW cannot be kept between 65º and 95º, I will drive a different car.

Years ago, Pete, the tech guy at Westach wrote to me:

"Hi Gary
We use standard copper wire to extend the leads up to 20 feet.

The cold junction happens as soon as you terminate the thermocouple leads with anything other then more thermocouple wire of the same type. So the cold junction "error" is still at the end of the thermocouple leads where they meet the copper wire. Be this at the back of the gauge or 20 feet away.

Thermocouple wire has a higher resistance value then standard copper so using it as an extension in a passive thermocouple system just doesn't work well.

Now if you were to have the cold junction exactly at 75 deg f and the hot end was at a known temp, say 400 deg f. the gauge will read 400 deg. Now throw in 20 feet of copper and yes the gauge might read 395. But due to the fact that we don't always know exactly what that cold junction temp is on an automotive application with changing temps and driving conditions etc. that has more of an effect on the readout then anything else.

Remember that the thermocouple wire cannot run all the way through the whole system, it has to change to copper somewhere. The connections on the back of the gauge, the wire from the back of the gauge to the circuit board, the wires from the circuit board to the meter movement, the meter movement itself is full of copper wire.

Yes it is true at an engineering standpoint to use thermocouple wire for the whole length but in real world applications it is the point of just where that cold junction is and what its temperature is."

So anyway, there is some food for thought.

I have been happy with Westach products for a long time. Their combination gauges save lots of dashboard real estate, and they are accurate and well made (in the US).

That's my 2¢ ... Good luck, Mondshine

Wed Oct 28, 2020 8:58 am

Wait, so If I use a westach gauge, I can switch to copper wire under the back seat, or in the engine bay, and run that up to the gauge in the dash? I already have a bunch of extra wiring run that way as it is and that would make things much easier to install a dual gauge versus buying two extended thermocouple leads and routing them up there.

Adding 25 dgrees to the gauge on a 100 degree day is no big deal, honestly. Half of my driving has historically been on hot days.

Wed Oct 28, 2020 9:04 am

saw2 wrote: https://www.aircraftspruce.com/catalog/inpages/CHT_gauges.php?clickkey=4628439

I have used a couple of these Micro 1000 cht gauges from Aircraft Spruce. They are also temperature compensated. They have the same gauge with a round bezel. The face matches very closely to the other VDO gauges I’m using. Have had one for about 10 years no problems at all. You order gauge, leads and temp probe separately.

I’ve had one in my buggy for about 10 years without a single problem. The one thing I do notice is how much price has went up in 10 years :shock:

I run the Micro-1000 gauge with a sender under the #3 spark plug on my 1835cc. Can't say I'm happy with it. On a 110* day on my commute the gauge will read 150-200*F. I've never seen it break 250*F even driving hard in temps approaching 115*. I would love to think my engine runs that cool but there isn't a chance in hell of that. Also the backlight is very dim, almost un-readable at night but since it doesn't give me an accurate reading it doesn't matter. Maybe someone has an idea why it seems to read so low.

Wed Oct 28, 2020 9:24 am

mondshine wrote: I have been using Westach gauges in several ACVW's for well over 20 years.
No Westach gauges are cold junction compensated, but the argument for cold junction compensation is a little bit like arguing about religion.

Having the cold junction inside the engine compartment is certainly a bad idea, due to the wild variation of ambient temperature in there. However, a thermocouple with 48" leads can easily be routed from the #3 spark plug to inside the cabin, under the rear seat bench where the ambient temperature is relatively stable; let's say a 30º spread. With the cold junction there, the temperature rarely varies more than 25º from the calibration temp of 75º (at least once the engine has warmed up).
When it's 100º inside the cabin of your car, you'll notice it. Same thing with 50º, so it's pretty simple arithmetic to add or subtract 25º to/from the gauge reading.

For me, it the cabin temperature in my VW cannot be kept between 65º and 95º, I will drive a different car.

Years ago, Pete, the tech guy at Westach wrote to me:

"Hi Gary
We use standard copper wire to extend the leads up to 20 feet.

The cold junction happens as soon as you terminate the thermocouple leads with anything other then more thermocouple wire of the same type. So the cold junction "error" is still at the end of the thermocouple leads where they meet the copper wire. Be this at the back of the gauge or 20 feet away.

Thermocouple wire has a higher resistance value then standard copper so using it as an extension in a passive thermocouple system just doesn't work well.

Now if you were to have the cold junction exactly at 75 deg f and the hot end was at a known temp, say 400 deg f. the gauge will read 400 deg. Now throw in 20 feet of copper and yes the gauge might read 395. But due to the fact that we don't always know exactly what that cold junction temp is on an automotive application with changing temps and driving conditions etc. that has more of an effect on the readout then anything else.

Remember that the thermocouple wire cannot run all the way through the whole system, it has to change to copper somewhere. The connections on the back of the gauge, the wire from the back of the gauge to the circuit board, the wires from the circuit board to the meter movement, the meter movement itself is full of copper wire.

Yes it is true at an engineering standpoint to use thermocouple wire for the whole length but in real world applications it is the point of just where that cold junction is and what its temperature is."

So anyway, there is some food for thought.

I have been happy with Westach products for a long time. Their combination gauges save lots of dashboard real estate, and they are accurate and well made (in the US).

That's my 2¢ ... Good luck, Mondshine

Yes....they are compensated. Westach states both in their specs...and I have spoken to them directly....and I know two people who have the gauge......that their CHT 2DC8 and 2DC8-35 are compensated. At least the two I mentioned....and specific gauges in their lone. Certainly not all of them.

And.....you cannot extend TC wires with copper. Because.....that MOVES the cold joint TO THAT SPLICE location. ....as the Westach guy mentioned.

This is why you either need to use specific splice wires of the same TC material.....AND..... the gauge has to be calibrated in its millivolt response.....to allow the use of extended TC wire length....and not set up just for a specific length and millivolt response.

You state that the TC wires must connect to copper at some point anyway.
...so extension wires can be copper.....which is both true and not true.

True....it needs to connect to copper at some point. False.....it can do so on the extender wires. No.
The gauge is typically set up so that the TC wires connect to copper AT THE connection posts mounted to the circuit board. A very short and calibrated length of copper.....and the gauge is balanced for what little resistance that brings into the sysytem. Thats resistance TO the small millivolt level current generated by the TC wire.

Thats the problem many people run into when hooking up TC's to gauges.....eapecially ones that ARE compensated. If its not hooked up correctly.....its instantly "de-compensated".

And.....when you select TC wire for extension....ideally....it should be OF THE SAME BRAND.

While TC's and TC wire are "advertized" to meet a standard engineering spec...they rarely are exact in the actual current they generate. They may still all be WITHIN that spec RANGE.....but the width if that tolerance range....is frequently enough to "de-compensate" the gauge.

Also......how the TC extender wires are connected.....its critical. Any added resistance....de-compensates the gauge.

The compensator circuit...MUST be set up AT THE COLD JUNCTION. The copper wire hook up....is AT THE COLD JUNCTION. The cold junction in these gauges....is designed into the gauge.
If you add copper wire between the TC and the gauge/cold junction......you just de-compensated the gauge.

Here is a basic compensation circuit.

https://www.analog.com/en/products/lt1025.html#product-overview

The only reason I can think of that Westach gave you the answer they did.....and it is telling.....is that ...yes.....their gauges are as advertized....compensated. However.....if you extend the wires.....it is instantly de-compensated....as your Westach guy stated....and as I stated above. You cannot extend with copper and keep a gauge compensated.

Since Westach states that THEY extend with copper.....hence in their mind the gauge is not compensated.

However......one has to ask.....if THEY extended their TC with PROPER TC wire.....would it maintain compensation....or is the gauge only compensation calibrated for a 48" lead?

Ray

Wed Oct 28, 2020 9:24 am

petrol punk wrote: ... the gauge will read 150-200*F ... Maybe someone has an idea why it seems to read so low.

Maybe it's calibrated in Centigrade? (150-200°C is approx 270-325°F, which is typical for the VDO gauge in my buggy.)

Wed Oct 28, 2020 9:31 am

Lingwendil wrote: Wait, so If I use a westach gauge, I can switch to copper wire under the back seat, or in the engine bay, and run that up to the gauge in the dash? I already have a bunch of extra wiring run that way as it is and that would make things much easier to install a dual gauge versus buying two extended thermocouple leads and routing them up there.

Adding 25 dgrees to the gauge on a 100 degree day is no big deal, honestly. Half of my driving has historically been on hot days.

Not in the engine bay!
The cold junction must be in a place where the ambient temperature is relatively stable.
All of the VW's I have driven with Westach gauges have had the cold junction under the rear seat bench, with 20 AWG wires to the dash. The 48" thermocouple leads will reach just fine.

I really liked that quad in my '71 Super; wish I still had it!

Another possibly useful item about Westach combination gauges is that you can order "off-the -menu". For example, a quad combination can have almost any four gauges you want; OP, OT, CHT, Volts, Amps, Tach, etc.
All it takes is time and money.

Someplace around here I have a dual OT/CHT gauge from a Type 3 that I sold 20 years ago. :wink:

Wed Oct 28, 2020 10:09 am

Ray-
Now you know 3 people that have them.

https://www.aircraftspruce.com/catalog/inpages/westach_2dc8.php

When I look at the 2DC8 (and the 2DC8-35) instructions, right under the word "! IMPORTANT!" it clearly states that the cold junction is calibrated for 75º, and the gauge will read high (or low) based on the ambient temperature at the cold junction.

This means that the gauge is not cold junction compensated.

Makes no difference to me, I like my Westach gauges.

Wed Oct 28, 2020 11:39 am

mondshine wrote: Ray-
Now you know 3 people that have them.

https://www.aircraftspruce.com/catalog/inpages/westach_2dc8.php

When I look at the 2DC8 (and the 2DC8-35) instructions, right under the word "! IMPORTANT!" it clearly states that the cold junction is calibrated for 75º, and the gauge will read high (or low) based on the ambient temperature at the cold junction.

This means that the gauge is not cold junction compensated.

Makes no difference to me, I like my Westach gauges.

Yes!...thank you!....and appaerently the 2DC8's...as you note ...are no longer compensated :cry:

I just got through speaking with one of my two buds that have the2DC8 in their Cessna's (one is a 172 and the other a 170).

Both have had their 2DC8 gauges for a long time. Both in the past have tested and KNOW that their gauges originally came compensated. Both are using the original 48" TC linkage.

Somewhere I have an old catalog page from Westach that directly stated in the questions below the 2DC8....that it was compensated.

And further oddities......in the original catalog page links from Aircraft spruce....you can see in their TC extension wire link....that TC extensions do not change gauge accuracy unless they go over 10'.....which is indicative that ACS is selling TC wire for extensions and not copper....which is good.

Although that has nothing to do with compensation.....its just odd to see Westach suggesting straight copper. But then again...if the 2DC8's and other have not been compensated for some time....well...there you go. No need for TC wire to extend.

Anyway...thanks for informing me....and making me dig into it. Yes...nowhere on Westach's site in Dual CHT's that have not been TSO'd....can I find compensated CHT gauges listed.

I guess I might try my hand at building a compensation circuit just for giggles....and I could probably just do what you did....and change gauge position relative to the face (which is what I assume you did).....after all...who cares what the CHT is until its warmed up.

Ray

Wed Oct 28, 2020 2:20 pm

Ray-
I never felt the need for TSO'd gauges in a car (or maybe I was just too cheap) but it seems, from the Westach website, that they no longer manufacture or support TSO'd gauges.
Sign of the times, I guess.

Wed Oct 28, 2020 3:14 pm

mondshine wrote: Ray-
I never felt the need for TSO'd gauges in a car (or maybe I was just too cheap) but it seems, from the Westach website, that they no longer manufacture or support TSO'd gauges.
Sign of the times, I guess.

Actually...that right there...says it all. While the TSO spec/process mostly concerns installation and interference with other gauge systems...in some aircraft specs its also written in gauge accuracy and spec.

If Westach is no longer supporting any TSO gauges.....it goes right along with not having any compensated gauges.

The only reason I would buy a TSO gauge...is if it was the only way to get a compensated gauge that I absolutely had to have.

I am going to explore the circuit patterns I have for compensation circuits.

I have had my eye on that quad gauge for a long time. It would be really useful. But oil temp will also use a TC and have the same issue. Ray

Wed Oct 28, 2020 4:07 pm

My Westach quad, as shown earlier in this post used a thermistor for OT, a transducer for OP, and a thermocouple for CHT.

Some of the very old Westach quads, seen on eBay from time to time, have two "Amphenol" style connectors on the back; rather than the Molex style pins. I believe these are TSO, but the availability of senders could be a problem, especially considering that Westach no longer supports that stuff.
I wonder if Westach is "on the way out".

Wed Oct 28, 2020 5:58 pm

[email protected] wrote: Hmmm...., never thought about a different level of illumination.

How did you go about painting the face? Is it an open gauge, or did you disassemble it?
A very sharp permanent marker and a steady hand. The gauge is fully closed, but it's very easy to disassemble.

Here you can see the difference in brightness between the CHT gauge (on the far left) and the rest of them. It's not terrible, but it is definitely noticeable:

When I switched all my dash lights to red LED, I had the same problem with the speedometer- it didn't have the same level of brightness as the rest of the gauges. The solution is simple: just paint the case a reflective silver and stuff more lights inside it, so I'll probably do the same to the CHT gauge as soon as I get around to it.

Wed Oct 28, 2020 5:59 pm

raygreenwood wrote: And...the square pattern mounting was difficult for me to get my head wrapped around. I figured if I bought one ...I would trim off the ears and find or make a round bezel.
Yep, that's what I did- trim the ears off the square bezel and fit a round one to it. It was a lot easier to do than I thought it would be.

raygreenwood wrote: I liked the Westach 2DC8 a little better. Its round....and I am sure the lighting is probably not much better....but the increments are 25*F between 100* marks. It goes to 700*F
I looked at that Westach gauge, but I also didn't see anything about it being temperature compensated, which was a deal-breaker for me. The smaller increments in that Westach are nice, but I think the aesthetic of the Micro 1000 is a little cleaner.

Wed Oct 28, 2020 7:56 pm

mondshine wrote: My Westach quad, as shown earlier in this post used a thermistor for OT, a transducer for OP, and a thermocouple for CHT.

Some of the very old Westach quads, seen on eBay from time to time, have two "Amphenol" style connectors on the back; rather than the Molex style pins. I believe these are TSO, but the availability of senders could be a problem, especially considering that Westach no longer supports that stuff.
I wonder if Westach is "on the way out".

May be.

Sometimes I see this in a whole range of related industries that first...they lose manufacturing market share here in the US due to competition...and/or they themselves not keeping up with the jones's....no new designs in decades etc. Then to keep up...they shift a portion of tbhe production off continent. Either just components or components and assembly.

Then...through personnel losses or quality issues.... they lose the ability to produce a product that can be calibrated to an industry standard. I just dont know.

The main company is Westberg mfg. Hard to find much info.

They still make really nice gauges though for the money. Ray

Wed Oct 28, 2020 8:02 pm

Floating VW wrote: [email protected] wrote: Hmmm...., never thought about a different level of illumination.

How did you go about painting the face? Is it an open gauge, or did you disassemble it?
A very sharp permanent marker and a steady hand. The gauge is fully closed, but it's very easy to disassemble.

Here you can see the difference in brightness between the CHT gauge (on the far left) and the rest of them. It's not terrible, but it is definitely noticeable:

When I switched all my dash lights to red LED, I had the same problem with the speedometer- it didn't have the same level of brightness as the rest of the gauges. The solution is simple: just paint the case a reflective silver and stuff more lights inside it, so I'll probably do the same to the CHT gauge as soon as I get around to it.

Hey...just thinking here....but the REALLY nice bezel lights that UMA uses.....are actually....simple PMMA "side-glow"....fiber optic strands. These come in diameters from about .060" to like 0.55"....and its dirt freaking cheap. You could put a ring around the inside of the bezel and light this with a high intensity LED with whatever color you want as a filter.

Like 3.25 feet for $5.99

https://www.amazon.com/3-28ft-Plastic-Optic-Source...8MSK6139BE

Ray

Wed Oct 28, 2020 8:28 pm

So....since we are on the subject of TC compensation....check this out:

https://www.youtube.com/watch?v=LKEZjhCWGyw

Here is the product data page with schematics, theory, operation and diagrams....and down on page 16 of 16.....the form factor. These compensation circuits are 3.20mm x 3.2mm max (some are as small as 2.80mm x 2.80mm) and as thin as 0.75mm and max of 1.10mm.

So in other words....we could fit these into a lot of different TC gauge enclosures.

https://www.analog.com/media/en/technical-documentation/data-sheets/ad8494_8495_8496_8497.pdf

Mouser electronics info'
https://www.mouser.com/new/analog-devices/adi-ad8494-ad8495-ad8496-ad8497-amplifiers/

Digikey has them....for $59 each.

https://www.digikey.com/en/products/detail/analog-devices-inc/AD8495-EVALZ/11483518

So...there are 4 models for different TC types. If they can work for what you need....$59 may be worth it. Ray

Thu Oct 29, 2020 10:11 am

raygreenwood wrote: So....since we are on the subject of TC compensation...
https://www.digikey.com/en/products/detail/analog-devices-inc/AD8495-EVALZ/11483518
So...there are 4 models for different TC types. If they can work for what you need....$59 may be worth it. Ray Just wondering if it would be feasible to use something like this CAN-EGT module https://www.diyautotune.com/product/can-egt-8-channel-thermocouple-interface/ to get the desired thermocouple temperature compensation and drive the gauges of choice? Apparently it's designed for MegaSquirt applications, but the description says " ...send a 0-5 volt signal based on the thermocouple inputs to work with external gauges." Its has eight inputs for K-type thermocouples, but if that's not an issue then it might provide more bang for the buck (350 vs 8x59=472). Of course it's more satisfying to personally fabricate something useful 8)

I'm with you on the scale graduations, and for me the lighting kits work fine in the custom combinations that Pete at Westach can set up.

Thu Oct 29, 2020 2:05 pm

crocteau wrote: raygreenwood wrote: So....since we are on the subject of TC compensation...
https://www.digikey.com/en/products/detail/analog-devices-inc/AD8495-EVALZ/11483518
So...there are 4 models for different TC types. If they can work for what you need....$59 may be worth it. Ray Just wondering if it would be feasible to use something like this CAN-EGT module https://www.diyautotune.com/product/can-egt-8-channel-thermocouple-interface/ to get the desired thermocouple temperature compensation and drive the gauges of choice? Apparently it's designed for MegaSquirt applications, but the description says " ...send a 0-5 volt signal based on the thermocouple inputs to work with external gauges." Its has eight inputs for K-type thermocouples, but if that's not an issue then it might provide more bang for the buck (350 vs 8x59=472). Of course it's more satisfying to personally fabricate something useful 8)

I'm with you on the scale graduations, and for me the lighting kits work fine in the custom combinations that Pete at Westach can set up.

Very nice!

So what gauges are we looking at in your pictures....from left to right?

Ray

Thu Oct 29, 2020 4:24 pm

raygreenwood wrote: Hey...just thinking here....but the REALLY nice bezel lights that UMA uses.....are actually....simple PMMA "side-glow"....fiber optic strands. These come in diameters from about .060" to like 0.55"....and its dirt freaking cheap. You could put a ring around the inside of the bezel and light this with a high intensity LED with whatever color you want as a filter.

Like 3.25 feet for $5.99

https://www.amazon.com/3-28ft-Plastic-Optic-Source...8MSK6139BE

Ray
Not a bad idea- thanks for the heads up, Ray.

Thu Oct 29, 2020 5:26 pm

raygreenwood wrote:
Very nice!
So what gauges are we looking at in your pictures....from left to right?
Ray Thanks, Ray! With apologies to the OP for stretching the topic, if you think it may be applicable to the accuracy question, and if you have time to consider it, I'd appreciate your thoughts on use of the diyautotune CAN-EGT to drive non-temperature compensated gauges, maybe with a trimpot to set the signal level. I can do the simple arithmetic for ambient cold junction correction in my head, but it's taking longer as time passes :wink:

Westach: CHT/EGT, Oil Press/Temp, Fuel level/AFR, Amps/Volts, Tach.

Details are clearer if you zoom in on the daylight photo below.

Charley