Thermocouple Wire Length

[Cody]

Bought the Autometer Pyrometer for my Transporter only to discover that the cable only reaches to  about the stick shift not teh dash.  Anybody know how much error to expect by adding on some extra cable to  get it to the dash?  Or is there a better answer?

[arb]

You should use the correct type of cable for your type of thermocouple.  You should maintain the proper polarity connections of the wire.  You should also make sure the connections are solid mechanical connections that allow the metal from the leads to make good contact.  Do not solder them.  If you use metals that are dissimilar from your thermocouple metals, you will be creating additional thermocouple junctions at each connection that will be adding their developed current to that of the probe, not good.

If anyone needs extension leads for k-type, I will sell by the foot.  PM for details.

Andrew

Andrew is right on the money.  When I melted super alloys in a lab, I had to make my own thermo couples. Splicing the leads always took special attention to wire, gauge, crimp coupling, etc. I would not spice it,  but return it to the vendor for the proper length you need.

[Cody]

Thanks for the offer to sell me some Andrew but probably the shipping would cost a fair bit to  Calgary and I wouldn't be able to show you  the leads/connectors in person either.  I appreciate the offer.

The dealer says they know nothing - don't want anything more to  do  with it.

There is a general supplier of thermocouples here in Calgary  that said they could work something out for me.  Just going to be difficult to get there during work hours.

The other thought is to  connect it as it is and drive a bunch checking out the temps on known sections of road/load and then do the cheap and simple copper wire extension and drive the same road/load and see how much of an offset there is.

Somebody on another BB did the thermoelectric calcs and suggested it'd be only ~1%

Cheers,

Cody

[Rabbit TD]

You should use the correct type of cable for your type of thermocouple.  You should maintain the proper polarity connections of the wire.  You should also make sure the connections are solid mechanical connections that allow the metal from the leads to make good contact.  Do not solder them.  If you use metals that are dissimilar from your thermocouple metals, you will be creating additional thermocouple junctions at each connection that will be adding their developed current to that of the probe, not good.

If anyone needs extension leads for k-type, I will sell by the foot.  PM for details.

Andrew

I'm waiting for my autometer EGT gauge to get here from egauges and I recieved my Spruce thermocouple  and 7 foot lead wire and installed it 2 days ago.  I've been reading about the thermocouple wire problems with the disimilar metals and such and it seems like it could get pretty messy if somewhere the wrong materials were used in the wrong place.  I know I shouldn't have that problem since I got their 7 foot wire for my Rabbit {I hope}.  I am wondering though if a person did add 2 equal lengths of wire connected by the twisting and bolting method you described would you get an accurate reading or not.  The part that I don't fully understand is that since these connections aren't subjected to heat [which is supposed to be where the small voltage is created if I understand right] would it affect the reading or not.  I've never had any experience with thermoocouples till now and it just fascinates me how these things work and that they could even create enough of a voltage at all to operate a gauge especially the further away from the tip it is but I can see if something wasn't done right it wouldn't take much of a resistance change or whatever to make a false reading.  I do know that some years back when I was studying for an ASE test that I read that a voltage can also be created in a cars radiator from the different properties in the cooling system such as steel, copper, aluminum, iron and God know what, reacting with the coolant and in some rare cases the small voltage finds it's way inside a coolant sensor and made them give a false reading. I know you seem to have a good bit of experience with these things so I thought I would ask, Again Thank's

[Rabbit TD]

Ambient temperature is still a considerable amount of heat.  Certainly much less than the inside of an exhaust manifold, but can still skew the reading.  Most EGT gauges will even tell you the cold side calibration and it's usually somewhere around 70°F.  What that means is that the gauge is calibrated to read accurately when the junction of lead to gauge connections is 70°.  If the temp at the gauge is higher or lower it will skew the reading accordingly.  In other words if the inside of your gauge cluster is 20°, your EGT reading will be 50° lower than the actual temperature at the thermocouple.  When additional junctions are added, the errors can compound.  From gauge to thermocouple should be one type of metal, from thermocouple back to gauge should be the other.  Considering the relative low cost and availability of proper wire, I can't see any reason to sacrifice the accuracy of what I consider to be THE most important gauge on a TD, especially considering that a false reading could mean melted pistons.

Andrew

Oh I agree 100% that the EGT is the most important gauge with a turbo, expecially if you are going to experiment and I know I will.  That's why I got the Autometer Sport Comp gauge [when it gets here that is]  I did notice though on my Spruce lead that it has male spade ends on the gauge side of the lead.  I don't know what kind of connector is on the autometer gauge because I don't have it yet.  They look to me like just generic steel crimp style to me but if the gauge has a posts on it can I just cut the wire and crimp on a hole type terminal or should I just wrap the wire and use the nut& washer if that's what it's got, I don't know if they are steel or what though to be sure and I don't want to takea chance on not making it as accurate as possible, this gauge, thermocouple, lead was close to $150 but not bad from some others I've seen.  I hope the Autometer works OK because I already had their boost gauge and I'm getting their water temp gauge for a 3 in a dash pod setup for the Rabbit.  The Pillar mounts seem nice but the posts on the Rabbit look too small to work.  I'm curious to see how fast this thing works with a propane torch.  For what these probes cost it's a wonder everyone isn't using them in everything.  One more plus, the pod is 10 1/8, 7 1/2, 3 1/2 and it completely covers the cracks in the dash cover, and also the center radio speaker  :lol:

[DYNOMAX]

www.auberins.com

He got all sorts of EGT´s etc.
I think i´m going to use the products from him.
I like the options that the equipment got.

[Cody]

included is the URL  for the posting where a fine fellow named Ryan did the calculations:
http://autos.groups.yahoo.com/group/vanagon/message/10029

The numbers he is using match up  with what I'd seen on some suppliers websites.

Autometer did not  include any reference to how it dealt with the cold junction.

My plan is to hook up the pyrometer as it sits (as per instructions) by  running the lead up  through the floor at the end of the supplied cable and run teh van through some standard road/load scenarios and get 'accurate' readings.  Then extend them with some spare 16g wire up  to  the dash to go with the oil pressure and turbo boost gauges and run the same road/load scenario and determine an offset.  David Marshall  (Hausenwork) mentioned on another board that he had done that and the error was insignificant.

I'll report back

Cheers,

Cody

[Rabbit TD]

included is the URL  for the posting where a fine fellow named Ryan did the calculations:
http://autos.groups.yahoo.com/group/vanagon/message/10029

The numbers he is using match up  with what I'd seen on some suppliers websites.

Autometer did not  include any reference to how it dealt with the cold junction.

My plan is to hook up the pyrometer as it sits (as per instructions) by  running the lead up  through the floor at the end of the supplied cable and run teh van through some standard road/load scenarios and get 'accurate' readings.  Then extend them with some spare 16g wire up  to  the dash to go with the oil pressure and turbo boost gauges and run the same road/load scenario and determine an offset.  David Marshall  (Hausenwork) mentioned on another board that he had done that and the error was insignificant.

I'll report back

Cheers,

Cody

You don't have anything to loose by doing a little experimenting and like you said before you will already have a baseline to go from, I'll be anxious myself to see if it made much of a difference, theoreticly it should but let's see how much if any, keep us posted.   :wink:

[fatmobile]

What wire lengths are people running for the A1s and A2s?
I can't remember what length I used for the Golf and would like to get some wires from Andrew.

[VWSmokr]

This discussion brings  a bunch of questions to my mind:
   
   Any feedback on the VDO pyrometers?  
   Are they the "K" style also?
   Andrew, what kind of terminals do the wires need to use?
   How long can the wires be, and can I 'coil' them a bit for flexibility to use in my tilt cab truck?

Probably sounds dumb to ask these questions after using the VDO for several years, but I just want to make sure my gauge is a reasonably accurate one ... before the new engine goes in.

Comments?

TIA

J.R.
SoCal

[Cody]

Thermocouple was installed in the Exhaust pipe abput 1.5" from the Turbo:



Installed the EGT gauge to Spec with the darn Gauge sitting on the floor of the Van beside the Passenger seat because that was how far the thermocouple wire would reach. Drove a standardised section of road and load and it seemed that we would top out at :



Then we added about 4' of wire to both sides of the circuit to extend it far enough to get to the Dash and ran the same section/load etc. and topped out at:



So the net effect of adding that length of standard 14g wire was not much considering the overall precision of the reading and the usage.

Then we enriched the LDA and the EGT's maxed out at 1150F (although now managing a higher Top Speed or the same Top Speed but with more gradient or wind).  Then we installed the I.C. and they dropped to about 1100F. Then I drilled the Exhaust manifold about 1.5" ahead of the Turbo and the same load road top out conditions It seems to top out at 1300F - 1350F.

So the effect of moving the Thermocouple from below to above the Turbo was about 200 - 250F.

This was at top end of loading the van (120km/h with WOT)

At this time the Turbo was putting out about 7.5 -8 psi max.

Cheers,

Cody

[saurkraut]

This discussion brings  a bunch of questions to my mind:
   
   Any feedback on the VDO pyrometers?  
   Are they the "K" style also?

I've run both the VDO and Spruce thermocouples with the VDO gauge.  The probes are both type K thermocouples.  I'm now runing VDO gauges with Spruce thermocouples in both of my TDs.

The VDO probe is slow, it will not show your max EGT as it seams to get slower the hotter it gets.

The Spruce thermocouple is very fast.  Its is almost as fast as the boost gauge.  Its avaiable with either 1/8" or 1/4" NPT adaptors.   You can install them in the same tapped hole as the VDO probe.  I think the VDO probe has a 1/4" NPT adaptor.

[BlueMule]

Andrew, much repect. This is the type of info I have been looking for. Can you provide the whole setup. In other words, gauge, wire, etc. I totally agree with you, it is better to get off the wallet and get something you know will be accurate than for me to mess around with something hit or miss.  

[Cody]

Andrew:

Thanks for the reply.  I'd like to note that when taking the settings/photos the conditions as stated were 4000rpm and WOT. Therefore the load is the same for each point those conditions are reached. Whatever the wind or gradient loads are. The combinations of factors are such that the van is using full throttle at 4000rpm. If the gradient/wind were not big enough the rpm would rise or I'd have left off some throttle. If the winds or gradients were higher then the rpm would have dropped. In either case the conditions of WOT and 4000rpm are not met and it is not a comparison point.

So they are scientifically valid comparisons, not that it is a science project.  It is just an attempt to find a convenient method of determining a reasonable offset due to conditions of installation.  While it is possible to acquire thermocouple wire extrensions (Actually free for  small lengths her in calgary), it is not always convenient to do so like when I was trying to get he Van ready for the X-mas ski trip  and places weren't open.

It is just that there are always errors in the system and its good to  determine the amount of error you've got.  The induced electrical potential of a bi-metal junction does not follow a polynomial.  Polynomials are used to approximate it. For a larger temperature range Polynomials approximate it more precisely than linear function but it still has errors.  Not to mention that the connections at the gauge are also inherently introducing error because they also are different metals than the hot junction and the gauge doesn't likely even contain a cold junction but instead approximates it (this is a fairly inexpensive gauge).

So there is always error in the system and it's not bad to figure it out. Certainly better than not having gauges at all and flying completely blind.

Cheers,

Cody

[VWSmokr]

This discussion brings  a bunch of questions to my mind:
   
   Any feedback on the VDO pyrometers?  
   Are they the "K" style also?

I've run both the VDO and Spruce thermocouples with the VDO gauge.  The probes are both type K thermocouples.  I'm now runing VDO gauges with Spruce thermocouples in both of my TDs.

The VDO probe is slow, it will not show your max EGT as it seams to get slower the hotter it gets.

The Spruce thermocouple is very fast.  Its is almost as fast as the boost gauge.  Its avaiable with either 1/8" or 1/4" NPT adaptors.   You can install them in the same tapped hole as the VDO probe.  I think the VDO probe has a 1/4" NPT adaptor.

saurkraut... thanks for the heads-up re. the slooow-reacting VDO thermocouple. It actually seems to be getting slower as time goes on; is that normal? I'll get a Spruce thermocouple in the VW diesel before its new TD engine goes in.

Decided to use a 3.25" diameter ISSPRO in the truck, and probably the Spruce t-couple. Will have to do some careful measuring of the lead lengths needed, to allow for the tilt cab feature. [But that's OT for here, 'cause it's a turboed gasser, and not even German-powered!]

Andrew, how much are the readings thrown off by the (I'm assuming) dissimilar metals of crimp-on connectors that are used to terminate the leads? Or, are there special connectors to be sourced & used at those points also?

Thanks, all.

J.R.
SoCal