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Temperature sensor

KTW

Feb 22, 2015
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I've made an emissions system smoker and the temperature control didn't come with a heat resistant probe so I purchased one but it didn't match the original probe.
I added 10.5k resistors to match the ambient temperature of the original but it is stuck on 23.5oC.
Does anyone know if I can get this heat resistant probe to work?
I think they just work on resistance.
Thanks.
temp. sensor.JPG
 
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TCSC47

Mar 7, 2016
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Could you give component numbers for the temperature sensors and the cct diag of the temperature control circuit?
 

KTW

Feb 22, 2015
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I was just checking the resistance and comparing the two and I find that the original is 12.5k at ambient and when heat is applied it changes to 8.0k and the numbers continue to drop.
The new probe is at .10k and the numbers change to .20k and continue to rise.
The original can change with body temperature and the new probe requires excessive heat to change the resistance and the two appear to work in opposite directions so I can't see this new probe will work with my control.
I can hunt for the specs.
I'll likely have to use a shielding braid over the original.

I think this new PT100 platinum sensor is for data.
http://www.ebay.com/itm/141937267189?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

Control
http://www.ebay.com/itm/Digital-LCD...stat-Sensor-/262563603517?hash=item3d2202a43d
 
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KTW

Feb 22, 2015
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I discovered the problem, two different sensors.

NTC thermistors decrease in resistance as the temperature increases. PTC thermistors are Positive Temperature Coefficient resistors generally made of polycrystalline ceramic materials that have a high positive temperature coefficient, which increases in resistance as the temperature increases
 

CDRIVE

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[QUOTE="KTW, post: 1722326, member: 39006"
The new probe is at .10k and the numbers change to .20k and continue to rise.
That's equivalent to 100Ω to 200Ω. Is that a typo?

Chris
 

KTW

Feb 22, 2015
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No typo, 105 ohms ambient temperature.
 

KTW

Feb 22, 2015
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Hi Chris, thanks for your input.
The probe that comes with the unit can sense temperature up to 110o C.
The element I'm using gets to 85oC so I'm ok temperature wise but the conductors are plastic insulated and that's why I was looking for a probe with higher temperature insulation.
What do you think about using fiberglass sleeving over the existing ntc probe?
 
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CDRIVE

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Unfortunately I don't think that will help. It won't prevent the existing low temp insulation from melting. Are you sure the insulation isn't Teflon?

Chris
 

KTW

Feb 22, 2015
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Not sure Chris, I contacted the seller but I'm doubtful if they would know.
We'll see.
 

CDRIVE

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Test the insulation at the end of the two conductors with heat from your iron but not the tinned tip. You don't want to yuck it up if it melts.

Chris
 

CDRIVE

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Hi KTW, that's not good news. It befuddles me why a manufacturer would make an extreme temperature Thermistor that doesn't provide wire lead insulation (Temp: min - Max) comparable to the range of the Thermistor and Probe? Perhaps they intended the Probe head alone to be subjected to those temps?

There was a recent topic along the same lines as yours. Let me see if I can find it.

Personally, I'd like to see these things manufactured with Teflon insulation for each lead and jacketed with the high temp, I think it's (Fiberglass?) flexible weave.

Chris
 

CDRIVE

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Found it!
https://www.electronicspoint.com/threads/thermal-fuse-ghd-please-help.282559/
Not a Thermistor but reading the last post pretty much sums it up. As I see it it's pretty much what I said in my last post. IE the entire assembly should be capable of withstanding (at least) the temp range of the probe.. and then some.

Could you please post a sharp photo of the probe? Especially the rear end.

Chris
 

KTW

Feb 22, 2015
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I just wrote to ask if it was ntc or ptc.
Thanks for taking the time to find that, I did search earlier and couldn't locate one similar.
 

CDRIVE

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Yes, it's absolutely frustrating. I clicked on every damn link the seller provided regarding the specs. I thought for certain that the Newark link would certainly provide specs but it was a dry well. Even the pdf datasheet provided nada.
http://www.farnell.com/datasheets/2015876.pdf?_ga=1.162269948.1387451233.1478563265

This is one of those times that you might be well advised to deal with Digikey. They will match your needs via on line or phone call help.

Chris
 

CDRIVE

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BTW, what is an emissions system smoker? Photos?

Chris
 

KTW

Feb 22, 2015
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Hi Chris;
Let me say thanks for the effort you put into this.

This is for a vehicle emissions leak test when the engine light comes on and tells you there is a small or large leak in the system.
I'm chasing down a small leak in my wife's jeep.
I plan on using the original nt probe for my initial test, it should work for locating the leak I'm chasing and I'll keep looking for something better suited to the heat.
For a quick description, place an element in baby oil and let it reach a temperature where it will smoke.
Apply very light air pressure and insert a plastic tube from the top of the can into the emission lines and watch for the smoke to appear to locate the leak.

emissions tester.JPG

emissions tester2.JPG
 
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