Temperature to voltage converter. - UK Vintage Radio Repair and Restoration Discussion Forum

Tractorfan · 20th Feb 2019, 9:24 pm

Hi,
I've had this lying around for years and I'm curious about how to get it to work with my digital multimeter.
It has a 'test' position on the C/F selector switch which displays about 5.30 volts. With a thermocouple connected, the readings don't make much sense when exposed to heat and wander hither and thither.
I admit I haven't tried it with a fresh battery, That is on my shopping list.
Has anyone else had experience with this type of converter?
I have a length of blue & brown thermocouple wire with a yellow plug marked 'Chromel/Alumel'. with the two cores joined together the reading increases with temperature, but not accurately as far as I can tell.
Any advice would be appreciated.
Thanks in advance.
Cheers, Pete.

MotorBikeLes · 20th Feb 2019, 9:52 pm

I don't have any tables in front of me, but I would guess if you put a cigarette lighter flame under the tip of the thermocouple, you should get 30 to 50mV, a few hundred Celsius degrees. Check the thermocouple with a DVM to confirm it is not O/C.
Cr/Al 'couples are OK intermittently for about 1200 Celsius but around 1000 for long term use.
Les.

Electronpusher0 · 20th Feb 2019, 11:03 pm

I have a spare type K thermocouple with a matching yellow plug that would plug into your box if you want it. Postage cost only.

Peter

Boater Sam · 21st Feb 2019, 3:13 am

The 2 dissimilar metal wires should be welded together at the tip for it to work, not just touching.

Terry_VK5TM · 21st Feb 2019, 3:53 am

Yep, needs a K type thermocouple, I have the Fluke version.

Check the battery as well, should be a 9v one (it is in mine).

Not sure about the yours, but mine reads ambient temperature if the thermocouple is not plugged in.

Electronpusher0 · 21st Feb 2019, 9:22 am

Quote:

Originally Posted by Terry_VK5TM

Yep, needs a K type thermocouple, I have the Fluke version.

Check the battery as well, should be a 9v one (it is in mine).

Not sure about the yours, but mine reads ambient temperature if the thermocouple is not plugged in.

That would be the inbuilt cold junction compensation.

Peter

TrevorG3VLF · 21st Feb 2019, 11:33 am

Chromel/Alumel makes a K type thermocouple so you are good to go.
The output should be quite linear with temperature.
The wires will have an oxide surface and will often work properly even if they touch.
I made the junction with a gas flame to give a small bead.

It is a pig to solder and if we wanted to do this, we coated the wire with silver solder (Easyflow) first. Copper/Constantan can used as an extension, you can get it as twin flex.

Refugee · 21st Feb 2019, 12:56 pm

I have got at least one DMM with one of those probes that plugs into a matching yellow socket on the front. I am pretty sure that they were almost all type K.
I also have an unknown probe that has a lug that can be bolted onto a heat sink.
I must dig the unknown probe out and try it to see if it tracks a type K.

gezza123 · 21st Feb 2019, 5:33 pm

HI,Peter.
this may be helpful.

RS May still do these good luck
gezza123

gezza123 · 21st Feb 2019, 5:35 pm

two more these are T TYPE

GEZZA123

20th Feb 2019, 9:24 pm	#1
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,183	Temperature to voltage converter. Hi, I've had this lying around for years and I'm curious about how to get it to work with my digital multimeter. It has a 'test' position on the C/F selector switch which displays about 5.30 volts. With a thermocouple connected, the readings don't make much sense when exposed to heat and wander hither and thither. I admit I haven't tried it with a fresh battery, That is on my shopping list. Has anyone else had experience with this type of converter? I have a length of blue & brown thermocouple wire with a yellow plug marked 'Chromel/Alumel'. with the two cores joined together the reading increases with temperature, but not accurately as far as I can tell. Any advice would be appreciated. Thanks in advance. Cheers, Pete. Attached Thumbnails __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

20th Feb 2019, 9:52 pm	#2
MotorBikeLes Nonode Join Date: Dec 2012 Location: Kirk Michael, Isle of Man Posts: 2,350	Re: Temperature to voltage converter. I don't have any tables in front of me, but I would guess if you put a cigarette lighter flame under the tip of the thermocouple, you should get 30 to 50mV, a few hundred Celsius degrees. Check the thermocouple with a DVM to confirm it is not O/C. Cr/Al 'couples are OK intermittently for about 1200 Celsius but around 1000 for long term use. Les.

20th Feb 2019, 11:03 pm	#3
Electronpusher0 Nonode Join Date: Jun 2016 Location: Bognor Regis, West Sussex, UK. Posts: 2,296	Re: Temperature to voltage converter. I have a spare type K thermocouple with a matching yellow plug that would plug into your box if you want it. Postage cost only. Peter

21st Feb 2019, 3:13 am	#4
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Temperature to voltage converter. The 2 dissimilar metal wires should be welded together at the tip for it to work, not just touching.

21st Feb 2019, 3:53 am	#5
Terry_VK5TM Nonode Join Date: Oct 2010 Location: Tintinara, South Australia, Australia Posts: 2,339	Re: Temperature to voltage converter. Yep, needs a K type thermocouple, I have the Fluke version. Check the battery as well, should be a 9v one (it is in mine). Not sure about the yours, but mine reads ambient temperature if the thermocouple is not plugged in. __________________ Terry VK5TM https://www.vk5tm.com/

21st Feb 2019, 11:33 am	#7
TrevorG3VLF Rest in Peace Join Date: Apr 2011 Location: Matlock, Derbyshire, UK. Posts: 1,378	Re: Temperature to voltage converter. Chromel/Alumel makes a K type thermocouple so you are good to go. The output should be quite linear with temperature. The wires will have an oxide surface and will often work properly even if they touch. I made the junction with a gas flame to give a small bead. It is a pig to solder and if we wanted to do this, we coated the wire with silver solder (Easyflow) first. Copper/Constantan can used as an extension, you can get it as twin flex.

21st Feb 2019, 12:56 pm	#8
Refugee Dekatron Join Date: Apr 2012 Location: Worksop, Nottinghamshire, UK. Posts: 5,553	Re: Temperature to voltage converter. I have got at least one DMM with one of those probes that plugs into a matching yellow socket on the front. I am pretty sure that they were almost all type K. I also have an unknown probe that has a lug that can be bolted onto a heat sink. I must dig the unknown probe out and try it to see if it tracks a type K.

21st Feb 2019, 5:33 pm	#9
gezza123 Heptode Join Date: Mar 2010 Location: Eastham, Wirral, Merseyside, UK. Posts: 788	Re: Temperature to voltage converter. HI,Peter. this may be helpful. RS May still do these good luck gezza123 Attached Thumbnails

21st Feb 2019, 5:35 pm	#10
gezza123 Heptode Join Date: Mar 2010 Location: Eastham, Wirral, Merseyside, UK. Posts: 788	Re: Temperature to voltage converter. two more these are T TYPE GEZZA123 Attached Thumbnails