Comark 3500 Digital Thermometer - UK Vintage Radio Repair and Restoration Discussion Forum

Julesomega · 1st Dec 2013, 3:02 am

I have made an attempt at calibrating my 3501 (Centigrade version of the series) but unfortunately my copy of extracts from the manual does not have Section 6 (Calibration) and other niceties such as the spec's. Taking a guess from the schematic I set iteratively RV1 (TC comp. bridge) for room temp, and RV3 for 100°C which seems ok over this limited range, but if anyone has the complete cal procedure I'd be most grateful.
- Julian

majoconz · 5th Dec 2013, 12:29 am

To obtain 100°C is not as easy as it sounds - you need a true barometric pressure and the water should be distilled - even then it's a bit of a guess unless you already have access to a lab standard thermometer.
0° is easy - crush up some ice - half fill a thermos flask with it - add cold water and put it in the fridge with no top on the flask for half an hour or so. Have a look at it to see if you have a slush of ice and water - add more ice or water and repeat if necessary. This relies on the latent heat of ice and water and if there is no or little heat going in, then you have a stable equilibrium at 0°C. I doubt if you need to go as far as a triple point Dewar flask!

MotorBikeLes · 5th Dec 2013, 11:42 pm

Quote:-- I doubt if you need to go as far as a triple point Dewar flask!
Which of course is NOT 0 degrees C. 0.15 degrees difference if my memory serves.
Pedantic Les.

majoconz · 6th Dec 2013, 12:58 am

http://www.bipm.org/utils/common/pdf...n_2_2_2013.pdf

First paragraph.

1st Dec 2013, 3:02 am	#1
Julesomega Nonode Join Date: Dec 2012 Location: Stockport, Greater Manchester, UK. Posts: 2,106	Comark 3500 Digital Thermometer I have made an attempt at calibrating my 3501 (Centigrade version of the series) but unfortunately my copy of extracts from the manual does not have Section 6 (Calibration) and other niceties such as the spec's. Taking a guess from the schematic I set iteratively RV1 (TC comp. bridge) for room temp, and RV3 for 100°C which seems ok over this limited range, but if anyone has the complete cal procedure I'd be most grateful. - Julian

5th Dec 2013, 12:29 am	#2
majoconz Heptode Join Date: Jan 2008 Location: Ashhurst, Manawatu, New Zealand Posts: 570	Re: Comark 3500 Digital Thermometer To obtain 100°C is not as easy as it sounds - you need a true barometric pressure and the water should be distilled - even then it's a bit of a guess unless you already have access to a lab standard thermometer. 0° is easy - crush up some ice - half fill a thermos flask with it - add cold water and put it in the fridge with no top on the flask for half an hour or so. Have a look at it to see if you have a slush of ice and water - add more ice or water and repeat if necessary. This relies on the latent heat of ice and water and if there is no or little heat going in, then you have a stable equilibrium at 0°C. I doubt if you need to go as far as a triple point Dewar flask! __________________ Cheers - Martin ZL2MC

5th Dec 2013, 11:42 pm	#3
MotorBikeLes Nonode Join Date: Dec 2012 Location: Kirk Michael, Isle of Man Posts: 2,350	Re: Comark 3500 Digital Thermometer Quote:-- I doubt if you need to go as far as a triple point Dewar flask! Which of course is NOT 0 degrees C. 0.15 degrees difference if my memory serves. Pedantic Les.

6th Dec 2013, 12:58 am	#4
majoconz Heptode Join Date: Jan 2008 Location: Ashhurst, Manawatu, New Zealand Posts: 570	Re: Comark 3500 Digital Thermometer http://www.bipm.org/utils/common/pdf...n_2_2_2013.pdf First paragraph. __________________ Cheers - Martin ZL2MC Last edited by majoconz; 6th Dec 2013 at 1:05 am.