Author Topic: Thermometer Soar TX-570 shows 10 degrees too low temperature  (Read 849 times)

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Offline AndersJ

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Thermometer Soar TX-570 shows 10 degrees too low temperature
« on: March 25, 2017, 12:25:24 am »
Suddenly it started showing about 10 degrees lower than it should.
Drifts a bit upon startup then stabilizes.
Any ideas any one?

Sorry, I cannot figure out how to rotate the image.
« Last Edit: March 25, 2017, 12:27:39 am by AndersJ »
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Offline mimmus78

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Re: Thermometer Soar TX-570 shows 10 degrees too low temperature
« Reply #1 on: March 25, 2017, 12:30:22 am »
Check inside. There should be an ntc near the k-type connector. They need to know temperature at the k-type connector to guess the temperature on the other side of the junction.
« Last Edit: March 25, 2017, 12:32:22 am by mimmus78 »
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Offline AndersJ

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Re: Thermometer Soar TX-570 shows 10 degrees too low temperature
« Reply #2 on: March 25, 2017, 12:41:41 am »
The NTC is there, and reacts to heat, so it is alive.
Can't say if it has drifted or is otherwise malfunctioning.


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Offline mimmus78

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Re: Thermometer Soar TX-570 shows 10 degrees too low temperature
« Reply #3 on: March 29, 2017, 05:03:04 pm »
Well, if you have a static offset you should check this part of circuit. Basically temperature shown on display is the sum of the temperature of the ntc + the temperature of the k-type probe. If you short the k-type connector with a single piece of wire, you should read the temperature of the ntc on display, this should be similar to temperature ambient (if meter is not manipulated too much).

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Offline AndersJ

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Re: Thermometer Soar TX-570 shows 10 degrees too low temperature
« Reply #4 on: March 29, 2017, 06:07:24 pm »
Shorting the connector does not affect the reading.
In ice it shows zero.
In boiling water it shows 50 degrees (C).
It seems to be span issue, since it shows about half of the expected reading.
At room temperature it displays approximately the expected temperature/2,
thus my incorrect and sloppy assumption about a 10 degree static offset.

A circuit diagram would help, but I have not been able to find one.
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Offline jeroen79

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Re: Thermometer Soar TX-570 shows 10 degrees too low temperature
« Reply #5 on: March 29, 2017, 06:22:26 pm »
Are there no trimmers to adjust the reading?

If the problem started 'suddenly', did anything happen to the meter?

Can you do some measurements around the K-type connector?
Is it dirty? Does it have a higher contact resistance?
Does it cause a drop in the thermocouple's voltage?
 

Offline mimmus78

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Re: Thermometer Soar TX-570 shows 10 degrees too low temperature
« Reply #6 on: March 29, 2017, 11:46:10 pm »
Can you take a photo of the inside PCB?

If there are no trimmers and it doesn't use a standard chip it can be hard to proceed with repair.

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Offline mimmus78

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Re: Thermometer Soar TX-570 shows 10 degrees too low temperature
« Reply #7 on: March 29, 2017, 11:50:39 pm »
I didn't asked, you tried to replace this k-type probe.

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