Dear Mohajer and all
If you are using type K thermocouplers you will have to turn off power to the
component before measuring the temp. Since they are sensitive to magnetic
fields.
Best regards,
Mr. Kim Boll Jensen
i-data, Denmark
Kamran Mohajer kmoha...@cisco.com on 99-08-24 23:50:26
I too, have noticed a variation in temperature, especially when measuring a
very hot component with forced air cooling. I usually try to get the highest
possible temperature reading by :
1. Use very small thermocouple wire, such as AWG 30. Larger wire sizes can
conduct heat away from the tip.
Hi Kamran,
I use both change of resistance and a thermocouple as a check. I would
expect the thermocouple to read a little below the resistance method. Some
standards require the change of resistance method (not the thermocouple
method) to be used for compliance assessment of winding temps.
Hi Kamran,
I've run into this problem myself. Usually, it is because the test
conditions you use are different from what the vendor is using. They may be
loading the EUT to full capacity and/or using a thermocouple attachment
method different from yours. In the case where your product's
Dear Kamran,
Obtaining a temperature test results that is 10-15 degrees higher or lower
than your vendor is not unusual at all. We experience this all the time
with major test houses. I have had many cases where an experience test
engineer in a test house measures as much as 20 degrees lower or
Kamran,
As John Crabb pointed out, making measurements at different points will give
you some variation due to hot spots etc. What most people miss is that
thermocouple readings are affected by magnetic fields. To get a correct
reading, turn power off and take a reading immidiately after the
Hello Kamran,
I have been faced with this problem many times in the (nearly 35) years
that I have been involved with such measurements. In my experience, this
is the major and problematic correlation factor (in the product safety
domain). It is the one that stands out above all others, when
Kamran,
The method used by most of the better magnetics houses is to embed
thermocouples into the transformer during construction of a sample. The
resulting temperatures will be higher than external measurements.
Scott Lacey
-Original Message-
From: Kamran Mohajer
Kamran,
When UL or Intertek does safety testing (UL 1950, IEC 60950) on one of our
units that has coils or transformers in it they apply the thermocouples to
the top (highest) horizontal surface of the coil or transformer for their
temperature rise (heating) tests. I can usually find the
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