The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
Subject: Re: question on measuring temperarures at high voltages
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Wed, 23 Oct 2002 06:50:27 GMT
NNTP-Posting-Date: Wed, 23 Oct 2002 08:50:27 MET DST
"Kooner" schrieb im Newsbeitrag
> I tried to measure the temperature of a LT1084 voltage regulator that
> is floating at 10kV. The 10kV is the output of a switching power
> supply. The regulator is in a TO-247 package. I placed a thermocouple
> on the body, which is supposed to be isolated from the leads and case
> (which are at high voltage). The thermocouple was plugged into a hand
> held temperature meter powered by a 9V battery.
> My question is why does the meter give an invalid reading? The
> temperature just bounces around. I'm guessing it's one of two things:
> 1. The thermocouple acts as an antenna picking up EM fields that
> induce a voltage.
Yes, this will probably be the reason. When switching off the circuit to be
measured do you get a stable reading?
> 2. The body is not totally isolated from the high voltage leads.
> Therefore the 10kV forces a current along the body, to the
> thermocouple, to the hand held meter to ground. But the hand held
> meter is not referenced to ground??
When the meter is placed on an isolating surface(rubber mat, dry wood,
plastic) it will still work, as long as there is no connection to mains. If
there is it will never work again.
I wouldn't hold that meter in the hand! consider that a 10kV potential can
bridge a substantial distance of air and zap...
do not fiddle around with voltages that high without a decent training.
There are temperature sensitive self adhesive plastic dots available, which
change the color when the set temperature is exceeded.
There are also infrared sensors for contactless temperature measurements.
Since your application doesn't require the accuracy of a thermocouple, be
smart and use one of those.
electronic hardware designer
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup