"Gunner Asch" wrote in message
news
On Wed, 13 Feb 2008 23:46:43 GMT, Winston
wrote:

Dan wrote:
I know this is off topic, but I know some of you know the answer.

I need to monitor the temperature of a heating element. I need to know
when it is on and when it is off. I don't need to know the
temperature, just that when it is getting hot and when it is not hot.
(...)

http://www.amveco.com/pdf/AC1020_11-01.pdf
http://rocky.digikey.com/WebLib/Amve...15,AC-1020.jpg

This is Digikey TE-1020-ND, a current transformer. Its small and will fit
within a 1" cube.
Disconnect the defrost heater and thread its wire through the hole in the
middle of this
part, then reconnect it. Solder a 100 ohm 1/8W resistor across the output
of the
transformer. Every amp flowing into your defrost heater will now be
indicated by a
voltage of about 0.1V AC at the output of the transformer, across the
resistor.

Connect one of these loggers (US$25.00)to the output of your current
transformer and log
the data to your PC.

http://www.dataq.com/products/startkit/di194rs.htm

That's what I would do.

--Winston


Wouldnt it be better to use a thermistor and have it actually tell if
there is a temperature change, rather than just power on the heating
coils? If you have an open in the coils..you will have power, but no
heat.


You will have both, voltage and current. That equals power (heat).

Using the current transformer means you don't need to disturb any factory
wiring and gives excellent isolation.

Sometimes the defrost heater is really buried inside the unit and would be a
pain to get to place the thermister (or any temp probe). Since he already
replaced the timer, it's a good bet the heater is bad or intermittent.

Tom