Greg Beat wrote:
> WCC103 temperature sensor has a resistance of about 1 to 2 ohms at
* room temperature (27 C)
> This resistance increases (thermocouple) as the temperature rises --
Thermocouples are voltage source devices, not variable resistance devices.
* the control board then compares this to the temperature set by the user
With thermocouples, you get the difference in the voltage between the
hot and cold junctions, so, for really accurate operation, you need some
other mechanism for measuring the cold junction temperature. In this
case, the variation in cold junction temperature and required accuracy
might be low enough that simply assuming 25C is good enough. Whether
cold junction compensation is included is a significant feature of the
design.
* (potentiometer). A "zero-crossing" circuit then turns off the heater
PS I've had to manually wrap the very long lines in this article.
--
David Woolley
Emails are not formal business letters, whatever businesses may want.
RFC1855 says there should be an address here, but, in a world of spam,
that is no longer good advice, as archive address hiding may not work.
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