[Elecraft] Weller WCC100

[Greg Beat]

David,
Thank you for that correction.
In addition, I left out these 2 paragraphs,
the second is critical for proper WCC103 sensor replacement.

The Weller WCC103 temperature sensor is actually an iron-constantan 
thermocouple
(possibly a Type J).  Weller used Type K thermocouples for its ECxxxx 
soldering station series.
Sensitivity believed to be about 50 µV/°C
The relationship between temperature and voltage produced is NON-Linear.

When replacing the WCC103 sensor the leads MUST be correctly installed
OR the soldering iron stays on continuously and eventually overheats.
The Iron (magnetic) lead connects to the RED wire
The Constantan (copper-nickel alloy/non-magnetic) lead connects to the 
YELLOW wire

What is a thermocouple sensor?
A thermocouple is a sensor for measuring temperature. It consists of two
dissimilar metals, joined together at one end. When the junction of the two
metals is heated or cooled a voltage is produced that can be correlated back
to the temperature.
http://www.omega.com/temperature/Z/pdf/z021-032.pdf

gb

----- Original Message ----- 
From: "David Woolley" <forums at david-woolley.me.uk>
To: "Elecraft Reflector" <elecraft at mailman.qth.net>
Sent: Sunday, December 30, 2007 4:30 AM
Subject: Re: [Elecraft] Weller WCC100


>> WCC103 temperature sensor has a resistance of about 1 to 2 ohms at room 
>> temperature (27 C)
>
> Thermocouples are voltage source devices, not variable resistance devices.
>
> 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.
-- 
> David Woolley