December 21, 2012 - December 27, 2012

December 27, 2012

Before the Christmas break an integrated circuit was ordered (I think) that will read a thermocouple, complete cold junction compensation, and act as an operational amplifier. My remaining concerns for the connection of the IC include:

1. Should I order some thermocouple extension wire or not? If I do, it will cost about $20, which I really didn't think I would have to spend. If I just extend the leads with copper wire I will (by this action alone) create the reference junction at the solder points. This will not be a problem if I am able to keep the solder points (reference junction) at the same temperature as the IC. Basically, If I keep the system from the solder points to the IC isothermal than it will not matter. I do not know the extent to which it does matter if I cannot keep the system isothermal.

I just found this quote (from the AD594/AD595 specifications sheet), so I think I can do it... "If the thermocouple reference junction is maintained at the AD594 temperature, the output of the AD594 will correspond to the reading that would have been obtained from amplification of a signal from a thermocouple referenced to an ice bath."

2. I do not know what a common is in reference to connecting circuitry. The alarm at pin 13, and pins 4, and 7 are connected to the common, as is the iron output lead of the thermocouple. I will need to know more about this before I can solder anything.