Bill of Materials

Description	Price	Qty	Subtotal	Shipping	URL of object or store
Sunterra 109006 Small Fountain Pump, 75 GPH, Black	14.99	1	14.99	0	http://www.amazon.com/gp/product/B000E5T70K
NORPRO 559 Immersion Heater for Warming Liquids	7.44	3	22.32	0	http://www.amazon.com/gp/product/B000I8VE68
SPST Rocker Switch with Neon Lamp	6.75	1	6.75	4.76	http://www.amazon.com/gp/product/B0002ZPBKW
Thermocouple Temperature Control Sensor Probe PT100 1m#	7.15	1	7.15	0	http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=350451552114&ssPageName=ADME:L:OC:US:1123
JLD612 Dual Display PID Temperature Controlle	33.5	1	33.50	2.77	http://www.lightobject.com/
25A Solid State Relay SSR DC In AC Out	10.5	1	10.50	2.77	http://www.lightobject.com/
Heat sink for 25A SSR	4.25	1	4.25	2.77	http://www.lightobject.com/

Time to try it out.
After realizing I ordered my PT100 probes on ebay from a company in China (virtual village), I realized my project that took 1 day to build and 5 days to order was going to be held up by a delivery time of 14-21 days.   (unfortunately, a state-side source for the PT100 probes at a $6 price isn't easy to find.)

Oh well.  Thanks to a friend at work, I was able to procure a sample K-type thermo-couple that worked great and using the settings in the PID controller, setting up the unit was a snap.

The Type-K thermocouple is an amazingly simple device.  the extension wire is solid-core copper and a nickel wires.  

Type K (Chromel / Alumel)
Type K is the ‘general purpose’ thermocouple. It is low cost and, owing to its popularity, it is available in a wide variety of probes. Thermocouples are available in the -200 °C to +1200 °C range. Sensitivity is approx 41 µV/°C. Use type K unless you have a good reason not to.

Cold Junction Compensation

From http://www.picotech.com/applications/thermocouple.html

Standard tables show the voltage produced by thermocouples at any given temperature, so for example in the above diagram, the K type thermocouple at 300 °C will produce 12.2 mV. Unfortunately it is not possible to simply connect up a voltmeter to the thermocouple to measure this voltage, because the connection of the voltmeter leads will make a second, undesired thermocouple junction. To make accurate measurements, this must be compensated for by using a technique known as cold junction compensation (CJC). In case you are wondering why connecting a voltmeter to a thermocouple does not make several additional thermocouple junctions (leads connecting to the thermocouple, leads to the meter, inside the meter etc), the law of intermediate metals states that a third metal, inserted between the two dissimilar metals of a thermocouple junction will have no effect provided that the two junctions are at the same temperature. This law is also important in the construction of thermocouple junctions. It is acceptable to make a thermocouple junction by soldering the two metals together as the solder will not affect the reading. In practice, however, thermocouples junctions are made by welding the two metals together (usually by capacitive discharge) as this ensures that the performance is not limited by the melting point of solder.

All standard thermocouple tables allow for this second thermocouple junction by assuming that it is kept at exactly zero degrees centigrade. Traditionally this was done with a carefully constructed ice bath (hence the term 'cold' junction compensation). Maintaining a ice bath is not practical for most measurement applications, so instead the actual temperature at the point of connection of the thermocouple wires to the measuring instrument is recorded.

Typically cold junction temperature is sensed by a precision thermistor in good thermal contact with the input connectors of the measuring instrument. This second temperature reading, along with the reading from the thermocouple itself is used by the measuring instrument to calculate the true temperature at the thermocouple tip. For less critical applications, the CJC is performed by a semiconductor temperature sensor. By combining the signal from this semiconductor with the signal from the thermocouple, the correct reading can be obtained without the need or expense to record two temperatures. Understanding of cold junction compensation is important; any error in the measurement of cold junction temperature will lead to the same error in the measured temperature from the thermocouple tip.

Linearisation