Thought I'd write piece on a simple circuit I have built to amplify the output from a thermocouple. I am using two types of type K thermocouple for my temperature measurements, I don't know the technical names for each type off the top of my head, and it is past 4:30 am so I can't be bothered to find out. I call the type in the first picture 'probe' and the inset picture 'bulb'. These thermocouples come in several 'Types' depending on the requirements and are in essence a bi-metal strip that produces a voltage change proportional to the change in temperature, and this voltage is generally in the millivolts scale. The Type K probes are found in all commercial micro-gas turbine engines to measure the exhaust gas temperatures and I will be using the same but I have limited space within the engine and will therefore use the bulb type. They also have a faster response time which will give better results when the engine is throttling away from steady state operation.
The circuit diagram shows the final layout circuit I will be using, it is based around the LM358N op-amp which I sourced on EBay as they were very cheap. I originally omitted the small ceramic capacitor but since I will be using several amplification circuits and thermocouples in parallel there may be some noise which this should help to minimise. At this point you should know I am relying on the electronics I have learned at uni, since my course is triple accredited, (or cursed depending on your viewpoint), we have to cover a certain number of mandatory electronic engineering modules. But I digress, anyway these circuits are pretty simple and if you have any suggestions for improvements please let me know...
I couldn't help but transfer the circuit onto a bread board for testing and it worked flawlessly, I even hooked it up to a DAQ and used WINDAQ in oscilloscope mode to see how stable the output was and it was surprisingly well behaved. I can't wait till my oscilloscope arrives as it will save me a lot of time messing about with a DAQ everytime I need to see how a circuit behaves. Dunking the bulb thermocouple into hot water then into cold showed a good response time, (something I need to further investigate to see how accurate temperature measuring will be when the engine accelerates or decelerates). Swapping over to a probe and holding a flame underneath it gave similar results. 
Just need to make up five of these circuits on some vero board and then I can carry on with the Labview dashboard program. The pressure transducers have also arrived so more fun things to come as I can't really do much with the RPM frequency to voltage converter yet as I really need the oscilloscope. I have also been thinking about buying one of the DIY PCB kits from Maplins and making my own PCB's. This would be a more elegant method than vero board. Hmm...
