I have been run off my feet with uni work since coming back after the Easter break, along with sorting out my PhD applications but I have managed to squeeze some time into building the amplifier circuit for the five thermocouples. Here it is in all it's vero board glory along with the data bus, neatly labelled up as despite the colour co-ordinating I know I will end up connecting the wrong signal wire to the wrong DAQ channel.
I have noticed that the outputs in my Labview vi appeared to have some noise that would cause the gauges to 'bounce' slightly. Looking at the number string of the load cell channel coming out of DAQ in Labview it appeared to fluctuate randomly between 70 and 100 when no load was applied and rising to nearly 4000 with two 1 gallon water bottles hanging off it, again with a random noise of around 10 units either side of the steady state value . At first this meant nothing to me and I had to firstly find out what the DAQ actually outputs, in case I had made a mistake with Labview and was reading some other signal. A quick skim read of the pdf manual provided by Starting Point Systems told me the DAQ gives an integer output between 0 and 4095 which corresponds to a 0 to 5v analogue signal. Ok, that seemed to fit with my measurements, but was the noise a problem with the Labview vi? Well a quick play with the µChameleon controller software showed the same noisy signal, so until I get my new oscilloscope there isn't much I can do except put up with it. Although I have said 'random noise' I don't think it is random but some sort of interference as putting a square wave through any one input channel on the DAQ will have a small effect on the outputs of the others. This effect seems to disappear once I have signals connected to those channels but I don't think it is. I have no idea if this means I need to shield all the signal lines or provide some better grounding for the DAQ.
I've also got my eyes on some Wren turbine parts on EBay, the seller has a spare outer engine case in the lot and that means I can take a drill to the engine for the temperature and pressure measurements without the potential of ruining an engine. I'm keeping my feelers crossed it doesn't go for a fortune!
