Hello all,
I am trying to obtain in-cylinder pressure measurements to perform heat release rate analysis on a 4-stroke DI turbocharged automotive diesel engine. From the engine I get the following three signals:
a voltage signal from the pressure transducer
a square wave signal from a crankshaft encoder which gives 2880 pulses per revolution, or equivalently 5760 pulses per cycle, or 1 pulse per .125 degrees CA
a square wave signal from a camshaft encoder, which gives one pulse per cycle at known CA (say the non-firing cycle TDC)
From various examples I found, I have come up with the attached VI. In it, the pressure data aquisition (port ai0) is clocked externally using the crankshaft encoder signal, which is connected to PFI1, and is triggered from the camshaft encoder signal, which is connected to PFI0. While this is fine if aquiring data for a single cycle, my main worry is that, from the way this VI is setup, in the case of aquisition of multiple cycles, if say one pulse from the crankshaft encoder is missed, then all the subsequent data aquired will be inaccurate by one CA step. To solve this I guess I would have to trigger the data aquisition once per cycle, but I have not found a way to do this.
Also, is there a way to start the data aquisition a pre-determined number of crankshaft pulses after the camshaft TDC mark? Since only the compression and expansion cycle data are of interest in the heat release analysis, aquiring only the data which are needed will reduce the output file size significantly, thus making the file management easier.
On an other note, I would also like to ask if the PFI ports take up any of the samling available on the DAQ card. Since the sampling rate of this card is 200kHz, when running at 4000rpm there will be 192000 samples per second, which is at the limit of the card. Unless the PFI ports I use to externally clock the data aquisition are only used for the clocking, then there might be a problem with the data aquisition at these engine speeds. To solve this possible problem, I also have a timer/counter card (PCI-6601) and an RTSI bus cable available. Would it be of any use to use the counter card to count the pulses from the shaft encoders, and then sycronize the two cards using the RTSI bus? If yes how can this be done? As I imagine it, the input of the counter card must be used to clock the DAQ card, and the counter card will probably use its internal clock.
Thank you for your information,
Panos
