pressure versus cranck angle encoder reading

[TDCenter]

I like to use labview to measure piston pressure vs cranck angle and I like to have it such that every time there is a transition in the A channel of the quadrature encoder feeding the counter of the DAQ card(E-series) a pressure sample is taken from the pressure sensor resulting in 1 pressure reading per degree of the encoder. If some one has a suggestion or a VI that does this or just performs a transducer reading per triggering of a counter I would greatly appreciate their help.
Thanks
Al

[Doug_Norman]

Hello Al,

If you want a pressure reading for each pulse of the encoder, all you have to do is use your encoder output A (provided its a TTL pulse train) as the clock source of a continuous analog input acquisition. Look for analog input examples that use an external clock source. Since it sounds like you also want to count the encoder pulses, your encoder output A will end up being connected to both a counter input and the AI clock source pin. You will have two separate measurements running, one being a counter measurement and the other being an analog input measurement. They can run simultaneously.

Regards,
Doug Norman

[TDCenter]

I am looking for a program that would measure engine pressure with respect to Crank Angle position. I have a PCI 6071E card and I have an optical encoder with index Z, A and B channels. Do you have a program that can measure the pressure with respect to CA and display it directly or are there two separate example in LabView library that can be combined to do this and use an E-series card. I also read the suggestion here, the index Z signal can be used for triggering. I like to use signal A or B as scan clock and I like for the position(CA) displayed to reset to zero each time a revolution completes. I appreciate it if someone can give me some suggestions on how to do this.

Thank You,
Al

[Innoworks]

Hi AI

I read your posts in the LabView forum. I need to do the same: Acquiring Data like: "1 Scan/°CA"
As said, I read your posts and tried the acquisition with example file "Cont Acq&Graph ExtScanClk D-Trig.vi"
It retrieved some data which looks not bad (I measured the pressure in cylinder of combustion engine...)
BUT: does it really take one Scan per degree of crank angle? OR: Does it just evaluate the frequency between the first two pulses (time between 1° and 2°)
which is the basis of the whole acquiring process? I agree that the Data will about the same, due to the constant speed of the engine during one revolution, but if I want to have it more exact - what can I do?

I would really appreciate to get some suggestions - or some code.

Please answer

Greetings Woodi

andi@fuerholz.ch

[unclebump]

I did something similar to this using a Yokogawa DL708 scope. I ran the encoder pulses into the external clock input. The scope then sampled the channels on every clock pulse. I had 14400 samples per revolution of the cranshaft. I had GCD-SE linear transducers monitoring the piston travel and bucket tappet displacements. The scope would show the opening and closing of the valves and piston travel. The scope had built-in measurements for Rdelay and Fdelay on the curves. The X axis for the datapoints was in encoder pulses so it was easy to convert it into degrees. The scope measured for about 20 engine revolutions. Then i modified the Yokogawa instrument driver to read the timing data with labview. I would think some labview cards could have done the same measurements. I could send some pictures and stuff when I get back to work.

[Innoworks]

Hi unclebump

Thank you for your answer. I guess I am going to prove this with an external signal generater, whether my programm scans 1/°CA or not.

Greetings

Woodi

[unclebump]

Here are a couple links to check out.


http://www.yokogawa.com/tm/appli/automotive/tm-appli_auto16.htm

http://www.yokogawa.com/tm/appli/automotive/tm-appli_auto12.htm

[Innoworks]

Thanks a lot!

[Kevin_Price]

Woodi,

If you use an encoder pulsetrain as an external sampling clock for your AI measurement task, then you'll be getting one scan per encoder pulse. Odds are, it probably won't be exactly one scan per degree of crank angle -- that'll depend on the encoder resolution. For example, a common resolution is 1024 cycles/rev which would give you one scan per 0.35 degrees.

-Kevin P.

[Innoworks]

Hi Kevin!

Thank you for your help! I configured my encoder to give one pulse per degree.
So does it give me really 1 Scan/ °CA when I am using "Cont Acq&Graph ExtScanClk D-Trig.vi" ?

Greetings Woodi