I have a magnetic pick up sensor

[surya]

I wanted to measure the speed of an engine (flywheel). I have a encoder type sensor with a magnetic strip inside (hall effect type),mounted on the flywheel (with 12 holes). The magnetic pick up sensor, generates a pulse train (Is this a TTL signal?). I wanted to measure the speed of the flywheel, by measuring the frequency/time period/width of the pulse. I have a AT-MIO-16E-10 data card inside my PC and AMUX-64T Multiplexer. Can I use them to measure the speed of the engine. I have a SCB-68 connection box, connected to another PC, which I'm using to measure the in-cylinder pressure (high frequency) triggered with a external scan clock, which has a "Crank angle encoder" as source.(pulse per every 1/2 CA =720 pulses/rev).
Index pulse (D
igital trigger) is connected to PFI0
External Scanclock source is connected to PFI7.
We are using slightly modified "acquire Nscans-external scan clk D.vi" for measuring in-cylinder pressure.
I just wanted an efficient way of measuring the speed of the engine with the equipment I have.

[Filipe A.]

Hello;

The best way to measure the speed of an equipment that gives out a digital TTL pulse train, is by using the general purpose counter of the DAQ device and configure this counter as buffered event counting. By configuring the counter like that, at every event of a pulse, the actual counter value is transfered to a buffer. Since you know beforehend the frequency of the signal connected to the source pin of the counter, you can calculate the external pulse train frequency by a simple calculation using the frequency of the source signal and the counter value at every event of an active edge of the external pulse train.

Unfortunately, the AMUX you have there doesn't have external connections to the general purpose counter available on your DAQ device. You ca
n accomplish that with the SCB-68 you have.

You didn't mention what programming language you are using, however, you can find examples showing how to do buffered event counting at both Labview and NI-DAQ shipping examples.

Hope this helps.
Filipe A.
Applications Engineer
National Instruments

[surya]

Hi Mr.Filipe A.,
Thanks for your response. We are using labview (version 5.0). I have few more questions.
1) I have a SCB-68, connected to another PC (first PC is connected with AMUX-64T), which I'm using to trigger the in-cylinder pressure (high frequency) with a external scan clock, which has a "Crank angle encoder" as source.(pulse per every 1/2 CA =720 pulses/rev).
Index pulse (Digital trigger for TDC) is connected to PFI0
External Scanclock source is connected to PFI7.
As the encoder and digital trigger are connected to two pins (PFI7 and PFI0 respv.). Will I be able to connect the speed pick-up sensor, also to the same SCB-68, (if so what are the available pins numbers, do I have to use to connect the gate source for my speed pick-up).

2) Can
I use the crankangle encoder only to measure the speed of the engine? if so how?. Im already using the crakangle encoder in "acquireNscans-externalscanclkD.vi.". Can I use it for two different applications?

3) If I have to get another SCB-68, will I be able to connect that in series with AMUX-64T, so that I can get the readings in first PC, only.

Thanks for your time,
Surya.