rpm measurement with scb 68 using pci 6229

[hgottipati]

Hi

I need to take RPM measurements with a LED Remote optical sensor which has 4 leads coming from it.

+v, common, signal (+v to 0 vdc pulse) and housing ground (common).

Can anyone tell me which lead will go into whcih pins of my scb 68.

Thanks 

[Vineet_A.]

Hello,

You can use the counters on the PCI-6229 to count the rising edges from your sensor.  What is the maximum frequency you're expecting from your sensor?  This will determine the pin you'll need to connect to.  If the frequency is too high, you'll probably need to use both counters on your PCI-6229.

The pinouts and details are available in NI-DAQmx Help, which installs with the NI-DAQmx driver software.  You can probably get to it by going to Start>>Program>>National Instruments>>NI-DAQ>>NI-DAQmx Help.

Here are the default pin assignments from that help file:

68-Pin M Series Signal Connections for Counters

The following table lists the default input terminals for various counter measurements on M Series devices, including M Series USB devices, such as the NI USB 6259 screw terminal and NI USB-6229 BNC devices. You can use a different PFI line for any of the input terminals. To change the PFI input for a measurement, use the NI-DAQmx channel attributes/properties.

Measurement	Ctr0	Ctr1
Count Edges	Edges: PFI 8 Count Direction: PFI 10	Edges: PFI 3 Count Direction: PFI 11
Pulse Width Measurement	PFI 9	PFI 4
Period/Frequency Measurement (Low Frequency with One Counter)	PFI 9	PFI 4
Period/Frequency Measurement (High Frequency with Two Counters)	PFI 8	PFI 3
Period/Frequency Measurement (Large Range with Two Counters)	PFI 8	PFI 3
Semiperiod Measurement	PFI 9	PFI 4
Two-Edge Separation Measurement	Start: PFI 10 Stop: PFI 9	Start: PFI 11 Stop: PFI 4
Position Measurement	A: PFI 8 B: PFI 10 Z: PFI 9	A: PFI 3 B: PFI 11 Z: PFI 4

 

Here's how those map to the SCB 

Default NI-DAQmx Counter Terminals (Connector 0)

Counter Signal	Default SCB-68 Pin Number	Signal Name
CTR 0 SRC	37	PFI 8
CTR 0 GATE	3	PFI 9
CTR 0 AUX	45	PFI 10
CTR 0 OUT	2	PFI 12
CTR 0 A	37	PFI 8
CTR 0 Z	3	PFI 9
CTR 0 B	45	PFI 10
CTR 1 SRC	42	PFI 3
CTR 1 GATE	41	PFI 4
CTR 1 AUX	46	PFI 11
CTR 1 OUT	40	PFI 13
CTR 1 A	42	PFI 3
CTR 1 Z	41	PFI 4
CTR 1 B	46	PFI 11
FREQ OUT	1	PFI 14

If you're using counter 0 to measure a "lower frequency", you should connect your signal to PFI 9, which is Pin 3 on your SCB-68.

Please post questions like these on the DAQ Hardware Discussion Forums.

Regards,

Vineet A.

[hgottipati]

Thanks for the reply Vineet. I am expecting a rpm of not more than 600. I think I have to use only one counter. 

So how about other other 3 leads coming from the sensor?

[Vineet_A.]

Hello,

Depending on the sensor, my guess is that the +V lead should connect to the 5V source and the others should be grounded.

The documentation for the sensor should be able to confirm that.

Regards,

Vineet

[aeastet]

I think your V+ will have to attach to the power supply for the sensor. The V+ should go to the power source the common should go to ground for that power source. Signal should go to the counter and you will have to jump between the common of the power and the common for the LED into the counter common.

[rares]

Hi Vineet,

I am also trying to measure the speed of a model turbine-rotor with scb 68 but using the NI 6289. The speed of the rotor is about 1000rpm (around 16Hz) but the sensor should detect every blade (there are 10 blades), so the frequency should be below 200Hz. I have a good understanding of the principle but I am new to Labview and new to NI hardware. 

My sensor has to be powered between 10-30V. Assuming I will use 18V to power the sensor is it ok to have a simple voltage divider to ensure the sensor's output pulse does not exceed 5V (asuming the ground of the 18V power supply is connected to the AIGND)? The divider's output will be connected to PFI9 (I plan to use counter 0).

Is there a sample labview program working with ni 6289 timers you can point me to?

Thank you,

rares

[Vineet_A.]

Hello Rares,

The timers on the NI 6289 are the same as many other NI-DAQmx devices, so any NI-DAQmx example should work for you.

For continuous counter measurements, I'd recommend starting with >> Meas Dig Freq-Buffered-Cont-Large Range 2 Ctr.vi which is available in the LabVIEW Example Finder if you have NI-DAQmx installed.  On the block diagram, you can change the measurement method input on the Create Channel function to "Low Frequency with 1 Counter".

If the sensor output isn't 5V TTL, it's possible to use a voltage divider but you'll have to consider both voltage and current limitations.  Also, the negative or common terminal of the sensor should be connected to digital ground, and not AIGND.

Regards,

Vineet

[raresstanciu]

Thank you Vineet. I will try using a divider and use a 12V power supply to power the sensor. I will connect its common line (ground) to digital ground as you suggested. I will check the Meas Dig Freq-Buffered-Cont-Large Range 2 Ctr.vi (the vi you recommended) and try to perform modify it to see it working. I will let you know. Once again, thank you.

Regards,

rares

[raresstanciu]

Vineet,

I would like to thank you for your time and help. I started with the program you suggested and after making the small modification you indicated it worked. I could see the frequency on my screen. Once again, thank you.

Best Regards,

rares

[Vineet_A.]

Hello Rares,

I'm glad it was helpful for you.

Regards,

Vineet