Measure rpm

Hello,
I am new to LabView. I have a cDaq 9172 and three modules (9263, 9201, and 9401). I am trying to measure rpm of a shaft with a 24 tooth gear and magnetic pick up. The shaft is expected to rotate in a range between 0.5 and 5 RPM which corresponds to 0.2-2Hz square wave signals (analog acquisition). I've tried using the frequency channel on the digital module (9401) but I couldn't get the programming to wait to aquire the relatively low frequencies. I've also tried post processing the analog signal (module 9201) but the Tone Measurement VI gives me inaccurate measurements at low frequencies (<1Hz).
Could someone please offer me a simple solution for measuring frequency accurately for the expected range so that I can calculate the RPM?
Much appreciated,
Jake

Nathanael,
Thank you for the response. I've been trying to measure the time between edges but so far no luck. Is there an example in LabView Help that I could mimic explicitly for this range of frequencies? I've been working on programming it myself based on a block diagram image I found in this forum but again I have not gotten very far. I've attached the programs showing where I'm at right now with it. Suggestions would be greatly appreciated.
In my experiment, the square wave signal from the speed sensor has an amplitude of 24V and a frequency range from 0.5-2Hz. I am attempting to simulate that in the attached VI by producing a similar square wave, checking whether the value is above 5V and if it is I want to start a timer to run until the greater-than-5V-condition is met again. I'm confused on how to make the condition TRUE for only rising signals (going from 0V to above 5V). Also, I'm not certain about the timing method. I'll try putting in the Tick Count (ms) as you suggested. Again, any help would be nice.
Regards,
Jake
Attachments:
SpeedSensorSimulator.vi ‏46 KB
MeasureTime.vi ‏11 KB

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Using a 9205 to measure RPM

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Not the cheapest route but there is a SCXI card that measures frquency.
http://sine.ni.com/nips/cds/view/p/lang/en/nid/1661
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This method is the easiest but the cheapest would be to get a cheap AI DAQ device that can measure several times faster than the generated signal (nyquist theorem) then analyze the series of AI reads to determine the frequency. Then convert frequency to RPM. Depending on the signal a USB DAQ device might work, if not a PCI or PXI + MXI card would still probably be cheaper than the SCXI route.
Unofficial Forum Rules and Guidelines - Hooovahh - LabVIEW Overlord
If 10 out of 10 experts in any field say something is bad, you should probably take their opinion seriously.

How can I measure RPM with CTR-500 module?

I have used the CTR-500 module for mesurement of motor RPM. But it doesn't have direct option to measure RPM ,
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min
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A second cause could be your vi. Suggest you post a copy of your vi.
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Hi CUA,
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i want to measure rpm using 100 ppr incremental encoder via digital input max speed (4000 rpm)
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pl provide me example code for this

Hi asaccullo.
The recommended settings for encoders are using the counters in the daq cards. Using digital I/O’s is not recommended, the encoders send digital signals but one of the main differences between using digital IO vs counters is that counters are designed to handle these type of events.
Here I found several examples in ni.com/code that you might check:
Imitation Quadrature Encoder with DAQmx Counter Tasks
Use Counter Frequency to obtain an Encoder Rotational Speed
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Regards,
steve.bm
AE | NI

How to measure RPM using digital I/O

Please tell me how to measure RPM using Digital Input or please give me a code for this.

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If you use DAQmx you can set up a frequency task and it will return the number of pulses in a specified time frame; then you can convert this to RPM based on your encoder resolution and take the same steps of running it through a filter to smooth it out if need be.
CLA, LabVIEW Versions 2010-2013

What is the correct way to measure RPM using Visual Basic?

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iDevice% = 1
ulGpctrNum& = ND_COUNTER_0
ulArmed& = ND_YES
ulTCReached& = ND_NO
iYieldON% = 1
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Finally getting around to this again. My previous post is incorrect, as the code I am using is based on the single period measure (it's right there in the code). I am having a problem with the values returned with this method. Occasionally, the card will return a lower than expected count, resulting in a very large (and incorrect) RPM value. I'm thinking this must have something to do with arming the counter at some unfortunate and coincidental point on the gate signal, resulting in a short count. It must be an unlikely event, because I get thousands of good, consistent values for every one bad one.
To resolve this, I am thinking of going to the single buffered period measurement as suggested above. My idea is to set up a buffer with two values,
and always take the second one (to avoid coincidental arming and short counts). I could also set it up to return more values, and the application could choose the most likely one (ie return three values, throw out the largest and smallest, etc.)
I would rather just use the buffer in continuous mode, since the RPM varies much more slowly than the counter counts, and any snapshot of the buffer at any time would be sufficient, even in the presence of overwriting, etc. This would allow me to arm the counter once and poll it on the fly.
My concern is that in continuous mode, the counter will be throwing a lot of errors which will interefere with the program flow. Can I just set the counter to suppress all errors when I do a buffered read? Worst case, I get a value as it is being written to by the counter, which will have some garbage value (hopefully a recognizable signature) which I can throw out in favor of the other values.
Thanks,
Doug

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; ;lgfh;lgf;lkgf,
One option would be to use the analog triggering on one of our full featured E Series data acquisition boards to trigger a digital pulse as outlined in the following Knowledge Base:
http://digital.ni.com/public.nsf/websearch/67CCAAF13C8617FC86256E01006C3D69?OpenDocument
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Whether you choose to go with the full featured E Series DAQ board or the SSR modules I recommend contacting our internal sales department at 1-800-433-3488 since they are wonderful at specifying systems.
Am
es
Applications Engineering
National Instruments

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I have an NI 9401, labview 8.6 and a 9172 chassis and I am trying to measure the rpm of my rotating shaft. The code I wrote works at low speeds but is not accurate at high speeds. Does anyone have a standard labview 8.6 code for obtaining the angular velocity of a rotating object?

Hi Eluan,
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| Zach J. | Applications Engineer | National Instruments |

Using cFP-AI-110 to measure rpm:capacitance in the card?

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Attachments:
rpmcircuit.jpg ‏9 KB

If the drawing is right, a pull up seems more reasonable to me
You don't want floating inputs at your cFP.
If the contact opens, the - input floats and need to be pulled to to + input to measure 0V
Greetings from Germany
Henrik
LV since v3.1
“ground” is a convenient fantasy
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hello,
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i wanted to measure rpm also does it matter whether the proximity switch has 2 or 3 wires and should it have an analog or digital/frequency output for cponnecting to the scc-68

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Hi,
please see the following link to NI-Discusion forum. There is simaler question.
http://forums.ni.com/ni/board/message?board.id=110&message.id=1764&requireLogin=False
I also send you tow links to LabVIEW examples. I hope it helps.
http://venus.ni.com/stage/we/niepd_web_display.DISPLAY_EPD4?p_answer=&p_guid=BCB1261CBE2635D2E034080020E74861&p_node=174404&p_rank=&p_source=Internal&p_submitted=N
http://venus.ni.com/stage/we/niepd_web_display.display_epd4?p_guid=BCB1261CBE2635D2E034080020E74861&p_node=
TN

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