Wiring a SCB-68 to measure the frequency of a TTL pulse signal

Sorry if this is a basic question but could someone please help me and tell me how to wire up a SCB-68 connector block (connected to a AT-MIO-16 DAQ board) so that I can measure the frequency count of a series TTL pulses (signal from photon counting). At the moment I don't understand how the PFI1-9 connections are related to the GPCTR0/GPTR1 counter connections on the block and how they're all realted to the source,gate and out 1-5 connections on the DAQ board.
Ultimately I want to be able to put this measured frequency into a Labview program with a controllable gate period.
Thanks in advance
Nick

You might want to search the Knowledge Base on the NI's Support Pages for "Cable Mapping for a 68 Pin Connector to a 50 Pin Connector". This should take you to a link that will explain the mapping of a 50way to 68way cable and subsequent lines you are looking for ( reference sub link 68F50M), I guess you have SH6850 cable connected from the AT-MIO16 card to the SCB-68.
Please check out the information about the pin outs, that should help you work out which pins map to the counters, eg GPCTR0_source would be pin 37 on your SCB-68
Regards
Joe (NI)

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How can I measure the frequencies of two analog input signals simultaneously?

Hi
I have two AI signals, and I need to determine the frequencies of those signals. The frequencies range from 1-125Hz. I currently have a VI where I can sample one of the signals for 1 second (sampling at 300 Hz for 300 samples) and determine the frequency.
I need to read two signals at the same time and get both of the frequencies at the same time, but I can only figure out how to read them individually, so I can read one signal, then one second later I read the second one, then I read the first one again, then the sceond one, etc.. How can I read two signals simultaneously?
Thanks
Attachments:
FreqMeas11.vi ‏41 KB
FreqMeas11.PNG ‏18 KB

"at same time", this depends on the hardware, you can do as has been previously stated just set up a 2 channel acquisition and you will get 2 sampled waveforms back. Most hardware A/D as multiplexed and true simultaneous sampling is not done. At 125Hz this is not an issue unless you are interested in very small phase changes between the samples. just keep this in mind if you are expecting samples to be completly synchronized.
Paul
Paul Falkenstein
Coleman Technologies Inc.
CLA, CPI, AIA-Vision
Labview 4.0- 2013, RT, Vision, FPGA

How to measure the baseline of a noisy, pulsed signal

Hi
I am measuring the torque exerted by a large motor on a shaft using a load cell and lever arm. The shaft runs at approx 150 rpm. I have attached a drawing that shows the output I get. This is a test rig.
I have written some code that measures the maximum peak out of a group of approx 5 peaks and writes this to a shift register. This gives me an idea of the maximum torque "spike".
I also wish to measure the baseline torque (due to the bearings in the machine). Even when highly filtered (my noise filter is set to 49Hz) the signal exhibits this noise which is probably due to vibration in the system. The signal is zeroed when the motor is not running.
Does anyone have an ideas on how to measure the "baseline" torque? The large spike in torque prevents me from doing a running average. Can anyone think of a way of averaging just the noisy part of the signal to get an average value? I aim to to subtract the average baseline torque from the peak value to get an idea of the torque due to the event which causes
the spike.
Any help would be greatly appreciated.
Many thanks.
Attachments:
drawing of torque signal.gif ‏26 KB

Thanks for the reply. I understand what you are saying. However, I might have to modify my method for measuring the peaks if I choose to implement your idea. I have taken a screenshot of my "peak finder" code and attached it.
Bascially, the reset terminal is wired to a timer which outputs a pulse every few seconds. This resets the vi (a standard NI one I think) and sets the peak magnitude back to zero. This way, I am windowing the signal and measuring the maximum peak in every window. This is what I need to do.
So I could use a logical filter to feed data to the running average only if;
the amplitude of the signal is less than a certain threshold
and if the current value has similar low peaks either side of it
How would you construct the code to delay the evaluation so that the values in front and behind of the current data point can be analysed?
thanks again
Attachments:
peak_find_screenshot.jpg ‏45 KB

I need to measure the frequency of a signal on Pin 39 (PFI 15) of a PXIe-6361 module.

I need to measure the frequency of a signal on pin 39 (PFI 15) of a PXIe-6361 module. All of the digital I/O pins are already assigned and in use. The signal frequency range is 50KHz to 500KHz. I have tried all of the sample programs for DAQmx Counter/Timer frequency measurement. If I modify them to use my hardware, I get run-time errors with conflicts with resources already assigned.

Hi Julia,
Thanks for the response. As I stated before, I have tried all of the examples available that apply. There are only three and one of those uses two counters. The two I have tried are:
Examples/Hardware Input and Output/Counter Measurements/Digital Frequency/
DigFreq-Buff-Cont-ExtClk-ArmStart.prj and
DigFreq-LowFreq1Ctr.prj
These examples default to using what appears to be traditional DAQ hardware (Dev1/ctr0 and /Dev1/PFI0). I changed the counter to mine (/PXI1Slot3/ctr3) and directed my signal source (PFI15 on pin 39) to the counter. No matter what I tried would not run. They would always compile but gave run-time errors ranging from resources already in use to “external trigger required”. I have no external trigger source and, if I did, there is no indication of how to assign it to the counter. NI has a very good X Series Users Manual that tells all of the great things you can do with the hardware, but there is NO CLUE how to do any of those things!!!! I know that some NI DAQmx functions use hardware resources that they never tell you about. I discovered that when trying to produce a single output pulse from a timer using counter #0. (Which, by the way, no one at NI could tell me how to do it.)
Measuring frequency should be very simple. The unknown signal is routed through a precise gate to a counter, and then the counter is read. NI DAQmx uses the opposite approach of using my signal as the gate and counting their internal source. However, the examples would not let me use the internal reference sources.
To answer your other questions, I am not performing any other measurements at the same time and the counter is not being used for anything else, period.
Any help would be greatly appreciated. Thanks again.
Wayne K.

How to measure the frequency of the data plotted on the waveform chart

i have made a virtual instrument in labview that acquire data (say sine wave) into a spreadsheet file and also on the chart from the function generator. I measured the frequency of the data from the chart but it is coming out to be very less. How can i calculate the frequency of the plotted sine wave and also from the spreadsheet file.

If you want to get an idea of the base-frequency of an periodic signal, you can measure the number of samples in between two maxima or in between two minima of the periodic signal.
Multiply the number of samples by the sample-interval (1/Fsample in [sec]) gives you a rough estimate.
FFT, I mentioned is one of the more advanced calculation-methods.
The method calculates the spectrum from a waveform.
Hope this helps,
Patrick

Help with measuring the frequency of a pulsing signal

Hi,
I am trying to use LabView to measure the flow from my ultrasonic flow meter. The meter sends a pulse for evey 10 litres of flow: I am picking up the signal in LabView without any trouble - it's basically a square wave that pulses at 10V and goes back down to 0V for the same duration.
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Any suggestions?
Cheers,
Liam

Hi, I have the same problem - my LabView edition is Student so I don't think I can access them.
Unfortunately the problem is still persisting. I have been working with someone who is quite experienced with LabView and he can't solve the problem either.
There was some progress when I used the Trigger and Elapsed time .vi's to measure the time between rising edge pusles. Since the pulses were quite slow, by putting the period-to-flow conversion equation in, the flow could seen reducing to a minimum value as the elaspsed time increased to the full period. I have fitted new, more accuarate flow meters into he pipes which now send 100 pulses for each litre of flow. These flowmeters now pulse so quickly that it's impossible to see what the minimum flow value is to get the flow.
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Hi princess! (it's funny writing that somehow)
Have you considered the example finder?
There should be examples on how to acquire and measure with the NI 5660.
And there should be a block in LV that was delivered with the NI 5660 software, that does something like "acquire spectrum" or something like that.
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It probably would be easiest to convert the sine wave to a square wave with a simple external circuit and then use a counter module to measure the frequency. There is a shipping example in LabVIEW that shows how to measure frequency with a FieldPoint Counter module.
JRA

Can I measure the frequency from all PFI pins?

I am using a PCI-6229 DAQmx card. I am trying to measure the frequency from pin PFI 5. I have been successful in measuring frequency from PFI0 and PFI1 but for some reason I am not able to measure on other pins. When I run the run the DAQmx Read sub VI it times out like it is not reading anything. I am using the same sub VI I created to measure 5 as I did 0 and 1 so I know that the VI is working. What is the matter? Are there only certian pins that I can measure? Would the sub VI time out because there is no signal on the pin?

Hello Flowserve1,
Thanks for your post!
The basic answer to your question, "Would the sub VI time out because there is no signal on the pin?", Is yes if there is no signal coming into the pin your are bring a signal in on. It sounds like you were able to do a "frequency" measurement on PFI0 and PFI1? Usually the counter tasks are used for such a measurement. How are you performing these frequency counter tasks on your PFI lines? It looks like on the pin read out that PFI0,1 and 5 are for digital tasks and PFI routing lines. Are you internally routing your signals to other places? If you want to measure the frequency using counters, this board has two of them so use Ctr 0 and 1 gate or source to make these measurements. Let me know if any of this helps you and perhaps you could post a piece of your code that you are using to make your frequency counts.
Cheers!
Corby_B
http://www.ni.com/support

How can I measure the frequency of an analog signal?

Hi, I am trying to measure the frequency of VAC signal coming from a gas turbine engine at my university. If I can get the values of frequency, I can determine the speed (RPM) of the engine. I am fairly new to LabVIEW and I have been looking through manuals like crazy in order to find out how to obtain the frequency. I have measured the signal with an oscilliscope and the highest frequecy will be about 1.5kHz. I am currently using a USB-6218 and it can collect the voltage signal with ease, but it won't give be analog frequency so simply. Can anyone explain a way for me to obtain the frequency values? And if you could show or tell me in a very simple way (because I am not very fluent in LabVIEW yet), that would be amazing! Thanks!

Check this out:
Attachments:
RPM.vi ‏17 KB

How to measure the time of evolution of a signal in a graph and to compare this time measured with a known value?

For my application, I am obliged to measure the time of evolution of a signal acquired (from T1 to t2) by an analogical entry of a module NI 9203, and to compare this value with a value known in order to judge if this time of evolution is correct or not.
PLEASE I prefer an example for better understanding.

Greetings Jacob,
I am not sure what you mean with 'time of evolution' but normally you acquire at a certain acquisition rate. How much time that has passed, you can calculate by checking how much points are between your two points of interest.
If you are acquiring at 5Hz, the time between every point is 200ms. If there are let's say 10points between your two points of interest, 2s have passed.
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National Instruments

Measure the height of an square pulse

I'd like to measure the height of an square pulse. The pulse is 10 mus broad and betwean 0V and 4V high. The occurence of the pulse is random, so the application must be triggerd.
I searched already the ni page and forum for matching solutions, but haven't found any so far.
I'm using a PCI-6115 DAQ-card.

10e4 and 10^4 are NOT the same thing.
You wouldn't think that 1.23e4 and 1.23^4 are the same thing, would you?
10e4 = 10 x 10^4 = 100,000
1e4 = 1 x 10^4 = 10,000
If you want to catch a 10 MicroSecond pulse, that would suggest a sampling rate of 100 kHz, bare minimum.
For 5 seconds, that's 5 x 100k = 5 million samples = 10 million bytes (assuming a single channel, recording as I16).
Depending on CPU speed, and RAM available, you could try the brute-force approach: record 5 seconds of data, then loop thru it and pick out the pulses.
I would suggest a trial:
1... Generate a 5-million sample array of I16 zeroes.
2... Change a few of the samples to +1000 (or something)
--- Now you have some phony data to play with.
3... Record the current millisecond timer value (T0).
4... Loop through the samples: If sample(I) > threshold and sample (I-1) is not (use a boolean shift reg.), then declare a pulse to exist at sample I. Append I to the array of indexes you're keeping.
5... When the loop is done, record the current millisecond timer value again (T1).
6... Subtract T1-T0 to get elapsed time. If it's greater than 2000 mSec, you can't use this approach.
7... Compare the results (indexes of peaks) to the peaks you put in (step 2). They should be the same.
If you can use this approach, it is the simplest to program.
Otherwise, you will have to use a double-buffered approach:
1... Define a CHUNK size of say, 2048 samples.
2... Set up a continuous DAQ operation to use a buffer of 2 * CHUNK samples.
3... Keep checking the DAQ backlog until the backlog is CHUNK or greater.
4... Read CHUNK samples from the buffer.
5... Search the chunk for pulses, append indexes to your results array.
--- Don't bother to read every sample in volts - too time-consuming - read it in binary (I16). Convert the peaks to volts afterward, if needed.
--- You need a threshold to distinguish a '1' level from a '0' level. The '0' level won't be 0.0000 volts, there will be some noise.
--- You might be able to measure the noise during the 2-sec down time, and establish your threshold that way.
--- The seconds approach assumes that the CPU is fast enough to process a chunk in less time than it takes to acquire one. If not, you're out of luck.
--- You don't want the chunk to be too small, as the overhead of calling the DAQ READ will swamp the processing time.
Steve Bird
Culverson Software - Elegant software that is a pleasure to use.
Culverson.com
Blog for (mostly LabVIEW) programmers: Tips And Tricks

Measuring the frequency using PCI 6221 Daq card

Hi
I want to find the frequency of an external signal.
How can i do that give me some idea or example.
Regards,
Hari

If you need to capture the waveform look at the aquire waveform examples and add the
Extract Single Tone Information VI
Owning Palette: Waveform Measurements
VIs
Requires: Full Development System
Takes a signal in, finds the single tone with the highest
amplitude or searches a specified frequency range, and returns the single tone
frequency, amplitude, and phase. The input signal can be real or complex and
single-channel or multichannel. Wire data to the time signal in
input to determine the polymorphic instance to use or manually select the
instance.
(copied from the help)
Greetings from Germany
Henrik
LV since v3.1
“ground” is a convenient fantasy
'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'

How to measure the frequency of a pulse being generated by a counter

Hi,
I am using labview 8.6 to generate 5 evenly spaced pulses for every 1 revolution of my shaft. However, I would also want to know the frequency of these pulses so I can determine the shaft speed. Since I am already generating the pulses using one of my counters, can I still tap into that or task another counter to measure the pulse frequency? If so, how? I have attached my code for generating the pulses and I am using an Ni 9401 module and an NI 9172 chassis. If someone can helo me modify the code to measure and tell me the pulse frequency as well, that would be really appreciated
Attachments:
autotrain2.vi ‏19 KB

You'd probably get a more coherent answer if you didn't bounce around from thread to thread so much...
How can I generate a pulse train from shaft encoder? (5/13)
pulse train from encoder (5/15)
how to measure rpm (5/20)
How to measure rpm using shaft encoder and labview (5/23)
This thread (also 5/23)
I see you ignored my suggestion from the other thread--Kevin's solution is good too but using an encoder task offers more noise immunity (I think this is probably the cause of the problem you reported on the other thread). You can fix it with digital filtering if you want to keep using a counter output instead of an encoder task. Noise during transitions is pretty common for a quadrature encoder.
A finite counter output task uses 2 counters on the 9172 (although you said 9174 earlier at one point--this wouldn't be the case on a 9174) so you wouldn't have one left to make your frequency measurement. With the solution you have now, you can change to continuous to free up a counter if you don't care about outputing an exact number of rotation's worth of pulses (I'm not sure if you do or not--I didn't read through all of the various threads relating to this application to find out).
For your actual question in this thread... Have you tried running one of the frequency measurement examples? From the code here I can't tell what you have tried (it just looks like a mangled version of the code Kevin gave to you in your other thread).
Best Regards,
John Passiak

Measure the Frequency Of User Report Running

Hi Experts,
Currently I am working on the BW3.5 version. Currently we are having 70 reports in the system. Our client requirement to list out the reports which is not executed frequently and label that obsolete.
So I want to find out how many times a particular query has been accessed.Unfortunately, the BI statistics cube are not activated in the current server. So I cannot utilize the BI statistics cube option.
I tried working with ST03N as well with table RSDDSTAT but didn't get a clear picture. I am still amazed how people find this mode useful to gauge the frequency of use. Probably I am not interpreting the data well. Would preferably like to know who have used a particular query on a particular day.
Please through your thoughts on the issue. Thanks.
Thanks,
RR
Edited by: Ragu R on Oct 7, 2010 1:39 PM

Hello Nacho,
the output terminal of the AI Start VI will never be able to give you the actual rate when you use external clocking. It's only valid whenever you use internal clock (and the board divides down the master clock to get as close as possible to the desired rate). This is what you get at the output.
You can test this by using an example with internal clock and choose a "rare" frequency/rate such as 1621.5. The board will really sample at a similar rate, but not always at the exact speed you may choose.
If you want to calculate the frequency, you'll have to use counters and feed the encoder signal (CH A) to the counter's source (or gate depending on which method you use to compute the frequency).
Regards,
Jorge M.

Wiring a SCB-68 to measure the frequency of a TTL pulse signal

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