Low frequency pulse duration measurement

We have low frequncy pulse duration measurement to be done . We have tried with pulse measurement but it shows error for the frequency bellow 1.5 Hz. We have input signal of frequency varie from 0.5hz to 3 hz .Please suggest us is there any other method that can be used for mesureing the pulse width with low frequency mentioned above .If this can be done using tick count , please send us the example .
Regards,
Sharanu

Hello Sharanu,
I'm not sure you will be able to measure a frequency below 1.5 Hz in
the traditional way. However, I would like to ask you some more
questions about your system.
1) What hardware are you using?
2) What is the error you are receiving (please include the exact error text)?
Eric
DE For Life!

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Pulse duration measurement of a single, non-periodic pulse

New to Labview. I'm trying to measure pulse duration of a single, Power- On-Reset, pulse using waveform data. The Pulse measurements VI requires two consecutive mid ref level crossings in the same direction. I have only one positive going mid ref level crossings & one negative in the waveform data. Am I missing something easy in the Waveform Measurements palette or do I need to use counters to accomplish this task? I would like to use waveform data.
Labview 8.6 Professional.

You could use the Transition measurement.vi twice, as shown on the attachment.
Message Edité par chilly charly le 09-01-2008 07:04 PM
Chilly Charly (aka CC)
E-List Master - Kudos glutton - Press the yellow button on the left...
Attachments:
Pulse duration.vi.zip ‏16 KB
Pulse duration_BD.png ‏11 KB

"How to measure very low frequency?"

I'm using Labview 5.1 and a data acquisition card PC-LPM-16PNP. How can I measure a low frequency signal like the human pulse of 72 pulses/min or 1.2 Hz. Thanks.

Virgo,
When measuring very low frequencies, I recommend measuring the period between pulses and converting to frequency.
To measure the period, there are a few methods. For something like a heartbeat, I would probably use a peak detector to locate the peaks and measure the distance between the peaks. For other signals, it may be easier to locate zero crossings. Sometimes filtering or smoothing is required to remove noise and improve the results.
Bruce
Bruce Ammons
Ammons Engineering

Measure the Pulse duration by using NI PCI6250 counter module

Hai All,
For my application i need to measure the pulse duration from encoder signal.Encoder PPR is 1024. Maximum speed is 4500 rpm.Encoder signal is connected with NI PCI6250 card Counter input. If i configured my NI DAQ task as a Pulse duration measurement icant able to get prober pulse duration. Pulse duration some times reads as zero or near to zero and values also varies. I dont want average pulse duration. I need each pulse duration.Can any one help me to solve my problem?...
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Vijay.

Can any one Help me to solve the above problem
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Low Frequency Measurements using counter timers

I am trying to measure multiple speeds using FP-CTR-502 modules. I am having a resolution problem. Looking at the post at the following URL (http://forums.ni.com/ni/board/message?board.id=110&message.id=3601&query.id=42252#M3601) looks like exactly what I need to do, but I'm not sure how to program this. Does anyone have any example code to get me headed in the right direction?

Hi Tcrower,
Here is the example that Carl L. was describing in his forum post along with his instructions. Also, there are thorough instructions for using the program in the front panel as well as in File >> VI Properties >> Documentation.
You can measure frequency in two ways using a counter.
1) Measure the time it takes for a set number of pulses to pass or,
2) Count the number of pulses that pass in a set amount of time.
For low-frequency signals it is best to measure the time duration of a set number of pulses. If we tried to calculate the number of pulses that passed in a set amount of time, we would need a long gate period to get accurate results.
The drawback of measuring the amount of time it takes for a set number of pulses to pass is that the sample period varies with the frequency of the signal.
To accurately measure low frequencies with a CTR module, select two counter channels, one output channel, and one gate input channel. Count Input 0 counts the pulses of the signal that we are measuring. The output of the counter is set to high for x pulses and low for x pulses, which is used as the gate of Count Input 1. The source of Count Input 1 is the internal clock reference (the example can be modified to use an external clock reference). During the high phase of Count Input 0, Count Input 1 counts the pulses of the clock reference.
During the low phase, we read channel 1 and reset the counter.
For example, if the output of Count Input 0 is set to high for 4 pulses and the signal has a frequency of 20 Hz, the output of Count Input 0 is high for 200 ms. During the high phase, we will count 200 counts if we are using the 1 kHz internal clock reference. So to calculate the frequency, we have F = #pulses/duration = timebase * terminal count/counts = 1000 Hz * 4 terminal counts/200 counts = 20 Hz.
Regards,
Hal L.
Attachments:
Low_Frequency_Measurement_(CTR).zip ‏77 KB

Low frequency measurement (1 to 5 Hz) issues - Reg

Hello All,
i am facing a problem in measuring Low-Frequencies in the range of 1-5 Hz. I am using VIs used for pulse-width measurement and the card is PCI-6031E. i am generating frequency using PCI-6013 card.
Actually i am trying to develop an application for measuring the speed (RPM) of the motor which runs very slowly. so if i miss one pulse per second also, when i multiply that with 60 it will be big error.
So if any can give me a solution that will be big help to my issues.
Thanks.

Hello sathiskumar,
I'm not sure what you mean by missing a pulse but I think what is
happening is that your counter is rolling over and starting to count
from zero again. Every time the counter rolls over, it will
output a pulse. You can connect this signal to another counter
and count how many times your first counter has rolled over. That
way, if you don't receive a pulse on your first counter before your
counter rolls over, the second counter will have a record of how many
times this has happened.
I hope this helps!
Eric
DE For Life!

How to measure the pulse duration of a TTL signal using AI?

Hi there.
I would like to know how to measure the pulse duration of a TTL signal using an Analog input.
These TTL signals comes from an ultrasonic sensor's output. The pulse width of the signal is
proportional to the distance of the object the sensor detected.
I have tried using the example "Measure Pulse Width.vi" which uses a counter to measure the
pulse duration instead. It provides me with correct results.
However, i will like to know how can i do it using the AI instead.
I tried it by using the example "Acq&Graph Voltage-Int Clk.vi" which i modified by including a
timing and transistion measurement vi. Pulse duration was selected as the output. A graph indicator was also added at the output of the pulse duration to monitor the incoming TTL signals.
However, everytime the TTL signals was detected on the graph indicator, the numeric indicator always produce a "zero" reading.
I have attached my vi for your reference.
Can anybody advice me what i have done wrongly?
Regard.
Attachments:
Acq&Graph Voltage-Int Clkv1.vi ‏190 KB

Hi Paul,
Today i tried using 2 different methods to read the pulse duration of my sensor signal.
Both methods use "Acq&Graph Voltage-IntClk" vi as a guide.
Method1:
Add a filter vi(lowpass/bandpass) and a timing and transition measurements vi.
Pulse duration is selected as the output. With some numeric conversion, a centimeter
reading indicator was created. However, the reading always remains as "zero"
Method2:
Add a Mask and Limit Testing vi and a timing and transition measurements vi.
By adjusting my upper and lower limits, i manage to "filter" a single pulse out from the actual signal.
However, like the earlier case, the cm reading still remains at "zero"
I have attached both the methods resulted waveforms for your reference.
Are there anything that you can advice on?
Regard.
Attachments:
Results_Waveforms.doc ‏141 KB

Low-Frequency measurements using counter/timer

I am trying to measure speed, and am using the FP-502 counter timer module to count the pulses from my sensor. The field point example that uses a fixed width gate pulse will not work for my appliation because I need a gate pulse so big that it updates way to slow.
Does anybody have any sugestions on how to measure a low frequency signal using a counter/timer?
Thanks
Dan

Hello guys
Thanks for all your sugestions I have the final results. I got it to work but I would like to add some comments for anybody who is trying to attempt this.
Triggeing on the gate is a must for low frequency measurements. I used the divide by sugestion however using a factor of 3 only gets you about 60 Hz after that you can't sample fast enough. My application required me to measure from 0 to 150 Hz. I added a "gear shifter" routine where the terminal count was set to 3 on frequencies lower then 45 Hz and 15 for frequiencies greater than 45 Hz. Using a terminal count of 15 for all measurements made the udate rate on really low frequencies way to slow i.e. .5 seconds for 20Hz (check the math on this).
I a
lso needed to cascade the counters. At low frequencies the count went higher than 6550. Using the previos channel function of the fieldpoint module enable me to get 32 bit worth of terminal count data.
Finally I needed to add a timeout condition for 0 Hz. If there are no pulses coming from the senser the program displays the last value read. That won't be 0. So I added a time out routine that if I didn't see a pule in a certian amout of time, output 0 and reset the gate count.
Thank you for you help you relly saved me. I hope my comments made sense.
Dan

Low frequency Voltage measurement

Hi,
I am using PCI 6025E to control load bank and to measure voltage, current and frequency of a generator.
While current and frequency measurement is not a problem, voltage measurement is toublesome.
Since on test bench already there are few PCI boards and huge number of sensors, I do not want to add NI 9205 or any other additional boards and clutter the area (other people are also working there).
The problem with voltage measurement is that out of three generators two run from 400 RPM to 1600 RPM i.e.. somewhat 15-55 Hz.
I had two solutions for this:
1, Putting a step down transformer (230 Vac / 5 Vac) and then measure the voltage. But when testing at somthing like 15 Hz I have to deal with magnetic saturation with commercially available transformer. I do not want to take pain to go on built my own transformer.
2, Using high precision voltage Divider. The problem is that what should be the galvanic isolation? Isolation transformer, but then again low frequency problem.
Hence could someone suggest me since there is a bit confusion in my head.
Thanks.
Solved!
Go to Solution.

If you have a sine generator (15Hz migth be hard for the soundcard ) you can do a calibration of your transformer.
(If only the voltage amplitude is of interest , use a isolated DMM as reference and run your generators)
Or you buy a isolation voltage sense amplifier. (weidmueller, phoenix, wago, ...)
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'

Measure period and pulse duration of ttl level continuously

Hello,
i want measure the period and pulse duration continuously of two signals with an usb-6009. Every 8s there is a high pulse for 15ms. I want to measure length of the pulse and pause. Can someone help me? I can`t get a start up with this problem.
The four measurements (two channels two measurements per channel) are a dataset. This dataset should be stored in a textfile continuously. But this not a problem.
thankyou
Schwede

Hi Schwede,
Thanks for the update - Im now back in the office!
I have some bad news, your using the wrong device - you need a device with at least two counters - to acquire for two signals. But, secondly,(see specs), the counter measurements support by the USB 6009 doesn't include pulse or width measurements.
The specs for the USB 6009:
Counter
Number of counters ................................1
Resolution...............................................32 bits
Counter measurements ...........................Edge counting (falling-edge)
To acheive the functionality you require I would recommend a USB 621x:
Number of counter/timers ............... 2
Resolution ....................................... 32 bits
Counter measurements.................... Edge counting,
pulse,
semi-period,
period,
two-edge separation
Also, this link is rather useful also:
How Many Counters Does Each Type of Counter Input or Output Task Take?
http://forums.ni.com/t5/forums/replypage/board-id/170/message-id/363123
Please let me know if you have any other questions.
Kind Regards,
Kind Regards
James Hillman
Applications Engineer 2008 to 2009 National Instruments UK & Ireland
Loughborough University UK - 2006 to 2011
Remember Kudos those who help!

Low frequency measurement from Parallel Port

Hi there...
I need to calculate the "on" and "off" time and duty cycle in pulse form from a parallel port. By making the circuit in 5 or 0 V, I just simply put it in my parallel port. The problem comes when I need to measure a very very low frequency. In this case, I want to measure the duty cycle from my operated refrigerator. I need to know when the thermostat goes "on" and when it comes to "off". In my experience, the thermostat will be "on" in about 5-10 minutes and "off" in about 20-30 minutes. So, the pulse might be take for a long periode each.
I've tried with Timing and Transition Measurement wizard or even by using Pulse Measurement.vi which is included in Waveform Measurement category. It only works for 2 Hz and . If I try to set it with 1 Hz or below, it comes the message :
"Error -20308 occurred at Timing and Transition Measurements -> Untitled 1
:4" (waveform index 0 of 1)
Possible reason(s):
Analysis: The waveform did not cross the mid reference level enough times to perform this measurement. Check the signal length, reference levels, and ref level units."
Could someone help me please ?
Regards,
Ricki

here is a quick shot to give you an idea
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'
Attachments:
port logger.vi ‏22 KB

There is no sound generated by Beep.VI when using frequency and duration time. why? Thanks

Hi,
I want to generate some beeps with certain frequency and duration time.
Setting "use system alert? (T)" true, I can hear the beep; Setting "use system alert? (T)" false, certain frequency and duration time, I can't hear any sound. Why?
attachment is the VI.
LabVIEW 8.2.1, WinXP
Attachments:
BeepWithFreq&Width.vi ‏8 KB

Your PC speaker only covers certain frequencies.. Mine goes as low as 37 Hz, which I cannot be distinguished from other lower frequencies. I have to go up to 80 Hz before hearing any difference. I can hear up to 14000 Hz and barely 15000 Hz. Now, you cannot compare this with a Hi-Fidelity sound system..
As for setting False, it will not play anything. So all appears normal.. And of course, if it does not play anything, the duration setting is ignored..
R
EDIT: I just read the othe people's posts.. The frequency & duration settings work fine on my machine. It is a PC, running Win-XP.
(Finally, I can say something positive about a PC running XP.. )
Message Edited by JoeLabView on 08-04-2008 06:13 PM

Pulse width measurements

Hello,
I am trying to measure the pulse witdth of a signal that has a pulse width of 800 micro seconds. I am using the pulse width measurement VI with an indicator on the pulse duration output. The sample rate I am using to sample the signal is 10000 samples/sec. The pulse width measurement VI is returning a value of 8. I'm assuming that it is taking the pulse width of the signal and dividing it by (1/10000) which is the time between each sample. Is this correct?
Thanks

Hi Jimmy,
You said that you were using the Pulse Width Measurement VI. Are you using the Express VI (LabVIEW 7 or higher), the regular VI, or are you trying to use a counter to measure do your PWM?
Perhaps you could post a snippet of your code. It sounds like you've got the right answer, but knowing which method you are using could definitely help.
Regards,
Otis
Training and Certification
Product Support Engineer
National Instruments

Wiring hardware for pulse width measurement

I am in difficulty.even with so simple pulse width measurement.
I am using labview 7.1, DAQmx, MAX, PCI - 6220.
I cannot find help document as to how to measure PW measurement and I find no connection diagram in MAX for using pulse width measurement.
I connect to PFI 9 (Gate) to 5V via switch. What about timebase counter as source? Ok I wanted to use internal clock from PCI-6220. But I cannot get to measure PW.
I want to MAX to measure. Once it is ok, then I will build a simple vi to understand its working better.
Pls help.

Hello,
LabVIEW has examples that are located in the Example Finder under the Help menu inside of LabVIEW. The examples specific to pulse width measurement are organized and located under the Browse tab of the Example Finder under the folders <Hardware Input & Output> <DAQmx> <Counter Measurements> <Period & Pulse Width>. The Example Finder has an information section that has information on the Description, Instructions for Running, Block Diagram Steps, and I/O Connections Overview. The last section will help with the connections. The input for the example titled Meas Pulse Width – Buffered –Cont.vi will be the gate of the counter specified in the “Counter(s)” control on the front panel … such as Dev1/Ctr0. So on your device the 6220, counter 0 gate is PFI 9 as you mentioned.
I understand that you are interested in getting started with the Test Panel in MAX first. The Test Panels are limited to Pulse Train Generation for counter output and Count Edges for counter input. Please use the Count Edges if you are interested in testing the device with a counter input task. However, the Count Edges will just be counting edges of the signal specified in “Edge Source”.
I also understand you are interested in using the internal clock from the 6220. The example I previously suggested uses a DAQmx Timing.vi to configure the duration of the task … for example finite or continuous. The Timing is set to implicit, since the signal wired into the gate of the counter is in fact controlling the timing. The source of the counter task for pulse width is the internal timebase when using DAQmx Timing (Implicit).
“Create a Counter Input channel to Pulse Width. It is important to set the Maximum and Minimum Values of your unknown pulse width as accurately as possible so the best internal timebase can be chosen to minimize measurement error. The default values specify a range that can be measured by the counter using the 20MhzTimebase.” - from the description of the Block Diagram notes on the example. I also link helpful KnowledgeBase below.
AE KB 2X6CMDDS: What Does Implicit Mean in the DAQmx Timing VI?
http://digital.ni.com/public.nsf/allkb/2B6477E3A9B7C07386256D1F0066FBDD?OpenDocument
Samantha
National Instruments
Applications Engineer

[cRIO] Pulse width measurement

Hello, I am working with cRIO-9074 with digial I/O module 9403. I was wondering where I could find examples or a list of function relevant to measuring the pulse width of a digital input (with resolution of about 10 usec).
- Thank you

I've implemented something similar using the example given above, however due to hardware limitations I'm unable to use the SCTL, this isn't too much of a problem as I simply use a while loop with a 4-tick loop timer, however when driven with a constant digital signal I get the pulse width measurements 'bouncing' between two values, it's not out by 1 or 2 ticks, it jumps around 1000 ticks, it also 'sticks' when I slowly ramp up the frequency, suddenly jumping to other values
any suggestions? I'm currently using the FPGA open function and accessing the FPGA in (I believe) scan mode, could this be the culprit? I've not undertaken the RT training course yet so I'd be poking in the dark a little
this is for a proof of concept demo in a few weeks time!

Low frequency pulse duration measurement

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