Pulse counting with voltage input

Im using compact field points analog I/O (AI-112) to measure the frequnecy of an anamometer.
Basically the sensor is just a switch that open/closes at a frequency which gives 1 pulse per second (1Hz = 1.25MPH).
I know the pulse counter I/O would be best for this, but I assume labview with realtime should be able
to handle this measurment. Im having trouble finding the right VI's to do the job. Any suggestions for
possible ways to count the pulses/ measure the frequncy would be appreciated.

Hello cfpboy,
I have a question about your signal first. How long does your signal remain changed when a pulse occurs? Does the signal stay "high" for 1 full second and then go "low" or does it pulse "high" once a second and then immediately return to "low". If it stays "high", then you could simply poll the input in a LabVIEW Loop set to occur once a second. You could then store the value in a shift register, and compare the current value to the previous value. If they are different, then the state has changed, and you could then increment your software counter. As you are using an analog input module, you will want to convert your voltage level to a "digital state" by checking if it is above or below a specified level.
One drawback of this approach is long term phase shifting as well as the possibility of reading while in a transition state. This could potentially throw off your measurements. As you are using LabVIEW Real Time, you can slightly mitigate some of these problems by utilizing a LabVIEW Timed Loop instead of a normal Loop.
Thanks,
Jonathan C
Staff Application Engineering Specialist | CTD | CLA
National Instruments

Similar Messages

How to trigger a counter with AI input

Hi,I have a question on how to trigger a counter with AI input.We are using a DAQ board with two counters(counter 0 & 1),and we have an external synchronization signal input at a frequency of 50 Hz or so.The counter is set to event counting mode.Now we want to trigger one of the counters so that the counter starts a new counting process each time it detects a rising/falling edge from the sync signal.Can anybody kindly show me how to achieve this?Thanks a lot.
Regards
Verdi

Verdi,
I think that the behavior you are looking for can be achieved by configuring the counter for buffered period measurement. The counter starts counting from some initial value with each rising or falling edge on the gate. You could also use buffered event counting, but the count value will not reset with each edge on the gate. I don't know what you're using to program the board, but you could start by looking at the counter examples that are installed with NI-DAQ.
Hope this helps,
Erin

Pulse count with a 9401 modules (cDAQ-9172 system)

I'm trying to do a pulse counting by a 9401 module in a cDAQ-9172 system. I have three 9401 modules . One of them is working as a trigger (start-stop count) and the other two (in slot 5 and 6) are for counting pulses from the 2 meters. It looks like a simple task but my problem is that I am counting always 3 to up to15 pulses less than my reference counter. everything points out to a task in my program is causing a delay. The question is where or what is causing such a wrong counting
Attachments:
COOMET Comparison DN80 short.vi ‏737 KB

First for triggering with cdaq you must use the 9405 or 9406 (for analog triggering or 9401 for digital triggering) module in slot 5 and 6 - look in following link. Signals are routed with the chassis PFI Lines and only available at Slot 5 and 6.
http://digital.ni.com/public.nsf/allkb/851828B06A20E01B862571DA0005591A?OpenDocument
http://digital.ni.com/public.nsf/websearch/EFD808DC883F095186257170005A634D?OpenDocument
Then the other moduls in other slots can be configured with these pins for triggering. When you wants triggering on both edges you can look in following link:
http://forums.ni.com/ni/board/message?board.id=170&message.id=248456&requireLogin=False
Best Regards

Read no. of pulse count with fixed time interval

Hi,
I am try to read no of pulse count ( Pulse period = 500ms, On time = 100msec and Off time = 400msec). Between pulses there is a fixed time interval of 2seconds. I am using NI USB DAQ 6341. Can anybody help me regarding this?

Thanks for replying. I have gone through that example, the given example are only increment count when pulese are detected.
In my case, i want to count the no. of pulses between the time interval of 2sec. e.g. Suppose my device generate 5 no. of pulses and after every 5 pulses their is 2sec time interval, here i need to read only 5 pulses not the continuous count. And no. of pulses are generated by device can be vary but the time interval between those pulses are fixed. Could you give me suggession regarding this?

How to use counter output pulses to trigger analog input?

Hello all,
I hope the kind people using this forum can help me, a lowly beginner LV programmer! I have been attempting to create a VI that produces a user defined number of TTL pulses, separated by every n seconds. Each TTL would be outputted to a stimulator, which in turn generates its own TTL. Using the stimulator-generated TTL, I would like to trigger finite analog data acquisition (e.g. for every TTL, trigger the collection of a data sweep that contains 4000 samples (collected at 4000 Hz), with 1000 samples collected pre-trigger. I would like to also be able to see each data sweep as it is triggered on a chart. As I understand things (lots of online/book/forum reading), I should be using the counter output to generate my TTL pulses, and syncing each counter produced TTL with analog input, as well as using a reference trigger. Also, the AI part should be started first, so that I don' t miss any counter outputs. If it matters, I also need to use one of the AI channels to acquire the TTL, so I can see my stimulator-induced responses to the stimulator in time.
I am able to generate the TTL pulses from the counter output, but I am having a problem with the AI part. I am unsure how to sync the counter output with AI. Also, since I need to acquire pre-trigger samples, I would be needing to acquire samples continuously, but when I set 'continuous samples' on daqmx timing, the VI doesn't work (hence why's its set to 'finite samples').
I hope someone out there can help, as I have been at this for what seems ages, with limited success. I am using a USB-6259 and LabView v8.2. Thanks!
Attachments:
RC001 v_1.vi ‏49 KB

Hello,
Due to the fact that analog tasks themselves are not retriggerable, a
pulse train produced by a counter is always used as the sample clock
for the analog input task in order to recreate a retriggerable effect
for analog input. This can be done by creating a finite pulse train set
to retriggerable using the DAQmx Trigger Property Node, or the pulse
train could be continuous and just be gated by another signal. Neither
of these methods can be properly applied in hardware to create a
retriggerable reference trigger. You can however implement something
similar in software by just stopping and restarting your reference
triggered analog input task within a loop. There will be some delay
between when the task is stopped and restarted, as these events require
software intervention, but if there is enough time between when each
trigger signal is generated, there should not be any noticeable delay
or missed samples.
I have attached an example of this!
Mark B
===If this fixes your problem, mark as solution!===
Attachments:
RC001 v_1mod.vi ‏25 KB

Need help with voltage counter

I have a system that passes current through a resistor when ever a button is pushed. The voltage across the resistor (about 100mV) is read by a cFP-AI-102 Analog Input voltage module. I'm trying to figure out a way to count the number of times this happens. In other words, I need to count how many times the button is pushed.
I've tried using a While Loop, but since it counts with every iteration I end up with way too many counts for each button push. Is there a way I only count once?
Thanks,
Eric

Hi!
If I understand, you want to measure how many times button is pushed, i.e. how many transition 0 -> 100 mV, right? I'd do that with a shift register and a while loop.... just save the past state of the analog in, if the comparison between the past state and curtrent state is > 50 mV, you have a push.... (actually it depends on how terminals are connected...)
Post your code, perhaps I can understand better the starting point.
remember: this way you're going to measure too many transitions, because usually, when a button is pressed or released you have some oscillating voltage (I don't know if you ever tried to handle a switch button with a microcontroller, there you can see this). But maybe, AI module sample at "low frequencies" respect to this phenomenon.
graziano

Measuring frequency with counter or analog input?

I have some frequencies which I need to measure. Some signals are digital and some are analog.
I have a PXI-6040E DAQ which has both counters and analog inputs.
I heard that you can measure higher frequencies with the counters than with analog inputs.
What is the range of frequencies an analog input can determine versus a digital counter?
Where is the cutoff that you must absolutely use a digital counter to determine the frequency?
Is the cutoff different for different DAQ cards? Or is generally the same.

Have you looked at the specs for the device? The max sample rate and the max counter input will be listed there. The max frequency for an analog input is based on nyquist sampling theory. Are you at all familiar with? It states your sampling frequency has to be at least twice the frequency you are measuring.
Since each device might have a different max sample rate, your last question is answered.

Measure pulse width with 4 counter simultaneously

Hello,
I am using NI PCI-6601 measure the pulse width with 4 counter simultaneously, due to only a DMA channel on this card so I selected interrupt data transfer mode to read data from PCI bus for 4 counters, but it working only for few seconds then a error message prompted:
Error -200141 occurred at DAQmx Read (Counter 1D DBL 1Chan NSamp).vi
Measurements: Data was overwritten before it could be read by the system.......(See attached picture: TestUI and Error MSG.bmp)
I know the problem caused due to system is unable to read back data from PCI6601's memory as fast as they card countered. My quesition is:
1. The timebase is 20Mhz(Sample rate), how to change the sample rate slower (like 100Khz) ?
2. Any good solutions can meet my requrement?
Attached is my source code, Test.vi is the main VI.
Thanks for your help.
Steven
Attachments:
Test.zip ‏557 KB

What's more, you could include four channels in one task, so you don't need to build four task!
Attachments:
4 counters in one task.png ‏719 KB

Access Counter with ANSI C

Hi Folks,
I am trying to access counter using ANSI C (python wrapper actually). Now I am able to read number of counts with sets of commands:
DAQmxCreateTask("", &task);
DAQmxCreateCICountEdges(task, "Dev1/ctr0", "", DAQmx_Val_Rising, 0, DAQmx_Val_CountUp);
DAQmxSetCICountEdgesTerm(task, "Dev/ctr0", "Dev1/PFI11");
DAQmxStartTask(task);
DAQmxReadCounterScalarU32(task, 10, &data, NULL)
This example cumulates all counts since task was started, so I can get all counts from begining of task or from previous call (using internal software buffer).
But what I want to do is count non-periodical series of 'events' represented with TTL/NIM pulses. So I want to set up measurement (integration) time for one single shot (let say 1000 ms) and then in loop read number of counts (=events) in this window (i.e. frequency in Hz). I probably need to trigger the 'counting function' in some way, probably something like DAQmxCfgSampClkTiming...
Can you please show me short, simple piece of code, how to do this?
Thanks a lot.
Radek

Hi Stefo,
Thanks for trying to help me.
I tried to use DAQmxCreateCIPeriodChan and it works fine, but it just not what I was looking for. In our application, we have to read counts from multiple counters (usually 3) in the same time window and the signal is NOT periodic (if it matters). Also it blocks one more counter for each one in the task, so if I need 3 Inputs, the 6601 cards with just 4 counters is not enough. Maybe if it is be possible to share that "gate" counter, I will need just 4 and also it will be maybe possible to count corresponding events in the same time window.
But I found a solution. This "code" (seems to) do exactly what I need:
(this is just important part of Python code, but I guess it is very easy to read, so...)
def cOut0(self, chan, up = 1, down = 0.1, samps = 1e3, num = -1):
   err1 = self.device.DAQmxCreateCOPulseChanTime(self.task, char(chan), char(""), int32(DAQmx_Val_Seconds), int32(DAQmx_Val_Low), float64(0), float64(down), float64(up))
   if num > 0:
       err2 = self.device.DAQmxCfgImplicitTiming(self.task, int32(DAQmx_Val_FiniteSamps), uInt64(num))
   else:
       err2 = self.device.DAQmxCfgImplicitTiming(self.task, int32(DAQmx_Val_ContSamps), uInt64(samps))
def cOut1(self, chan, freq = 1e3, duty = 0.1, samps = 1e3, num = -1):
   err1 = self.device.DAQmxCreateCOPulseChanFreq(self.task, char(chan), char(""), int32(DAQmx_Val_Hz), int32(DAQmx_Val_Low), float64(0), float64(freq), float64(duty))
   if num > 0:
       err2 = self.device.DAQmxCfgImplicitTiming(self.task, int32(DAQmx_Val_FiniteSamps), uInt64(num))
   else:
       err2 = self.device.DAQmxCfgImplicitTiming(self.task, int32(DAQmx_Val_ContSamps), uInt64(samps))
def cIn5(self, chan, trig, rate = 1e9, samps = 1e3):
   err1 = self.device.DAQmxCreateCICountEdgesChan(self.task, char(chan), char(""), int32(DAQmx_Val_Rising), uInt32(0), int32(DAQmx_Val_CountUp))
   err2 = self.device.DAQmxSetPauseTrigType(self.task, int32(DAQmx_Val_DigLvl))
   err3 = self.device.DAQmxSetDigLvlPauseTrigSrc(self.task, char(trig))
   err4 = self.device.DAQmxSetDigLvlPauseTrigWhen(self.task, int32(DAQmx_Val_Low))
def wait(self, tOut = -1):
    tOut = float(tOut)
    err = self.device.DAQmxWaitUntilTaskDone(self.task, float64(tOut))
def gCts(self, tout = 1.0, buff = False):
    tout = float(tout)
    ret = numpy.zeros(1, dtype=numpy.uint32)
    err = self.device.DAQmxReadCounterScalarU32(self.task, float64(tout), ret.ctypes.data, bool32(0))
    return ret[0]
And here is terminal output (important part):
>>> devOS.createTask(taskName = "OS")
>>> devOS.cOut1(chan = "/Dev1/ctr0", freq = 1e5)
>>> devOS.startTask()
>>>
>>> devOG = pydaq.nidaq()
>>> devOG.createTask(taskName = "OG")
>>> devOG.cOut0(chan = "/Dev1/ctr1", up = 1, down = 0.1, num = 1)
>>>
>>> devIA = pydaq.nidaq()
>>> devIA.createTask(taskName = "IA")
>>> devIA.cIn5(chan = "/Dev1/ctr2", trig = "/Dev1/PFI32")
>>>
>>> devIB = pydaq.nidaq()
>>> devIB.createTask(taskName = "IB")
>>> devIB.cIn5(chan = "/Dev1/ctr3", trig = "/Dev1/PFI32")
>>>
>>> devIC = pydaq.nidaq()
>>> devIC.createTask(taskName = "IC")
>>> devIC.cIn5(chan = "/Dev1/ctr4", trig = "/Dev1/PFI32")
>>>
>>> import time
>>> def fce(n):
   T1 = time.time()
   r = []
   for i in xrange(n):
       t1 = time.time()
       devIA.startTask(); devIB.startTask(); devIC.startTask();
       devOG.startTask()
       devOG.wait()
       devOG.stopTask()
       c = [devIA.gCts(), devIB.gCts(), devIC.gCts()]
       devIA.stopTask(); devIB.stopTask(); devIC.stopTask();
       t = time.time() - t1
       r.append(c)
       print "%d: %d %d %d (%d s)" % (i + 1, c[0], c[1], c[2], t)
   T = (time.time() - T1) / float(n)
   print "Total Average Time: %d s" % (T)
   return r
>>> a = fce(10)
1: 100000 100000 100000 (1 s)
2: 100000 100000 100000 (1 s)
3: 100000 100000 100000 (1 s)
4: 100000 100000 100000 (1 s)
5: 100000 100000 100000 (1 s)
6: 100000 100000 100000 (1 s)
7: 100000 100000 100000 (1 s)
8: 100000 100000 100000 (1 s)
9: 100000 100000 100000 (1 s)
10: 100000 100000 100000 (1 s)
Total Average Time: 1 s
So conclusion:
1) I know I can put all Input Tasks together to only one task, but when I try to read the counts with DAQmxReadCounterU32 function, I get error -200523. So what Read function is for task with multiple counters?
2) All those Trigger functions I used I found somewhere on the internet. Where is documentation? I can not find it in NI-DAQmx C Reference Help. Also in the header file, there are a lot of functions prototypes of which are not mentioned in the documentation.
3) When I change the lowTime parameter in function DAQmxCreateCOPulseChanTime, the time of measurement does not change, so it seems that this part of pulse is not part of 'task' and/or the DAQmxWaitUntilTaskDone function waits just when the trigger pulse is high. This decreases our death time, because it seems not be possible to set duty cycle to 100 %, but still it is little confusing for me.
Diky moc
Radek
P.S.: Ten "editor" na vlkadani dotazu je udesnej... :-)

How can I generate synchronized pulse trains with 6602?

Hi,
I would like to generate multiple pulse trains with different frequencies with the 6602 TIO card. Currently I am able to generate pulse trains with different frequencies. But is there any way to synchronize all the pulse trains? For example, I'd like to have all pulse trains with their first low-to-high at the same moment.
Thanks!
Dan

Dan,
Absolutely, the NI-TIO chip on the PCI-6602 supports a start trigger. If you configure all of the counters that are generating a pulse train to use this start trigger, they will be synchronized. The example Generate Pulse Train - Start Trig (NI-TIO).vi demonstrates this process for one counter. In LabVIEW 7, this example can be found in the following location:
Examples >> Hardware Input and Output >> Traditional DAQ >> Counters >> NI-TIO
You will need to add code for the other counters, but this example should give you the general idea. Furthermore, this example demonstrates how you can use one of the digital lines to generate the start trigger.
Good luck with your application.
Spencer S.

Pulse count fieldpoint

Hi! I need to write a VI with a pulse counter employing fieldpoint. Here's my problem: I have an energy meter with pulse output. I can set pulse frequency, pulse lenght and number of pulses for kWh. I have to read the signal from that instrument but I don't really understand how. I mean, I do not have to measure the frequency of the pulses 'cos I already set it, I'd rather read the signal from the meter in a specified period of time and count the number of pulses in that time. How can I do that?
I can both connect the meter to a cFP AI-110 or cFP CTR500. There are mainly two things I don't understand:
-how can I count the pulses in, let's say, 30 s?
-how can I define the reset condition?
Thanks!
Valeria

Valeria,
CTR500 is the best solution. Have you verified that the pulses from the energy meter are compatible with CTR500 inputs? If so, the two counter method will give you the best results. The first counter creates a window of known width which is then used to enable another counter that counts the pulses. There is an example .vi that ships with LV called "Frequency Measurement.vi" that demonstrates the 2 counter method. Instead of calculating frequency you will need to calculate energy.

Analogue Signal Pulse Count

I am using CDAQ with a NI9229 4 Channel analgoue input card.
I have a sensor that outputs an analogue 5v square wave signal. The pulses are triggered from eithe a north or south pole of a magnet. I have an aluminium wheel with 30 magnets, all magnets are in opposition to each other. when the wheel is rotated the output is a square wave.
My magnet wheel is rotating at 182° per second. Over 360 degrees there is 30 magnets. Thus making the sensor switch 30 times.
The time to revolve the wheel one revolution is 1.978 seconds.
I have set up the NI9229 to the following
- sampling rate is set to 25kS/s So to record the data for one revolution it works out as 49450 bits.
- Have set the trigger levels for recording a hi or lo pulse to 2.7 and 0.7 volts.
50000 samples would be two seconds worth of data which would be more than 360° of rotation of the magnet wheel.
The problem I am having is that my pulse count changes between 30 and 31. But as I am only recording 1 revolution of data there is physically only 30 switches. Do you know why I am getting a change of 30 and 31.
Attachments:
pulse count 2.PNG ‏20 KB
pulse count.PNG ‏19 KB
front panel.PNG ‏83 KB

I think I know what the problem is now but don’t know a way around it.
I have attached two screen shots. One shows that the rising edges are counted as 15 and the falling as 16 the other shows both are 15. This is due to where it starts to take data I believe.
For detecting the rising or falling edge I compare the data to 4.0 or 0.5v If its below 0.5 then sends a hi signal and counts 1, if its above 4.0 it sends a hi signal and counts1.
But depending on when it starts taking data the signal is already a falling or rising edge. Comparing one bit of data on a rising edge to see if its below 0.5 will send a hi as it hasn’t started to rise as shown in the first picture.
Is there a better way to count pulses
Attachments:
1.PNG ‏61 KB
2.PNG ‏64 KB

Measure pulse frequency with 4.7 volt peak amplitude

used two shipped Measurment Studio Vb.Net 2005 Examples:
1-Example 1 : CountDigEvents "MEASURES PULSE COUNTS" and Example 2: MeasDigFrequency_LowFreq1Ctr "MEASURES PULSE FREQUENCY"
2-Example 1 works fine measuring pulse counts , however Example 2 did not recognize pulse frequency , the pulse amplitude voltage is 4.7 volt peak
3-during testing used counter ch0 channle by connecting Sorce0 and Dgnd pins to signal source.
4-using Nidaqmx 9 and MIO-16xe-10 daq
5-pulse frequency around 10 khz
QUESTION:
-please advice what to do to make frequency measures ?
Thanks

Hi MyKat,
Note that the connections are different for edge counting and low frequency frequency measurements with one counter. For the latter, you'll need to connect the signal to PFI 9 rather than PFI8 as you did for edge counting.
http://zone.ni.com/reference/en-XX/help/370466W-01/mxdevconsid/eseriessigcounters/
Regards,
-Jim B
Applications Engineer, National Instruments
CLD, CTD

CDAQ module for high speed pulse counting

I need to know a USB module which can be used for pulse counting. The pulses are generated from an encoder attached with an stepper motor. It generates 15 pulses per step.Pulse amplitude is 0 to 5V. I am using a compact DAQ system (ni 9178).

The counters are on the cDAQ chassis backplane (there are 4 of them on the 9178). So, in order to use an external signal with the counters you would need a way to route the signal to the backplane. Your available options are:
1. Any digital I/O module with 8 or less lines on it (some modules are input-only or output-only--input modules can be used for counter input tasks only, output modules can be used for counter output tasks only). Modules with over 8 lines transfer the data serially to the chassis backplane and so do not support routing signals through to the counters.
2. The 2 PFI lines on the 9178 (I should have mentioned this earlier, this might be a good option for you to route your encoder pulses without having to purchase an additional module if you only need 2 inputs--that is, no Z index signal). The bandwidth on the chassis PFI lines is lower than that of the 9401 and 9402, I believe the chassis PFI lines should take signals up to ~1 MHz.
3. An analog module with triggering capabilities (at this time only the 9205 and 9206) can route a digital signal (the 9205 and 9206 have a PFI line) or an "analog comparison event" (see my post here) to the counter terminals.
In case 1 above, you configure this by selecting the counter using the module's name (e.g. "cDAQ1Mod2/ctr0"). Default input terminals will be used (check the device pinouts for your module in Measurement and Automation Explorer) or you can select which terminals to use for your inputs using a DAQmx channel property node.
In cases 2 and 3, you would need to select the counter as the internal backplane counter (e.g. "cDAQ1/_ctr0"). You will need to select which terminal your signal is coming from (since the internal backplane counter does not have default terminals. This same method can be used to count internal signals (e.g. sample clocks, counter outputs, etc.) without having to use any of the 3 routing options mentioned above.
Best Regards,
John Passiak

Measuring PWM duty cycle with Analog Input

Hello folks,
I have a NI 9205 module and was wondering if there was a way to measure the duty cycle of a PWM signal that I am generating with a separate microcontroller? I have found a lot of examples with Digital inputs but not analog.. Is this possible?
Thank you,
Bob

Hi Robert,
I'm not sure what that error is, try searching for it.
If you want to measure a PWM signal you would usually use a counter input. A counter is a dedicated piece of hardware that is used to measure digital signals. Since the NI 9205 is an analogue device and it doesn't have any counters onboard, you will not be able to select counter input.
I would recommend you get the right tools for the job and buy a digital acquisition device with an onboard counter. It will make reading PWM much easier for you. The NI 6008 has a counter onboard and is only £99. It will also offload processing from software to hardware since you don't have to calculate duty cycle.
If you still want to use analogue post back and we can look into why its not working for you. Tips to start you off: Voltage is the correct setting and Look in the manual and make sure you have connected it like you have configured it (differential, RSE, NRSE page 14)
Lewis Gear CLD
Check out my LabVIEW UAV

Pulse counting with voltage input

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