Digital frequency measurement speed in labview

I am using a USB 6210 device to measure low frequencies of 50 to 1000 Hz. I need to log the frequency every 50ms. I do this in a while loop in labview using a 1 counter low frequency measurement in labview and saving the data using express VI.Each iteration of the loop takes atleast 60 to 100 ms just to read the frequency inside the loop. How do i increase the speed of measurement in Labview ?
Solved!
Go to Solution.

PraveenB,
Here is a table of the Counter terminals and related PFI lines. This can be found in the NI DAQmx Help. (http://digital.ni.com/public.nsf/allkb/CCDFC93878BD8781862570FC00559980?OpenDocument)
Default NI-DAQmx Counter Terminals
Counter/Timer Signal
Default Pin Number
Signal Name
CTR 0 SRC
1
PFI 0
CTR 0 GATE
2
PFI 1
CTR 0 AUX
1
PFI 0
CTR 0 OUT
6
PFI 4
CTR 0 A
1
PFI 0
CTR 0 Z
3
PFI 2
CTR 0 B
2
PFI 1
CTR 1 SRC
4
PFI 3
CTR 1 GATE
3
PFI 2
CTR 1 AUX
4
PFI 3
CTR 1 OUT
7
PFI 5
CTR 1 A
4
PFI 3
CTR 1 Z
2
PFI 1
CTR 1 B
3
PFI 2
FREQ OUT
8
PFI 6
When you choose counter 1 in the Create channel VI it automatically reserves the gate which is PFI2. If you use Counter 0 then PFI 2 will work fine. Likewise if you use Counter 1 you can use anything but PFI 2.
Message Edited by Jason_D on 10-24-2008 11:43 AM
Sincerely,
Jason Daming
Applications Engineer
National Instruments
http://www.ni.com/support

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PCI-6280 (M-series) digital frequency measurement

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Get with your fellow hardware users :: [ NI's VirtualBench User Group ]
Get with your fellow OS users :: [ NI's Linux User Group ] [ NI's OS X User Group ]
Get with your fellow developers :: [ NI's DAQmx Base User Group ] [ NI's DDK User Group ]
Senior Software Engineer :: Multifunction Instruments Applications Group
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Applications Engineer :: High Speed Product Group (until Sep 2008)
Attachments:
gpctex5.cpp.gz ‏4 KB

You should connect the signal (whose frequency needs to be measured) to Ctr-1, and there gonna be an internal connection between the output of the first counter and the gate of the second counter (as described here).
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Digital Frequency Measurement for cRIO

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Hello,
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Dracyon,
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Measuring digital frequency

Dear,
I am working on a test stand that will be used for fatigue tests for a suspension, chassis etc. De vehicle components will be charged by hydraulic cylinders. These hydraulic cylinders are controlled by an AO and DO module (NI9263 & NI9401). Feedback is given by load cells. These load cells are connected with AI module (NI9201). When a cylinder reaches a certain force (certain amplitude load cell NI9201) the cylinders stops pulling and will make an outward movement. This signal is 0 when outgoing and 1 when certain force is reached. A green led starts to burn (signal is 1) when the force is reached. Now I want to count the amount of times that the signal is 1 so that I can make a security system that will limit the amount of ingoing and outgoing movements of the cylinders. Can you help me?
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Go to Solution.
Attachments:
test stand juli 2010 (dynamisch).vi ‏4087 KB

Dear,
I am still unable to count the digital frequency. The signal from the load cells (0 or 1) can not be added to the digital frequency block diagram that was sented by Bas van Dijke. Which wires do I have to connect? I also have tried to manipulate the signal from the load cell, but this didn't work either. Can you look at the attached VI?
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test stand juli 2010 (dynamisch).vi ‏4089 KB

How to use a photogate for frequency measurement using a NI USB-6211

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Configuring a counter input task will be a little different depending on the type of DAQ card that you are using to read the digital pulses. You just need to wire the voltage from the photogate to one of the counter pins on the card. Then follow one of the many examples for measuring the frequency of pulses. If your card allows it, I would suggest choosing the Counter Input >> Frequency measurement from the DAQmx Create Channel VI. If you have questions about how to do this with your specific DAQ device, please provide more information
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Frequency measurement keep reading value when stop rotation

Hi,
i am doing the program in the attachment
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2. when i stop the motor the program still read values and not going to zero |
Note my driver send the feed back as a signal"Pulses" with difference frequencies depend on my speed . i send digital values to the driver pins 111 to make it rotrate forward and 100 to make it stop rotating + analog value to change the speed
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speed calibration.vi ‏161 KB

As I understand this you are trying to read the frequency of an quad encoder and the reading is fine as long as the quad encoder is at a steady speed but when it is changing speed you are getting random frequency values. I looked at your code and nothing seemed to jump out at me as being wrong with it but I do have a couple suggestions to see if we can narrow down where the issue may lie.
If you could just try running on of the examples found in the example finder (Help»Find Examples...) specifically example Hardware Input and Output»DAQmx»Counter Measurements»Digital Frequency»Meas Dig Frequency-Buffered-Cont-High Freq 2 Ctr.vi. And just wire the output to a waveform chart or a dial and see if you are seeing the same results there. If that is giving expected results i would just implement your formula node and averaging into that example and save it as your code. I have attached an image of such an implementation.
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Attachments:
example code.png ‏44 KB

NI9411 wrong frequency measurement of flow sensors / 24 impulse signals

Hello Ni Forum,
I already searched for similar problems, but haven't found anything helpful. So I'm posting our problem here. I'm apologizing in advance for bad english, it's not my mother tongue
We're encountering some strange behaviour of our NI9411 Module. We're using it in a Compact Rio with some other modules (2x Analog In).
Our goal is to measure the frequency of three flow sensors (impulse high = 24V, 0-22kHz) among with a torque sensor (TTL 5V, 30-60kHz) and a speed sensor (TTL 5V, 0-51,2kHz).
They are wired as follows:
DI0a = torque sensor
DI1a = flow sensor 1
DI2a = speed sensor channel A
DI3a = speed sensor channel B
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DI5a = flow sensor 3
Correspondig ports b are left unconnected, as it is said in the data sheet. All ground ports of sensors are connected to COM port of 9411. The module was connected to a 24V power supply.
Now the torque and speed sensor measurement works fine. But measuring the signals of the flow sensors seems to be difficult.
If an external frequency generator (impulse high about 9V, f=1,000kHz) is connected to port DI1a instead of the sensor signal, LabView shows exactly 1,000kHz. DI5a showed an avarage of 10 Hz, with a range from 10 to 60 Hz. DI4a equaled constant zero. The flickering up to 60Hz of DI5a was gone after disconnecting the 24V supply of the module. This changed nothing on the phenomenon described below.
If the signal high impulse voltage is raised, the measured signal frequency goes up to 1300 Hz @ 24V signal high impulse voltage. The signal additionally raises, if an oscilloscope is connected to DI1a, to 2180 Hz (range 2110 to 2240Hz). However, there is no change of frequency if the osci is connected to DI5a. With the 24V supply connected, DI5a showed a frequency up to 600Hz @ 24V signal high impulse voltage on DI1a, also rising when connecting the osci on DI1a. As mentioned, there was no frequency measured on DI5a after disconnecting the 24V power supply.
The signals of the generator showed some peaks on each edge (rising and falling) with values for example of 11V above high impuls voltage of 9V (20V together). That may causes that wrong frequency measurement.
The signals of the flow sensors do not have such peaks, the LabView-frequency nevertheless does not match the real frequency, as shown below (all values in Hz):
LabView
ideal values
Flow Sensor 1
Flow Sensor 2
Flow Sensor 1
Flow Sensor 2
4600
12200
740,6
6760,0
6400
13500
1481,3
7500,7
9700
16400
2962,6
8982,0
12900
19500
4443,8
10463,2
We're kind of helpless now. How can we get the signals of the flow sensors measured the right way? Are we doing something essentially wrong? Thanks in advance for offered help. I hope, I've given any necessary information. Any missing details will of course be delivered.
Puls-Measure-VI is attached beneath.
Regards,
Johannes Rost
Attachments:
vi.png ‏20 KB

Dear Lynn,
thank you for your reply. The impedance was an issue that our local technical distributor already suggested to check. According to the datasheet of the flow sensor (see attachement) it can drive a current of 25mA. The signal generator we used is a test generator that can be used instead of the flow sensors to check the any evaluation unit the sensor is connected with. So it should generate signals that are equal to those the sensor would have generated. And even with this the frequencies measured with LabVIEW are not as expected.
We are in contact with the sensor manufacturer to exclude mistakes in connection on the sensor side. But the behavior with the signal generator makes us think that is has to do something with the characteristics of the NI9411 that we don't know yet.
Attachments:
block diagram signal amplifier and signal description.png ‏151 KB
technical data.png ‏124 KB

Why does my AI acquisition slow down to my frequency measurement rate?

I'm using Labview/Daqmx to program my SCXI 1520 and TC modules while at the same time using the multifunction capabilities of the E-card controlling the SCXI. This has been fairly easy until I wanted to use the frequency and counter measurements (outputs/DIO works great). I'm using a waveform with buffered acquisition for the read on the AI channels and obviously there is no waveform for the frequency measurement so I'm just combining the signals using the dynamic data. This works great when my input frequency is higher than my acquisition frequency. When my input frequency is lower than my acquisition frequency the acquisition slows down to that frequency and the AI read falls behind (buffer fills while waiting for another frequency measurement). I'm assuming the frequency read is not keeping up with AI read. I understand that as the frequency is reduced it takes more time to calculate the frequency. So how do I "read" the frequency measurement at the same rate as the AI data? I'm fine with using the last frequency measurement until a new frequency measurement is available but I can't even seem to be able to do that.
An example of the problem is measurement of vehicle pedal force (AI channel) with pulse input for vehicle speed. Assuming 100 Hz acquisition and the vehicle stopped or going slow (very slow pulse train) I should be able to acquire data at 100 Hz even if I just use the last data point for the frequency channel until another point is available.
Please help, thanks.

Basically, the very fact that you're *doing* a frequency read suggests that you don't know the expected freq ahead of time, and probably suggests that it can vary. The waveform datatype assumes a constant interval between samples which wouldn't generally be true for frequency measurement, and that's why you can't use it. Since the actual timestamps of the frequency measurements are NOT the same as those in the analog waveform, it's likely a mistake to pretend they are.
My method is to create my own array of "timestamps" for the frequency data. Create a For loop with a shift register initialized to 0 from outside the loop. Let your freq array auto-index the loop. On each element, perform (1/x). Add result to the left-hand shift register value and write it to both the right-hand shift register and to an auto-indexing output. When the loop completes, the output array will hold timestamps that correlate to your freq measurements. From there you can choose whether to display on an X-Y Graph, or whether to perform some interpolations to calculate freqs at the analog sample times or vice versa.
-Kevin P.

How to increase measuring speed of Agilent 34401A

The process of my program (written in Labview) is:
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2) Multimeter Agilent 34401A measures the current value of this channel, and send this value back to the computer for storage. After this, the program goes back to step 1) for next channel, and this program executes like this.
The functions mentioed above are all realized, and the program works well, but the problem is the speed is slow. It takes a little more than 1 second to measure one channel, totally I have 2048 channels (32 groups and 64 channels in each group, I used two layers of "for" cycles), and it takes about 32 minutes to finish measure all these 2048 channels, too slow, I'd like to reduce them to 10 minutes.
I tried to reduce the resolution to 4.5, turn off the autozero function of multimeter, but nothing happens, no change of the speed. Now every time the multimeter measures a channel, it makes a "click" sound, does it mean that every trigger the multimeter only takes one measurement? Is there anyway I can increase the measuring speed? Can I send the multimeter 64 control condes a time, and then let the multimeter takes 64 measurments in one trigger? Is it right? If so, how can I realized it? If I'm wrong about it, can you give me some solutions?
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I don't have the manuals with me, but I do have a couple of these in my lab. There is an internal buffer where you can store (I think) 512 readings. You can use a digital output to trigger the DMM, and only transfer after every 512 readings (4 times) or perhaps one read per group as you mentioned. I suggest one read per trigger (you can do many more) since it is easier to synchronize with your channel changes. I believe the commands are INIT and FETCH?, check your manual. The two times I know the instrument "clicks" are changing functions and certain range changes. I suspect in your attempts to speed things up you are sending some config. commands each time. Configure it once initially and make certain you are only sending measurement related commands during the scan, any config. changes (even if you resend the current value) will likely cost you time.

Frequency Measurement Algorithm

I'm writing a VI where I need to measure the
frequency of a pulse. This frequency is proportional to a physical measurement,
in this case flow rate. I know how to get the frequency measurement into my VI,
and all is well as long as the frequency is higher than my VI update rate. But
things become more complicated and non-trivial when the frequency drops below
the VI update rate, because during some loops there will be no pulses occurring
since the last loop. In this case I could just assume that the frequency is the
same as last time, and for constant frequencies this works well. But there is
also the case where the flow rate has suddenly stopped, and hence a zero pulse
frequency. If I assume that the last known value is also the current value, my VI will be stuck
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must be the same as a digital frequency to analog converter, but I couldn’t
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something like this using Labview?

Hi,
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F(0) = 0;
F(i) = [ F(i-1) + N(i)/T ] exp (-t/T);
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t - iteration time
T - the integrator time constant
For a fixed frequency the estimator output stabilizes at N/t, but if the pulses stop coming, e.g. N=0, the output will decay to 0.
Use smaller T for a more "responsive" frequency estimator, larger T for a more "steady" one.
Hope this helps! Zador.
P.S. Here's a link to a previous discussion on pulse detection:
http://forums.ni.com/ni/board/message?board.id=170&message.id=191867#M191867

Digital frequency measurement speed in labview

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