Measure frequency of Z pulse of an accu coder shaft encoder to measure speed using an 6034 E card

Hi,
I would like to measure the speed of a engine which has an accu coder encoder hooked onto it. It provides 3 pulses A, B, and Z. I am using a 6034 E PXI card. I wanted to know if there are any examples/ideas that could help me with this (I am new to the digital programming in Labview). I have moved to NI Daqmx 9.8 recently from the older version which supported legacy codes and hence in process of updating the code. I also want to know if an external clock source is required to do this. this.
Solved!
Go to Solution.

Hello,
There are several examples in the NI Example finder (you can get here by going to Help >> Find Examples in a LabVIEW window). You can browse to the encoder examples by going to Hardware Input and Output >> DAQmx >> Counter Input. You should be able to find a few examples that will be helpful.
Also, this link is a good resources for getting started using DAQmx: http://www.ni.com/white-paper/5438/en
Thanks!
Stephanie S.
Application Engineer
National Instruments

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Problem in edge separation measurement by using NI PCI 6251 card

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Hey JmBone,
It's possible that you are just suppose to send a 32-bit integer to control the 32 valves. The 'byte offset' is probably just there to allow grouping of 8 valves (8 bits as 1 byte). So instead of sending an 8-bit number with some offset, you just send a 32-bit number and only change the bits corresponding to the valves you want to change. It would be easiest to just have a 32-bit binary array in your code for changine the individual valves and then cast that to a U32 integer before sending it to the Set Attributes VI. Maybe I am misunderstanding the manual, but I don't think 'byte offset' is a parameter you are suppose to specify, and is just there to indicate how the valves can be bundled into a single 32-bit value.
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How to generate digital pulses to run stepper motor in a sinusoidal motion profile using NI DAQ 6229 card

Hi,
         I need to make a stepper motor undergo rotary oscillation with a sinusoidal motion profile. As it nears the extreme points it should decelerate and finally slow down to zero velocity and then it should reverse direction and accelerate until it reaches the other extremity where it should slow down and stop and reverse direction and repeat this motion.
        The hardware is NI DAQ 6229 and the stepper motor can be controlled using digital Hi-Low (1,0) pulses. For each high pulse(1's) the motor turns 1 step. I am able to generate a analog sine wave and convert it to digital data using Analog-to-Digital.vi But i am not able to convert the digital data to a stream of 1's and 0's in the correct sequence to get the sinusoidal profile with the amplitude and frequency i require.
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Any ways of making this approach work or any new approaches to this problem would be helpful. Thank You.
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Hi,
   I finally figured out a way to do it. The analog sine wave is converted to digital and sampled. Consecutive values are compared and if the least significant bit(LSB) changes then a pulse is sent to the stepper motor to turn one step.
I have included the sub-VI's that accomplish it for the particular stepper motor and connector block i have. The front panel of both sub-VI's are quite messy but the block diagrams should be much clearer. The sub-VI's get their inputs from a third VI which i have not included. So take a look at the VI connector panel to figure it out. Hope this helps. Kinda messy but worked out fine in the end for my application.
Thanks again for all the help. I appreciate it very much.
Regards,
Prabu Sellappan
Graduate Student
Aerospace and Mechanical Enggineering
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Attachments:
start motor test waveform dtest.vi ‏73 KB
sine profile generation subVI.vi ‏41 KB

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

In NI-DAQmx, how to change the frequency of a pulse train?

I was using "GPCTR_Change_Parameter()" to change the frequency of my pulse train in Traditional NI-DAQ and Labwindows/CVI; is there any function can do the same thing in NI-DAQmx without restarting the task?

You can do this in one of two ways, depending on the version of NI-DAQ you are using. If you are using 7.2 or later, you can use the counter write functions (ex: DAQmxWriteCtrFreq()), which are available for each flavor of pulse generation tasks (Freq, Time, Ticks). If you are using NI-DAQ 7.0 or 7.1, you can modify the attributes directly (DAQmx_CO_Pulse_HighTime, DAQmx_CO_Pulse_LowTime, etc). Keep in mind that for each attribute pair, one of the attributes will cause the counter to load the new pair. The attribute that causes the load is LowTime, LowTicks, and Frequency.
I hope this helps!
gus....

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

What sensor should be used to measure speed of motor

Hi,
I am using NI PCI-6624 to control the speed of dc motor. I have used "PWM-Counter Output.vi" example to generate PWM pulses to control the input power of motor. I am using "counter output" and "analog input" terminals of PCI-6624. Counter output terminal is used to generate PWM signal and "analog input" terminal will be used as an input from speed sensor.
Can someone tell me what sensor I can use to measure the speed of motor. Please note that the output of the sensor will be the analog input to PCI6624, so it is essential that speed sensor's output is ANALOG.
Please help me in this matter and tell me which sensor can be used and from where I can buy it ?
Thanks

Ayaz,
the straight forward low-cost solution for velocity measurements is using a quadrature encoder. With your DAQ device you could use the second counter of the board to measure the frequency of one phase, but that's jus one option amongst others.
I haven't come across sensors that output a voltage that is proportional to velocity but expect such a device to be much more expensive and probably less accurate.
Do you plan to do closed loop velocity control? Are you using Windows or a realtime system?
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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.

You probably aren't going to find anyone to just give you code. Especially because you don't specify the hardware you're using. Doing this on FPGA is different than using DAQmx to do it. With FPGA you count pulses over a specified time. Using boolean logic from the digital DI node is a common way but there are others. (if you are using FPGA I can draw up an example, but I believe there is one on NIs website if you search google for it),. Then, if you want, you can run the data through an IIR filter, especially if you have a low resolution or slow moving encoder. Either of these conditions can result in very large difference of RPM even if the actual speed is not varying much (if you need an example why I can provide more detail, but some simple math calculating RPM should explain this. Obviously lower resolution will giv eyou less accurate results).
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

Measuring speed with incremental single counter

Hi,
I need to measure the rotational speed and acceleration of a wheel that has 3 hall sensors on it. I will use only 1 of them en it gives 24 pulses 0-5V for a 360° rotation. How can I measure the speed with only a pulse train. I dont have the Quadric encoder...
Now I'd like to measure the rotational speed using a counter of some sort, but the software I tried writing for it isnt working.
Thank you for your help

Hey Nitch,
Concerning the measurements errors:
As you get error when speeding up, it looks like the pulses coming from the hall sensors are to short to get measured by the counter.
Following the USB-6008 specifications, the pulse needs to have a minimum lenght of 100ns (both in high and low state).
As a counter is using edges to count the pulses (for USB-6008 only the falling edge) the edges need to comply with the TTL specifications which means that the rise and fall time of the pulse needs to be within the 50ns range.
So please have a look at the pulse lenght at higher speeds (are they at least 100ns?) and make sure the pulse comply with the TTL specifications.
If not you will have to add some additional electronics to reshape the pulses.
Looking at your program.
It's not nescesarry to have two loops. It's very well possible to have two DAQ tasks within the same look.
Have a look at the Examples which come with LabVIEW --> Exampled Finder --> Hardware Input/Output --> DAQmx --> Synchronization --> Multi-Function.
There are some examples which so the combination of analog and digital input.
Anyhow you will have to remove the right while loop as the DAQ Express VI which apparently gives you the "spanning, stroom, gashendel" values will only start once you have done the counter measurements. I assume that you would like to have the "spanning", "stroom", "gashendel" and"speed" synchronized measured.
Then you have the choice to log to file during acquisition or after the acquisition.
If you would like to log on the fly don't use the express VI's, but use the lower lever "File I/O" functions. These are faster (less processor time usage).
As you VI is written now, the left while loop will only output the lastest counter value measured to the next loop when you click the stop button for example.
You have to "Enable Indexing" of the m/s output tunnel. Right click on the tunnel and you will be able to select "Enable Indexing".
This way the application will automatically create an array and each loop iteration the measured value will be added. One the measurements have been done you can do analysis and save the data using the full array instead of point by point.
Again, also bring your "spanning, stroom and gashendel" inputs to the left loop.
In your right loop you also have a loop counter.
You can simply use the loop iteraction counter (the square box in the left bottom corner with the i). This is also counting from 0 and incrementing by 1 each loop iteration.
Again, you can do this in the left loop and forget the second loop completely.
Hopes this will bring you a step further.
Don't hesitate to post the VI itself. This is always easier to look at than an image.
This way we can also make some modications and post it back.
Best regards,
Joeri
National Instruments
Applications Engineering
http://www.ni.com/ask
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I want to measure rpm using 100 ppr incremental encoder via digital input

i want to measure rpm using 100 ppr incremental encoder via digital input max speed (4000 rpm)
am using 9178 c-DAQ chassis and 9426 digital input module
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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steve.bm
AE | NI

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Like I said. I have to calculate the impedance based on the data of impedance and phase. I don't know how to realize that, I have no idea. I guess that i have to know some equation how to do that calculation, because i have to calculate real and imaginary part (reactance and C or L). Aftert that I must connect input and output channel in the configuration for measuring impedance, and I have to connect different resistors, condensators, paralel combinations of resistors and condensators.
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Measure frequency of Z pulse of an accu coder shaft encoder to measure speed using an 6034 E card

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