Encoder Frequency to RPM

Hey people,
Im working on a project that involves testing a dc motor. One of the functions in this program is to calculate the speed at which the motor is rotating. I know how to convert from counter frequency to rpm, but my issue lies with the frequency I get from my encoder. I am using CI Freq daqmx create channel wired to an implicit daqmx timing function. When I run my VI I notice the the frequency consistently drops to 0 every so often which messes with the data. I have my project attached, the specific subvi this occurs in is the measure motor speed.vi. Any feedback would be much appreciated. Thank you!
-Zachariah
Attachments:
DC Motor Dyno Test.zip ‏1138 KB

Z_Squared42 wrote:
Heres a snippet of the particular part code in which I am experiencing problems with a spike in frequency...
This is not a snippet is is a screenshot. It is a static picture that like any other image, where a snippet is a static image with a LabVIEW VI embedded in it so others can open your code.
http://www.ni.com/white-paper/9330/en/
With that out of the way you could use a feedback node in that VI, or wrap it in a while loop that had a TRUE wired to it to turn it into a Functional Global. Then data can be stored in the uninitialized shift register like the previous good value. If you get a value you suspect is bad just use the last good value. You don't want to do this forever of course, if you get several bad values in a row you need to assume the value is actually bad so you'll need code to know how many bad reads is actually a bad reading. In your case getting two bad readings in a row maybe good enough to say the signal is bad.
EDIT: Also this maybe a band-aid for a much bigger issue. You mention having trouble finding a good reading and a larger issue might be in your setup.
Unofficial Forum Rules and Guidelines - Hooovahh - LabVIEW Overlord
If 10 out of 10 experts in any field say something is bad, you should probably take their opinion seriously.

Similar Messages

How to Measure Frequency to RPM NI-DAQmx Tasks

Hello,
I am trying to measure frequency using NI DAQmx task and then convert this to an RPM if at all possible.
I have the following hardware options at my disposal.
I have SCXI 1126 Module along with a SCXI 1327 terminal, as well as a PXI 6289 Multifunction DAQ.
I have wired in a mag sensor to ai7 on my 1126 and when I pass a metallic object I get a amplitude of 6 - 8 so I am able to read the mag sensor.
What I am trying to do is to somehow convert this analog measurement into a RPM while only utilizing the NI DAQmx task.
Any help would be appreciated.
Tim
Solved!
Go to Solution.
Attachments:
Freq Set Up.jpg ‏2993 KB

So I would select new in "Custom Scaling"
Then would I select linear?
Your calculations are simple but I am unsure if this would give me the desired result. From my attachment I am seeing an input amplitude of 6 Hz for each pulse. What I mean by this is that every time I bring a ferrous object near my mag pick up I get a pulse, this is what I was trying to illustrate in the attachment. The analog pulse comes in a 6 Hz so I would simply multiple this pulse by 60 (assuming I get one pulse per rotation) to get RPM?
How would this make sense if I only input one pulse for a long duration of time?
I have notice the amplitude of the pulse input increases with increased pulse frequency. Does this mean the lowest RPM I can record is 360 RPM?
Tim

Quadrature encoder frequency division dotNet Net VB C#

Hello,
following a long search on this forum, I have decided to start this thread for dotNet developper.
I have a PCI-6602 with a quadrature encoder (A,B,Z). The pulse frequency is average (10kHz).
I am only using A and B channels.
The function I have to implement is to generate an output every N pulses in the forward direction. N being an integer and ranging from 1 to let say 100.
I have no constraint on the output. I am it can be a bit toggling or a pulse generation.
What functions shall I call in MeasurementStudio.Net to implement this ?
How many counters should I use ?
On the register basis, my guess is that I have to pre-load a value in the register.
Then when downcounting the counter reaches 0 this in turn does 2 things:
reloads the counter to its preset value
triggers the output generation (TerminalCount)
Thanks for any help you may bring
NOTEs FOR NI guys:
By the way, in the NI samples, quadrature doesn't work all the way. I nthe sample "CountDigEvents" with CountDirection set to "Externally controlled", backward motion is never displayed. This is because the counter is read as a UInt32.
Solved!
Go to Solution.

Hi,
Your first ideas are pretty good, it should be a good way to implement a solution for your problematic.
I am not used to work with MeasurementStudio, but this is few links which you could use or which could help you with theoretical points:
http://zone.ni.com/devzone/cda/tut/p/id/3167
<link no longer exists>
http://zone.ni.com/devzone/cda/epd/p/id/2999#0requirements
Hope it could help
Mathieu B
National Instruments France
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Forum Aéronautique, Spatial et Défense. Avec la participation exceptionnelle de Bernard DUPRIEU, Res...

RPM Measurement using Quadrature Encoder and PXI 6602 counter

Hi,
I am on a project at work where I need to verify the speed (in RPM) of an unloaded motor which can operate up to 1400 rpm. After doing some research, i determined that a quadrature encoder could be used to make the measurement. I am looking at this encoder http://sine.ni.com/nips/cds/view/p/lang/en/nid/205321.
I have a PXI 6602 counter/timer module in which I would like to interface to the quadrature encoder. I would like to create a VI that allows me to calculate the speed using the encoder. Can someone provide me with details of what needs to be in the VI or an example which can do this? At the most basic level, i want to calculate the speed on demand. After doing this, i would like to figure out how to quickly calculate the speed so that i can determine response time of the speed changing within sub-millisecond resolution (1 ms resolution max).
Further, i created a VI that allows me to change the pulse width of a 100 Hz pulse train at run-time which tells the motor controller the desired speed. I would like to be able to use this VI to change the speed of the motor and the first VI (that I am seeking help about) to calculate the response time (time between the initial speed and settling at the new setpoint).
I am familiar with the NI example finder, but have not been able to find an example that I can use.
Thanks,
Gary

Hey Gary,
I think for you setup, you should try using the Meas Dig Frequency - Low Freq 1 ctr. You can find it by searching example finder with 'low freq'. This vi tells you the frequency of a digital signal by sampling between two pulses and inverting the time between pulses. If you hook up your encoder to a counter and have that counter specified in the vi, it will be able to give you on demand readings of frequency (you can do some multiplication to get the rpm value, freq*60/pulses per revolution of encoder). A simple way to take continuous readings is to put a while loop around the daqmx read and the data output of the read. You can also replace the numeric indicator to a waveform chart to graphically display the change of frequency or rpm readings over time.
You should be able to integrate this as two separate tasks with the pulse train vi you created earlier.
Hope this helps
Luke W

Can I measure frequency with a SCXI-1120 module and SCXI-1320 terminal block?

I am attempting to measure a square wave from a directional encoder to display RPM of a dynamometer. The waveform will have a frequency of 0-4KHz, with 3.6KHz being nominal, at about 5volts RMS. How can I measure the frequency of this waveform with the hardware I am currently using? In addition to what is listed above, I am using a PCI6034E GPIB card and LabView software.

In order to measure frequency, I would not recommend to use the SCXI-1120, but the SCXI 1126, which is a programmable isolated F-to-V module.
If by any reason you do not want to use SCXI-1126, then I would suggest to use the counter/timers of your board. The counter/timers are TTL compatible, and are the devices that we mostly recommend for doing precise frequency measurements.
In order to have access to the counter/timers of your board through your SCXI chassis, you will need SCXI-1180, which is basically a feedtrhough panel for your DAQ board.
Once we have access to the counter/timers through the SCXI chassis, we can proceed with the coding.
I found a pretty good webpage that clearly explains how to perform frequency measurement with the DAQ-S
TC counter/timers (DAQ-STC is the type of counter/timer chip that you DAQ device has). Here is the link to it:
Pulse Width & Frequency Measurements
As you will see, this link contains tutorials, application notes and example programs. I would recommend to pay special attention to the example program called: DAQ-STC: Measuring frequency.
Good luck with your application!

Need help for encoder count program !!!!!!!!!

I am a new labview user.
And i am trying to complete a project for my course.
For a quick background on what I am working with, I am using a NI PCI-73566-Axis Stepper/Servo Motion Controller for PCI, NI UMI-7764 Series, NI USB-6009 and a IDEC SC1B Rotary Encoder.
I am try to design a encoder count program and a new program to convert the encoder signal to RPM.
But I just don't know where should I start? How can I get the same block diagram like P11 in the attach file?
Please check more detail from the attach file.
Attachments:
P11.jpg ‏127 KB
P8.jpg ‏149 KB
P15.jpg ‏141 KB

Hello,
The two objects on the block diagram are DAQ Assistants and can be found under Functions»Measurement I/O»NI-DAQmx. From what I can gather, this is acquirign signals that you should have connected to the USB-6009.
-Zach
Certified LabVIEW Developer

Using a 9205 to measure RPM

I have not used labview in over 10 years but now have an application that requires but I am more then rusty. I am trying to measure RPM using a 9205 module and I am sure there is a way to do it. I have a pulsed voltage output from my measurement circuit and so far I am capturing the voltage. Can someone suggest a way to convert these voltage pulses to an RPM value. I am sure some type of leading edge counter would work.
Thanks

Not the cheapest route but there is a SCXI card that measures frquency.
http://sine.ni.com/nips/cds/view/p/lang/en/nid/1661
There may be some other frequency cards this is one I have used in the past. With this card you can create a virtual channel and ask it what frequency the analog signal is going into it. From here there is a conversion from frequency to RPM depending on the type of resolver or hall signal you are using to generate that signal.
This method is the easiest but the cheapest would be to get a cheap AI DAQ device that can measure several times faster than the generated signal (nyquist theorem) then analyze the series of AI reads to determine the frequency. Then convert frequency to RPM. Depending on the signal a USB DAQ device might work, if not a PCI or PXI + MXI card would still probably be cheaper than the SCXI route.
Unofficial Forum Rules and Guidelines - Hooovahh - LabVIEW Overlord
If 10 out of 10 experts in any field say something is bad, you should probably take their opinion seriously.

What is the "Smart Encoding Adjustments" option?

While choosing my importing settings, I couldn't help but notice the option "Smart Encoding Adjustments" at the bottom of the MP3 Encoder settings (just above the High-Pass Filter option and buttons).
I searched the discussions, I searched Google, and even the iTunes Help that comes with the software - all to no avail.
Does anyone know exactly what this entails? Maybe it's common sense to someone who knows the ins and outs of how exactly VBR MP3 encoding works, but I just don't know what to assume. I do make the assumption that most people consider it irrelevant, but why would the programmers give it to us as an option? I suppose I could experiment and encode two identical files with Smart Encoding Adjustments being the dependent variable, but I don't know exactly what evidence to look for. File size? Quality?
Whatever. I'm just looking for help and would sincerely appreciate any response that would aid me in my understanding.

Yes, Thanks! It's still quite vague, but I suppose if I'm looking for something extremely technical, I should just learn it on my own and go with other software options.
This is what I got from the article:
"If you choose to customize the MP3 encoding configuration, you can enable the Smart Encoding Adjustments option to allow iTunes to automatically adjust some of the internal parameters to improve the sound quality of converted files based on the original bit rate selection. This can include reducing the number of channels, encoded frequencies, or the sample rates."
I don't quite know how it could improve the sound quality by reducing any of those three variables, but then again, I suppose it all doesn't matter when not working with professional equipment and software.
Thanks for pointing me in the right direction.

How to convert pulses into RPM

I am using a counter to count the pulses given from a hall sensor to detect the speed of a motor. I can see the pulses on the graph and I have the operation running in a while loop but I am having issues with setting up a fixed time for the counter to run. I am using a USB 1208LS DAQ which requires Universal Library and I don't know how to convert the pulses that I get into a frequency or RPM's.
I just learned how to use Labview so this is getting pretty frustrating.
Thanks!

I am not very familiar with the hardware you have or the Universal Library. It seems from the spec page for the device however that it does not have any counters on it. So is this being read in as a digital channel or an analog channel, because I did not see any specifications on the sampling rate of the digital channels?
If this is coming in as an analog signal there are some signal processing VIs that you can use to determine frequency. Specifically Extract Single Tone Information.VI will find the frequency of your analog signal.
Doug Farrell
Product Manager - Condition Monitoring
National Instruments
National Instruments Condition Monitoring

How do you convert the encoder counts to RMP of the motor using a myRIO in LabVIEW?

My intent is to gain hardware interfacing and general Labview experience. I am using a myRIO to control a Pittman 8222 34V Brushed DC motor (Motor Specs).
I recently created a code to control the angle of this motor using PID, which was visually implemented using the black disc with a white tick mark on it (see attached picture: "IMG_2523").
I now want to control the speed of this motor againg using PID, but I am not sure how to properly convert the encoder counts to RPM of this motor. I have attached 2 screen shots of my block diagram and my front panel for reference ("Capture" and "Capture2"). In the front panel picture, you can see my "actual" speed of the motor is a very choppy signal when it should theoretically be a flat line. To get the RPM, I currently use a shift register to store the current count value (which I converted to deg, then to radians), and then subtract the previous run's value, then divide by the while loop sampling time (10 ms). This would give me rad/s, which I then wrote a subVI to convert it to rpm.
Any help would be greatly appreciated, thanks.

Hi,
One thing you could try doing is verifying that the conversion from rad/s to rpm is working correctly.
This tutorial might also be helpful. It's not using the same hardware that you are, but goes through the general steps using PID control.
CompactRIO Motor Control Basics Tutorial: http://www.ni.com/pdf/labview/us/compactrio_motor_control_basics.pdf

Analog and Encoder being collected only on encoder pulses.

I currently have the setup below and the XValue timestamps from the Write to Measurement File are not exactly at the rate I specified in the DAQ Assistant. The DAQ Assistant just has analog channels with Samples to Read set as 10 (or 1, which does not affect this example) and the Sample Rate (Hz) set to 10 Hz. The main problem that I am having is that the analog channels seem to follow the Frequency Counter in the sense that it alters the XValue timestamps in the Write to Measurement File and will only log the analogs and frequency channel when the encoder (frequency counter) encounters the edge of a pulse. How do I get the analog channels in the DAQ Assistant to log as well as getting the Frequency Counter to log simultaneously with the correct XValue timestamps from the Write to Measurement File with or without the encoder moving?
Also, is the 100 ms Wait Until Next ms Multiple needed for the Frequency Counter?
Thanks in advance for the help.

The *.vi works correctly except for the fact that when the encoder is not reading any pulses, not moving, it delays all data acquisition for all channels (analog and counter) until the encoder rotates again or the counter channel for the encoder times out according to the timeout specified. I would like for all of the channels to be able to continue logging at the specified rate in the DAQ Assistant for the analog channels and the specified rate for the counter channel (encoder) if the encoder is not reading any pulses. Also, when the counter channel is reading pulses, the timestamp XValue of the Write to Measurement File is not at the exact rate I specify in the DAQ Assistant. An example of some data is shown below.
X_Value
Analog
Encoder
0
2.231008
0
9.237507
0.942442
0
20.366281
3.523876
5.227699
20.725778
-4.150966
1.09365
22.304438
6.117589
70.197237
When the encoder is not receiving counts, it halts all data to be written to the Write to Measurement File and the X_Value timestamps are not exactly at 10Hz as I requested in the DAQ Assistant.
Thanks again for any help.

Variable frequency driver control by analog voltage output

I need to drive a variable frequency inverter to drive a compressor and I am too newbie in this kind of works. The inverter can be controlled by analog voltage input and I have NI9188 and NI9263. I have never used analog output modules before and I have some doubts about them.
1. how could I drive the motor continuously?
2. do I have to use device internal clock or software clock?
3. in some examples, a waveform is generated and sent to the write daqmx vi to generate analog output. do I need to do it? (By the way, I prepared a control subVI to send the required input voltage data to the write daqmx.)
4. It is talked about pulse with modulation sth like that. What is it exactly? Do I need to concern about it?
I need to drive the compressor with two temperature feedback so I prepared a huge program by master/slave design pattern. I attached it. Does this program work? I do not want to harm the motor so I could not test it.
Egemen
Attachments:
Control Project.v0.zip ‏2672 KB

Hi newbieeng,
I hope you are doing well today! I can help answer questions, but I can't debug a program and say whether it will work or not.
A lot of these question depend on your specific application and can't be answered in general. I would take a look at the specifications document for the NI 9263 and also the specifications for your motor. I'm including a link below to the specifications document for the NI 9263. I would highly recommend looking at the current draw of the motor. The most the NI 9263 can drive is 1 mA per channel.
OPERATING INSTRUCTIONS AND SPECIFICATIONS
NI 9263
http://www.ni.com/pdf/manuals/373781e.pdf
As far as hardware timing vs. software timing, it really depends on what you want to do. Hardware timing provides most more precise control over the timing of the output.
From one of the subVIs you provided, there seems to be a mention of a relationship between frequency and RPM. Is this representative of a control signal the motor expects? Is this the pulse width modulation (PWM) you were talking about? If your motor requires PWM, then you will need to send it the appropriate signals. I'm attaching a link below to an example regarding PWM.
Pulse Width Modulation
https://decibel.ni.com/content/docs/DOC-17537
Hopefully some of this is helpful!
Josh B
Applications Engineer
National Instruments

Help with Audio Settings

I'm a neophyte when it comes to audio recording. My projects
are software demos with a few PowerPoint slides for introduction
and wrap-up. After I record the PowerPoint show and the on-screen
demo action, I use a headset/microphone to record narration for
each C3 slide in the project.
Is there a good description/discussion somewhere of the
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In particular, what do "Encoding Bitrate", "Encoding
Frequency", and "Encoding Speed" mean? And what effect does
changing each of them have on the sound quality and file size (both
when I'm recording the audio and when I publish the movie)? What
settings would be best for "voice-over" narration? (I do not use
background music.)
The C3 online help for this dialog box isn't much help at
all. For example, here's all that it says about "Encoding
Frequency" and "Encoding Speed":
= = = = = = = = = =
Encoding Frequency
Select the frequency at which audio encoding must be
performed.
Encoding Speed
Drag the slider bar to set the required audio encoding speed.
Increasing the encoding speed reduces the quality of the encoded
files.
= = = = = = = = = =
That's a bit like saying "In your car, the brake pedal is
used to apply the brakes" without saying that you apply the brakes
to stop the car.
I'd appreciate any and all insight you can share on this
subject, and/or references to things I should read to learn about
these.
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Bill

i hate to rain on everyone's parade here but this problem lies elsewhere and not with the photo-jpeg video.
i was given several drives chock full of offline rt video and it plays fine out to my monitor. video was captured at offline rt preset resolution (320x240 photojpeg, square par), sequences are offline rt, control is apple dvcpro firewire to a jvc br-dv600ua vtr.
granted, the video looks less than desireable but it's useful none-the-less. i forgot to mention that this in a fcp 4.5 project on my panther boot drive.
perhaps the original poster will give some more info to help nail down the problem. or maybe my quicksilver system doesn't know it isn't supposed to display offline rt video.
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Giving advice on audio recording

I first started using Captivate when it was Robodemo 5 and
that was not all that long ago. I remember when I first downloaded
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did have problems. The most long lived problems were with audio
recordings. I know that many people have. On some of the forums I
read where one person had given up on Captivate. They did not like
the inconsistent recording of the audio. Sometimes it would be deep
and resounding the next slide would sound as if you are at the end
of a tunnel,and the very next recording would sound metallic and
soft sounding.
Just like with everything else if you are persistent enough
you will find a solution. I tried various mikes some expensive
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Inconsistent recordings. The recordings to me were passeable but
all not that great. Then I ordered one of those newer usb condensor
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All I can say is wow! Those new podcasting mikes they level
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Most of us are not radio announcers or professional
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Hello Rick!
The microphone is around 80 dollars, it comes with a soft
ware preamp, and I have always recorded directly into Captivate.
Even a low bit rates and encoding frequencies it still sounds good.
All my Captivate files are produced for the web. Html and .swf
files.
It is the mike Rick that made the difference. It is a Samson
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through podcasters. I wondered what podcasters were using to record
audio. Audio quality would be important to them. What I wanted was
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fanatics about the mikes they use.
Here is the advert from Samson.
"The C01U USB Studio Condenser Mic is the first affordable
studio condenser mic with a USB interface.
For the first time ever, musicians who record music on
computers have a simple, affordable way to capture high-quality
vocal and acoustic instrument performances.Seamless integration was
the idea, and it was obtained by creating a studio condenser
microphone that can be plugged into any computer with no in/out
boxes, no expensive computer pre-amps, just a USB cable.
The C01U condenser microphone is based on our wildly
successful C01. It features a 19mm internal shock mounted diaphragm
with a cardioid pick up pattern ensuring pristine studio quality
recordings."
Most online music stores carry these . Find one that you can
trust. Just Google Samson microphones.
Everyone can have good quality audio recorded directly into
Captivate. For those new at audio recording listen to podcasters
and other broadcasters. Animate your voice to make it more
interesting,speak at the same volume level, get a "pop" filter or
make your own with a nylon and reformed wire coat hangar. Practice
with your voice ,adjust the settings ,test various settings out and
soon you will be saying " wow"!
http://www.samsontech.com/products/productpage.cfm?prodID=1810

Enoder issues on 6023E - urgent!

Hi, I have a NI 6023E and I'm trying to get labview to read velocity (or frequency) from an encoder on a motor.
When I hook the encoder to the DAQ card and program using Labview, I'm getting very strange results. If I use a function generator to send the DAQ card a 80 Hz frequency square wave, the "measure frequency" vi returns 88 Hz. If I input 20 Hz, Labview reads 22 Hz. Unless both the function generator AND oscilloscope estimate are wrong, the NI card/VI I'm using is wrong.
I've tried using Windows 98 + labview to collect the ticks and divide by the elapsed time, but the output chart (over time) is jagged and inconsistant. According to the oscilloscope, the function generator stays consistant.
I have a data and ground wire from the encoder. Where do I hook them up to the card, and how can I get Labview 6.1 to read the correct frequency?
Thank you very much! I need this program to work in 2 days.

Sweet! The function generator frequency is measured accurately. Thanks!
I still have a problem with the motor encoder output. The encoder frequency varies much more than the function generator (both vary to some degree), but my program is having a very difficult time measuring quickly. I set the measuring delay to 0.001 second, and it works quite well for the function generator. But when the encoder is hooked up, it pauses every few tenths of a second for a couple seconds. When it measures the frequency, it gets it right. It's just pausing between readings too long.
Is this due to the inconsistency of the encoder, or something more sinister?
EDIT: The signal from the motor is typically around 1kHz. The program can quickly read an accurate signal from the function generator between 10 Hz to about 4 MHzMessage Edited by idbeu on 10-20-2005 10:17 AM

Encoder Frequency to RPM

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