Encoder quadrature Count issues

Hello,
I'm interfacing a servo motor through an SCB-68 Board with an R series FPGA and my computer. I have a pulse generaton programme to control the stepper motor which works fine. I have hooked up the encoder and used the general example vi "Quad ctr - R series.lvproj" with the inputs changed to my inputs on the board.
Now it seemed to work fine, but then I changed the direction of the servo motor. The pulse count does not rise the same when going counterclockwise as opposed to clockwise. I.e if i do one whole revolution both clockwise and counterclockwise i get a different amount of pulses outputted. Does anyone have any idea why this might be? I've tried the SCTL in simulation and the pulse count is fine if i manually change the A and B channels. Also, i've tried a dc motor with a different encoder and the same problem arises.
Any help would be greatly appreciated,
Sam

How much is it off by? Is it always a consistent number of pulses off? Just to verify it is the same channel you're reading correct, so there's no possibility its a phase issue since pulses are often out of phase on these encoders so you can determine direction.
CLA, LabVIEW Versions 2010-2013

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Count Digital Events1.vi ‏32 KB
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Hello, PRO
Can U explain me how count pulses from optical mouse? I have 2
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Hello;
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Servo motor encoder pulses/counter data erroneous

First off, I am very new to using labview. I am trying to complete a project a former employee was working on.
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Thanks
Solved!
Go to Solution.

The model number of the servo motor is R88M-W10030L. The servo motor rotates at a constant speed. The program is designed to drive the servo motor connected to a ball screw in one direction. Once the load sensor reaches a desired load, it will reverse at a constant speed until no load is on the sensor. Throughout, it records load vs. displacement. I have found a few things that will alter the pulses counts. If you apply resistive pressure on the servo motor while it is rotating, the pulse output will vary. Also when you apply pressure to the casing of the servo motor itself, the pulses will often jump around. I was almost certain my false pulses were caused by vibration. After have no success adjusting settings to reduce vibration(according to the user manual), I ran the program while moving around several wires to see if any were loose, etc... After applying force to the power lines and encoder cable, the program ran several times with an average of 2000 pulses per revolution and would actually subract pulses while going in reverse(what I want it to do); Although the average was around 2000 pulses per revoltion, i saw positive and negative jumps in pulse counts while traveling forward at constant speed. Today I re-wired the equipment, seperating as many wires as possible. After the re-wire, the equipment/program is back to sending 34000+ pulses per revolution, and does not subract pulses while reversing. I have read the 'Using Quadrature Encoders with E Series DAQ Boards' article. Referring to the article, I am running similar to "method 1". I am already using a signal conditioning box, but have the counter data run directly through. Do you believe running the signals through a SCC-CTR01 might solve the problems?

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I have using an 9215A USB (4AI).
2 AI are logging data in to a txt-file and the other 2AI will be used for counting the edges from a quadrature encoder (A and B pulse train).
Every edge falling or rising I will write a line in the txt-file also show a egde counter in the VI (total edges read).
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BR
Johan

the 9215A do 20kSam/s , that not too much, so .... your encoder should change state 10k/s max.
first approach: continious read (with max speed) with two buffers, while one buffer is filled by the DAQ, analyse the data of the other. Three independend loops : first wait for and read buffer-> send data via queue to second analyse loop -> send data via second queue to third loop that does the file handling.
second approach: create a trigger so the second loop can be avoided. The DAQmx/Hardware does might not support the trigger on both edges on two channels, but additional hardware like LS7084 o. HCTL2022 can help you to create the trigger signal. These little bugs are designed for incremental encoders and create a pulse for every change in the A B lines
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'

Quadrature counter dividing and triggering

I'm currently looking into using an NI USB 6353 device in a project, and I'm confused about its capabilities. Here is what I'm trying to achieve:
1. Reading an A/B (no Z) quadrature input to increment/decrement a counter (preferrably in X4 mode).
2. Produce a digital output signal with transitions on each counter increment/decrement.
3. Frequency dividing the counter transitions to produce a digital signal used to trigger various external hardware. The divider should be specifiable (probably around a few thousand).
4. Using another frequency divided version of the counter to trigger simultaneous analogue/digital sampling on the device.
5. Have the ability to make the counter time based (just incrementing at a set frequency), rather than using the quadrature input. The resulting signals should all still be divided and output correctly.
Being able to use the digital outputs on the device independently (on demand, timing isn't particularly important here) would be great, too.
Is this possible using the DAQmx C or C# API? Are there any other devices I should be looking at?

Hi Matthew,
Matthew S wrote:
Wouldn't the change detection mean that I couldn't sample the digital input lines at a divided rate? Or can I simply implement the change detection using a single DIO port and still have the remaining DI lines to use?
I'm glad you brought it up--I guess I overlooked that you were planning to use clocked DI. If you're using DI change detection you cannot sample the DI lines off of another clock source. Unfortunately, port 0 is the only port that supports change detection (even though the manual currently implies otherwise) as well as the only port that supports clocked DIO. You can still do static DI on other lines, but the clocked DI subsystem can only have one timing source. You can always oversample your DI using the change detection, then index out 1 out of every N samples in software (the DI should be good at rates of up to at least 1 MHz continuously).
Matthew S wrote:
It sounds like the X-Series can do what we need. We'll probably stick with the 6353, because we need at least 20 analogue inputs, and sampling rates of at least 1MSps.
Keep in mind the 6353 is multiplexed--the aggregate rate is 1 MHz, but sampling 20 lines at the same time would only give you 50 kHz per channel.
Matthew S wrote:
I'm slightly confused as to how to use the change detection to implement what we want. Essentially, we'd like to take the X4 quadrature input and convert it to a step signal (as in, step/direction) that will be used to control a hardware variable antialiasing filter. Will this require another counter? If this can't easily be done on the USB DAQ device, we can do it using external hardware.
You can get the step from your x4 encoder with change detection easily enough, but I don't think there is a good way to get the direction as an external hardware signal. I think the better option is to use a flip flop to latch the encoder state (either latch A using B as the clock or vice-versa) to obtain the direction.
Matthew S wrote:
How hard is it to get the direction and also speed (or frequency) of the
original quadrature input for each AI and DI sample taken? I assume
that the frequency measurement would require another counter? How about
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If you're using a latching circuit to output the direction, you could just sample this off of one of the DI lines (assuming you have one available). To measure the frequency of the encoder, I suggest looking into the method described in Figure 7-15 of the X Series User Manual to use another counter to measure the frequency of either A or B. During each sample clock period the counter counts the number of encoder pulses as well as the number of internal timebase ticks that occurred during those pulses. The driver uses this information to return the average frequency of your signal in between sample clock pulses.
So... you were right to have some concerns about using change detection alongside clocked DI. You'll have to pick one or the other--I think I'd prefer to oversample DI and throw away samples, depending on the maximum frequency coming from your encoder. Also of concern is the number of counters (there are 4 available on the board). In addition to the 4 counters, keep in mind taht there is a Frequency Generator that can be used to output specific frequencies:
{20 MHz, 10 MHz, 100 kHz} / {1:16}
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Encoder triggering counter capture

Hi, I'm doing some research into how I can implement the below application. From what I've read, I'm 95% sure I can do what I want with a timer/counter card. But I figured I'd throw it out there to make sure. My application is as follows:
I have (or will have) a scanning head that rotates through 180 degrees across the sky. The scanning head has a mirror on it that directs light into a PMT (photon-multiplier-tube). The PMT outputs a TTL pulse every time a photon hits it (sometimes you get double hits, but we'll ignore those for now). The idea is that we want to count the number of pulses from the PMT for incremental portions of the scan.
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So, is this doable? Can I link events to the encoder count value and have them trigger the system to capture the current count and then reset it? I don't know anything about how you setup these events, so any advice would be great!
Thanks!

Actually, I should take a step or two back from the brink. I still do foresee some monkey wrenches
if you really need dead-on hardware sync of these signals and sampling times. However, maybe I'm
much too quick to assume the need for that kind of dead-on sync.
If you can approach the app by capturing "sufficient" data within and across all these position bins,
you can probably get a very good approximation with some fairly straightforward software post-
processing, and simple interpolation/curve fitting. Not sure how much "sufficient" is, but likely a
manageable amount.
And yes, "digital change detection" is simply the ability to detect TTL transitions. When a transition
is detected, a pulse is generated on the board, and tasks can be configured to use that pulse to
sync up triggers, sample clocks, or other timing signals. Both the M-series and X-series multifunction
boards support it. The 6602 doesn't. If you're going for true dead-on hardware sync, I still suspect
you'll end up wanting the change detection feature. If the software post-processing is good enough,
you probably won't need it.
One last thing: the ability to filter digital TTL signals has been improved on data acq boards over the
years. I suspect the X-series will give you better filtering options than the other boards but I can't
speak from direct experience.
-Kevin P

Velocity Measurement from FPQuad-510 encoder pulse counter

Hi, I have a quad-510 quadrature encoder counter and a 1024pulse/1rotation encoder. How can I read or calculate angular velocity(accurately and without much delay) from encoder readings?
Is there a special vi or another algorithm (other than derivative.vi) that could help?
Thank you.

Caner,
What do you see listed for the status of the velocity channels in MAX?
Also check your channel configuration to make sure you have an appropriate range set.
Regards,
Simon
Message Edited by Simon H on 02-02-2007 06:50 PM
Attachments:
MAX_CTR.png ‏26 KB
MAXDataConf.png ‏11 KB

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How do I use daqmx to get encoder direction/count on M-series board?

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Hi Zibin
I have been trying to work out what is not working I need some more information
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What have you set your time out value to?
What exact errors are you getting and when do you get the error?
What would really be helpful is if you could send me your code because by the sound of it, it should just work the card is more then capable of doing what you want so chances are it is the code.
Regards
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NI UK

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Hi,
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Encoder quadrature Count issues

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