Using a Quadrature Encoder as a clock at best precision possible
I would like to use a Quadrature encoder as a clock for analog data acquisition. Currently, I am using only one line of the encoder and the clock "ticks" when the line goes high. This is only one quarter of the precision the quatrature encoder is capable of, since it can count from both lines when they go either high or low. I was wondering if I can get the counter to send a pulse everytime it increments and use that pulse train as my clock. This would increase my analog data acquisition frequency four fold.
Hello,
It is not going to be possible to count both rising and falling edges with a single counter. You could route the A phase and B phase of your encoder to different counters to capture the different edges on the signals, but that will not help you in using this encoder as your clock source. What you may want to invest in is a quadrature clock converter. You can find more information on this at the following tutorial:
Using Quadrature Encoders with E Series DAQ Boards
Best,
Jared A
Similar Messages
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How do I use a quadrature encoder as an external clock (PCI 6229)
Hello, ( a similar post has been placed on DAQ forum apologies as I did not know best place)
I have a PCI 6229 M Series data acquisition card. I want to use a quadrature encoder to be the external clock driving the acquisition of a number of signals. I have set up reading 24 signals each time a clock pulse is received using the DAQ assistant and set my external clock to pin pfi8 (I think) this is then connected to an encoder output. This works well enough until the encoder is run too fast when it appears I am either missing pulses or getting bounce.
How can I set up to clock using a quadrature encoder? I have seen a number of questions on this forum regarding quadrature encoders and reverse counting but not on using them as an external clock.
Basically I want to have the stability and "bounceless" nature of using two outputs from a quadrature encoder whilst still using an external clock. Is this just a case of configuring controls to certain pfi's? If so how is it done?
Any help or pointers would be helpful. So far I have managed very nicely by simply using the DAQ assistant and the interface it has would suggest that if configured for a certain pfi pin I could actually still use it.
Thanks in advance.
KevinHi,
Well I've had alook into this for you and I'm not quite sure I understand what you are looking for.
Is it possible for you to phone back in to support?
The reason you are seeing bounce at high speeds, or indeed loss of points, is due to the sampling rate that you have set up.
What you will find is that the trigger will start an aquisition of a number of points at a certain rate. If your sampling rate is too low then you will not finish that sample batch before the next set of samples is recorded.
It is possible to use an external clock into a trigger or digital line, however this will limit the number of samples you can take to the speed of your encoder.
If you increase your sampling rates, and then configure a start trigger from a single input from the encoder you will be able to record a number of samples after a rising/falling edge. (Set the clock as an internal clock)
Hope this helps
AdamB
Applications Engineering Team Leader | National Instruments | UK & Ireland -
Generate a pulse train using a count from a quadrature encoder as the clock
I am trying to generate a pulse train with the same frequency as my quadrature encoder. Every time the encoder counts, I want the pulse to go high until the next count and then go low and so on. I am using a 6602 PCI card and a BNC 2121 accessory.
Maybe I'm not understanding your app, but I *think* you and I are approaching it from two very different directions.
As I understand it, you'd like to emit a pulse with each quad state change. Then that pulse would act as a counter Source signal. The counter will then increment on each pulse, to keep track of accumulated position. Further, you'd use your device-under-test (DUT) as a counter Gate signal, which would buffer the position count each time there's a rising edge on your DUT. The end result is a buffer of position values, captured at each rising edge of your DUT.
I'm talking about a different approach to produce the same data. You'd use 2 tasks on a M-series board. One of them is a hardware-timed digital input task based on "change detection." Each time one of the specified bits has a transition, your whole set of digital input bits can be captured and an internal "change detect pulse" is generated on the board. This task should be sensitive to the DUT edges.
The other task would be a buffered position measurement. It would receive the reference encoder inputs and internally do quad decode and keep a running count. The sampling clock for this task would be specified as the other task's "change detect pulse."
Net result: on each specified edge of your DUT, you'll buffer a reference encoder position value and a digital state of your DUT. You can choose to be sensitive to rising edges, falling edges, or (!!!!) both at once. You can also choose to be sensitive to many bits simultaneously. These are better capabilities than you get with the 6602 alone.
I *think* the 6220 should be ok, based on a quick overview of specs. I assume your 3.6 MHz is the rate of ref encoder quad state changes, right? In the approach I'm suggesting, you only need concern yourself with the rate of DUT edges which appear to be in the 10's of kHz or less.
Gotta go for now. Post back if any further questions.
-Kevin P. -
Learning how to use a quadrature encoder
Here is my first post....
My question involves use of NI cDAQ 9411 and a Unimeasure TTL encoder. This is all very new to me, actually my first endeavor. First off, I am wanting to veryify my pinout connections, I have tried a few configurations based on the help topics I have reviews. I am unsure if the Ao and B0 channels need to be connected? I am using the encoders to build up a deflection / load measurement system. I have seem mutltiple ways to hook these things up. (The pinout of my devices are in the attached PDF document)
Also, I am curious if there are any tutorials specifically for the NI9411 and an encoder. I have been trying to use signal express, but I keep getting "Clock" errors. I have not got to the point to actually see counting or measuring when I pull on the encoder string. Perhaps there is a good tutorial explaining the use of clocks?
Thanks!
Solved!
Go to Solution.
Attachments:
Encoder-Pinout.pdf 141 KBAfter many hours of searching and help I found a solution to the issue. The issue had to deal with providing an external power source to the 9411 modules. THe 9411 apparently could not power my 5 volt encoder. Fortunalty, this was an easy fix. Thanks!
My next question is in regards to using multiple encoders with my chassis. I have been spending the day sorting though the various posts trying to sort through the best way to make this happen. I am unsure if I should by using "Tasks" or if I should be using the Express DAQ Assistant. I am using cDAQ 9172 and the 9411 modules in slots 5 and 6. I would like to aquire continous information from the encoders.
I would appreciate any assistance.
Thanks! ~J -
Quadrature encoder as Clock input?...
Greetings!
Can anyone give me some advice on using a quadrature encoder as a clock input to an m-series daq?
-Thus accepting A B and Z inputs..
My aplication calls for measuring an Analog input on every rising edge (from the Clock generated) , now I've been scanning up and down the forum -found some posts, mostly concerned with the E-series.
Some pointers will be appreciated!Hmmm, not sure how to comment. When I think of "jitter", I think of an undesired variation in time intervals. I wouldn't think that the digital filtering features would be a very natural way to address jitter.
It may be a moot point though. Digital filtering can be configured for "PFI" pins on the M-series board, but those pins can't be used for correlated DIO -- only for software-timed static DIO.
I haven't found the need to use digital filtering in quite a while. Need or lack thereof pretty much depends on the type of sensor signals you have and the kind of electrical environment you're in.
-Kevin P. -
Speeding up quadrature encoder read out
Hi,
I`m using a quadrature encoder together with a 6259 DAQ Card and BNC2110 Terminal Block.
I managed to have it working with the DAQ-Assistent at 80Mhz using the Counters and reading one value at a time. Before the DAQ-Assistent I used a DAQmx command to connect PFI10 and PFI9 as the BNC2110 Terminal only outputs PFI0-9. This works but it is really slow, the distance between each measurement point is around 6 us. The VI is in the attachement (AquadB_one_value.vi)
So I thought I might use the n-values version with the DAQ-Assistent but this does not work and I dont see any reason why, it is complaining about that connection between PFI10 and PFI9 which it didnt do before in the one-value-version. The VI is also in the attachement (AquadB_n_values.vi)
I also tried another method using a VI I was given some time ago and modified it but here the distance between each measurement point is also around 6us. This VI is also in the attachement (Counter - Read Encoder.vi)
Or am I missunderstanding something? The minimum achievable time distance between measurement points should be 1/80.000.000 s where of course the value can only differ 1/0/-1 because it has only calculated one new change in the A and B Signals right? I thought with using the n-values it is storing all the calculated values in the memory and I am transferring them afterwards for doing all the "post-processing"?
If I am wrong, how can I spped up the read-out of the calculated values any other way?
Best regards
Attachments:
AquadB_n_values.vi 56 KB
AquadB_one_value.vi 49 KB
Counter - Read Encoder.vi 98 KBHi Dani_munich,
I just realized that you asked the same question in our Service request. In the service request, I was missing out more information which I found them here by chance . I will further assist you in the SRQ you have created. I also sent you an email.
Regard
Anoj
Anoj Mubarak
National Instruments -
Programming quadrature encoder
I'm trying to program a incremental optical encoder with nidaqmx 7.4, with C#, using the PCI-6071e card. I want to measure position, velocity, and acceleration.
As per the "How Do I Use a Quadrature Encoder with My Data Acquisition Board?" document, channel A of the encoder is connected to ctr0_source, channel B is connected to DIO6, and index is connected to ctr1_source.
I'm trying to run the the MeasAngularPositionBuffered_Cont_ExtClk example. However, an exception is thrown when calling myTask.CIChannels.CreateAngularEncoderChannel.
The messagebox says "Selected physical channel does not support the measurement type required by the virtual channel you are creating. Create a channel of measurement type that is supported by the physical channel, or select a physical channel that supports the measurement type"
Also, there is an option in the example program to enable the Z index. How does that program know which channel to read the index pulse?
I'm new at data acqusition, so any other hints regarding optical encoders are appreciated.
Thanks,
GerryYou also may be able to measure position using the "Count Edges" measurement with an external direction control. This may be enough for your purposes. Just bear in mind that quadrature encoders typically give off noisy signals, so you might have to build an external circuit to clean up the input signals. Let me know if you need more information on doing this with your E Series device.
gus.... -
Read RPM from Quadrature Encoder
Hi Everyone,
I wish to measure the RPM of a shaft using a quadrature encoder and a PCI-6259 card. I've seen a few examples on reading position, which i have managed to get working, but Im not sure on how to get RPM. Any tips or code examples would be greatly appreciated.
Thanks,
DavidHi All-
Thanks for the suggestion DJ, but your VI will not work as it is written using the Traditional (Legacy) NI-DAQ driver and David's M Series card is only compatible with the NI-DAQmx driver.
To answer David's question, it is not possible to directly measure position and count edges at the same time. What you can do is count edges with external Up/Down control (basically the same as a X1 encoder) and then use the edge counting to calculate both frequency and displacement in ticks/degrees/RPM/etc. I have attached an example I did recently that shows how to use an edge count with external Up/Down control (i.e. PFI10 or PFI11 for M Series ctr0 or ctr1, respectively) provided by the 'B' phase signal and the 'A' phase provided to the counter source.
Hopefully this helps-
Tom W
National Instruments
Attachments:
32bit_Cnt_Edges_to_Quad.vi 73 KB -
Can I use the 'Export Signal Property Node' on a quadrature encoder?
Hi,
So I don't know which counter board I'd be using yet for this (it's used in conjunction with a PCI-6280--the PCI-6280's counter inputs are all taken and so I need another board), but assuming this is possible at all in DAQmx I wouldn't mind knowing whether, say, the PCI-6601 (or any other timer board for that matter) could do this. I'm programming this in LabVIEW 2010 by the way.
I want to have a counter which counts the number of pulses on one channel (I'll call this the 'clock' channel) between when another channel goes from low to high (which I'll call the trigger). It's basically a pulse width measurement, but I only care if there are more than n clock pulses between triggers. I need to have a hardware-timed digital signal which goes from low to high if there are ever more than n pulses between trigger changing state from low to high.
What I am planning to do is this:
Wire 'trigger' to the z-input of the quadrature encoder, and set the z-input value to some arbitrary large value such that, at the quadrature encoder counter task's settings, the counter reaches terminal count in n pulses.
Configure the quadrature encoder counter using DAQmx Export Signal Property Node (tutorial I was looking at is here: http://zone.ni.com/devzone/cda/tut/p/id/5387 ) to toggle a digital channel ('counter event output') from low to high if the counter reaches terminal count (ie, if the encoder reads n pulses).
If the encoder ever reads n pulses on 'clock' between two rising pulses on 'trigger', it sets counter event output high.
Is this possible? Reading through the manual of M series PCI-62xx devices, the index pulse loads the counter with a particular value so it seems like you could conceivably set the counter to the terminal count if you wanted. My only real problem is whether DAQmx Export Signal Property Node works on all counter tasks or just on edge counting tasks.
Thanks in advance for your help. If this isn't possible, I can reply with more details on the problem this is supposed to solve so that you can help me figure out an alternate method.
Solved!
Go to Solution.There is probably a way to do it, but it it may be easier to use an X-series board for the job. They support a new counter capability for count reset on a digital edge without needing to be configured in encoder position mode. I am not sure exactly how that feature's been implemented however, so maybe it won't make things easier after all.
The plan based on the hoped-for behavior:
1. Configure an X-series counter for pulse generation based on "ticks" of your clock channel.
2. Set both initial delay and low time to the critical # of ticks.
3. Configure for count reset on a digital edge (if possible in pulse generation mode)
4. Configure the count reset value to be the critical # (or possibly 1 less, if possible in pulse generation mode)
5. If you want the output to remain high indefinitely, configure the counter task to use its own output as a
pause trigger, and pause while high.
The way pulse generation works is to preload a # of "low time" ticks into the count register. Then every source edge will decrement the count. When the count reaches terminal count (0), the counter's output is toggled (or can be configured to pulse). The register is then loaded with the # of "high time" ticks and the process continues.
You would be perpetually interrupting the count-down process as long as you got your triggers in time. The count would keep getting reset to the # of low counts, keep decrementing toward 0 without reaching it, and so on. If ever you did reach 0, the output state would toggle high, then the high state would prevent subsequent clock signals from decrementing the count.
You can conceivably do a similar thing with a 6601, but I'm pretty sure you'd need 2 counters working together to get it working.
-Kevin P -
This is for LV6i, W2000, all PCI equipment.
Using a quadrature-measure position-VI, I get 7200 edges/rev from the encoder of my physical system. This equates to 0.05 degrees of angular displacement. This amounts to an angle stamp as opposed to a time stamp.
I need each of these 7200 edges (source: 6602 NI-TIO) to trigger (using RTSI) the acquisition of a single sample from each of 2 channels on an E-Series DAQ board (maybe more channels later). I only need/want one rev (7200 samples per channel) of data for each run of the test. As I write this I think I want pre-triggering and a little more than a rev of data. So the
re is a buffering step. Anyway, you can get the idea.
I need this angle stamp and the DAQ samples to be placed in an array and on the hard drive for graphing and other mathematical treatment, analysis, etc.
I think there must be a way to use the quadrature output of the counter/timer as a scan clock for the DAQ board, but I haven't seen an example to guide me.
It seems like all of the RTSI or other triggering examples I have seen trigger once to start a continuous scan, not a series of discrete samples repeated quickly. I am not sure how to fill an array with this data. Again, examples are for continuous sampling, not a series of discrete readings.
Any hints on any part of this task will greatly appreciated. This is my first LV project.Sounds like a fairly ambitious first project!
I assume your 7200 edges/rev come from an encoder with 2 channels in quadrature which each provide 1800 cycles/rev. You can clock in analog data at 1800 scans/rev with either of the two encoder channels, but will probably need an external quadrature decoder circuit to produce 7200 scans/rev. Either method can be done with screwdriver and wire or else by using another counter from the 6602 and the RTSI bus. Here are two approaches in detail, but you could mix-and-match as needed.
Note also that if you can be sure that your reference encoder will be uni-directional, you wouldn't need to measure position -- position could be determined by the array index of the analog scan data. This would simplify things greatly.
1800 scans/rev, screwdriver & wire
Wire both encoder channels to your 6602 breakout box and configure your counter for the 4x quadrature option. Send a wire from one of the encoder channel connections at your 6602 breakout box to a PFI pin at your E-series board breakout box. Config the analog acquisition to use an external scan clock and specify the correct PFI pin -- there are built-in examples that will guide you. Now one edge of one encoder channel acts as a scan clock for your analog acquisition. Inside the 6602 breakout box, route the same signal to one of the default gate pins and configure your encoder counter gate to use that pin as its gate signal. Note that there will be a race condition governing whether the encoder value updates from the encoder inputs before or after the value is latched by the gate.
7200 scans/rev, extra counter & RTSI
Make sure you have a RTSI connector between your two acquisition boards inside your PC. Build a quadrature decoder circuit that will convert your two encoder channels into a clock and direction output. (Consider the LSI 7084 decoder chip or similar). Setup your "encoder" counter for buffered position measurement. Use "Counter Set Attribute" to define "up down" as "digital" (don't use it to define "encoder type"). The clock output goes to the counter SOURCE and the direction output goes to the counter UP_DOWN pin.
Use "Adjacent Counters.vi" to identify the counter considered adjacent to your encoder counter. Configure it for "retriggerable pulse generation". Use "Counter Gate (NI-TIO).vi" to specify "other counter source" as the gating signal. Configure the output pulse specs to be short duration (make sure total of delay + pulse width is less than the minimum period of the incoming encoder clock signals). Use "Route Signal.vi" to send this counter's output onto the RTSI bus, say RTSI 0.
Now configure the analog acq. to use RTSI 0 as its external scan clock. Also configure the encoder counter to use RTSI 0 as its gate signal. Voila! Now your quadrature decoder clock output acts as a scan clock for analog acquisition and a "gate" to buffer your encoder measurement. The short delay helps ensure that the clock updates the position measurement before the gate fires to latch the value.
Respond if you need clearer explanation. There's a fair amount of decent info "out there" if you scour the online help and this website. Good luck! -
Do I need extra logic circuit for quadrature encoder using M-series DAQ PCI-6221?
Hi,
I understand that extra logic circuit, say quadrature clock converter LS7083/7084, is needed to enchance the reliability or integrity of the data for E-series board DAQ in accordance to application note: AN084.
This is due to the vibration/jitter of the motor during running.
Currently, I'm using M-series PCI-6221.
Is it this new model itself can eliminate to construct this extra circuit?
Coz I observed error is accumulating after motor rotating certain period of time. It defintely affect the control performance.
Other than using hardware, can we use software to eliminate/mitigate the error?
Please enlighten me. Thanks.
Best regards,
IANESHello,
The ap note you are referring to discusses circuitry that conditions the quadrature encoder signals before they get to the DAQ device to eliminate 'false' signals being sent to the DAQ device. The same system would apply to an M Series Device. I am not aware of any way to achieve this functionality in software. FYI, there is some good documentation for counters and counter applications for M Series. Take a look at the attached M Series help file. Hope this helps some.
-Alan A.
Attachments:
M_Series_Help.zip 1145 KB -
Using a Counter(PC-TIO-10) to Perform Quadrature Encoder Buffered Position Measurement in Visual C++
I have Driver Ni-Daq 6.9 and Using a Counter to Perform Quadrature Encoder Buffered Position Measurement in Visual C++ 6.0
(I think Ni-Daq not support PC-TIO-10 because card not support pulg&play, you can hint me driver for support this card. ) and i want example program for read counter. i use Visual C++ for run,i don't use Measurement Studio.NI-DAQ 6.9 supports the PC-TIO-10.
I attached an example that will show you how to do it in CVI (ANSI C).
Attachments:
Cviencod.zip 19 KB -
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,
GaryHey 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 -
Measuring distance using quadrature encoder
I am currently doing a project that requires the positioning and characterization of TV signals. As such, the position of the TV receiver is one important variable that i have to measure. I am required to automate the measurements and data logging using a PC/notebook. I have purchased a 2-channel HEDS-9000 quadrature encoder with 2000 CPR & the HEDS6120 codewheel - both from Avago Tech, to be interfaced with the notebook/PC. My idea is to get a TTL-to-RS232-to-USB converter to interface with the PC, so that i can feed the output from the encoder to the PC. However, i dun have much idea on how I can use LabView to interface the encoder and the PC. Can anyone offer some valuable advice?
Btw, the encoder module consists of 5 pins - Vcc, GND, CH.A, CH.B, with one pin not used.
Thanks !!Hi,
I think one of the best and reliable options that should meet your needs is a bus-powered USB-M-Series device like the USB-6210.
The USB-6210 is a multifunction data acquisition device with 16 analog inputs, 4 digital inputs, 4 digital outputs and 2 counters. Each of the counters can interface directly to the quadrature encoder signals of your HEDS-9000.
It's very easy to use this device with the NI-DAQmx API for position measurements in LabVIEW. In fact there are some shipping examples that you can use for getting started.
I hope this helps,
Jochen Klier
National Instruments Germany
Message Edited by Jochen on 02-09-2007 09:18 AM -
Using more than 4 quadrature encoder input for MyRIO
Hello,
I am doing a project where I need to drive 6 motors, each with quadrature encoder feedback to control position.
Currently, I've been using the MyRIO Encoder VI's, but there's a limit to 4 encoders. What is the best way of reading 6 encoders simultaneously with the MyRIO?
Thanks,
Timothy
Solved!
Go to Solution.If you need to modify the myRIO FPGA personality you have a few options.
The best option is to start with the myRIO FPGA sample project, add and remove components as needed and then build your bitfile. Any registers (LV FPGA controls / indicators) you don't modify will still work with the Advanced IO VIs and Express VIs. In order to use the new bitfile (FPGA Personality) you'll need to update the Open FPGA VI Reference in myRIO v1.1 Open.vi (LabVIEW 2013\vi.lib\myRIO\Common\Instrument Driver Framework\myRIO v1.0\myRIO v1.1 Open.vi).
After doing this any time you use a myRIO Express VI or Advanced IO VI it will use your custom bitfile. Any peripheral channels you've left in place will continue to work. Any channels you've removed will still show up in the VIs, but will not work (they will probably throw errors at runtime) and any new channels you added will not show up in the VIs. For new channels you'll need to use the FPGA Read / Write nodes to read and write the configuration and data register you created in the FPGA personality. These changes will persist on that computer until you change the Open FPGA VI Reference back to the original bitfile.
Let us know if you have questions about any of this.
Thanks!
-Sam K
LabVIEW Hacker
Join / Follow the LabVIEW Hacker Group on google+
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