Quadrature encoder read

Hi.
I'm a new user to labview, so try to be as soft as possible.
I want to control an electric motor(24v, 3I) via labview.
I use labview 6i(budget,budget) and a pci6024e board.
I have a quadrature encoder connected to the motor and I've build
the pid vi to control it.
1.what is the best way to connect the encoder?
i have tried to use software counters, with no luck so far.
2. I need to find a way to build a vi that can give me the response of a known transfer function to a pulse.is there a vi example or do I need to build it by solving the DE?
Thank you
ran

Hi Ran,
There are a few examples of either counting digital pulses on your quadrature encoder, or measuring the revolution frequency (frequency measurement). Depending on your application you will need to connect your device to your E series card to either the gate (frequency, period and time measurements) or the source (simple event counting) of the counters. These are decribed clearly in the E Series Help File. http://digital.ni.com/manuals.nsf/websearch/0E0DFDBB7706687A86256F6300560584?OpenDocument&node=10968_US
In addition, we have a few examples and tutorials on this website. You can simply make quick searches with the few key words i have just mentionned.
You also have to make sure that the signal coming out of your encoder is in the appropriate format (5V digital). In some cases, you would need a voltage divider.
As for the second question, I would need some clarification. You can definately process the information you have acquired in any way you want. You can search for our VIs by selecting the search button in the function pallette. Most data processing VIs are for analog signals.
Best regards,
Nathan Yang
Applications Engineer
National Instruments

Similar Messages

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 KB

Hi 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

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,
David

Hi 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

Reading Angles From a Line Driver Quadrature Encoder

I currently have a Quadrature Encoder (Line Drive) and am trying to interface it with a PCI-6602 Counter/Timer Card. I have currently had no luck in correctly hooking it up and reading the angle. Past experience with Quadrature Encoder have all been open collector; I have been able to to successfully hook up an open collector encoder with the 6602.
Any help in hooking up the Line Driver encoder with the PCI6602 would be appreciated.
Thanks.

Justin,
Normally, the mfgr. would include a recommended "Line Receiver" interface circuit for the encoder. I've found that some line-driver encoders actually can be successfully connected directly to the 6602 for quick-and-dirty testing, though you wouldn't want to wire that up arbirtrarily or rely on it for the long term. In any event, it sounds like you'll need to add a line receiver interface.
-Kevin P.

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.
Kevin

Hi,
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

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

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

Simulate quadrature encoder output without hardware

I am brand new to Labview and have not had any training other than youtube and this fine forum. I am a mechanic trying to solve a problem using labview. I am posting this new question because I don’t have any hardware so I can’t use the examples I’ve seen others pointing to.
I’m trying to simulate the output of a quadrature rotary encoder. Once I have done that I want to use Labview to program an instrument that reads that signal and makes mathematical calculations to it but I need the signal first. The encoder will attach to a shaft that will rotate clockwise and then counterclockwise at a rate of about 122 times a minute. The total shaft rotation will be between 0 - 18 degrees. It is important to me to know the direction of the shaft. The quadrature encoder will send out 2 square waves with one wave behind the other. The way I’ve tried to do this is by using 2 Simulate Signal modules each sending out a square wave at 2 Hz. I’ve connected a single knob controller to the both frequency inputs of the signal modules to simulate the speed the shaft rotates back and forth. I’ve done the exact same thing to the amplitude input to simulate the degrees the shaft turns before changing directions. My problem is the changing directions. I can delay the phase, which is what I want to do, but I can’t do it in real time and I can’t do it in a single 180 degree step. What I would like is a switch to change the B channel from +90 to -90 when it is toggled. If I could then toggle the switch when the amplitude reaches 18 degrees or less I will have an encoder signal. Thanks for any help you can provide.
steve
Attachments:
Rotory Encoder.vi ‏59 KB

Steve,
From what I understand, you want to make a 180 degree phase shift every N intervals? I modified your code to do this. Let me know if that gets at what you are doing.
Cheers,
Chris LS
National Instruments
Applications Engineer
Visit ni.com/gettingstarted for step-by-step help in setting up your system.
Attachments:
Rotory EncoderEdit.vi ‏61 KB

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,
Gerry

You 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....

Troulbe in measurement quadrature encoder with 6601

Hi,
Thanks for Ross's help.But I cannot differ 6601's x4 mode from other counter/timer counting mode. In measurement position, what difference between them. And I just want to know whether my application viable.
We are trying to measure position with 6601. The frequency of quadrature encoder is from 100Hz to 8MHz. Now, we connet the A,B and Z channel directly to counter . Using the example in CVI, we change the filter to 100ns and use x4 mode. It works perfect at low frequency.
The problem is when the frequency of encoder is higher than 2MHz, the accuracy decreases greatly. I'd like to know about following:
1.Can 6601 do the previous task enough? Or I must change to use 6602.
2.If
6601 is available, is there any way to increase measurement accuracy ?(in software or wire connection )

>jimmyjimmy2000
"Hi,
Thanks for Ross's help.But I cannot differ 6601's x4 mode from other counter/timer counting mode. In measurement position, what difference between them. And I just want to know whether my application viable.
>>mross>The application is viable. However, the use may be difficult.
>jimmyjimmy2000
We are trying to measure position with 6601. The frequency of quadrature encoder is from 100Hz to 8MHz. Now, we connet the A,B and Z channel directly to counter . Using the example in CVI, we change the filter to 100ns and use x4 mode. It works perfect at low frequency.
The problem is when the frequency of encoder is higher than 2MHz, the accuracy decreases greatly. I'd like to know about following:
1.Can 6601 do the previous task enough? Or I must change to use 6602.
>>mross>The 6601 is just as good as the 6602 at 2MHz. Therefore, a 6602 will have the same problem of inaccuracy.
>jimmyjimmy2000
2.If 6601 is available, is there any way to increase measurement accuracy ?(in software or wire connection )"
>>mross>Yes, in the wire connection you can make improvements.
6601 can count as fast as 20MHz (60MHz with prescaling). The signal is noisy (containing addtional, incorrect information).
You must use an oscillosope to look at the signal. Look at it when 6601 is counting correctly, and look at it when 6601 is "malfunctioning".
The counter will increment whenever the signal is high for more than 5 nanoseconds. The conditions for "High" and "Low" signals must be strictly met. If the signal is greater than 0.8V, the counter may increment. The signal must then drop below 2 Volts for a "Low" to be seen.
This sounds wrong, but is true. The counter is expecting TTL signal conditions (Transistor -Transistor Logic). This specification is very broad.
A "High" will absolutely be recognised if the signal is greater than 2.0V.
A "Low" will absolutely be recognised if the signal is less than 0.8 V.
However, the range from 0.8V to 2.0V is "undefined." This means the counter could increment at 0.8V. It has been my experience that National Instruments TTL will always see 0.8V as a "High." If your noise exceeds 0.8V you will never be able to count accurately.
The problem will be solved when your encoder signal is read cleanly by the 6601. This is why I gave you the URL for US Digital in the previous answer. The circuits they sell can help to clean up the counter signals. You will have to see what works best, since I don't exactly understnad you application. If the noise is very bad, you may wish to use the Encoder to Binary Number circuit. There will be no noise in the reading of a binary number. Since your encoder may run as fast as 8MHz, you must be sure the circuit you choose is also this fast.
The other solution is to eliminate the noise which is causing the counter to trigger falsely. THis can be a very interesting problem to solve. Please look a this NI link:
Field Wiring and Noise Considerations for Analog Signalsv
http://zone.ni.com/devzone/conceptd.nsf/webmain/01F147E156A1BE15862568650057DF15?opendocument
Follow these instructions very carefully.
Also, this book is helpful to explain noise and how one may reduce it.
From Amazon.com you can get Grounding and Shielding Techniques, by Ralph Morrison.
http://www.amazon.com/exec/obidos/ASIN/ 0471245186/104-3492923-2811911
Be very careful how you wire the circuits. Try to use only one ground point.
The worst source of noise can be the motor and drive that spins the encoder. Be particularly careful in wiring this apparatus. A simple solution can be to use an air powered motor insted of an electric motor.
Good luck,
Mike Ross

6602 quadrature encoder with c code

I need to implement a quadrature encoder on the 6602 board usinng c language.
I found some good function, for example DAQmxBaseCreateCIAngEncoderChan, but i think this function is only for DaqmxBase,
is there some similar function for Daqmx, or have i to do it myself?
From where can i start?
Thank you in andvance
There are 10 kinds of people. Those who understand binary notation, and those who do not.

Solved my problem.
I installed the daqmx version on CD and it was old.
Now i installed the new version daqmx 9.0 , that i toke from the site.
This version has the function i need DAQmxCreateCIAngEncoderChan,
it compiles , now i have only to attach my encoder.
Thank you lo stesso
Message Edited by blacksocket on 02-08-2010 05:32 AM
There are 10 kinds of people. Those who understand binary notation, and those who do not.

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

Quadrature encoder, velocity

Hi,
I am using DAQ 6062E, with BNC 2120. I have a quadrature encoder, and I need to get the position, and velocity. I have modified BNC2120_Quadrature_Encoder vi from NI. I can compute the velocity (delta position/time loop) easily, however this is not very accurate. I need to have a high accuracy velocity, and I think I have to use the second counter to measure the frequency of channel. However, I am not able to calculate the velocity with this method. I have attached my vi. I appreciate if somebody can help.
My encoder is connected to CTR Source 0 (PFI8), and UP_DOWN (P0.6)
I have connected CTR Source 0 (PFI8) to CTR 1 Gate (PFI4)
Thanks!
Attachments:
try encoder_with frequency.vi ‏58 KB

I get reasonably accurate velocity from quad encoders by connecting the source of my counter to the internal 20MHz clock then gating said
counter with my index pulse(Z) or either A or B, depending on the speed at which I am running. This will give you a count of time between
revolutions if gating with Z, or it will yield time between X degrees if gating with A or B.

Quadrature encoder synchronize sample

Using a USB-6251 to measure a quadrature encoder, i would like to determine the angle that an external discrete changes state. I tried connecting the discrete to a DIO input and using CVI PC code to read the encoder angle when the change of state occurs. The problem is the latency of the PC code which adds up to 4 degrees (with variability) to the measured angle. An ideal solution might be to trigger a measurement into a buffer within the USB-6251 when the discrete changes state, then read the value into the PC at a later time. Is this possible with the USB-6251?
Solved!
Go to Solution.

Thanks Adam,
I solved my problem using that idea with the addition of using buffered sampling and the discrete as a trigger. Committing the task to hardware also seems like a good idea but may not be required.
The setup code looks like this:
   // Start an Encoder channel on counter 1 to monitor the angle of label detector PNP edges
      status = DAQmxCreateTask("PNP Rising Edges",&pnpTaskHandle);
      strcpy (chanString, devName);
      strcat (chanString, "/ctr1");
      status = DAQmxCreateCIAngEncoderChan (pnpTaskHandle, chanString, "", DAQmx_Val_X4, 1, 0, DAQmx_Val_AHighBHigh,
                                                                              DAQmx_Val_Degrees, 4096, 0.0, "");
      sprintf (chanString, "/");
      strcat (chanString, devName);
      strcat (chanString, "/PFI1");
      status = DAQmxCfgSampClkTiming (pnpTaskHandle, chanString, 1000000, DAQmx_Val_Rising, DAQmx_Val_ContSamps, 10
                                      0000);
      if (status < 0)
      DAQmxGetErrorString (status, errString, 1000);
      DAQmxTaskControl (pnpTaskHandle, DAQmx_Val_Task_Commit);
      // Start the task
      status = DAQmxStartTask(pnpTaskHandle);
      angleTaskStarted = 1;
Reading the value looks like this:
      status = DAQmxReadCounterF64 (npnTaskHandle, DAQmx_Val_Auto, 0, npnEdgeArray, 1000, &npnSampsRead, 0);

Quadrature encoder

Hi,
I'm trying to make an position measurment with a quadrature encoder.
My hardware is a6031E card, and I 'm using DAQmx 7.4.0.
I read the AN84. So I connected Channel A to Ctrl0_src (PFI8) and
Channel B to ctrl0_up-down (Port0.6). I used the
"quad_encoder_with_E-series_(STC)-daqmx.vi".
It first didn't work : il was counting up and not down or the opposite whether I was couting rising or falling edge.
Then it worked (I cannot see what I changed, I think I did not change anything but it's impossible).
And now, it doesn't work anymore. Even when I create a global channel
and test it in MAX, it counts up good, but when irotate the shaft the
other sense, it stays at his level and doesn't count down.
Can somebody telle me where I made a mistake and what I forgot.
Thanks.

Merci de me répondre.
J'avais bien configuré mon compteur en "controllé de manière externe" mais ça ne marchait pas.
J'ai trouvé la réponse ce matin : mon codeur disposait de sorties
totem-pole, et je l'alimentait en 12Vdc. J'ai vérifié la doc ce matin,
et le fabricant garantit un niveau bas maximum de ... 2 Volts. En fait,
des fois, il descendait en dessous du niveau d'acceptation bas TTL et
souvent non ! Du coup, avec 2 volts sur mon entrée count up-down, je me
trouvais souvent dans une sorte d'idle state, puisque mon signal sur
cette broche était plus haut que le niveau d'acceptation bas TTL et
plus bas que le niveau d'acceptation haut TTL.
J'ai changé de compteur pour un avec des sorties TTL directes, et tout marche parfaitemement bien.
Merci encore de vous être intéressée à mon problème,
Bonne fin de journée,
Olivier Quillard

Quadrature encoder read

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