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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Any ideas on how to use a 6602 to do frequency division?

Uisng traditional DAQ.
The 6602 user manual says it can do frequency division but I can not find an shipping example for this operation.
In the end I want to be able to use the 6602 to handle the interface to a quadrature encoder.
I want the 6602 to generate a sample pulse I can use for other DAQ work.
I would like to get one pulse for both transitions of both the A and B signals, or otherwise stated;
A pulse when
A goes high
B goes high
A goes low
B goes low
I was thinking if I could configure a counter (or group) to operate as a frequency divider and use each of the encoders as a clock signal AND just do a divide by "1" I would have what I was after.
Big Picture (incase it makes a difference)
A quadrature encoder is coupled to a resolver I am testing. I need to corelate the angular displacement with the measurement from the resolver. While the shaft of the encoder and resolver are spinning, I want the encoder to clock the analog input samples.
Thank you for reading,
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

Ben,
First the executive summary: Sorry, No Can Do.
You won't be able to generate a sampling clock pulse on the transition to each of the 4 quadrature states. Here's a thread I was involved in where a similar question was asked. If you need to correlate in exactly that manner, you may want to pick up a quadrature decoder chip such as the 7084. It'll generate a "pulse" whose width is controlled by selection of an RC time constant during circuit build. I put "pulse" in quotes because it isn't truly a TTL signal due to the long transition time. I would recommend that you plan on adding a Schmitt trigger to square it up, perhaps another to re-invert it back to original polarity.
However, all that being said, you may be better off using an internal sampling clock to drive analog and encoder position acquisition anyway. On many encoders I've used, the transitions are NOT perfect 1/4 divisions of the cycle. You can sometimes see this on the spec sheets where the A to B relative phase is given as, say, 90 +/- 15 degrees. There will also be a tolerance on the phasing of A's rising and falling edges, maybe 180 +/- 10 degrees (it's often a little tighter than the A to B phasing).
In practice, I've typically found that these deviations tend to be systematic rather than random. Of the company's 1000 similar encoders, the phase stays within the range 90 +/- 15. With my 1 instance, the phase may be 84 +/-3 around a full rev of the encoder. The point is that if you generate pulses with the quadrature transitions, the samples still won't *really* be equally-spaced in position. They'll just think they are.
I'd suggest at least considering high-speed sampling with an internal clock that's shared by both tasks. Then do a little bit of curve-fitting / interpolation to the data when you need to derive more precision.
Re: frequency division. You have to select a specific edge (either rising-only or falling-only) as the active edge. Your counter will then ignore the other type of edge. Also, you'll need to specify the # of edges each for the idle and pulse states. These must each be >= 2. So you can't divide by 1 - the best* you can do is to divide by 4. (*Technically, you could sort-of divide by 2 if you configure the counter to pulse rather than toggle its output. However you can't control the pulse width, and as I recall it's fixed at 50 nanoseconds.) Write back if you'd like to see an example.
-Kevin P.

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.

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

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

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

Troulbe in measurement quadrature encoder with 6601.

Hi,
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 )

Jimmy,
You would need to specify what type of accuracy you are looking for, which is pretty much dependant on the type of operation you are performing. You could be looking to timestamp your encoder positions or you could also be looking to perform position/angle tracking over time. You could also be performing single point vs. multiple point (buffered) operations. You could mention which one of the CVI examples you are using and that could give an idea of the type of operation you are performing.
The NI-6601 is able to perform quadrature encoder measurements and the only limitations you can have in regards of frequency are the filtering parameters (if you use filtering) and the actual maximum timebase of the board (20 MHz).
Please keep in mind that by ena
bling filtering at 100 ns you are only guaranteeing that pulses with widths of 100 ns or longer are not being filtered out. This limits your encoder phase frequency to around 5 MHz. (Each encoder period has a 50% duty cycle, therefore the pulse duration is half the encoder period). You can refer to the board�s manual for more information on filtering.
We would have to know the following in order to provide further help:
a) Type of operation being performed
b) Specific example you were using
c) Type of accuracy you were looking for
d) Range of accuracy you needed on your measurement
Regards
Alejandro Asenjo
Applications Engineer
National Instruments

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 counter with 8 channels

Hi,
I need to acquire the signals (A and B) of four quadrature encoders. The signals have a maximum frequency of about 5kHz and should be read out with about 100 Hz. Is there a device that fulfils these requirements? It seems that a frequency of 5kHz is no problem since e.g. the USB-6008 has a counter for frequencies up to 1 MHz. However, I can't find a simple low-cost device that provides several counters. Does anyone know such a device with 4 or 8 counters?
No other analog or digital channels are necessary, but a USB connection and Matlab support would be ideal.
Thanks in advance.

Depending on your definition of low-cost, the 9171+9401 might suit your needs:
4 counters capable of quadrature encoder measurements (the single counter on the 6008 only does simple edge counting).
USB connection.
MATLAB support via the Data Acquisition Toolbox (according to their website).
I don't believe NI currently has any other option that meets these requirements at a lower cost. If USB isn't mandatory, you could also consider the PCIe-6612 which provides 8 counters.
Best Regards,
John Passiak

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

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

Quadrature encoder interface to PCI-6229

Using PCI-6229 with LV7.1.
I need to connect an incremental quadrature encoder ( A,B and Z )
signals directly to the card and use the CTR0 to give me the angular
position information. Encoder is a 2500ppr type.
As per the specification summary of the PCI-6229 card, this is
possible. If so which terminals to use ? ( I have also posted a
similiar query in the other hardware forum )
can someone help me out in this ?
Thanks
Raghunathan
Raghunathan
LV2012 to Automate Hydraulic Test rigs.

Dear David,
the search terms that you gave helped a lot also. I could get sample code for checkout of an encoder with LV7.1. Good.
I am not sur eif you have actually worked with the encoder + LV
combination. Normally any optical encoder will produce high
frequency jitter if it happens to stop just at the point of transition
of either the A or B channel . I do suppose that the DAQmx VI
will handle this and not produce spurious counts - or do I need to
configure a filter for the relevant PFI lines ?
Thanks
Raghunathan
Raghunathan
LV2012 to Automate Hydraulic Test rigs.

Want to get velocity with quadrature encoder

I can count and measure the displacement from the encoder signal with your quadrature encoder example file.
But, can you please advise me know how to implement to get velocity or RPM from that somewhat easily?
Thank you for your help.

Hey Encoder,
You can measure velocity by using a buffered, counting operation. With a buffered operation, the count is latched on the rising/falling edge of the gating signal. Therefore, if you provide a signal to the gate with a known frequency, you will be able to mathmatically determine the frequency of the signal connected to the source.
You can usually use another counter to provide a gating signal with a known frequency. There are example programs that illustrate how to do this.
DAQ-STC: Measuring the Frequency of a TTL Signal (Easy-Level VIs)
http://sine.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=B45EACE3DD4756A4E034080020E74861&p_node=DZ52329&p_source=External
Measure a TTL frequency with DAQ-STC or NI-TIO in Visual Basic
http://si
ne.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=B45EACE3D7A756A4E034080020E74861&p_node=DZ52329&p_source=External
I hope this helps.
Regards,
Todd D.
NI Applications Engineer

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

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

Quadrature encoder frequency division dotNet Net VB C#

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