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

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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.
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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.
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Nathan Yang
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Hi All,
I've got a bit of FPGA code here that I've been running on the cRIO 9073. We've been using 250/500 count quadrature encoders just fine with it, but have recently moved up to a 2000 count encoder and it seems to be missing counts. I'm not using a machine to rotate the encoder, just my hands. Is there anything I can do to speed up the operation of this loop in the FPGA?
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Attachments:
quad_encoder.png ‏51 KB

Ken,
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32bit_Cnt_Edges_to_Quad.vi ‏73 KB

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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.
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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

RPM Measurement using Quadrature Encoder and PXI 6602 counter

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Hello, ( a similar post has been placed on DAQ forum apologies as I did not know best place)
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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.
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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.
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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.
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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.
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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

Need COTS Analog Speed Signal from Encoder

Hello everyone, need some shopping help.
I have a customer who wants to get a scaled analog output corresponding to rotational speed from an encoder instead of doing traditional freq measurements. We want a stand alone package that does the frequency measurement on board and just puts out a scaled analog output.
Need < 100 mS latency and ability to resolve 5 rpm to 1000 rpm. Just don't know where to go to buy one.
Anyone know of such a device?
Thanks
Wes Ramm
Wes Ramm, Cyth UK
CLD, CPLI
Solved!
Go to Solution.

One example of many manufacturers of frequency to voltage converters:
http://www.dataforth.com/functional.view.aspx?ptypeid=11
Look at the detailed specs to make sure the unit's input voltage range is compatible with the encoder along with the response time.
-AK2DM
~~~~~~~~~~~~~~~~~~~~~~~~~~
"It’s the questions that drive us.”
~~~~~~~~~~~~~~~~~~~~~~~~~~

How to calibrate Quadrature Encoder signal

I have PCI-6601 and CB68-LP connector. How can I use these to interpret quadrature signals coming off an optical encoder (to sense the angular position of an-observatory dome). The encoder is 16-bit(don't know what this means in terms of PPR). I want to have a display in Labview that will show me the position of the dome in a fraction of 360 degrees with some reference(true north?), the dome rotation controlled by a three way switch(clockwise-off-anti-clockwise). I don't have much experience with labview and any help will be appreciated.

If the encoder is 16 bit then it would seem that: -
360/65536 = 0.0054931640625° or there abouts.
You can break the project down into two halves nicely.
1) Hardware interfacing.
2) Software read out.
The hardware interfacing means two basic things:
1.1 What is the encoding technique
1.2 How are the signals conditioned for output to an external device.
The software is classic:
2.1 Input
2.2 Process
2.3 Output
The optical encoder could be one of a few types and you need to understand both the signalling / interface and the coding technique to progress further. A good start will be the manufacturers data sheet for the product. Contact the manufacturer.
Once you understand the coding technique you will then know if the unit is absolute or relati
ve. This will then allow you to determine how you can point to true north (easily with an absolute encoder, it always tells you exactly where it is).
If it is a classic quadrature encoder then the relative phase of the reference and movement signals gives you direction. Counting transitions gives you realtive movement. But if the power went off on the PC. you don't know where you are unless you go to a home position! That could be 359° round !!!
Good Luck

Speeding up quadrature encoder read out

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