Using LS7083 for quadrature encoders
I just read Application Note 084 from 7/9/1999 that recommends using an LS7083 quadrature clock converter to eliminate miscounts due to vibration at low speed on an E Series board. It makes sense from what I have read, question is: does this apply to the M Series board I am using as well - PCI6220?
Ed
Ed,
True quadrature conversion is a built-in feature of the M-series boards so there should be no need for an LS7083 or similar interface circuit.
Personal testimonial: I've been using an M-series counter connected directly to a quadrature device for several months with no miscount issues. The device is a non-contact laser interferometer that resolves at the sub-micron level, and we're getting very repeatable measurements. This in an environment where the otherwise unnoticeable air currents from normal operation of the HVAC system cause a vibration-like fluctuation in counts.
-Kevin P.
Similar Messages
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Wrong results using quadrature encoders with NI DAQCard-6036E
Hello,
I'm experiencing some troubles using two quadrature encoders with a NI multifunction I/O.
The encoders are Micro-Epsilon WDS-7500-P115-CR-TTL. They are incremental encoders in TTL logic. They are connected to a HP laptop running Windows XP Professional. The connection is via the multifunction I/O NI DAQCard-6036E. Each encoder is connected to the DAQ board with four wires: +5V, DGND, track A, track B. I used the system in my office for a while and everything was fine. Then I moved it in another place and now it shows a fuzzy behaviour.
I made the following tests:
Test 1) I connect track A&B to analog inputs on the DAQ card. Then I use SignalExpress v2.5 to perform a DAQmx analog input acquisition. The waveforms I get are exactly as expected.
Test 2) I connect track A to the counter source and I leave track B disconnected. I use SignalExpress v2.5 to set a DAQmx edge counter, with the "Count up" option enabled. Also this test is fine. When I pull the encoder cable I get +N counts and when I release the cable it goes back to zero position, giving other +N counts.
Test 3) I connect track A to the counter source and track B to P0.6 (or P0.7 for the second encoder), which is the pin used to control the count direction. I use SignalExpress v2.5 to set a DAQmx edge counter, with "Count up". In this way the DAQ should ignore track B and count always up. Actually it does, but the count rate in one direction is double with respect to the count rate in the other direction. This means that when I pull the encoder cable I get +N counts and when I put it back to initial position I get other +2N counts. In this way the counter indicates +3N at the end, while it should be +2N.
Test 4) I connect track A to the counter source and track B to P0.6 (or P0.7 for the second encoder). I use SignalExpress v2.5 to set an "Externally controlled" DAQmx edge counter. Now I get +N counts when I pull the encoder and -2N counts when I put it back to zero position. In this way the counter indicates -N at the end, while it should be zero.
Test 5) I repeat test 4 using LabWindows/CVI v8.1 and I get the same result.
Test 6) I swap lines A&B. Now track B is connected to the counter source and track A goes to P0.6 (or P0.7 for the second encoder). Using SignalExpress to perform an "External controlled" count, I get +2N counts when I pull the encoder and -N counts when I put it back to zero. So, at the end the counter indicates +N, but it should be zero.
Do you have any idea on how to solve the problem? Thank you very much in advance.A few things:
1. I'm not from NI and won't try to speak for them. But I don't believe these forums are meant as a primary means of support, probably not an *official* means of support at all. Most of the folks here (like me) are NI's more-or-less satisfied customers, not employees. If you buy a service contract, you can get instant phone support. If you rely on free support from the forums, I think you'll get good help most of the time, but there's just no guarantee.
2. "I just got a [email] reply from MicroEpsilon. The encoders work fine." Um. Based on what, exactly? Of *course* they will expect their own stuff to be just fine, and in fact I very much suspect they're right. But NI will expect their board to be just fine, and I expect they're right too. Or at least it was fine *before* you hooked things up. Leading us to #3.
3. Part of the app note on Quad Encoders on E-series boards warns against connecting differential encoder outputs directly to your board. I think it mentions that a 24V differential (for example) can damage the board. But even a low-voltage differential signal isn't electrically *compatible* with your counter inputs. Your first posting claimed that the encoders produced TTL. Your June 30 post referred to inverted A and B signals for rejecting common mode noise over long transmission lines. These are classic code words that scream "differential output", *not* TTL. So now we can start addressing some specific tech issues.
4. Your E-series board is not inherently capable of handling true quadrature, as the app note says. (The newer M-series multifunction boards *do* have the capability.) You can get kinda sorta close, but you'll be at risk of count errors due to direction changes or during vibrations when otherwise stationary.
5. You will also need some type of differential to TTL conversion on your (A, /A) and (B, /B) pairs.
6. You will need a common "ground" reference for all your digital signals (probably not a true earth ground). So the ground for your conversion circuit and its TTL outputs must be tied to your DAQ board digital ground. Also the return terminal from any related external power supply. Sounds like failure to do this had been an issue with a past implementation of yours so perhaps it's an additional factor at play this time too?
7. What are you trying to measure? For what purpose? What decision is made from the data? How much do you care about its accuracy? These are leading questions, but I'm suggesting that meeting schedule with an unreliable app that produces untrustworthy data just might not be the best goal to strive for right now. If you care to maintain accurate position count despite direction changes or vibrations, you *need* something more than your E-series board. If you want reliable edge counting operation with *any* DAQ board, you *need* electrically compatible signals.
-Kevin P. -
Measure Angular Position using quadrature encoders
Hi I’m new to LabView and NI and would like to know whether the angular position, measured using two quadrature encoders can be measured (and interfaced with LabView) using the following National Instruments hardware:
NI cRIO-9014 (CompactRIO Real-Time Controller)
NI-9403
NI-9215
NI-9263
If it can be done I would really appreciate some pointers or suggestions of how to start either setting the hardware up or writing the LabView program.
Many Thanks
AlexHi Alex
Welcome to the world of LabVIEW and NI. You're off to a great start with the hardware and software that you already have. It sounds like you just need a bit of extra knowledge to get you started. A great place to look for help is in the LabVIEW Find Examples.. This can be found on the LabVIEW splash screen pictured in the attached image.
For your specific set up I would also suggest navigating to the following links:
NI CompactRIO Starter Kit and Hardware Setup Wizard Frequently Asked Questions (FAQ)
It may well be an idea for you to attend one of our customer education courses which would really give you a headstart in your application. Information regarding this can be found here:
LabVIEW Real-Time training
I hope this information is of some help to get you started.
Kind regards,
Daniel T
Applications Engineer
National Instruments UK & Ireland
Attachments:
Find examples.PNG 253 KB -
How to wire VI for 2 encoders using NI9401
I have the attached vi that measures period. My understanding is that the NI 9401 can measure period for up to 4 encoders at once. Do I need one DAQ sequence per encoder, (e.g. the attached vi should measure period for 2 encoders simultaneously)? I want to run up to 16 encoders, so, do I need to copy/paste this code 16 times in order to collect period data for 16 encoders simultaneously?
I am using cDAQ9174 and NI 9401. My understanding is that the 9401 can measure up to 4 encoder signals. If I put a second NI 9401 into the cDAQ9174, can I measure 8, or does the cDAQ9174 limit the number of counters that can be accessed independently? If I have to use two cDAQ9174's, plugged into one PC, does Labview recognize the eight slots as unique, e.g. 1-8, instead of two sets of 1-4 for the addressing of the channels?
Any generic advice on measuring many encoders (period) simultaneously is welcome.
Thanks,
Dave
Solved!
Go to Solution.
Attachments:
counter forum feb 13 2013.vi 31 KB- Even if you put two NI 9401 into the cDAQ-9174, remember that the counters are in the chassis and this device just has four counters.
- You can run counter tasks in parallel.
- If you plug two cDAQ-9174, MAX recognizes two different devices.
Regards -
Hi,
I'm using a quadrature encoders with a PCI6025E board to measure an angle,
I want to use the COUNTER1 so I have connected line A of the encoder to PFI_3 and Line B of the encoder to LINE DIO7.
I have configure the 6025E with this code to read the counter 1 value :
status = GPCTR_Control(1, ND_COUNTER_1, ND_RESET);
status = GPCTR_Set_Application(1, ND_COUNTER_1, ND_SIMPLE_EVENT_CNT);
status = GPCTR_Change_Parameter(1, ND_COUNTER_1, ND_SOURCE, ND_PFI_3);
status = GPCTR_Change_Parameter(1, ND_COUNTER_1, ND_UP_DOWN,ND_HARDWARE);
status = GPCTR_Control(1, ND_COUNTER_1, ND_PROGRAM);
All the status code return by this functions are 0 and so OK.
But when I Get the counter value with GPCTR_Wathch().
When i tur
n the encoder in one way it count up well, but when i turn the encoder in the other way (down) I read a count that is is two times more than the count up (count down = 2 * count up) !!!!
Does someone have meet this problem before?
Any solution to solve this problem ?
Thanks.
dpasssounaudHello,
Your programmation seems to be OK. And the connections too.
Please, test the program in the attached file and tell me about the results.
Sanaa T
National Instruments
Attachments:
Mes_Ang.zip 5 KB -
Huge latency reading quadrature encoders
I'm using a PCI-6601 to read two quadrature encoders on a pan-tilt mechanism. The software uses the DAQmx C interface and polls the encoder positions at 200Hz. The problem is that there appears to be a huge latency on the order of ~50msec between when the encoders move and when the positions being read out reflect the movement. That can't be normal.... is it?
I am able to get data off the DAQ at the 200Hz rate, and the values all look reasonable except that they're time delayed by the aforementioned 50ms. So I'm getting a resolution of at least 5ms, just time-shifted. The first thought was that the values were being buffered somehow, but there doesn't appear to be any buffer, at least that I can find. As I understand it quadrature input shouldn't be being buffered in the first place, and in any case a buffer should be read out with the call to DAQmxReadCounterF64 (the DAQ returns only 1 value), and indeed explicitly setting the input buffer via DAQmxCfgInputBuffer does nothing.
To double check the results I tested NI's sample code for reading quadrature encoders (http://zone.ni.com/devzone/cda/epd/p/id/5735) and I get the same latency (minus the ~5ms that was caused by the 200Hz timer, as the sample code polls in a tight loop.)
Any idea of what might be going on here?
Thanks!
GeneHi Gene,
I just wanted to make sure you were indeed using DAQmx (since you linked the DAQmx Base example). I might expect the DAQmx Base version of the code to take longer to execute, but re-reading your post it sounds like the problem isn't with the code keeping up but rather that the values themselves are delayed by ~50 ms.
A buffer would only be allocated if you configure sample clock timing on your encoder task. The example you linked doesn't do this, so I'll assume your code doesn't either. It's probably worth noting that you can configure a hardware-timed sample clock so you can deterministically sample the count register at regular intervals, but this isn't going to help with latency.
So taking a step back for a moment, I am now curious on how you are measuring the 50 ms latency. To verify a 50 ms delay would require measuring the actual time difference between the start of the counter task and the first pulse of the encoder and then comparing the measured time with the time you are seeing in software (assuming ~5 ms per sample from your 200 Hz polling loop). I would not expect a 50 ms latency in your measurement, so it's probably worth elaborating on exactly what you are seeing and how you are characterizing it.
Best Regards,
John Passiak -
3 quadrature encoders on one 9411
I'm trying to read three quadrature encoders using a 9411 in a cDAQ. In the cDAQ is a 9437 reading a load cell.
Sample rate is set to 1613 HZ, and the counters use the cDAQ/ai_clock .
Reading one encoder on DI0a/DI1a, I have no problems. As soon as I add a second encoder on DI2a/DI3a, I begin to get strange results. It's as if the position skips or jumps occasionally.
I guess before I start troubleshooting I'm wondering if there is any reason I should not be able to measure three quad encoders using the 9411.
The three encoder readings are three different tasks. Perhaps I should make them one task? These tasks are all read in a loop, 20 readings at a time, but they're reading in parallel.
Using LV2013, Win 7.
Hoping to get some advice on the code.
Jeff
Attachments:
Hole Punch Tilt Measure Fixture.zip 119 KBSure! Keep in mind that I'm not a pro at Labview. See if this works for you. Should be in 2011
Attachments:
Hole Punch Tilt Measure 2011 Folder.zip 110 KB -
We have purchased 5 apple minis and would like them all on one account, that way we can monitor the use of these units. They will be used strickly for a business application. Can I use one account in itunes or must i have multiple.
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Probably best to create unique Apple ID's for each... this will also make things easier in the future as purchases are eternally tied to the Apple ID they were purchased with. -
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I can not send email from my iPad . Have been using it for over a year, all of a sudden I can only receive email. I have a wifi connection in my home and have a A T &T cellular data plan?
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OK, I try to change a template using Word for Mac version 14.3.4 2011 edition.
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I am running 10.6.8 and using iweb for my web site. After several SEO analysis they all indicate I need H1-6 header tags. After looking at the source code I see there are none in iweb. Are they necessary to add? Why would one add these tags and how do I add H Tags to iweb? And are there examples to look at? I am slowly learning about simple web design and assumed that iweb was stand alone without having to write code. Is this one of the reasons iweb is no longer supported? Thanks for looking at this!
A simple text page like this:
Heading
sub heading
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Is traditionally represented by html tags like:
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I would guess that the use of h1-h6 tags helps search engines to understand the structure of a page as the tags imply a certain structure.
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How do i use ibooks for saving my lecture notes / power point slides please?
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A useful story for you, will hope
Today I upgraded to CS6, both Design/Web Premium and Audition.
After really being attracted, and thinking a lot about it, I didn't do so via Creative Cloud. I think you might like to consider why, and things that can be good to do about it.
I'm a long-time customer and adept with the tools, but it's important to know that what I do with them is to the side rather than in the center of my endeavors. In that, I suspect I'm like very many of your customers besides those directly in design shops.
Probably many of us have also been the every-other-release updaters, which rather than 'avoiding paying up' put our income stream for you in a balance with value received. I might add that I've been an consultant executive starting new media business within a big name, and fully understand the draw that subscription business models can have, if you can subtly choose and thus successfully manage them.
Here are the deepest problems Creative Cloud showed to me at present:
Apart from the first year offer, Creative Cloud would be more expensive to me. Yes, you added the extra apps, but not in proportion to their use value for me. Maybe the 'new apps' really will help me keep up with things like eBook and Html5 developments successfully, but that's an open question, isn't it, given history?
Once on this gravy train of subscription to you, I would be committed_forever_ to keep paying, if you look at your offer practically, and with the idea of needing to use the tools. That is not something my gut would let me do. Paths can change, and particularly will on the mature side of the ledger and with the kinds of creative things those of our weight can very usefully offer, which often need to be done on a stringent budget until they can flower.
Tools. The very point in having tools is that they are there when you need them to be, both in moments where learning takes place, and in intervals of creating deliverables. That's an emotional matter, surely, and you should know strongly at the heart of any purchase of the kinds of things you make, especially by individuals or individual decision-makers, who in principle I am going to presume are in fact a significant proportion of your buyers.
What can you do about this? And maximize your profits?
Primarily, I think you should modify the Creative Cloud exit terms. Instead of reverting to whatever products we had going in, which would then be obsolete, we should revert to the recent version of those products. Thus if I had come in at CS5.5 Design Premium, I might exit when CS8 was current, and in my CC use: that CS8, now stand-alone, is what I should go forward licensed to use. Now my investment is covered, and you get all the subscription business you can receive from me, while keeping the incentives to keep me going forward, whether CC or standard licensed. I now would be free to be in or out as suited my own situation -- an immense and proper comfort.
I also feel it would do very much for Adobe customers in daily use and in their perceptions that you use the relaxation a more committed revenue stream gives you to fully share any application fixes and upgrades as soon as they are ready. It should be a privilege of all who support you, not just those who can reasonably choose to do it in the subscription way. What's begun in a much better sharing by certain courageous managers on the forums would blossom, with the turnaround on fixes and improvements available most fairly.
Can you improve the way the rates work? An elephant in the room is surely that you can always raise the rate charged. But also, there can be times surely for many where the rates just go over what the current use of the subscription will bear. I would think there's a place for the 29.95 rate to be always available, below a certain time-percentage use level per month of the tools. Now you have something a customer can stick with -- through life changes, illness, investment in new venue, and so forth. You also have an entry available for all those who need to learn them, your future customers, and I don't have to mention what alternative method enough of them use when you don't have this. So, a flat rate, for maintenance and for the new?
Let me return to the thought of tools. A person's paintbrushes ought to be always there; we don't rent them, even if in some production of art we may pay for materials including brushes at a stream. Inspiration asks that those brushes be there every time needed, to express what may become value (which will be shared with you), even or especially when we are not in such a stream. Especially in a picture like this, a satisfied and secure customer is a much better customer, don't you think?
The short of it is, subscriptions give Adobe a kind of security. Any but the most corporate of your customers need their own security in return. By improving the terms of the Creative Cloud, you will improve our ability to support you in it. Removing the threat of what happens when circumstances indicate we leave,and during periods it doesn't make individual sense to participate, would create the real virtuous circle here.
Thanks for considering this, as well as you've considered some other things and made appropriate changes, which we notice in recent times. Appreciated.Better exit strategy? Agreed. I get the impression that Adobe's still mulling that one over and we may see more mutually beneficial terms emerge in future.
Don't know that anyone other than Adobe is happy with the current all-or-nothing terms.
Mid-cycle feature updates for perpetual customers? Won't happen other than the 0.5 releases (wonder how much longer they'll be around?). That's one of the UPSes (Unique Selling Propositions) of the Cloud.
Clearly, Adobe eventually wants to deliver all its software via subscription. They are going in the same direction as mobile (cell) phone carriers and utilities (gas/water/electricity) providers.
2010/2011's subscription model offered little value to most and got a muted response. The 2012/2013 Cloud model is much closer to the mark and the adoption rate is much higher but still being tweaked (e.g. Lightroom just arrived).
The Cloud's value obviously tempts you (so you're obviously on the fringe of the target market)- but not quite enough yet to sign up. I'm sure the balance will tip soon and tempt you again.
I'm sure the Cloud offerings will improve over time.
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