Can a NIDAQmx task contain two counter inputs?

Hi I am using PXI-6602 to measure angular position with three digital enoders. Currently I am creating three different task each with one ctr input and then synchronizing them together. Is it possible to create just one task having all three ctr inputs such that there is no need of synchronization etc.
Vicku.

Hi vicku,
I understand that you cannot have multiple counters in one task; in order to use multiple counters, you must create a separate task for each counter. Are you having problems trying to synchronize these tasks? If so, please post back the details so we can try to help.
Ana P
National Instruments
Applications Engineer

Similar Messages

Two counter inputs and counter output NI 9401

I am trying to configure two counter inputs and one counter output on one NI 9401. I have looked and found how to configure digital lines in booth directions but it seems like I can only do two counters in all on one module. Can someone verify this for me or let me know how to get all three on to one module?
Thank you

Hi mschoenwald,
The counters are actually located on the backplane of whatever chassis you are using--I'll assume you are using cDAQ and not cRIO.
If you have the older <link no longer exists>, then there are only 2 counters available in general. You can access both from a single parallel (8 lines or less) digital module in slot 5 or 6 of the chassis.
The 2nd generation Compact DAQ chassis (including 9174, 9178, 9181, 9188, etc.) includes 4 counters. You may access them from any slot with a parallel module. There is no restriction preventing you from accessing all 4 simultaneously from a single module.
The 9401 is bi-directional and configurable by nibble (line0:3 may be configured one direction, and line4:7 another). However, it is quirky in that it requires the line direction to be configured before any of the tasks are started. This is because the data lines themselves are used to set the line direction behind the scenes. The best way to work around the behavior is to use DAQmx Control Task to explicitly reserve your tasks before any of them are started (see here). Keep in mind that the counter output should use the opposite nibble from the two counter input tasks.
Best Regards,
John Passiak

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Synchronizing two counter frequency inputs with multiple analog inputs

Hello all,
I'm fairly new to LabVIEW and I'm trying to collect data from multiple sources with synchronized timing on the acquisition but I'm having trouble figuring it out. My problem is that I've got two counter frequency inputs, one optical tachometer reading one pulse per revolution, and a max machinery flow meter with a k factor of 12000. I can't seem to figure out how to sync the timing with my multiple analog inputs. I've been attempting to get the tachometer to sync with the analog inputs first by following the example linked here. (https://decibel.ni.com/content/docs/DOC-10785) So far each time I run it I either get a timeout error on the DAQmx read or a "Multiple sample clock pulses were detected" error (see attached image). It seems if I slow the sampling rate way down to say 10 hz and ensure that the tachometer signal is over 800-1000 RPM (13-17 Hz) before starting the VI then the program will run without errors until the RPM drops below that threshold then the "Multiple sample clock pulses" error occurs. The code is attached below.
Does anyone know of a more effective way of syncing counter frequency inputs with analog inputs? I'd like to have a VI that can show 0 RPM (and eventually 0 flow as well, but I think I need to figure out the timing of one counter before I add another as it seems I can't have two counters in the same task). Any help on this would be greatly appreciated.
LabVIEW version 13.0
cDAQ-9178 Chassis with NI 9401 for the two counter inputs and NI 9205 for the analog inputs.
Thanks!
Richard
Solved!
Go to Solution.
Attachments:
SimpleDAQ.vi ‏44 KB
LV_Error.JPG ‏31 KB

Maybe third times the charm?
So I've finally got a good handle on why the VI is having problems at low RPM though I'm somewhat embarassed how long it took me to do that
Because I have the counter time synced to my Analog input task if it doesn't see at least two pulses between the two clock pulses set by the analog input task I get the -201314 "Multiple sample clock pulses" error. This seems fine at first as it just sets a minimum RPM that I can measure and it's well below the area I'm interested in so no problems there. I tried a simple error handler that would clear the error when it happend assuming the loop would keep iterating until the RPM went above that minimum at which point I would get a signal again. This is not the case, the read function just continues to spit out the -201314 error even after the RPM is back in the readable range. So then I tried adding two case structures so that when the error occured it would stop the task, clear the error, and then start the task again on the next loop iteration (Code Attached). This also doesn't work as the error shows up again on the stop task and then AGAIN on the start task on the next loop iteration. It seems this error is not actually being cleared and once it happens it stays with the task regardless of what the error cluster is carrying.
Anyone have any ideas? The only solution I can think of is to just clear all tasks and recreate them each loop iteration until the RPM is readable again but that strikes me as a horribly clunky solution.
Richard
Attachments:
SimpleDAQ_1_Start Stop.vi ‏48 KB

Encoder position WITHOUT counter input

Question:
I have three incremental encoders connected to my M-Series DAQ board (PCI-6229) that has TWO Counter input channels. I am measuring the position of each encoder. How do I measure the position of the third encoder if I have used-up both counter inputs? Is there a manual way to accomplish this using my older version of Labview (version 7 express)? Any help is appreciated.
-Clarkam1

clarkam1 wrote:
Ben,
I'm on an extremely small budget and can only use the items available to me at present time. That being said, is there no way to use one counter for multiple encoders? Or could an external device be used to count which the DAQ board would read? I appreciate your timely responses. I'm trying to explore all other options.
So do you work for free?
If you are determined to get all three counters going with that device, you have a big challenge ahead of you. I'll try to explain. At teh input of your counters you have signal conditioning that feeds the counter itself. To do the same thing using analog input channels (since all of the counters are already used) you will have to develop code that simulates the signal conditioning, converts the analog to digital (this may sound easy but if you need to implement over-sampling its not) and then do the work of the counter, again in software.
If my customer was forcing this on me I would first review the behavour of the hardware and use it to establish the requirements of my code. So if you do not have an EE background, you will first have to learn the hardware so you can write software that does the same thing.
So if you work for free then you may want to chase down the examples that NI ships for their FPGA targets that implement serial protocols and the like. You may be able to harvest some code and examples from there. If you don't work for free, then you really have to decide if you want to re-invent in software what you can purchase.
Ben
Ben Rayner
I am currently active on.. MainStream Preppers
Rayner's Ridge is under construction

Two Counter channels in one task ID with DAQmx?

I am writing a program which will control the movement of a gimble on the X and Y axis with servo motors while recieving
position feed back from two encoders on those axis. I am using a 6251M series card's AO to control the movement
of the gimble, while running the encoders into a 6602 for position. When setting up my task ID in MAX I noticed I could add
both ctr0 and ctr1 to the task ID, but when I tried read the counters with that task I got an error in Labview and with the
test function in MAX saying I need to use a multichannel read. I can not find a multichannel read under the counter
section of my DAQmx read, and was wondering if this is even possible. I am used to programming with Traditional DAQ
and know you have to keep separate counter task ID's, but having bought an M series card and having to use DAQmx I
was wanting to know if I could combine them.
Thanks

You can have multiple channels in a single task, but those channels all
have to be of the same type. You can have analog inputs together
with other analog inputs, but cannot combine digital inputs/outputs,
analog outputs or counter tasks with that analog input task.
Once you pair only like tasks together then you shouldn't run into any more issues like this.
Best of luck,
Otis
Training and Certification
Product Support Engineer
National Instruments

6602 on Traditional DAQ : can't assign gate(0) to source input of counter (0)?

We are replacing a system that used PC-TIO-10 boards with 6602 boards.
In an attempt to minimize system changes, the new system has been wired
identically to the old system, which used the gate lines to count by
opening the gate on the rising edge of the gate line and counted on the
falling edge.
Apparently, we are prevented from using the gate line as source to a
counter. It is confusing enough that the manual says each of the fourty
counter I/O lines can be assigned to any of the counters and any of the
counter functional inputs: I still don't know if this is true or if it
is an improper interpretation of the manual.
Additionally, using DAQ 7.4, we are specifically limted to using source(x) lines as source inputs to the counters.
a) Is it really not possible to connect a gate() line to the source input of the same counter?
b) If so, is it possible to connect the gate(x) input to the source
input of counter(x+1) or (x-1) without affecting counter (x), which is
how it appears in the VI's?
c) If worse comes to worse, we are driving the gate inputs with the
output of an MC14490 hex contact bounce eliminator. Can we tie the gate
and source inputs to a single counter together, and in software set the
source as input and set gate on, and count events that way?
and I guess,
d) we're hopelessly crazy and misinformed, and have to remake the
interface boards and/or completely rewrite the software to use DAQmx?
ray

We are replacing a system that used PC-TIO-10 boards with 6602 boards. In an attempt to minimize system changes, the new system has been wired identically to the old system, which used the gate lines to count by opening the gate on the rising edge of the gate line and counted on the falling edge.
I don't understand the function you were accomplishing. What do mean by "opening the gate" on the rising edge?
It is confusing enough that the manual says each of the fourty counter I/O lines can be assigned to any of the counters and any of the counter functional inputs: I still don't know if this is true or if it is an improper interpretation of the manual.
No, the assignments are not that flexible. However, you certainly can assign any counter's default source pin to be used as a source by any other counter's task (or by several tasks at once). There are a few other special-case assignments, but for the most part they are flexible within their own category. Any source pin can be the source for any counter, any gate pin can be the gate for any counter, etc.
a) Is it really not possible to connect a gate() line to the source input of the same counter?
b) If so, is it possible to connect the gate(x) input to the source input of counter(x+1) or (x-1) without affecting counter (x), which is how it appears in the VI's?
c) If worse comes to worse, we are driving the gate inputs with the output of an MC14490 hex contact bounce eliminator. Can we tie the gate and source inputs to a single counter together, and in software set the source as input and set gate on, and count events that way?
a) I'm not at hw now and can't recall for sure about using a counter's own gate signal as a source. See b).
b) I'm pretty sure a counter can use as its source the gate signal from its paired counter (x+1 or x-1).
c) Um, it isn't clear to me why you need both source and gate connected this way if you are just counting events.
d) we're hopelessly crazy and misinformed, and have to remake the interface boards and/or completely rewrite the software to use DAQmx?
I don't think so. If the PC-TIO-10 was just performing event (edge) counting, then you shouldn't need to worry about the gate inputs on the 6602. The new counters can simply count source edges without regard to a gate input.
Can you describe how the source and gate inputs were used to accomplish the measurement you needed on the PC-TIO-10? It's been a long time since I used one and I only ever used it for period measurement...
-Kevin P.

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Two analog input tasks

Hi,
I have a VI with two analog input tasks. One outputs a waveform, from which I determine the frequency of that waveform. Another one just samples the signal once, because all I need is to one value from the signal.
Is there any way to synchronize these tasks? Right now I perform one task then the other because from what I know, you cannot perform two analog input tasks at the same time.
I've attached a VI. Thanks for the help.
Attachments:
Master_v2.vi ‏98 KB

duplicate post. Try to to keep the same question in one thread. What is wrong with adding all of you channels to the single task as recomended?

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Counter Output/Counter Input PXI Signals Behaving Erratically

Question for all your LabVIEW guru's out there,
I am running a frequency loopback test using the NI PXI 6229 MIO DAQ card. I am generating a "Counter Output" pulse train signal which feeds through my device under test and then back out of my device under test and back into the PXI 6229 for a "Counter Input" frequency measurement. Both the "Counter Output" and the "Counter Input" are assigned different PFI lines using DAQmx in LabVIEW.
I have 4 lines to test on my DUT. All four lines run this same frequency measurement but with different PFI lines on the PXI 6229. Each line is test independently.
This is my setup for the 4 lines:
Path 1: P2.0 (Counter Output - Pulse Train) -> DUT (Device Under Test) -> P2.1 (Counter Input - Frequency Measurement)
Path 2: P2.2 (Counter Output - Pulse Train) -> DUT (Device Under Test) -> P2.3 (Counter Input - Frequency Measurement)
Path 3: P2.4 (Counter Output - Pulse Train) -> DUT (Device Under Test) -> P2.5 (Counter Input - Frequency Measurement)
Path 4: P2.6 (Counter Output - Pulse Train) -> DUT (Device Under Test) -> P2.7 (Counter Input - Frequency Measurement)
where:
P2.0 = PFI8
P2.1 = PFI9
P2.2 = PFI10
P2.3 = PFI11
P2.4 = PFI12
P2.5 = PFI13
P2.6 = PFI14
P2.7 = PFI15
I have a LabVIEW VI which generates the "Counter Output" and reads the "Counter Input" frequency. I am seeing weird behavior from the PXI 6229 card. I can test "Path 1" and "Path 2" and the frequency I read is what I generated. No issue there. However, when I test "Path 3" and "Path 4" the frequency measurement is erratic. The readings are two different frequencies repeated over and over again and none of those frequencies are the expected frequency which was generated out of the "Counter Output." If I reset the card, and start by testing "Path 3" and "Path 4" the frequency readings are correct and the erratic behavior is gone. However, when I try to then test "Path 2" and "Path 1" now those lines have the erratic frequency issue. I can continue resetting the card and see same issue. The PFI lines that I test first will always pass.
To summarize:
Steps Taken:
1. Test Path 1 = SUCCESS
2. Test Path 2 = SUCCESS
3. Test Path 3 = Erratic Frequency (Two Frequencies repeated over and over again in my frequency results array)
4. Test Path 4 = Erratic Frequency (Two Frequencies repeated over and over again in my frequency results array)
5. Reset the PXI 6229 Card
6. Test Path 3 = SUCCESS
7. Test Path 4 = SUCCESS
8. Test Path 3 = Erratic Frequency (Two Frequencies repeated over and over again in my frequency results array)
9. Test Path 4 = Erratic Frequency (Two Frequencies repeated over and over again in my frequency results array)
I am wondering if Port 2 (P2.0-P2.7) on the 6229 card has certain dependecies and this is why I am seeing issues. I am trying to get around this issue so that I don't have to always reset the card.
Are P2.0-P2.3 (PFI8-PFI11) and P2.4-P2.7 (PFI12-PFI15) treated differently or require different setup? How do I resolve this issue?
Thanks so much!

I have a theory...
The DAQ card follows a policy called "lazy uncommit" wherein the terminal used for the output will continue to be connected to the counter even after the task has completed (until the terminal is needed for something else). So as you run more tests, the counter output will end up driving more lines. This behavior should be easy enough to confirm.
As the DAQ card drives more lines, I'd imagine this affects the actual signal. You could scope it to check, but it sounds like either the rise/fall times are becoming longer or some extra noise is being introduced on the line.
The readings are two different frequencies repeated over and over again and none of those frequencies are the expected frequency which was generated out of the "Counter Output."
This implies you are picking up an extra edge during transitions--this isn't too uncommon if the signal is noisy since there is no built-in hysteresis on the DAQ card. I would expect the measured frequencies to have periods that sum to either the full period or the semi-period of your actual signal (depending on how many duplicate edges are detected).
Suggestions are as follows:
To stop the DAQ card from driving multiple PFI lines, it would probably be easiest to just programmatically reset the device in between your tests (using DAQmx Reset Device). If you can't reset the device (e.g. because you are running some other task that can't be interrupted) then you can instead configure a dummy task that uses the PFI line in question as an input.
To stop the DAQ card from picking up multiple edges during transitions, you should configure a digital filter on the input terminals. If you reset the device it sounds like this might not be necessary... it's up to you if you want to configure this or not.
Best Regards,
John Passiak

Speed up time of AI Create Channel.vi task containing thousands of channels

I am creating an AI task containing a total of 8000 channels of different channels with each channel being acquired many times before the next channel is acquired. The channel list is something like 0,0,0,...,1,1,1,...,2,2,2...3,3,3... where each channel number would be acquired 2000 times. The purpose is to perform averaging. I am seeing that DAQmx Create Channel.vi takes about 100 msec to create 1000 channels for a total of 800 msec to create all channels (DAQmx 9.4, LV 11, WIN 7, CoreDuo P8700 2.5 GHz). I would like to speed this up by a factor of 10 if possible. Test vi attached.
Attachments:
Create Multiple Channels duration.vi ‏17 KB

Hi SteveP,
The DAQmx task contains data structures representing channels, which in turn contain other data structures representing channel properties and such. Most of the execution time of DAQmx Create Channel is spent allocating and initializing these data structures. They are separate from the task's input buffer (where data is stored until DAQmx Read is called). The input buffer is allocated when you reserve the task (which is normally done by DAQmx Start Task), and it is indeed allocated as a single large array.
DAQmx support for repeated channels focused on the SCXI use case, where hundreds of milliseconds of channel creation time seemed to be an acceptable tradeoff for measuring thousands of thermocouples. During development of NI-DAQmx 7.0, we used 3072 channels as our large system benchmark for channel creation, since that's the maximum number of channels supported by an SCXI task: 8 chassis x 12 modules x 32 channels (ignoring CJC channels). Repeated channels also make your use case possible, but this wasn't the original goal, otherwise we would have tried to make it easier to use for this purpose.
When replying to your previous thread on this topic (DAQmx AI Task with many samples CH0, then many CH2, then many CH3), I assumed that you were doing this because you were having problems when you took the straightforward approach to averaging, but Ben is right to point out that there are ways to deal with ghosting, cross talk, etc. What is the source impedance of the signals that you are measuring? How Do I Eliminate Ghosting From My Measurements? lists some options for dealing with high source impedance.
Failing that, is it possible for you to reduce the frequency at which your program creates and destroys tasks? If you can extend the task lifetime by reusing the same task more than once, you can avoid the channel creation overhead, or at least amortize it over the lifetime of the task. Note that you don't have to clear one task before you create a second one; you only have to make sure that two tasks don't have the same hardware reserved at the same time--if you do, you will get a reservation error. In most cases, stopping the first task before starting the second is sufficient to avoid this. It is possible to create multiple tasks up front, then switch between them throughout the rest of your program.
Brad
Brad Keryan
NI R&D

A task containing a single global NRSE ai channel thinks it's differential!

Help, surely this is a bug (either in my brain or in labVIEW!).
I'm running DAQmx on a PCI-6229 m series DAQ device, SHC68-68-EPM cables and the CB-68LPR break out PCBs.
I'm measuring ground referenced signal sources of a few volts in amplitude, some of which share a common ground and I am therefore using NRSE measurements on those to preserve free slots.
I've set up a global channel called ILD1 as dev1/ai0 set as NRSE. The connection tab on MAX gives the connections I would expect:
signal: pin 68 (ai0)
ground: pin 62 (aisense)
When I run the test panel for the global channel, I see exactly the measurement I expect so this works fine.
I have then set up a task containing this global channel (and no others). The task seems at first to recognise this as being NRSE (having inherited this from the global ILD1 settings). However, if you look at the connections tab, the connections are now different:
signal: pin 68 (ai0)
ground: pin 34 (ai8)
Running the test panel on this task gives a voltage that floats towards a maximum value. This is consistent with the fact that the task seems to think it's now doing a differential measurement, but I have not connected ai8 and so this input is floating.
So the question is how can the global channel be NRSE (which I want), and a task based solely on this end up as differential? How can I fix this to preserve as many ai pins as possible (e.g ai8 would be useful for something else!)
Thanks

HI probably-
probably wrote:
I have ai0-ai7 set up as NRSE, as they share a common GND which I have connected to aisense. I have four other signals to collect, which also share a common ground (but possibly different from GND). My thought was that to prevent any gnd offsets, I would measure these as differential mode. So I set them up on ai8-ai11 (I assumed that ai12-ai15 would be the other terminal on each of these signals). However, you can't do this: a mixture of differential and NRSE is not allowed on the same connector. Setting the four up on ai16-ai19 allowed me to measure them in differential mode. I presume this is because of the way the multiplexer works on the input amplifier?
btw, I've found this forum tool pretty good, apart from accidentally pressing tab to get a space, then return by accident and submitting a partial post
A mixture of NRSE and differential channels is certainly allowed on the same connector. The problem arises in the placement of channels. In differential mode the channels are connected on two seperate channel input pins; the positive pin goes to pin ai[X] and the negative pin goes to pin ai[X+8] where X is the channel number specified for differential input. So, on a card (or a single connector on a two connector card) you can only create differential channels on the first 8 analog input channels. Differential input channels on ai8-ai15 are not allowed because there isn't an [X+8] pin to access.
If you arrange your four differential channels somewhere in the first 8 inputs (i.e. ai0-ai7) and the NRSE channels anywhere else you will be able to acquire all signals in the same task on the same connector at the same time.
EDIT: I forgot to mention one caveat that might be obvious but is still worth mentioning- using a differential channel on a pair of inputs reserves the second pin. So, if you create a differential channel on ai6 for instance, both ai6 and ai14 will be reserved. This means that you will not be able to use ai14 for NRSE input.
Hopefully this helps-
Message Edited by Tom W. on 08-20-2005 06:52 PM
Tom W
National Instruments

Can a NIDAQmx task contain two counter inputs?

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