Multiple hardware-time-gated edge counting with cDAQ 9188 and NI-9402

[_Basil_]

Hello! The application I'm going to develop must do the following:

1. It must open a gate of the device for a certain and reproducable time (order of 100 ms) with a distinct (however, changing from opening to opening) separation between openings (both time-critical, not SW-timed):                      ____~~~~~____~~~~~________~~~~~________________~~~~~___________
2. While (and in the best case only while) the gate is opened is must count digital edges produced by the same device. A device produces no signals if the gate is closed. While the gate is opened, device produces several digital pulses randomly (!), but not more frequent than once per 50ns (20MHz): _____~_________~_~_~________________~___~___________ Output: 1, 3, 2

What concept would you advice me to use in such application if I have LabVIEW 2013 SP1, cDAQ-9188 chassis and NI-9402 digital I/O module (I can't use "Wait for next sample.vi" according to the help I read, for example)?

Any comment will be appreciated!

[kpnk]

So, in order to clarify what do I mean about concept, I decided to add this self-reply. I tried to use HW timing for my digital output, which is, according to the DAQmx Help, supported by my combination of devices, and received Error -200077 (see attached picture for details).

Is it something I have understood wrong in DAQmx Help, or there is actually a contradiction?

And, after all, if I can't use HW timing for my task - with what kind of approach may I implement (if any) to guarantee duration of my outputs?

[OlegS]

Dear kpnk,

of cause you can use HW timing but the "Hardware-Timed Single Point" is a very Sampling Mode for deterministic RT applications and is also just supported by advanced DAQ hardware you can see here.

Does My DAQ Device Support Hardware-Timed Single Point Sampling Mode?

What you need is a simple continues edge counting which is controlled by a Gate to activate and deactivate the counting.

In this Getting Started document is described in details and how to implement it.

Using Duplicate Count Prevention for Counter Tasks in NI-DAQmx

Kind Regards,

SG3 | Applications Engineering | National Instruments | NIG |

[_Basil_]

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@SG3 wrote:

What you need is a simple continues edge counting which is controlled by a Gate to activate and deactivate the counting.

In this Getting Started document is described in details and how to implement it.

Using Duplicate Count Prevention for Counter Tasks in NI-DAQmx

Kind Regards,

SG3 | Applications Engineering | National Instruments | NIG |

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Dear SG3, thank you very much for your reply! I will try to implement this approach and will keep this thread updated.

[_Basil_]

Dear SG3, I constructed two VIs for my aims, one is based on this duplicate count prevention feature you forwarded me to. Since I have not found any example VI (just a flowchart), I attach the one with my comments. Do you think, that I have understood everything right? The idea is, again, to count edges only when a gate at the device is enabled (and I think, for this reason, one have to deal with the gate terminal of the counter channel I use).

Second VI (also attached) was based on this example and was modified by me in order to enable a single digital line with a period set at "Sample Clock Rate" for "Amount of pulses" times is a row - this is for enabling a gate of the device itself.

Now I want to merge this two VI's to fulfill simultaneously all my needs - to enable the gate at the device and to enable edge counting from the device at the same HW-timed period of time (and all this - many times one after another).

Do you think, that my way by now doesn't lead to nowhere? By now I have obvious troubles of writing digital output (second VI) while trying to count edges (first VI) - the error is that one can not use a terminal which is already reserved for another task.

I have somehow a feeling, that I am doing something either too complicated while there is a simple solution, or something completely wrong.

[_Basil_]

A fruitful continuation of this thread is here (for anybody who will be probably interested in future).