Counter tasks in NI9401 with cDAQ-9174

[Xooch]

I'm not able to find a clear definition of how many tasks I can have with this module/chassis.

My goal at the moment is to have 3 pulse inputs to the 9401 and have the module count pulses on all three inputs utilizing three of the four counters available. However, the DAQmx help file states "For most devices, only one task per subsystem can run at once, but some devices can run multiple tasks simultaneously." Looking at the link in the help file for the 9174, "The NI cDAQ-9174, 9178, and 9188 chassis can run up to three analog input tasks simultaneously, each using independent timing and triggering configurations." Obviously an analog input task is not a counter task, but counter tasks aren't specifically discussed.

The problem is that I've been able to use two counters in two tasks at the same time. When I attempt to add the third, I get an error. Why am I even able to run two tasks since what's stated above says I can only run one?

I've tried to add more than one virtual channel to the same task so as to have more than one counter in a single task, but this also results in an error.

Is there a way to utilize three counters simultaneously? I'm starting to think I'll need to use the module as a simple digital input and use software to count transitions, but I'd like to avoid this because using the counters would be so much simpler.

[Paul-B]

Hello Xooch,

What kind out counter task are you using. Also what is the error code number you are getting.

[Xooch]

Unfortunately I'm not in a position at the moment to run my program and get the error numbers.

However, I am trying to accomplish one of the following with the hardware mentioned in the subject line:

1) Count edges using 3 32-bit counters and 3 inputs

2) Count edges using 2 64-bit counters and 2 inputs

I don't need to accomplish any type of start synchronization or read synchronization with a sample clock. I'm performing a long term count and comparing a reference to a DUT, and the amount of error introduced by having a slight start or read delay between the counters would be very very small compared to the overall count.

From my experimentation neither of the above is possible. I have actually completed my testing using 2 32-bit counters and compensating for the counter overflows in software (I'm counting up to about 30 billion edges over the course of 60 to 70 hours). However, it would be nice to know if I'm wrong in my conclusion for future use.

[sarcanji]

Hello all,

I have a question related to NI9401 and cDAQ-9174 (I am quite new with these devices, I used LabVIEW long time ago and easy projects and now coming back to it). My configuration at the moment is:

3 x 9401

1 x 9174

I read that the 9174 has 4 counter, can I measure the frequency of 16 inputs with this 4 counters? If yes, how can I do it? I am getting crazy with my 3x9401 (2 of them will be dedicated to measure the frequency of pulse and the other will be used to generate a PWM signal)

Thanks in advance

[bahannah]

sarcanji,

In our cDAQ chassis, the chassis does have 4 counters. If you look at the Counter Section of the User Manual for the cDAQ-9174, it will walk through how to make specific measurements using the chassis counters. If you navigate to page 5-10 of the manual, it specifically discusses frequency measurements. Depending on the frequency that you want to measure, you will need 1-2 counters per signal, which would mean that you could measure the frequencies of 4 signals at the most with your cDAQ chassis counters. 

It may be best to create a new forum post for this question so that you can get more views, as the age and average activity of a post is taken into account in our display algorithms.

Regards,

Hannah 

Applications Engineering 

National Instruments 

www.ni.com/support 

[sarcanji]

Hi bahannah,

Ok, so I will forget the idea doing it with the Counters, I will have to measure the frequency not using them.

Correct me if I am wrong, reading the data sheet from NI9401, with 8 Inputs I can meassure up to 9MHz signals, right? But we are not using the Counters of the cDAQ. The Problems would be accuracy of the frequency and the time to measure would be longer than using the Counters of the cDAQ, right? But if I understood properly, I could measure up to 8 Inputs/device (16 frequency Inputs)

Thanks

Regards