USB-6221 not detecting high frequency digital input

[Eric_L]

Hello Jak888,

You’re going to have to use the gate and aux pin on the counter. If the rising and falling edges are from the same signal, you will have to connect the signal to both the gate and aux.

Eric

[PeterFoerster]

OK, thank you. I got it to work when I connected the signals as you specified + The ground of my input connects to pin 37 SRC.

I hope that's right?

I think the LV help could be a bit more precise on these topics... Maybe show you in the example VI, how you have to connect the signals to make the VI work properly. Or have I just overlooked this?

BTW: Where can I get data about the accuracy of this measurement? How many samples does it acquire and how big is the error?

[Eric_L]

Hello Jak888,

The connections are listed in the DAQmx detailed help if you want to look at a reference in the future.

The accuracy will be dependent on the clock source that the counter is using for the measurement. In the case of the 6221, you can have a clock source up to 80MHz which will give you good accuracy for fast signals, but will be a hindrance for measurements taking more time. (24 bit counters on the 62xx cards which will allow the counter to roll over too quickly)

Eric

[PeterFoerster]

Sorry for digging up this thread (again).

I implemented the frequency measurement as we discussed before: I am using counter 0. The line, the rising edge comes in on is connected to both Gate and Aux Pin. The Ground is connected to the next available digital ground. When I am running this VI, alone it works flawlessly.

However, I am using this VI to acquire the frequency of a asynchronous DC Motor and when I start the driver for the motor I get no useable output: The Frequency measured is around 1E6. Apparently I am receiving some noise, that the card triggers on. I looked at the noise with an oscilloscope and found out that there was very little noise. The noise reached a maximum of <0,5 V. Why does the counter trigger on such small signals? Is there any way to stop it from doing this? Is it possible to build some sort of "software low pass"? Are my connections even right?

Any help is greatly appreciated.

[Eric_L]

Hello Jak888,

What does the signal from motor look like when it is running? To confirm that the counter is functioning properly, you can create a pulse generation task and measure that signal with the counter to see if it is behaving as you expected.

A filter can be enabled on the counter by using a DAQmx property node. Please have a look at the following link which describes how to set up this property node.

https://decibel.ni.com/content/docs/DOC-9493

Eric