external counter timebase source in two edge separation task

[UliK]

Hi all,

I use a NI 6220 board and want to perform something very similiar to what is described in the knowledgebase article "How Do I Count Digital Edges Between a Start and Stop Trigger on an NI 6602 Counter/Timer Board?".

Does anybody know how I have to change the example program "TwoEdgeSep.c" to use not the internal timebase but to use an external source (the one I want to count the edges?

Thank's for your time,

Uli

[John_P1 · Accepted solution]

Hi Uli,

You would need to add a call to DAQmxSetCICtrTimebaseSrc before the task is started to configure the hardware to use an external timebase.  You'll also probably want to change the DAQmx_Val_Seconds parameter to DAQmx_Val_Ticks in the DAQmxCreateCITwoEdgeSepChan function assuming you want your measured result in terms of ticks of the external clock.

Best Regards,

[UliK]

Hi John,

thank you very much, this works as intended. For the sake of completeness I copy the configuration part of the program:

 /*********************************************/
/*/ DAQmx Configure Code
/*********************************************/
DAQmxErrChk (DAQmxCreateTask("",&taskHandle));

DAQmxErrChk (DAQmxCreateCITwoEdgeSepChan(taskHandle,"Dev1/ctr0","",100,1000000,DAQmx_Val_Ticks,DAQmx_Val_Rising,DAQmx_Val_Falling,""));

DAQmxErrChk (DAQmxSetCICtrTimebaseSrc(taskHandle, "", "/Dev1/PFI8"));

I connected the trigger signal (TTL with a roughly 1 s period) to the AUX and GATE input and the external source ca. 200 kHz to PFI8 and it correctly measures the edges within a half period.

[thinnker]

Hi John,

I searching for the same problem, how to solve it Labview.

I like to know,how to add external time base for two edge separation task.

Regards,

Hari

[John_P1]

Hi Hari,

In LabVIEW you would use a DAQmx channel property node:

Best Regards,

[thinnker]

Hi John,

Thank you for reply. i wrote the program as you mentioned.

But it gives errors.

my specs:

PCIe 6351 DAQ card.

External timebase Source 10khz.

Time between to edges 14ms.

I got output with internal timebase fine.

i need the output using external timebase.

any example code.

Regards,

Hari

[thinnker]

Hi John.

I got the solution.

i have one question how to calculate the MAX & MIN value for the CounterTimeBase Rate.

Because of the TimeBaseRate errors were occured.

Regards,

Hari

[John_P1]

What errors were you getting?

The counter can count between 2 and 2³²-1 ticks.  So... the rate that you specify will determine the minimum and maximum value (in terms of seconds) that you can count.  These values are set when you create the channel:

It seems intuitive to try to put "0" for the minimum value, but that will give you error -200527 (Requested values of the Minimum and Maximum properties for the counter channel are not supported...).  The real minimum value (in seconds) should be no less than 2 * (1/ timebase rate).  I'm not sure if this is your issue or not, I'm just speculating.

EDIT:  I just realized the default (if left unwired) for the minimum value is 1 µs.  This would be below 2 ticks of your 10 kHz timebase so would give the same error.  You need a minimum value of at least 200 µs.

The actual timebase rate itself shouldn't have a minimum or maximum value that I'm aware of (I guess maximum would be 100 MHz on your X Series, but in reality you can only pass through ~25 MHz from an external PFI line due to bandwidth limitations).  

Best Regards,