Use 9403 to read 20 MHZ frequency?

[Controls_Engineer]

 I have a 20 MHz crystal oscillator in my system and need to test it make sure it is working. The only hardware I have available is NI 9205 and NI 9403 installed in a cDAQ-9174 chassis.

How can I measure the 20 MHz frequency using this hardware?

Thanks.

[Izzzzz]

Hello Controls_Engin…,

The current modules 9205 and 9403 you have do not allow you to use the counters onboard your 9174. This Knowledge base article discusses the modules you need to use in order to access the counter on board your device. Please note that you should look at the specifications of each module and ensure you do not pick a module that has a lower bandwidth than 20MHz.

To measure the 20MHz frequencies please connect the output of the Crystal Oscillator to the input of a supported module. Then you will need to use a counter task.  The highest available time base onboard your 9174 device is an 80MHz time base.   Your quantization error will be dependent on the amount of counters you use and your measurement time. This can be described by this DAQmx help manual.

Because you are trying to measure a high frequency I would suggest using two counters and a measurement time that reduces your quantization error.  This community example along with the modification I made to it below should provide the LabVIEW code you will need to measure this frequency.

Regards,

Izzy O.

Applications Engineer

National Instruments 

[John_P1]

The 9205 actually does have a PFI line on it which can route signals to the backplane counters (see my 2nd example here).  However, I'm not sure how cleanly it would pass the 20 MHz signal.  Since you already have the 9205 I'd suggest just trying it out.

If not, you might try a 9402 or 9401.  The 9403 is unfortunately not capable of routing signals to the backplane.

Best Regards,

[Izzzzz]

Just for clarification there is no PFI line on the 9205 that you can route signals to the backplane. John_PI example uses an analog trigger in order to create an analog comparison event (the event being a digital signal) equal to the rate of your analog trigger signal.  This analog comparison event signal can then be sent to the counter on the back plane to measure the frequency. This is a great idea to get around having to acquire a digital module to access the counters on the back plane with the stipulation, already mentioned, that the module you are using must have a bandwidth equal or greater to the signal you are measuring. The 9205 has a max bandwidth of 370 KHz for the analog trigger and 250 KHz for the analog input.  Hey Controls Engin…. what frequency signal are you trying to measure? The max input on the 9502 is an 18MHz signal and the 9401 can allow a 10MHz signal through.

Regards,

Izzy O.

Applications Engineer

National Instruments