QuickDAQ 'FFT Analyzer' mode does not recognize hammer impact as trigger

[ConnectTheDots]

I have a question regarding the QuickDAQ Software. We have the DT9837-B device and want to use it for impact testing and have set up the software in 'FFT Analyzer' mode like explained in the User Manual. But the hammer as trigger is not recognized. We have set up the device and software as follows: Hammer connected to channel DT9837-B(00)-0, Accelerometer connected to channel DT9837-B(00)-1; In the acquisition config -> Trigger Source is set to 'Analog Threshold Pos Edge' with a Threshold value of 50lbf and channel DT9837-B(00)-0. Trigger Mode is 'User Accept-Reject'.

As soon we hit 'recording' we see the 'waiting for trigger' information, but the hammer impact is not recognized. When using the trigger as 'software' we do get good results on the hammer channel once we hit with the hammer - so it is not a broken cable. Also when switching to 'data logger' mode and selecting 'Analog Threshold Pos Edge' as Trigger Source with channel DT9837-B(00)-0 the hammer impact is recognized as trigger.
Is there a specific setting we have to be aware of in the 'FFT Analyzer' mode that the hammer impact is recognized as trigger?
Thanks for your help.

[JRys]

Hello,

Could you attach (or include link to) the data sheet for the sensor at the end of your hammer? I have a 50g 100mV/g accelerometer on the end of my hammer and am not experiencing the same trouble. My QuickDAQ version is 3.7.0.49. I've configured the FFT Analyzer for an Analysis Frequency of 399Hz and the FFT size is 1024. Each trigger will take a little over 2 seconds to acquire. The trigger is Ain 0 Analog Threshold Pos Edge set to 1g which is approximately 0.1 volts from the accelerometer. A lite tap is all that is needed. Below are my results halfway through a 10 trigger sequence. 

On Ain 1, I've connected a signal generator set to sine wave 158 Hz 1.0v peak (IEPE current off), hence the hump in the blue trace.

Best regards,

John

[ConnectTheDots]

Hello John,

for Ain0we are using the 086C03 and 086D05 impact Hammer from PCB (https://www.pcb.com/products?model=086c03 and https://www.pcb.com/products?model=086d05); for Ain1 we are using the 352C03 accelerometer from PCB (https://www.pcb.com/products?model=352c03&item_id=products&m=002c10).

We have QuickDAQ Version 3.7.0.49. The Frequency is set to 118Hz with a FFT size of 2048 as we need a resolution of 0.125Hz or better.
The Trigger is set to 'analog threshold pos edge' with 20lbf (0.2V) - but even when I play with that value (going higher or lower) I don't get the trigger input. 

Again, when using 'software triggered' I do see my hammer impacts on the Ain0 channel with an impact force of about 2.5lbf

Probably there is a simple basic setting that I screw up and that is causing all those problems.

Thanks!

[JRys]

I believe the issue is the low analysis frequency not being able to capture the sharp edge of the impact. 118 Hz is approximately 236 S/s or about a sample every 4mS.  I originally used 399 Hz but when I dropped to 118Hz it wouldn't trigger. However, switching to Analog Threshold Neg Edge seemed to make a positive difference - I'm not sure why. Or increase the analysis frequency and FFT size appropriately. I'm sorry there not a more concrete solution.

best regards,
John

 

[ConnectTheDots]

Hi John,

thank you, that was the hint. When using 400Hz or higher it accepted the trigger.

Best regards