Help with Triggering problem (NI 5922)

[Sura19]

Hi there,

I have been using NI 5922 as my hardware for dynamic measurement and a Labview signal express as a software.  For NI 5922, it has 3 input channels, ch0, ch1, and trig. I try to use an accelerometer as my impact triggering sensor. When I connected the sensor to ch0 channel and use the edge triggering with ch0 as a triggering source, the system works. However, when I connected my accelerometer to Trig channel and used external trigger as a source and leave other parameters the same, it did not work. But, that Trig channel worked with the function generator before. 

Could you help me with this issue?

Thanks

[Henrik_Volkers]

The sensitivity differs between CH0,1 and TRIG , see spec of the 5922

If you feed the accelerometer signal only to the trigger,  increasing the signal conditioner gain could be one way to get better triggers. and you can add an external DC blocking capacitor if needed. (for shock I would try a 470nF to 1µF foil cap)

from spec:

TRIG (External Trigger, Front Panel Connector)
.C..o..n..n..e..c..t.o..r............................................................BNC
.I.m...p..e..d..a.n..c..e............................................................100 kΩ in parallel with 52 pF
.I.n..p..u..t. .v..o..l.t.a..g..e.. .r.a..n..g..e..............................................±2.5 V
.C..o..u..p..l.i.n..g...............................................................DC
.L..e..v..e.l.. .a.c..c..u..r.a..c..y.....................................................±0.3 V up to 100 kHz, typical
.M...a..x..i.m...u..m... .i.n..p..u..t. .o..v..e..r..l.o..a.d.....................................|Peaks| ≤ 42 V

and:

TRIG is an analog edge trigger only.     but that's the trigger type you seem to use.

So TRIG is fine with 'high' level rect signals ..

[Sura19]

Hi Henrik,

Thank you very much for bringing up the idea of adding more gains into the TRIG channel.

I have replaced my amplifier to have a better gain and it worked! 

However, there is still a triggering issue with the time stamps when recording data.

The instrument I am using is PXI chassis, which contains 3 blocks of NI-5922 (each NI-5922 has only 3 channels as mentioned above; ch0, ch1, TRIG). In my application, I am using 5 accelerometers and one of them is used as a triggering sensor for my hammer. That means, in Labview SignalExpress, I have to synchronize two blocks of my NI-5922 in order to take inputs from 5 accelerometers (one as a triggering input). So, in the software, I use NI-scope acquire to handle that. I also tried this with BNC-2111, but I am still facing the problem. 

The main problem is that every time I make an impact from a hammer, data that come from those 4 accelerometers do not appear at the same timestamp. For example, data would show up at 1 ms for my first impact. Then, I stop recording data and run the software again to make second impact. The data for second impact would show up around 5ms, or even sometimes they would show up around 0.5 ms, like there are some variations of arrival times of my data, which is something that I would not like it to happen in my application. 

In SignalExpress, I have tried immediate, edge, hysteresis triggering, but I am still facing the issue. 

Any idea of what is going wrong with this? I have attached some pictures below for more clarity.

Best Regards,

Sura19

[Henrik_Volkers]

First you want that all (seems to be 3)  5922 run from the same 10 MHz Ref clock  (PXI_Clk10 , or PXI-Clk)

Why not use 5 of the 6 analog channels to read the 5 accelerometers and use analog triggering?

configure the all inputs (vertical (range)  and horizontal (same SR))

configure one trigger channel

use NI-TClk to synchronise the  cards and to start the measurement  (see NI-TClk help)