IEPE accelerometer shock test help

[Alfonso978]

Hi All,

I have been tasked to design a shock measurement system for a pneumatic cylinder hitting a metal plate. This impact happens 1 time every 3 seconds for a period of 5 minutes approximately. We are trying to measure the sudden acceleration (for every impact) the metal plate has once it is impacted by the pneumatic cylinder. I am not very familiar with IEPE accelerometers and I would just like to get some confirmation on the compatibility between the NI 9234 module and the Kistler 8704B5000 accelerometer.

I know the specs linked to the accelerometer show a constant current source of 2...20 mA and de 9234 module offers a 2mA constant current, so we are on the limit but the module should work just fine. Acceleration range = +/- 5000 g.  Overload = +/-10000 g. Datasheet attached at the end.

This accelerometer has a sensitivity of 1 mv/g so, I made a test using MATLAB and the NI 9234 module (Plot attached as image). The problem is that I am getting the exact same value in almost every hit (5117.26 g) so, maybe there is an issue with the selection/compatibility of the components. And also I would like to ask if  the code is correct or if there is anything else missing/incorrect with the setup?

dq = daq("ni");
ch = addinput(dq, "cDAQ1Mod1", "ai0", "Accelerometer");
dq.Rate = 12000;
ch.Sensitivity = 0.001;
data = read(dq, seconds(320));
figure
plot(data.Time, data.cDAQ1Mod1_ai0);
ylabel("Acceleration (Gravities)");

[santo_13]

I can help answer questions about how to use the 9234 module with the IEPE accelerometer but nothing on the MATLAB side.

Just looking at your code snippet, you don't configure the IEPE to be internal excitation with 2mA anywhere and not reading the TEDS data on the accelerometer.

[Henrik_Volkers]

Some hints on the shock measurement:

metal on metal shock will easely create shocks higher than than the 50 km/s² (~5 kg oh no, 5000 g.. get rid of that non SI unit, if you want to do something serious with that data, you need to convert it anyway 😉  ) 

Depending on the masses and shape you also create signal content beyond 6 kHz (your 12 kHz samplerate)  , the coarse max in the spektra will be around 1/ ( pulse length) , but if you are interested in the peak value the higher frequencies have an impact!  (simulate it)

Use the highest samplerate you can get with your DAQ (~51 kSPS), I use 1M up to 10M SPS ( for pulse length sometimes lower than 13 µs)

Oh and use crease,oil,vaseline if you srew mount the sensor on a (flat!) surface..    and use the mounting torque mentioned in the user manual.

Another point you should look at: the IEPE supply with only 2 mA limits the slew rate in the positive slope. The small current must load the cable and sensor capacity... if you don't know how to check that, provide sample shock data and we maybe can check that for you.