IEPE accelerometer shock test set up

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 the NI 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.

This accelerometer has a sensitivity of 1 mv/g , I made a test using MATLAB . 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(380));

figure

plot(data.Time, data.cDAQ1Mod1_ai0);

ylabel("Acceleration (Gravities)");

[Charles]

I would check one of a few things:

1. perhaps the scaling of the raw sensor values to the acceleration reading is off -- check the documentation/datasheet of the sensor to ensure your code scales raw sensor values properly
2. the test setup may just be exceeding that maximum 5000g acceleration, and the sensor seems to be at that point. It is likely saturating -- ie it cannot read any further if there is a real acceleration of more than ~5000g.
3. perhaps you are reading the data with the wrong datatype -- unsigned vs. signed, integer vs float, etc. I don't think this is happening, but it could be worth checking if all else fails.

Good luck!

[Mathieu NOE]

yeap

looks like the sensor is overloaded , you are exceeding the +/- 5000 g range of the sensor (and maybe also your acquisition device is overloaded - what is the range ?)

also , after overload, sensors take some time to recover (mechanically and electrically). Read the settling time listed in the specs for the sensor models you use.

Within the settling time after an overload event, there is no amount of processing that would give me confidence in the measured acceleration.

Avoid overloading your sensors. You could damage your sensors and shorten their usable life. If you need to measure higher acceleration levels, invest in additional sensors that can accommodate the maximum expected accelerations. If overloading sensors is unavoidable even with careful mounting procedures, wait until the system has recovered/settled before processing acquired data.