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High Speed Impact testing using split hopkinson bar and LMS for data acquisition

Hi

 

I am looking to characterize high speed impact properties for a plastic. For data aquisition I am using LMS Scadas front end and Impact testing module in the LMS Test.Lab. I am using a force transducer (Sensitivity of 0.9 mv/lbf) and an accelerometer (sensitivity of 1 mv/g). When I impact the striker bar on to the test specimen, I see overload of the channels. I maintained the physical input value less than the value the transducer can handle to avoid overload. Is there any alternate way to avoid it? 

 

I See auto-ranging as an option , but I do not want to run my test twice. (One Impact during the autoranging and the other one during the final measurement). Also, Can the sensitvity of the transducers be changed?

3 REPLIES

Re: High Speed Impact testing using split hopkinson bar and LMS for data acquisition

Here is my advice:

 

1.  It does not sound like auto-ranging will help.  It sounds like you need to maximize the input range of your data channel to it's fullest extent. Under "Tools -> Channel Setup Visibility" add "Range" to your visible channel fields in the Channel Setup worksheet. Set the Range field to 10 Volts (10 V). Note that you may need to scroll to the right with the scroll bar at the bottom of the channel setup.

range.png

2.  For the Scadas, step 1 allows for the largest possible voltage input.  If you still have overloads with a 10 Volt range, you must try different transducers that are less sensitive.  If an accelerometer is constructed with a 1 mV/g sensitivity, changing it in the LMS Test.Lab software does not change how much voltage it actually outputs during the test.  The software 'Actual sensitivity' field is only used after the voltage is recorded.  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Re: High Speed Impact testing using split hopkinson bar and LMS for data acquisition

Hi

 

Thanks a lot for your quick response.

 

I have tried the steps that you have said, but still I can see an overload on my load sensor. Is there any other procedure to overcome it without switching to the lesser sensitive load sensor.

Re: High Speed Impact testing using split hopkinson bar and LMS for data acquisition

In my opinion, if you wish to avoid overloads, switching to a less sensitive load sensor is the only way.