topic Re: Absolute energy in DASYLab

Absolute energy

Bilko — Tue, 03 Feb 2009 16:15:35 GMT

I am currently processing analogue signals taken from a piezoelectric transducer (lamb waves), running them through amplifiers and converting them to digital format. The output i have set is a graph which shows the voltage of each event, with associated ring down counts. I have set threshold voltages to only count an event once it passes a set threshold. I am looking to integrate the area between the threshold line and when the voltage passes up through the threshold until it passes back below the threshold. I am doing this to establish the energy of this event, as a measure of its integrated area size, absolute energy. Obviously the output oscilloscope ranges positive voltage to negative, therefore i need to interpret the signal as the integral would equal zero, would this be to find the absolute value of RMS?

Any help would be most appreciated.

Sam

Re: Absolute energy

Mark M — Thu, 05 Feb 2009 12:31:35 GMT

Hi Sam,

Are you using LabVIEW or DASYLab?

Why don't you add a DC offset after the amplification stage to shift all the values into the positive domain in your scope? The other way would be to integrate the positive half and the negative half seperately and then summate them together?

Re: Absolute energy

Bilko — Thu, 05 Feb 2009 13:36:38 GMT

Hi Mark,

I am using DasyLab. My knowledge of the software is very very limited. I am not sure what you mean by an offset? How would i make the values positive then integrate them when the ring down counts surpasses a set threshold level?

Sorry but i am a complete novice at this, and have a short time frame to get to grips with the program as my thesis is due in in the next month or two!

Could you explain the steps please?

That would be most appreciated.

Sam

Re: Absolute energy

Mark M — Thu, 05 Feb 2009 14:21:52 GMT

blank_page

Hi Sam,

The offset I meant was just to add a DC voltage after your amplifier circuit so everything will be shifted up, then you will end up with only positive values. As I don't know how exactly your system is set up and the hardware are using, I cannot offer any kind of specific steps for you to follow. But to add a DC voltage to your AC waveform, simply connect a DC voltage source (power supply, batteries or voltage follower) to the same point you are measuring.

Unfortunately we cannot support you with any DASYLab programming queries, please consult this forum post to get the support for DASYLab.

Re: Absolute energy

CJ_Butler__DASYLab_Pro — Fri, 06 Feb 2009 21:11:30 GMT

The Differentiation/Integration module allows you to define trigger conditions for the start and stop of the integration, when you select the "With Input" mode.

Are you working with V10?

Message Edited by CJ Butler -- DASYLab Pro on 02-06-2009 04:11 PM