Negative voltage signal

Hi everybody...
I m using an impact hammer to give excitation to a structure and i m measuring the response using an accelerometer...I want to measure the force with which i m hitting the structure with hammer...For that i am using a multiplier to multiply the voltage signal from impact hammer(in millivolts ) and the sensitivity of hammer namely 2.14 N/mV to get the force value indicated in a indicator....The problem i m facing now is that i m getting this value in negative which should not be so....
Please help me in this regard.....Suggest me possible solutions to arrive at the correct force value....
Awaiting for replies;;;;;

That's right.
     There are several possibilities:
     1.- As they suggested, just invert polarity.
     2.- Most sensors are strain sensors (we don't know what kind of sensor you have). They would generate either positive or negative voltage depending on which side they are bended to. Just like in a weight scale, we calibrate and use the static voltage (whatever it is), then output is positive if depressed, but would be negative if we pull from it. You would just flit over your sensor.
     3.- During impact, the material is bended producing certain polarity, then bounce back producing the opposite polarity. If you just use a digital sampling meter, your measurement will depend on the moment the data is sampled. If you need to record the peak, you also need an analog peak detector, which output is what you're trying to measure. But first, you need to know your polarity.
     Have fun.

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Attachments:
6_Channel_Data_Logger-Rev0.vi ‏1 KB

ood quality digital meter all voltage signals where equal and also using the labview test panel all voltage signals where equal. When measured by my vi i found that the voltage signals where not the same 2 of the channels displayed almost twice the amount.Hello;
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AK2DM:
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~~~~~~~~~~~~~~~~~~~~~~~~~~
"It’s the questions that drive us.”
~~~~~~~~~~~~~~~~~~~~~~~~~~

When measuring 6 voltage signals in labview I found that there was a difference in voltage signals in my program but not in the test panel. The test panel is correct. What is wrong with my program?

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Christopher G. Relf
Certified LabVIEW Developer
[email protected]
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Attachments:
3457.vi ‏132 KB

Hello,
I checked the VI that you sent and the only thing that I could see is not proper is that the LVM file is open and close every time you write to it but that doesn�t seem to be the problem.
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I want to make voltage aquisition with a PXI 6713 card. I take the Channels ai16 to ai33. The voltage at the clamp is 3.886VDC ( measured with a DMM ). When i measure the voltage and calculate it into a current ( see my applikation atteched ) the result is something between -10 and -24mA?!?!?
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analog_voltage_aquisition.jpg ‏33 KB

Is it a trick question??
First of all, Looks like you mentioned the card wrong PXI 6713 is an AO card, without any AI channels
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Message Edited by devchander on 07-28-2006 07:35 AM

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1520 is supposed to have differential inst. amp. Then why we need to refrence floating voltage signals to measure correctly ?

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Rajendu,
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