voltage to force translation ?

A transducer or sensor is connected to Force measurement unit.  When force is applied to sensor, Sensor Developments Inc. PMAC 2000 Force measurement unit displays the Force in Newtons.

On back of PMAC 2000 unit, there is 9-pin I/O Connector.  Please find description of this connector attached.  My interest is Analog Output pins from this connector.  I need to connect these Analog Output Pins to my Microcontroller based embedded application.  My target Microcontroller A/D is 10-bit and A/D Reference Voltage is 5V.

Please check my connection as follows:

AOUT - (Pin 4) connects to unused Analog Pin in my microcontroller.
AOUT + (Pin 2) connects to different unused Analog Pin in my microcontroller.

Do I need to connect GND (Pin 3) to Ground on my target board ?

My understanding is that sum of AOUT+ and AOUT- is 5V.  In my embedded software, how should I calculate voltage, should I simply subtract AOUT- from AOUT+  ?
What is the translation of voltage to force in Newtons ?   What voltage is what amount of force ?

The attached description says AOUT+ is driven positive or negative with respect to AOUT- .  Please provide examples of some AOUT+ and
AOUT- voltages I will see on my Microcontroller Analog Inputs ?  I don't think I can have negative voltages going into my Analog Pins on my Microcontroller because A/D reference voltage in my microcontroller is 5V.  So, I believe Analog Input values going into my
microcontroller need to be 0V to 5V.  If yes, how do I know PMAC 2000 will send Analog Voltages in between 0 to 5V ?

Attached is also the manual for PMAC 2000 Force Unit.

On page 28 of the manual, please explain following:
"The Output impedance of each is 620 ohms and the output voltage is +1.0V nominal for 2mV/V full scale sensor.
What is 2mV/V ?  Is this a typo ?
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>> Do I need to connect GND (Pin 3) to Ground on my target board ?
      Yes, to the GND (or 0 volt point) of your uC.

>> My understanding is that sum of AOUT+ and AOUT- is 5V.  
      Probably but not relevant.

>> should I simply subtract AOUT- from AOUT+  ?

>> What is 2mV/V ?
      This is the typical way to describe the output of strain gages and other passive bridge-type sensors.

If you put 1V on the bridge and apply the full-scale rated stress, you will get 2mV differential on the sense leads.  If you put 5V on the bridge, you will get 10mV.  You have to amplify this (with a diff-input, diff-output amplifier in your case), and send it to your uC.  

The design of the amplifier (a differential output with a common mode voltage of 2.5V) and presumably a 5V power supply insure the voltage inputs to the uC will be in the proper range.
naseeamAuthor Commented:
Some more information from PMAC 2000 Manual as follows:

The analog output is the signal from the transducer, amplified and relayed through a low pass filter.  The instrument provides an excitation of 7V.  The amplifier has a gain factor of 76 for a nominal output of 1V at 2mV / V.  This signal is transmitted through the I/O Connector.

>>  You have to amplify this (with a diff-input, diff-output amplifier in your case),
Do I need to do this or is it already done by the transducer or Force Measurement Unit?
The PMAC 2000 provides an excitation of 7V.   This is the voltage on the bridge (rather than the 1V or 5V I mentioned).

>> The amplifier has a gain factor of 76 . . .
      The amplifier is already included.  You can connect the output signals directly to your uC.  
       You might want look at them with a voltmeter first, just to get a feel for what's going on.
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naseeamAuthor Commented:
Does this mean AOUT+  -   AOUT-   will never exceed 14mV.
No.  The voltage at the sensor outputs will not exceed 14 mV if you do not overstress it.
The voltage at the amplifier outputs will be 76 times larger.  That is what the amplifier gain does for you.

   (14 mV) * (76) = 1.064 volts

And you can overstress the sensor to get more voltage out too.  The linearity suffers at first, and then at some higher level you may break the sensor.

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naseeamAuthor Commented:
so AOUT+  -   AOUT-  will not exceed 1.064 Volts if sensor is not overstressed ?
Please click http://www.experts-exchange.com/newRequest.jsp?qid=28687978

To request your question be moved from "Automotive" topics to the correct / relevant topics designation, that will get further expert input / assistance on your question.
>> so  (AOUT+)  -  (AOUT-)  will not exceed 1.064 Volts if sensor is not overstressed ?

That is correct.  Good luck with your project.
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