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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. Some description of this connector is as follows:

AOUT - is pin 4. GND is pin 3. AOUT + is pin 2.

This I/O connector is used for Analog Output. The analog output is a differential output across AOUT+ and AOUT-. It has common mode voltage of 2.5V with respect to chassis ground. AOUT- is the reference and AOUT+ is driven positive or negative with respect to it. The Output impedance of each is 620 ohms and the output voltage is +1.0 V nominal for 2mV/V full scale sensor.

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 ?

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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Okay so far.

I suggest you contact the maker of the PMAC, Sensor Developments Inc.,and ask them for the manual and if they have an application note. I tried looking but they do not seem to have any details online.

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Does the documentation say the analog signal is differential?

That would be a differential signal.

Should be in the manual.

Voltages are always relative to a reference point. So I suspect this answers your earlier question about connecting the ground. (i.e., the answer is NO)

Depends on the sensor. Sorry I cannot help more. I have a meeting soon.

ed

Reply to
Ed Prochak

The spec is what I'd expect from a bridge force transducer. The 2mV/V FS says for each volt of excitation (you didn't tell us about those connections!), you get 2mV F.S.

However I don't understand what this "+1.0V" is. I doubt that the excitation voltage could ever be high enough to get 1V out FS. And yes, you'll almost certainly want something like an instrumentation amplifier between the transducer and your ADC unless you've got a high gain differential amplifier front-end built into your microcontroller.

You should DuckDuckGo (search) for how you should use a resistor-bridge force transducer.

Hope that helps you get started-

Reply to
Frank Miles

V

connect

5V.

AOUT-

voltage

with

don't

+1.0V

FS

connections!),

almost

and

Following is additional information from the PMAC 2000 manual:

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.

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formatting link

Reply to
learn

V

connect

5V.

AOUT-

voltage

with

don't

+1.0V

FS

connections!),

almost

and

Following is additional information from the PMAC 2000 manual:

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.

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Reply to
learn

  1. You need the ground reference.

  1. To know force, you need the conversion factor of the load cell, from Newtons to mV/V.

  2. The information has been vague if the output signal is differential (between AOUT+ and AOUT-) or twice the single-ended output, e.g. AOUT+ to centerpoint voltage.

I'd connect the ground to the A/D converter ground and the outputs to two separate A/D inputs, and collect some data and compare them to the instrument indications.

--

-TV
Reply to
Tauno Voipio

It

is

it.

+1.0

is

embedded

is

2000
2mV/V

transducer

built

resistor-bridge

7V.

/

Thank you very much for all great replies.

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learn

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