Hello,

This is a trivial question but I am trying to interpret.

My force transducer specification states that its output differential voltage is: 1.5 output mV/mm displaced/Volts applied

Does this mean:
Output units: \( 1.5\frac{mV}{mm*V}\) or Output units: \( 1.5\frac{mV}{\frac{mm}{V}}=1.5\frac{mV*V}{mm}\)

I want to assume the first, but this system seems somewhat ambiguous, similar to saying 1.5 mV per mm per V.
Is there a name for this type of unit writing convention?


Thanks!

 

I believe it's the latter. I would expect output voltage to increase with supply voltage, not decrease.

By the way, it's refreshing to see someone care about their units!

 

I believe it's the latter. I would expect output voltage to increase with supply voltage, not decrease.

By the way, it's refreshing to see someone care about their units!

Thanks for the reply! Wouldn't that also be the case for 'mm' as well. I would expect that the output would be larger for increased displacement.

 

Oh crap, you're right. The units all need to cancel to leave only mV, and only your first equation will do that when multiplied by mm and volts. I knew you had to multiply by the volts but confused that point with the units for the "constant".

 

It's tricky.

In the case of the first equation, I would think the plain-English way of writing it would be: mV per mm-V instead of mV per mm per V. Where 'per' is used in the place of '/'.

 

Frequently the Sensitivity of a transducer is stated as mV/Volt and what tells us is if we apply for example a 10.0 Volt stable excitation voltage to the sensor the full scale output voltage will 10 * mV or if it is Sensitivity = 2.0 mV/V the full scale output will be 20 mV. If the transducer is a load cell rated for 100 Lbs full scale when full scale force is applied the output will be about 20 mV.

Using these load cells as an example the output is 4 mV/V so with a 10 Volt Excitation the full scale output will always be 40 mV. Note that the 300, 500, 1K and 2K have outputs of 2 mV/V so their full scale output will be 20 mV. Next we take the full scale mV and divide it by the full scale rating. In the case of the 500 Lb load cell it becomes .020 Volt / 500 Lb = .00004 volt per applied pound of force. Roughly 40 uV / Lb of force. Once we know the full scale output voltage of a sensor we can then divide the number of units full scale into the full scale output voltage and get the voltage per unit output whatever the engineering units are.

That is my take on it anyway. Do you have a data sheet for the sensor?

Ron

 

Frequently the Sensitivity of a transducer is stated as mV/Volt and what tells us is if we apply for example a 10.0 Volt stable excitation voltage to the sensor the full scale output voltage will 10 * mV or if it is Sensitivity = 2.0 mV/V the full scale output will be 20 mV. If the transducer is a load cell rated for 100 Lbs full scale when full scale force is applied the output will be about 20 mV.

Using these load cells as an example the output is 4 mV/V so with a 10 Volt Excitation the full scale output will always be 40 mV. Note that the 300, 500, 1K and 2K have outputs of 2 mV/V so their full scale output will be 20 mV. Next we take the full scale mV and divide it by the full scale rating. In the case of the 500 Lb load cell it becomes .020 Volt / 500 Lb = .00004 volt per applied pound of force. Roughly 40 uV / Lb of force. Once we know the full scale output voltage of a sensor we can then divide the number of units full scale into the full scale output voltage and get the voltage per unit output whatever the engineering units are.

That is my take on it anyway. Do you have a data sheet for the sensor?

Ron

Thanks Ron!

Here is a scanned copy of the transducer manual.

 

Hello,

This is a trivial question but I am trying to interpret.

My force transducer specification states that its output differential voltage is: 1.5 output mV/mm displaced/Volts applied

Does this mean:
Output units: \( 1.5\frac{mV}{mm*V}\) or Output units: \( 1.5\frac{mV}{\frac{mm}{V}}=1.5\frac{mV*V}{mm}\)

I want to assume the first, but this system seems somewhat ambiguous, similar to saying 1.5 mV per mm per V.
Is there a name for this type of unit writing convention?


Thanks!

Force transducer? Sounds more like a displacement transducer, such as an LVDT or something.

Regardless, it is

\(
V_{out} \; = \; X \; \cdot \; V_{applied} \; \cdot \; 1.5 \, \frac{\(\frac{mV}{mm}\)}{V}
\)

where X is the amount of the displacement.

Which is equivalent to

\(
V_{out} \; = \; X \; \cdot \; V_{applied} \; \cdot \; 1.5 \, \frac{mV}{mm\cdot V}
\)

which is further equivalent to

\(
V_{out} \; = \; X \; \cdot \; V_{applied} \; \cdot \; 1.5 \, \frac{1}{m}
\)

So if you apply 10 V to the transducer and the displacement is 10 mm, then the output should be 150 mV.

 

While they mention Force and Displacement it looks more like displacement to me. I believe Mr. WBAHN has it covered above and the last page of the manual, just above the bridge image seems to cover the outputs.

Ron

 

Thanks all!

 

I found a good lab textbook going over the specifics of this device. See attached.

"The Laboratory Computer - A Practical Guide for Physiologists and Neuroscientists"