Voltage to Pounds calculation Text - Physics Forums Library

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shankaryr

Jun12-08, 05:22 PM

Hi there,

I have converted a resistance value to a voltage level. My objective is to convert the voltage level to force in terms of Pounds. Could anyone suggest me a formula which could be used or a software which can do this. Can I use excel to convert this if there is an already stated formula.

This is kind of urgent and all help is appreciated

Thanks

russ_watters

Jun12-08, 05:44 PM

Force of what?

mgb_phys

Jun12-08, 05:48 PM

Is this some sort of load cell ( a weighing machine ?)
The easiest way if you don't have the specs is to measure the voltage with no weight.
Then add 1lb and measure the voltage, then measure it with 2lbs ( or whatever range of weights is reasonable)

Jeff Reid

Jun12-08, 05:51 PM

Voltage is a potential. You need to multiply by the current in order to caculate power, the rate at which work is done.

Force times speed also equals power, so

Voltage times current = power = force times speed, but how would you relate current and speed?

shankaryr

Jun12-08, 05:55 PM

I am connecting a force sensing resistor to a data aquisiton device (labjack). The FSR takes in force applied on it and outputs resistance value. Now, i have used a Data acquisition device labjack to convert the resistance value to voltage for which i have used a voltage divider. Now, my objective is to convert the voltage applied to pounds to calculate the force applied on the FSR. For this i need a relationship between force in lbs abd voltage.

shankaryr

Jun12-08, 06:03 PM

Ideally, what I would do is to apply a known amount of force (weights in lbs) on the FSR and get the resistance value. But since I am thinking of making this a computer generated output, I need the value to be generated by an electonic device. If i have the relationship I might be able to use excel or probably labview to convert the voltage to pounds.

So, if anyone has an idea, please let me know and it would be well appreciated.

mgb_phys

Jun12-08, 06:23 PM

Assuming the device is linear then you just need the scale and offset as I described.
Measure the voltage with no load and then measure the change in voltage per lb.

If you need an analogue output from this sensor (eg. 1V = 1lb ) you can do this with a single op-amp.

Redbelly98

Jun12-08, 08:20 PM

shankaryr, there is no basic general formula that we can give you. You must calibrate your apparatus by applying a known force and measuring the resistance or voltage yourself.

As mgb_phys said, you should do the measurement when there is no force. Also do it with close to the maximum force you expect to use.

If you want to double-check the linearity, you could also do the measurement with about half the maximum force.

Good luck :smile:

shankaryr

Jun12-08, 11:31 PM

Thanks. I shall do the above said steps.

stewartcs

Jun13-08, 08:42 AM