# Finding mass using force sensor and usb daq6366

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Hello Everyone,

Need some verification with daq program.

I have one force sensor that connectd with my usb daq device. with this force sensor, unknown object is connected(hanging) and i want to find the mass of this object (F=ma) so i am taking continous sample and generate waveform graph. After the scaling, my waveform will be in Newton unit.

my question is: if i take RMS of this waveform(1d Array data point) and divide by g (9.8 m/s2) then whatever value come is my correct mass? (F=ma).

Edited by Gab

Say the mean. RMS would give you an estimate of the standard deviation of your measurement.

you mean to say that i should find mean instead of RMS  Right?

• 2 weeks later...
On 11/19/2017 at 9:51 PM, ensegre said:

Say the mean. RMS would give you an estimate of the standard deviation of your measurement.

Hello,

I dont think so i got right value because actual weight of my system is ~400 g but my daq program giving me a strange value (like 40g, 29g, etc..). if i read more sample than some time this value increase.

anyone has an idea?  why this happen for stable mass system hanging with spring ?

You should check your (raw) input signal. Sounds to me like the input signal from the force sensor is not as stable as you think it is. The equation is a simple conversion from force to mass, so it'll produce the same output given the same input. Even if you don't take the average over your input signal, the calculated mass should stay within reasonable limits.

59 minutes ago, Gab said:

actual weight of my system is ~400 g but my daq program giving me a strange value (like 40g, 29g, etc..)

Check the datasheet of your force sensor. Its output might be scaled (the same could apply to your DAQ settings).

59 minutes ago, Gab said:

why this happen for stable mass system hanging with spring ?

How stable are we talking about? 400 g isn't that much (in my world that is )

Edited by LogMAN
1 hour ago, LogMAN said:

You should check your (raw) input signal. Sounds to me like the input signal from the force sensor is not as stable as you think it is. The equation is a simple conversion from force to mass, so it'll produce the same output given the same input. Even if you don't take the average over your input signal, the calculated mass should stay within reasonable limits.

Check the datasheet of your force sensor. Its output might be scaled (the same could apply to your DAQ settings).

First of all thanks for reply. Scaling is not a problem. I am 100% sure. moreover, i am reading voltage from force sensor(ICP) then using sensitivity, convert into EU unit(Newton).

1 hour ago, LogMAN said:

How stable are we talking about? 400 g isn't that much (in my world that is )

Here stable mean to say there is no any kind of damping oscillation wave because of spring.

Edited by Gab

Still, you read masses that are way off compared to the values you'd expect, right? Since you do voltage measurement you also have to consider side-effects from other parts of your setup (like wires running alongside that transfer signals which may induct into your wires).

I suggest you take a graph of your input signal over a reasonable duration and have a look at it. Try to figure out if the source signal is acceptable for your needs. If that's the case and the output is still wrong, maybe you can share some sample data and a VI to find a solution.

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