Calibration of torque meter

[ijk]

Hi all,

I am new to Labview and am using a torque meter.

I have calibration values of voltage and torque (from the manufacturer)

I input these as a custom scale and table in the Nidaqmx vi (not in MAX).

When running Labview, the voltages I get do not correspond to the torques, like they should if the interpolation was working properly.

For example, with no torque applied, the voltage fluctuates between very small positive and negative values but the torque gives -0.11 Nm (and fluctuates e.g. within -0.1 to -0.12 range) which does not correspond to the voltage.

Can anyone suggest why this is?

Some other info - the torque meter gives a small voltage signal out ie up to +- 16mV

The hardware I'm using is SCXI 1102 which has a +- 10V input range.

Its true that I'm not using much of the input range, but is that connected to my problem?

Thanks,

ijk

[RavensFan]

It is impossible to answer your question without more information. What kind of torquemeter is this?  What is its output, analog voltage +/- 10V, or a ratiometric signal like a strain gage bridge?

What is the torque range?  .11 Nm could be big if you are dealing with a low torque torquemeter, or could be really small if the torque range of the torquemeter is on the order of thousands or more Newton-meters.

16 mV out of a 10V range is also not much.  (about .16%).  You could be picking up electrical noise in your system.

[Broken_Arrow]

Your torque sensor is most likely a strain gauge (wheatstome bridge). Since you're using SCXI, you'd be much better off with an SCXI-1520, which is a strain module. But, you can still do what you need to do with a plain analog input, but, you need to condition your signal. Google "strain amplifier".

[ijk]

It is impossible to answer your question without more information. What kind of torquemeter is this?  What is its output, analog voltage +/- 10V, or a ratiometric signal like a strain gage bridge?

What is the torque range?  .11 Nm could be big if you are dealing with a low torque torquemeter, or could be really small if the torque range of the torquemeter is on the order of thousands or more Newton-meters.

16 mV out of a 10V range is also not much.  (about .16%).  You could be picking up electrical noise in your system.

Thanks for the responses

It is a strain gauge type - the max output is 16mV which corresponds to 20Nm.  I will look into amplifying the signal.  It still doesn't (in my mind) explain why a really small voltage (2e-5V) fluctuating positive and negative would give a consistent -0.11Nm (with slight fluctuation).  -0.11 Nm should be a voltage of about 0.1mV.

[ijk]

It is impossible to answer your question without more information. What kind of torquemeter is this?  What is its output, analog voltage +/- 10V, or a ratiometric signal like a strain gage bridge?

What is the torque range?  .11 Nm could be big if you are dealing with a low torque torquemeter, or could be really small if the torque range of the torquemeter is on the order of thousands or more Newton-meters.

16 mV out of a 10V range is also not much.  (about .16%).  You could be picking up electrical noise in your system.

Thanks for the responses

It is a strain gauge type - the max output is 16mV which corresponds to 20Nm.  I will look into amplifying the signal.  It still doesn't (in my mind) explain why a really small voltage (2e-5V) fluctuating positive and negative would give a consistent -0.11Nm (with slight fluctuation).  -0.11 Nm should be a voltage of about 0.1mV.

[ijk]

Will look to see if we have a SCXI 1520.

Thanks

[RavensFan]

.11 Nm out of 20 Nm is only .55%.  Not a huge number.  Anything based on wheatstone bridge is going to have an inherent unbalance in the bridge.  It could easily lead to a slight voltage output when there is no load on the torquemeter.

As Broken Arrow stated, an SCXI-1520 is the more appropriate module for reading bridge signals.  And you'll be able to do null balancing of the bridge during a no load calibration.