Reducing noise in strain gauge using an RC circuit

In summary, the conversation discusses the design of a filter to reduce the noise caused by vibrations of a motor (40Hz) on a strain gauge signal monitoring load on a cantilever that measures periodic load changes at a rate of 1/minute. The filter is intended to reduce the motor noise signal by 90% and the options of using a low pass filter with a cut off frequency of 40Hz and the equations linking frequency to gain are explored. The use of transfer function and choosing appropriate components for the filter are also suggested.
  • #1
liam1992
20
0
Vibrations of a motor (40Hz) cause noise on the signal of a strain gauge that monitors load on a cantilever that measures periodic load changes at the rate of 1/minute. Design a filter that reduces the signal caused by the vibrations by 90%.

I thought about a low pass filter that has a cut off frequency of 40Hz but I'm not sure about the reduction by 90% bit. Is there an equation linking frequency to the gain of a circuit because a 90% reduction would be -20dB according to gain=20log(Vout/Vin) or -10dB if you used gain=10log(Pout/Pin). I am unsure how to do this and any help would be greatly appreciated.
 
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  • #2
liam1992 said:
Vibrations of a motor (40Hz) cause noise on the signal of a strain gauge that monitors load on a cantilever that measures periodic load changes at the rate of 1/minute. Design a filter that reduces the signal caused by the vibrations by 90%.

I thought about a low pass filter that has a cut off frequency of 40Hz but I'm not sure about the reduction by 90% bit. Is there an equation linking frequency to the gain of a circuit because a 90% reduction would be -20dB according to gain=20log(Vout/Vin) or -10dB if you used gain=10log(Pout/Pin). I am unsure how to do this and any help would be greatly appreciated.

I suppose it makes a difference if the question wants exactly 90% reduction in the motor noise signal (is that voltage or power?), or whether they mean at least 90%.

If the true signal from the sensor has a frequency of 1/min ~ 0.017 Hz and the motor noise is at 40Hz then there's more than two decades of frequency to play with; You can afford to put your sensor signal closer to the center of the pass-band of your filter rather than have it degraded by the "turn" at the cutoff corner. So, for example, you might stick your corner frequency at 40Hz/100.

For an RC filter a simple approach is to choose a 'likely' value for the capacitor; for low frequencies like this start with a large but manageable capacitor value -- say 100 μF. Then use the formula for the corner frequency to find a corresponding R value. If you don't like the values you get, pick another C and try again.

Write the transfer function for the filter and verify your signal magnitudes.

You could also use the transfer function itself to choose an appropriate co-component (the R for a given C, or C for a given R) by setting the transfer function magnitude expression equal to the desired gain (attenuation) for the signal to be suppressed.
 

What is a strain gauge?

A strain gauge is a device that measures the strain or deformation of a material. It consists of a thin wire or foil that is attached to the material and changes resistance as the material is strained. This change in resistance can then be measured and used to calculate the strain.

Why is noise reduction important in strain gauges?

Noise can interfere with the accurate measurement of strain in a material. This can lead to inaccurate data and potentially affect the results of a study or experiment. Therefore, reducing noise is important to ensure the accuracy and reliability of strain gauge measurements.

What is an RC circuit and how does it reduce noise in strain gauges?

An RC (resistor-capacitor) circuit is an electronic circuit that consists of a resistor and a capacitor connected in series or parallel. The capacitor acts as a filter and blocks out high-frequency noise, while the resistor helps to smooth out any remaining noise. This reduces the overall noise in the strain gauge signal.

Are there any other methods for reducing noise in strain gauges?

Yes, there are other methods for reducing noise in strain gauges, such as using shielding to block out external electromagnetic interference, using high-quality amplifiers, and using low-noise power supplies. Additionally, proper installation and grounding techniques can also help to reduce noise in strain gauge measurements.

Are there any limitations to using an RC circuit for noise reduction in strain gauges?

While an RC circuit can be effective in reducing noise in strain gauges, it may not completely eliminate all sources of noise. The effectiveness of the circuit may also depend on the specific application and the type of noise present. It is important to carefully design and test the circuit to ensure optimal noise reduction.

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