I Can’t Hear You!
Noise Control In Strain Gauge Measurements.
We are all familiar with noise in everyday life. It can make conversation difficult – perhaps you are in a modern restaurant without soft furnishings, or maybe the kids are shouting again! This is directly analogous to electrical noise in measurements; those of us old enough to remember analogue TV and radio will be very familiar with the effects of a poor signal and lots of noise!
In reality it’s not the noise that is the issue, but the ratio between the noise and signal. You can close the door on noisy kids, add soft furnishings to a room, or perhaps start talking louder yourself. In other words, improving signal-to-noise ratio is to increase the signal, decrease the noise, or both.
In real measurements it may not be so simple. Noise comes from many diverse sources and can be intermittent or unexpected, and is often unknown until a test is actually performed. Switching on a light, powering the PC, energising a shaker table, or perhaps there’s arc welding in the next room or a nearby airport with radar, these can all add to the noise.
It may be the case that filtering can be used to remove much of the noise, but every filter adds some time delay and artefacts to the signal, so this should be the last tool in the armoury with exception of anti-aliasing filters, an essential in any digital system.
Noise can be controlled by using best practice. The use of twisted and shielded leads, connecting the shield correctly (earth or driven guard depending on the instrumentation), using full bridges or local bridge completion, and the use of conductive foil tape over the installation can help minimise pickup. In magnetic fields you can use MuMETAL® shielding and Inter-8® cable in conjunction with our H-series magnetic field strain gauges.
Maximising the signal is also something that can be designed-in from the start. The primary effect is achieved by optimising the excitation voltage to the strain gauge. High-resistance gauges allow more voltage because they draw less power and therefore exhibit less self-heating. This is one of the main reasons that 350-ohm gauges are much preferred to 120 ohms, a historical hang-up from the early days of their invention. As foil rolling and etching processes have been improved higher resistances are possible, with 1000 ohms being more widely used in the last few years.
Our Advanced Sensors Technology has increased our capability to reliably increase this still further, with more and more 5000 ohm patterns available even in our Precision Gauge range (previously it was exclusively for our Transducer Class gauges). Compared to a 350 ohm gauge, more than 10x the voltage can be applied, and therefore you’ll get 10x the signal, possibly the easiest way to improve your measurements.
Steps For Reducing Noise In Your Measurements: (Article)
Noise Problem And Solution. (Article)
A Gauge Is Just A Gauge? (Article)