Steps for Reducing Noise in Your Measurements: Part 1, Planning

Here is a step-by-step guide to reducing or eliminating noise from your strain measurements.  In Part 1, we will look at the planning and preparation that can result in reduced noise:

Prior Planning:

1. Since you are measuring strain in units of microstrain (με), or possibly mV/V, it is convenient to quantify noise in the same units in which you are measuring.  Decide the acceptable noise level for the test and then that will become your goal later if actions are needed to reduce noise.

2. Select a strain gage size and resistance that will allow you to use the maximum excitation voltage possible.Maximum excitation voltage gives you maximum signal-to-noise ratio, but there are limits to how much excitation voltage can be used.See other StrainBlog posts regarding excitation voltage and self-heating:

   Bridge Excitation Levels for Strain Measurement

   Excitation Voltage

3. Select instrumentation (signal conditioning or complete data system) that has these features:

   1. Selectable and wide-range excitation voltage.

   2. Make sure the instrument has the ability to turn off excitation voltage while keeping the inputs active.

   3. Selectable low-pass analog or digital filters.

   4. Grounding for shielded cable or a form of active shield.

4. Are there any obvious sources of electrical noise on or near the test article?If so, categorize them as either high-voltage sources of noise (RF sources, ignition systems, etc.) or high-current sources of noise (electric motors, cables, alternators, anything with a dynamic magnetic field).

5. Select the best cable for your strain gage installation.For high-voltage noise sources, select a shielded cable.For high-current noise sources, select a twisted cable.Cables are available that are both twisted and shielded.

6. Plan a routing for the cables from the strain gages to your instrumentation that puts as much distance as possible between the cable and noise sources.If you must get near a power cord, try to route the strain gage signal cable perpendicular to the cord, and never parallel to the cord.

In the next tip, we will provide the steps for reducing noise that occurs during the test while measuring strain.