Typical Strain Gage Excitation Values
Calculations can be made according to the
following formulas for recommended power-density
levels:
Power Dissipated in Grids (watts)
Power Density in Grids (watts per unit area)
where:
= Gage Resistance in ohms
= Grid Area (active gage length x grid width)
= Bridge Voltage in volts for an equal-arm bridge
arrangement, where the voltage across the active arm
is half the bridge voltage.
When the grid area, gage resistance, and grid
power density are known, the bridge excitation
is:
This value represents a general recommendation or
starting point for determining optimum excitations
levels for grid areas having constant power-density
levels. The calculator includes a list of the grid
areas for a number of standard Micro-Measurement
single-element gage patterns and resistances.
Instruments with Fixed Bridge Excitation
When the bridge voltage of an instrument is fixed
at a value that is higher than recommended, several
alternatives are available:
- Select a higher resistance gage.
- Select a gage with a larger grid area.
- Reduce the bridge voltage with an inactive
series resistor.
The inactive resistor (
) required to reduce the power density to the desired
range can be determined from the following
relationship:
Select the nearest precision resistor value (
) higher than the calculated value (
).
For actual strain values (
), accounting for the
actual value
of the inserted inactive resistor (
), all indicated strain readings (
) must be multiplied by an attenuation factor,
, where:
and
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Vishay Measurements Group
