Hioki MR8740-50, Instruction Manual

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223
Information for Reference Purposes
Scaling method for strain gauges
This section describes how to determine the scaling conversion ratio when measurement is
performed with strain gauges and Model U8969 Strain Unit.
The appropriate conversion equation into stress varies depending on how the strain gauges are
used.
Three methods are available: the 1-gauge (for a gauge), 2-gauge (for two gauges), and 4-gauge
methods (for four gauges). The 2-gauge method is used for strain measurement involving
temperature compensation.
E: Young’s modulus,
ν
: Poisson’s ratio,
e
: Measured strain value
Measuring tensile and compressive stress: Stress (
σ
) = E ×
e
When 2- or 4-gauge method measurement is performed involving temperature compensation,
position the gauges perpendicularly to each other.
The stress (
σ
) is multiplied by 1 / (1 +
ν
) for the 2-gauge method, and 1 / [2 (1 +
ν
)] for the 4-gauge
method.
Measuring bending stress: Stress (
σ
) = E ×
e
When 2- or 4-gauge measurement is performed involving temperature compensation, the stress (
σ
)
is multiplied by 1/2 or 1/4, respectively.
Measuring torsional stress: Stress (
σ
) = E / [2 (1 +
ν
)] ×
e
(2-gauge method)
When the 4-gauge method is used, the stress is halved.
Refer to the instruction manual of the strain gauge for how to combine strain gauges for each
measurement.
Example: Measuring compressive stress
Using the 1-gauge method, material of measured object: aluminum, Young’s modulus: 73 (GPa)
(Refer to the table below.)
σ = 73 × 10
9
× (Measured value) × 10
−6
(unit of measured value: me )
= 73 × (Measured value) (unit: kPa)
= 7.44* × (Measured value) (unit: gf/mm
2
)
*: 1 Pa = 1.01971621 × 10 −7 kgf/mm 2 = 1 N/m 2
Conversion ratio: 7.44, unit: gf/mm 2
Enter this value as the scaling conversion ratio.
13
Appendix