Campbell Scientific CDM-VW300 Series Dynamic Vibrating-Wire Analyzer System - Manual (Page 86)

Appendix E. Calculating Measurement Error
where N is the noise value given in TABLE 5-3, CDM-VW300/305 Effective
Frequency Measurement Resolution, corresponding to the sample rate being
used.
E.2 Example Error Calculation: DGSI Embedment
Strain Gage
For Durham Geo Slope Indicator embedment strain gages, K = G, where G =
4.0624E–03.
So, for microstrain,
µε = Gf 2
And for effective resolution,
∆ µε = 2GfN
E.3 Example Error Calculation: DGSI Spot-Welded
Strain Gage
For Durham Geo Slope Indicator spot-welded strain gages,
µε = Af 2 + C
Where A = 7.576E–04 and C = –2030.1
So, K = A, and the above formula stands as it is for specifying the output.
When calculating the effective resolution, the constant C does not vary with
frequency, so it can be ignored for the very small changes in frequency that are
of concern. The formula becomes,
∆ µε = 2AfN
E.4 Example Error Calculation: Geokon 4420 Crack
Meter
The displacement, s, measured by the crack meter is given by the formula:
s = (Gf 2 / 1000) + Kt,
where G is the linear gage factor, K is a thermal factor, and t is the temperature
of the sensor. During a short measurement interval, the assumption is made
that there is no change in the temperature of the sensor. So, for small changes
in sensor displacement, K is assumed to be constant, and the Kt term is ignored
when calculating the output error. The resulting equation is,
∆s = 2GfN / 1000
E-2