Campbell CDM-VW300 Series Manuál stáhnout pdf (Strana 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,

µ = Gf

And for effective resolution,

 µ = 2GfN

E.3 Example Error Calculation: DGSI Spot-Welded

Strain Gage

For Durham Geo Slope Indicator spot-welded strain gages,

µ = Af

+ 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,

 µ = 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

/ 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

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Campbell CDM-VW300 Series Manuál Strana 86