Foundation, Concrete and Earthquake Engineering

Different Types of Earth Pressure Cells, Their Applications and Construction of Isobar Diagram Using Them-20

2.18 Measuring Temperatures

Each Vibrating Wire Pressure Cell is equipped with a thermistor for reading temperature. The thermistor gives a varying resistance output as the temperature changes. Usually the white and green leads are connected to the internal thermistor. The GK-403 readout boxes will read the thermistor and display temperature in °C automatically.



Pressure Calculation

The basic units utilized for measurement and reduction of data from Vibrating Wire Earth Pressure Cells are "digits". The GK-401, GK-402 and GK-403 Readouts all display "digits" in the Earth Pressure Cell reading position. Calculation of digits is based on the following equation;

Equation 3.1. - Digits Calculation

To convert digits to pressure the following equation applies;

Equation 3.2. - Convert Digits to Pressure
The Initial Reading (R0) is normally obtained during installation (usually the zero reading). The Calibration Factor (C, usually in terms of psi or MPa per digit) comes from the Calibration Sheet (Figure 3.1). To convert the output to other engineering units, the Calibration Factor is multiplied by the conversion multiplier listed in Table 3.1
Table 3.1 - Engineering Units Multiplication Factors
For example, assume an initial reading of 9101, a present reading of 7380 and Calibration Factor of 0.06943 psi/digit. The calculated pressure is;

119.5 psi = (9101 - 7380) × 0.06943

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