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Installation and Configuration Manual 55
Safety Certification Return PolicyProduct DataCalculated Parameters
Appendix A
Calculated Parameters
A.1 Introduction
The following information details the equations used in the Micro Motion
®
signal converters to
translate the raw data from the meter into fluid parameters and covers the following:
• Viscosity equations
• Quality factor (Q)
• General viscosity equation (η - eta)
• Density equations
• General density equation (ρ - rho)
• Temperature correction equation (ρ
t
)
• Viscosity correction equation (ρ
v
)
• Pressure correction
• Velocity Of Sound correction equation (ρ
vos
)
• Density scaling
• Kinematic viscosity equation
A.2 Viscosity equations
To derive the fluid's dynamic viscosity the frequency of oscillation at two points on the meter's
resonance curve are taken, manipulated to calculate the meter's quality factor (Q) and then calibrated
against actual fluid viscosity determined by a prime standard.
(For details of the principle of operation, see Chapter 1.)
The Quality factor from the 7827 meter is calibrated against the fluid’s dynamic viscosity in
centiPoise (cP). The order in which the calculations are applied are according to the following.
A.2.1 Quality factor
The meter operates at two time periods (τ
A
and τ
B
) which correspond to the two –3 dB level points on
the frequency spectrum. In doing this, one may calculate the meter's quality factor by using the
following equation:
Q = 1 / [ ( τ
A
/ τ
B
)
0.5
- ( τ
B
/ τ
A
)
0.5
] [1]
Where:
• Q = Quality factor of meter (no units)
• τ
A
= Time period A of meter (µsec)
• τ
B
= Time period B of meter (µsec)