8-16 Qualitek mR Owner’s Guide
8.10 Temperature Compensation (Temp Comp)
8.10.1 Introduction
The QMR pressure decay tester determines the leak rate of the component by
pressurizing the component to a set pressure and then measures the resultant
pressure change over time. The pressure decay technique assumes the component's
volume and temperature have remained constant and any pressure loss is due to
leakage.
However, the pressure decay measurement is dependent upon temperature and
volume changes defined by the ideal gas law:
PV = nRT
Where:
P = Pressure of the gas (abs)
V = Volume
n = Number of molecules
R = Ideal gas constant
T = Temperature of the gas (abs)
Based on the above law the pressure within a sealed volume will decrease if the
volume increases or the temperature decreases over time. Temperature changes can
affect the physical dimensions of the component and/or the air temperature within
the component. Both of these changes can affect the measured pressure and
compromise the measured pressure decay measurement. In many applications
small changes in volume or temperature can be accommodated but in some
applications these changes will cause testers to falsely indicate leak tight or leaking
components.
The component's temperature may change due to the air supply temperature,
ambient temperature changes due to sunlight, proximity to heaters or air
conditioners, a manufacturing processes prior to testing where the component is
heated due to a drying or welding process, the component is stored at a different
ambient temperature prior to testing.
This document describes the setup and operation of the QMR Temperature
Compensation option to minimize the effects of temperature changes on the
pressure decay measurement.
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