Chapter List

2.1 Automotive Pressure Measurements

Various pressure measurements are required in both the development and usage of vehicles to optimize performance, determine safe operation, assure conformance to government regulations, and advise the driver. These sensors monitor vehicle functions, provide information to control systems, and measure parameters for indication to the driver. The sensors can also provide data log information for diagnostic purposes.

Depending on the parameter being measured, different units for indicating pressure will be used. Since pressure is force per unit area, basic units are pounds per square inch (psi) or kilograms per square centimeter. For example, tire pressure is usually indicated in psi. Manifold pressure is typically specified in kiloPascals (kPa). A Pascal, which is the international unit (SI or Systems Internationale) for pressure, is equal to 1 Newton per meter ² or 1 kg m ^-1 s ^-2. Other common units of pressure measurement include: inches, feet, or centimeters of water; millibars or bars, inches, or millimeters of mercury (Hg), and torr. The conversion constants as defined per international convention are indicated in Table 2.1.