Appendix A Glossary

Page A.6

P
Pa See Pascal.
Pascal The unit of force. 1 Pa = 1N/m2
Percent mass The percentage that the mass of a substance has compared to the total
mass for a mixture of substances of which it is a part.
Periodic time The duration of one cycle of a wave-form, equal to the inverse of the
frequency.
Platinum resistance thermometer A highly-accurate thermometer, based around a coil of very pure
platinum wire, which is extremely stable over time. It can be used
instead of an analogue input to the signal converter or flow computer.
POST See Power-on self test.
Power-on self test A standard routine which an item of equipment goes through when it is
powered up to make sure that it is operating correctly. The progress of
the test is usually shown on the instrument display.
Protect ground Another name for Chassis earth.
PRT See Platinum resistance thermometer.
Pressure The measured pressure of the fluid in the pipeline.
Primary variable A variable (such as time or distance) which is directly measured.
psi Pounds per square inch. Imperial units of pressure.
Pulse output An output of single pulses, sent to equipment such as pulse summators
or electro-mechanical totalizers.
PV See Primary variable
R
Radio frequency interference Interference from sources which transmit at radio frequencies; that is,
frequencies in the range of about 100kHz to about 300GHz.
Reynolds number A dimensionless constant given by P
U
Q
vlvl
Re
Where: v = fluid viscosity
l = length
Q = kinematic viscosity
U = density
RFI See Radio frequency interference
RS-232 An international standard for serial data transmission. It specifies
voltage levels, timing and control.