Process Variables: Definition & Units


Process Variables are:
• Flow.
• Pressure.
• Temperature.
• Level.
• Quality i.e. % O2, CO2, pH etc.

Flow: Any fluids or liquids flowing from one place to another place is called flow and it is defined as volume per unit of time at specified temperature and pressure
Conditions, is generally measured by positive-displacement or rate meters.
Units: kg / hr, litter / min, gallon / min, m3 / hr, Nm3 / hr. (Gases)

Pressure: It is defined as Force per unit Area. P = F/A
Units : bar, Pascal, kg / cm2, lb / in2.\

Level: The height of the water column, liquid and powder etc., at the desired measurement of height between minimum level points to maximum level point is called level. The measurement principle is, head pressure method.
Units: Meters, mm, cm, percentage.

Temperature: It is the degree of hotness or coldness of a body is called temperature.
Units : Degree Centigrade, Degree Fahrenheit, Degree Kelvin, Degree Rankin.

Quality: It deals with analysis.( pH, % CO2, % 02, Conductivity, Viscosity )

Boiler level control system
Pneumatic proportional control action and its Practical Automatic and manual mode