Basic Instrumentation

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Pressure [P]: psi, kg/cm², bar, Pa (or kPa or MPa); gauge or absolute in each case

Flow [Q]: gallons/minute, ft³/minute or hour, m³/hour, liters/second

Level [h]: inches, feet, millimeters, meters

Temperature [T]: °R (rare), °F, °C, or K (no degree symbol)

"Parameter" is a nice buzzword; it has its uses and misuses.

Generally the change of the physical properties of a material or a system due to the change of the measured parameter is used as the principle of sensor. Different types of sensing element or system is used for different types sensing parameters. For example, the change of resistance of a resistor due to the change of temperature is used for temperature sense. Sensors are also commonly known as transmitter or transducers, though there is difference among them. Sensor (mechanical, electrical, photonic or any other system) is the sensing element whose physical property changes, transducer (generally an electrical and electronic system) converts the physical property of the sensor to electrical system and transmitter (generally electronic system) converts the electrical system to the standardized process or control signal (generally 4 mA for 0% and 20 mA for 100%) which is used by the controller. In most cases, the sensor, transducer and transmitter are integrated together and that is the reason they are used synonymously. In any automatic system, controller gets the input from sensor (or transducer or transmitter) and compares the difference (delta) of sensing signal to its set point, and based on the difference, it sends the control element to correct the system.

Here is the list of some common type of sensing elements:

Temperature Sensor:

Thermocouple: (Type E: -100 to 1000, Type J: 0 to 750, Type K: 0 to 1250)

RTD (Resistance Temperature Detector): (-200 to 650)

Thermistor: (-40 to 150)

Filled System: (-200 to 800)

Flow sensor:

Orifice

Ventury Tube

Flow Nozzle

Pressure Sensors:

Bourdon Tube

Bellows

Diaphragm

Capacitive or Inductive

Resistive, Strain Gauge

Level Sensors:

Float: (up to 1 M)

Displacement: (0.3 to 3 M)

Differential Pressure: (No upper limit)

Capacitance: (up to 30 M)