Understanding Pressure, Illumination, and Flow Transducers
Pressure transducers can be divided into several groups, including:
- Mechanical: These measure pressure directly compared with that exerted by a fluid density and known height, or indirectly through the deformation experienced by various constituent elements of the transducer.
Mechanical Pressure Transducers
U-tube manometers are used to measure atmospheric pressures. They consist of a U-shaped tube with mercury, one branch open and the other connected to the pressure to be measured.
Bourdon tubes are elliptical section tubes closed at one end and curved like an almost perfect ring. When pressure is applied, the tube tends to straighten out.
Spiral and propeller elements are formed by rolling a Bourdon tube, resulting in a considerable shift from the free end and a larger movement of the pointer.
Diaphragms consist of one or more circular capsules welded together at their edges. Applying pressure deforms the capsule, and the sum of these distortions gives the total measurement.
Bellows are similar to diaphragms but are a single piece and flexible in the direction of their axis.
Electromechanical Transducers
Electromechanical transducers combine an elastic mechanical element with an electrical transducer. These can be:
- Resistive: Pressure moves a cursor along a resistance similar to a potentiometer.
- Capacitive: Pressure is measured through a metal diaphragm.
- Strain gauges: Based on the change of length and diameter of a wire conductor or semiconductor under pressure. They can be cemented or cementless.
Piezoelectric Transducers
Piezoelectric transducers rely on the appearance of electric charges on specific crystalline areas. They are very sensitive and used for high vacuum measurement.
Vacuum Transducers
For very sensitive vacuum measurements, the McLeod gauge (also called McLeod vacuum gauge) is used.
Thermal Transducers
Transducers based on thermal energy emitted by a filament passing an electric current are inversely proportional to the environmental gas pressure. Ionization transducers are also used.
Measurement of Illumination
Photo resistors, also called Light Dependent Resistors (LDR), are photoresistive cells whose electrical resistance depends on the flow of light incident on them per unit area.
Photodiodes and Phototransistors
Photodiodes operate based on a reverse-biased diode when subjected to light.
Phototransistors operate similarly to normal transistors, usually for switching applications.
Optic Sensor-Based Elements
Optic sensor-based elements can be classified into barrier reflection in a mirror or proximity sensors.
Comparators and Actuators
Comparators compare a setpoint signal with the output signal measured by the sensor, generating an error signal. They appear only in closed-loop control systems with a feedback block and can be tires, mechanical, electrical, or electronic equipment.
Actuators are final control elements that function as control elements of a valve. Examples include switches and relays capable of following an electrical or pneumatic signal from the regulator.
Flow Control
Flow control is an essential element in the automatic control of industrial processes. It involves varying the control flow of oil using a continuously variable orifice area. It consists of a body (containing the shutter and trim), a servo (responsible for triggering the shutter up or down), and a lid.
During operation, valves are subject to corrosion processes. No single material is resistant to all types of corrosion, so combinations with materials like Kobe City are often used.