Measurement and instrumentation involve the use of instruments and sensors to measure physical parameters such as temperature, pressure, flow, and level. These measurements are crucial for controlling processes in industries like oil and gas, chemical, and power plants.
Temperature Measurement Instruments:
- Thermocouples:
- A sensor that generates a voltage based on the temperature difference between two junctions.
- RTDs (Resistance Temperature Detectors):
- Measure temperature based on the change in electrical resistance of the material.
- Bourdon Tube Pressure Gauge:
- A mechanical sensor that measures pressure by the deformation of a tube.
- Strain Gauge Pressure Transmitter:
- Measures pressure by detecting changes in the electrical resistance of a strain gauge.
- Orifice Plate:
- Measures flow rate based on the pressure drop across a constriction.
- Electromagnetic Flowmeter:
- Measures flow based on the voltage generated when a conductor moves through a magnetic field.
- Float-type Level Gauge:
- Measures the liquid level by floating a device on the surface of the liquid.
- Radar Level Transmitter:
- Measures level using the time taken for radio waves to travel to the surface of the liquid and back.
Accuracy:
- Refers to how close the measured value is to the true value. High accuracy is essential in process control to ensure products are made to specification.
- Refers to how consistently an instrument measures the same value when used repeatedly under the same conditions.
- The smallest change in the measured quantity that an instrument can detect.
- The minimum and maximum values that a measurement instrument can accurately measure.
Control Valves and Actuators Control Valves:
Control valves are used to regulate the flow, pressure, and temperature in industrial processes. They act as final control elements in a closed-loop system. Types of control valves:
Globe Valves:
- Provide good flow regulation and are commonly used for controlling pressure and flow in systems.
- Used for on/off control, and offer low resistance to flow when fully open.
- Typically used for controlling large volumes of fluid with minimal space.
Actuators:
Actuators are devices that convert control signals from the controller into physical action to adjust the process. The most common types of actuators are:
Electric Actuators:
- Operate using electric motors and are used for controlling valves, dampers, and other equipment.
- Operate using compressed air, and are commonly used in control valves for fast and accurate control in industries like oil and gas.
- Use pressurized fluid to move the actuator and are typically used for heavy-duty applications in industries like mining and shipbuilding.