Closed-loop control – Feedback, Feedforward, Cascade, Split Range, and Ratio control
Feedback control: Feedback control is a control system in which the control action depending on process output. This type of control system measures process variables on the process output. Every time there is a measurable change in the process outlet, due to the effects of disturbances (load) the feedback control system reacts to provide corrective… More
What is RTD? It’s Types.
RTD is the acronym for resistance temperature detectors. RTDs are sometimes referred generally as resistance thermometers. A resistance Temperature detector (RTD) is a popular choice of temperature sensors which measures temperature using the principle that the resistance of a metal changes with temperature. Principle: RTDs work on the basis of relationship between metal and… More
Gateway, Bridge and Router
GATEWAY: Gateway is a network device used to connect two networks. Usually, the gateway is used as a liaison between the local network (LAN) and the public network (internet). In addition, the gateway also acts as a regulator of which packets are allowed to pass which are not. This gateway can be a special device,… More
Miniature Circuit Breaker(MCB) and its types
A circuit breaker is an automatically-operated electrical switch. It is designed to protect an electrical circuit from damage caused by overload or a short circuit. Its basic function is to detect a fault condition and, by breaking continuity, to immediately discontinue electrical flow. Definition As the name implies it is a miniature form of the… More
Reliability Centered Maintenance and its strategies
RCM is identified as one of the most powerful tools a company can use to get more value from its physical assets. It is the foundation of highly successful maintenance programs to ensure that machines help operations to deliver the results as required, yielding or exceeding the anticipated financial outcome required by the participated departments.… More
Cushioning in pneumatic cylinder
Pneumatic cylinder end caps have to withstand shock loads at the extremes of piston travel. These loads arise from the kinetic energy of the moving parts such as piston cup rings of the cylinder and load. When the piston of a normal cylinder is about to complete its stroke, the piston runs into a cylinder’s… More
Thermocouple: Principle, Construction, Characteristics, Advantages, and Limitations.
A thermocouple is a device that converts thermal energy into electric energy. The amount of electric energy generated can be used to measure temperature. A thermocouple is a thermoelectric transducer, used as a primary transducer. Changes in temperature are directly converted to electrical signals. Seebeck Effect: If two wires of different materials are joined together… More
Types of errors in measuring instruments
The performance characteristics of a measuring instrument are categorized as Static and dynamic characteristics. A static error is one of the static characteristics. We know that the static error is the difference between the true value of the measured variable to the value indicated by the instrument not changing with time. The static error may… More
Transducer and its classification
A transducer is a device that can convert a physical quantity into another. Most transducers convert nonelectric quantities into electrical quantities. So transducers act as energy converters. A transducer can be divided into a primary sensing element and a converter element. A primary sensing element detects a quantity to be measured and a converter element… More
What are LVDT, RVDT, and their comparison?
Linear variable differential transformer LVDT and rotary variable differential transformer RVDT are two specialized transformers. A basic LVDT and RVDT comprise one primary coil, two secondary coils, and a movable core. If a first coil across which the AC voltage applied is called the Primary coil and two coils that produce output are called secondary… More
Remote seal capillary system and tank level Calculation
The remote seal also referred to as diaphragm seal are connected to a measuring instrument using a direct connection or a capillary. A remote seal system consists of an external sensing diaphragm mounted to the process and connected to a differential pressure transmitter with oil-filled capillaries. The capillaries and seals are filled with incompressible oil… More
Bonded and Unbonded Strain Gauges
Working Principle: The strain gauge working principle is based on the fact that the electrical resistance of materials varies with deformation. A strain gauge is an example of a passive transducer that converts the mechanical displacement into electrical quantity. We know, the resistance of the conductor depends on the length and cross-sectional area. The resistance… More
Orifice plate and types of tappings
An orifice plate is the most common type of restriction that is used in flow measurement. An orifice plate is primarily a thin metal plate with a hole bored in the center. It has a tab on one side where the specifications such as Tag number, orifice bore diameter (in inches), the material of orifice… More
Cable tray types for selection
A cable tray is a rigid support structural system used to securely fasten, or support cables or trays. Cable Tray is used to supporting a large number of cables or conduit tubing between the two points. Tray material shall be selected according to environmental conditions and installation requirements. Cable trays offer higher safety, reliability, enhanced… More
Thermocouple Junction types
Basically, there are 4 types of junctions in the thermocouple. Grounded junction thermocouple Ungrounded Junction Thermocouple Exposed junction Thermocouple Isolated Thermocouple junction. Grounded junction thermocouple: It is the most common type of junction in which the thermocouple junction and sheath both are welded together. The three metals, two thermoelements, and sheath alloy form a single… More
Thermistor, its types, and applications.
While selecting a temperature sensor type, one restriction concerns range over which it can stay reasonably accurate. A thermistor is a resistance thermometer sensor whose electrical resistance varies in response to a change in its surrounding temperature. Change in temperature contribute to change in its electrical properties like resistance, it can also be called a… More
Vibration measurement, proximity probes.
Vibration systems use transducers which convert mechanical motions into electrical signals. What is Vibration? Rapidly changing too and fro motion either in vertical or horizontal of an object with reference to a centerline is called vibration. Vibration is a mechanical phenomenon. A vibration monitoring system is used to monitor the health of a machine in… More
Use of a positioner in control valve
The main purpose of having a positioner is to guarantee that the valve does in fact move to the position where the controller wants it to be. Pneumatic valve positioners are one of the most commonly used valve accessories. The addition of a positioner can correct for many variations. # Changes in packing friction due… More
Control Valve Positioners: Types
Primarily there are three types of valve positioners Pneumatic positioners receive a pneumatic signal (typically 3-15) from a controller. The output from the positioner is a pneumatic signal, send it to the valve actuator. Benefits of Pneumatic positioner: Easily repairable. Lower cost of ownership than other type of positioners. Electro-pneumatic positioners receive an electric signal… More
Instrumentation Interview question and answers
1. What is Intrinsic safety? By a method by which limiting the amount of electrical energy in a circuit is too low to avoid an explosion in hazardous areas. 2. What is IS and non IS cables? IS (Intrinsic Safety) cables are with some specific considerations with voltage, current, inductance, and capacitance. The color is… More
Fundamentals of loop-powered devices.
What is a loop-powered device? Loop powered devices are electronic instruments that can be connected In a transmitter loop, without having a separate or independent power supply. These devices are arranged to use the power from the current flowing in the loop. Common loop-powered devices include sensors, transducers, transmitters, indicating meters, data loggers, PLCs, and… More
What is Cv and why it is important for a modulating valve ?
Cv is the capacity of the valve to deliver flow with an available differential pressure (∆P) across the valve. It specifies the differential pressure that should be used when selecting the full flow Cv of the valve. Cv by definition is the number of US Gallons per minute (GPM) a valve will flow with a… More
Working Principle of Ultrasonic Flow Meters, advantages and limitations.
Inside the Ultrasonic Flowmeter, pairs of sensors are fitted across the tube in opposite to each other. Each sensor alternately can transmit and receive ultrasonic signals. Simultaneously the transit time of these signals is measured. The ultrasonic signals are generated by piezoelectric crystals applying a voltage. Conversely, the piezoelectric crystal creates a voltage when the… More
Cv and Kv relationship
Flow coefficient (Cv) is an imperial measurement and is defined as the flow of water through a valve at 60°F in US gallons/minute (gpm) at a pressure drop of 1lb/in². Cv = Q * √ (SG/ ΔP) (units in US GPM, psi) Q = Flow in US GPM, SG = Specific Gravity, ΔP = Differential… More
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