Tag: instrumentation and control
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4-20 mA Transmitters (2-wire, 3-wire and 4-wire Types)
Background of 4-20 mA Signal Transmission Initially signal transmission was dominated by pneumatics before the advent of 4-20 mA signal standard. The standard was 3-15 psi pneumatic signal where the 3 psi was the ‘live zero’ and 15 psi represented the 100 %. Any pressure below 3 psi was considered ‘dead zero’ and an alarm…
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What is a Smart Sensor?
A smart sensor is the integration of a sensor with an analogue to digital converter (ADC), a processor and digital to analogue converter (ADC) for actuator control. A typical application of a smart sensor set up is a temperature control of a furnace as illustrated below. The electronics in the smart sensor contains all the…
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P&IDs and Loop Diagrams
Process and Instrument Diagrams (P&IDs), also called Piping and Instrumentation Diagrams and Loop diagrams are construction and documentation drawings that show the flow of the process and illustrate the instrumentation control and measurement instructions, wiring and connections to the process. The sections or subsystems of the process that are usually shown are called loops. A…
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Feedforward Control
Feedforward control is based on principle of pre-emptive load counter-action i.e. if all major loads (i.e. disturbances) on a process variable are monitored, and their effects on that process variable are well-understood, a control system programmed to take the appropriate action based on load changes will shield the process variable (PV) from any adverse effect.…
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Solid-state Relays (SSR) Features and Operation
A solid-state relay (SSR) is a purely solid-state device used for turning ON and OFF AC loads such as motors. Features of a Solid-state Relay Let’s consider the figure below: Physically, the SSR is packaged in a box with four electrical terminals: two input terminals and two output terminals. The input or control voltage of…
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What is Motion Control?
Motion control generally refers to an open loop or closed loop electromechanical system in which things are moving. A motion control typically consists of a motor, mechanical parts that move and often feedback sensor(s). Typical examples of motion control applications are: Servomechanisms Numerical control machines Industrial robots Variable speed drills Digital torque wrenches Hard-drive head-positioning…
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What is Sequential Control System?
This is a control system that manages a process defined by a series of tasks to be performed i.e. a sequence of operations, one after the other. Each operation in the sequence is performed either for a certain period of time (in which case, it is time-driven), or until the task is finished e.g. as…
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What is Process Control?
Process control can be defined as a control system that manages a particular industrial process so that a uniform, correct output is maintained. It does this by monitoring and adjusting the control parameters such as the flow rate or temperature to ensure the output product remains as it ought to. A typical example of process…
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Basic Features of Programmable Logic Controllers (PLCs)
Introduction to Programmable Logic Controllers What is a Programmable Logic Controller? A PLC is a user friendly; microprocessor-based specialized equipment that carries out many types of control functions with levels of complexity for use in industrial automation applications. Its objective is to monitor crucial process parameters and adjust process operations accordingly. A PLC can be…
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What is the Controller?
A controller is a device that generates an output signal based on the input signal it receives. The input signal is actually an error signal, which is the difference between the measured variable, and the desired value, or setpoint. The input error signal represents the amount of deviation between where the process system is actually…