Category: Mechatronics, Industrial Control & Instrumentation
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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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Basic Features of Modern PID Controllers
Most modern PID controllers have the following features: Manual versus automatic mode Output tracking Setpoint tracking Alarm capabilities Process variable (PV) characterization and damping Setpoint limits Output limits PID tuning security Manual and Automatic Modes When the controller manually calculates the output values based on process variable (PV) and setpoint (SP) values overtime, it is…
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Electromechanical Relays (EMR)
Electromechanical relay (EMR) is a device that uses an electromagnet to provide the force to close or open switch contacts i.e. it is an electrically powered switch. When the electromagnet (also called coil) is energized, it pulls down on the spring-loaded armature. Relay contacts can be described as normally open contacts (NO), which are open…
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Direct Digital Control (DDC)
In direct digital control (DDC) a single computer is able to carry out PID control for multiple loops at the same time make that loop data accessible between loops for purposes of cascade control, feedforward control, ratio control or any other control strategy. The DDC controller is also accessible on networks like ethernet for operational…
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Digital PID Controllers
Digital PID controllers have replaced most pneumatic and electronic analog controllers in industrial control applications. Digital PID controllers are preferred over the analog types because they employ microprocessors which can execute multiple functions at ago hence they bring with them many advantages in addition to their ability to network with PC workstations and other controllers…
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Features of a Reed Relay
The reed like contacts of a reed relay are encapsulated in a small sealed glass tube that is evacuated or filled with an inert gas like dry nitrogen as illustrated in the figure below: The contacts are activated by an external magnetic field. The contacts are either dry or mercury-wetted. Mercury-wetted contacts have a thin…
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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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The Basics of Ladder Diagrams for Programming PLCs
The ladder diagrams are universally used as a symbolic and schematic way to represent the interconnection between the elements in a Programmable Logic Controller (PLC). The ladder network is also used as a tool for programming the operation of PLC. The elements are interconnected between the supply lines for each step in the control process…