Category: Mechatronics, Industrial Control & Instrumentation
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The Construction & Principle of Operation of Load Cells
A load cell converts a force (usually the gravitation force from an object being weighed) to a strain which can then be converted to an electrical signal by strain gauges. A load cell will typically have a local circuit as illustrated in figure 1(a) with four gauges; two in compression and two in tension and…
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How Controllers are used in Industrial Automation Systems
In many process control systems, microprocessor based programmable logic controllers are used for decision making due to the sophistication of the system and the large number of process variables involved. The PLC can be configured to receive a small number of inputs (both analog and digital) and control a small number of outputs or the…
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Features & Configuration of a Smart Pressure Transmitter
Smart/Intelligent pressure transmitters are microprocessor-based, and they provide additional functional capabilities beyond their basic role of just sensing and representing a process variable; for example they provide computing, diagnostics, and networking capabilities . We shall consider a capacitive sensing pressure transmitter with a typical functional diagram illustrated below: The process pressure is transmitted through the…
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The Conditioning of Thermocouple Sensor Voltages
Consider the circuit below: From the figure above, the sensing junction and reference junction are connected in series. When the junctions are at the same temperature the voltage output from the junctions is zero and the output from the amplifier is zero. When the junctions are at different temperatures, there is a differential voltage at…
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RTD 2, 3, 4 Wire Sensor Connections
The resistance temperature devices (RTD) can be connected directly to the controller peripheral amplifiers using 2-wire, 3-wire or 4-wire lead configuration. The wires in all these connections are in shielded cables. The RTD is usually driven from a constant current source (I) and the voltage drop (V) across the RTD is measured. RTD 2-wire connection…
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How Signal Processing Circuits are protected from high currents & voltages
Protection against high currents and voltages is a very important requirement for signal processing circuits. A high current can be protected against by the incorporation in the input line of a series resistor to limit the amount of current flowing to an acceptable level and a fuse to break if the current exceeds a safe…
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Features of Stepper Motors & How they are applied in Industrial Control
A stepper motor is a permanent magnet or variable reluctance DC motor that has the following characteristics: It is able to rotate in both directions It can move in precise angular increments It can sustain holding torque at zero speed Can be controlled with digital circuits Stepper motor moves in accurate angular increments, known as…
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How Servo Motors are used in Process Control
Servo motors are continuous motion mechanisms that use feedback signals to provide position and velocity control in a closed loop system. Servo motors can rotate to a given position be stopped and reversed. The angular position and speed can be precisely controlled by a servo loop, which uses feedback from the output to the input. …
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Methods of Protecting Instruments from Explosive Atmospheres
The protection method used in a specific hazardous location depends on the application, the technology available and the specific explosive atmosphere present. In this article, we discuss the following methods of protection: Table 1 provides the summary information for each protection method. The codes are used in the markings or labels for apparatus and enclosures.…