Tag: Industrial control
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How Modbus is used in Industrial Networks
Modbus is an open standardized communication protocol that was founded by Modicon. Initially it was designed for the communication among PLCs in industrial applications but it also gained significance use in building automation domain for instance in HVAC systems, DDCs and room control. In a nutshell, Modbus is an application layer messaging, protocol placed at…
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Analog vs. Digital Controllers
Analog signals pass continuously through a full range of values for example a measuring device converts the process variable (PV), say temperature, into a signal corresponding to this temperature. Each temperature value corresponds to a value of the electrical signal. Digital signals belong to the group of discrete signals; here the individual signals are represented…
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Position Control System using a Microprocessor-Based Controller
Consider the following figure illustrating a position control system employing a microprocessor-based controller with parallel ports: The system above has one output port and three input ports (each port has its own address). The output port is partitioned: Six bits are converted in a Digital Analog Converter (DAC) to provide the analog motor-drive signal, the…
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Steam-heated Reboiler Control System
When steam-heated reboilers are used in distillation columns and the heating medium is steam, a flow control loop for the steam will typically be incorporated. The control valve can then be placed either in the steam or condensate line. Steam pressure compensation is always recommended in these cases, and the controls are illustrated in the…
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Basic Features of Sercos Automation Bus
Sercos is a short form for serial real-time communication system; a digital automation bus that interconnects motion controls, drives, I/O, sensors, and auxiliary devices such as cameras and weighing stations. Sercos is an open controller-to-intelligent digital device interface, designed for high-speed serial communication of standardized closed loop data in real time (RT). Sercos I and…
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How cycloconverter is used as a direct frequency converter
The cycloconverter provides direct ac to ac transformation with control over both the output voltage magnitude and output frequency. It employs phase-angle-controlled bridges to synthesize voltages. The most common form is the three-phase to three-phase converter illustrated below: Each output needs two three-phase thyristor bridges. One bridge is used to synthesize positive voltages at the…
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Industrial Process Temperature Control System
Let’s consider the industrial process control system shown below: The requirement is to control the temperature ϴ in the tank. The voltage r, obtained from a potentiometer, is calibrated in terms of the desired temperature ϴc. This voltage represents the input quantity to the feedback control system. The actual temperature ϴ, the output quantity, is…
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DC Motor Power Op-amp Speed Controller
Let’s consider the functional diagram below: The D/A converter outputs a voltage directly related to the potentiometer position. However, the D/A converter’s output current is limited and not enough to drive a motor. A power operational amplifier (op-amp) circuit, configured as a noninverting amplifier can drive the motor at the higher currents required. In effect,…
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Power MOSFET Motor Control
Because of the very high input gate resistance of MOSFETs, MOSFET’s fast switching speeds, and the ease at which they can be driven makes them ideal to interface with op-amps or standard logic gates. Nevertheless, care must be taken to ensure that the gate-source input voltage is correctly chosen because when using the MOSFET as…