Interview questions based on industrial automation - part 2

instrumentation

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For part 1: Interview questions based on industrial automation - part 1

What is a transmitter?

A transmitter is a field mounted device, mounted close to the sensors. The sensor senses the physical variable in the process and converted into some form of electrical value. This sensor value is converted into an electrical signal in 4-20mA range. Electrical signals are used so that long-distance communication is possible.

What is a smart-transmitter?

Smart-transmitters are the microprocessor controlled transmitter, produce a digital output. Smart transmitters allow to digitally control from remote positions.

What is square root extractor?

The square root extractor is an electronic (or pneumatic) device that takes the square root of the signal from the flow transmitter and outputs a corresponding linear flow signal.

Differential pressure is measured across the differential pressure devices in the flow stream. The differential pressure is related to the flow of the stream, but not linear. Flow is related to square root of the differential pressure.

What is a control valve?

A control valve is a final control element used to control fluid flow by varying the size of the fluid passage in response to the signals received from controllers.
Control valves are used to control condition such as flow, level, pressure , temperature.

What are actuators?

Actuators are the driving unit of a valve, which consist of diaphragm and piston that operates the valve stem by receiving the control signal.

Actuators are divided into three based on the source of energy used for the movement of the valve stem.

What is a valve positioner?

A valve positioner relates the input signal and the valve position, and will provide any output pressure to the actuator to satisfy this relationship, according to the requirements of the valve, and two ensure actuator stem take a position proportional to the input signal.

What are the different types of Diretional control valve?

  • Check valve
  • Shuttle valve
  • Two-way valve
  • Three-way valve
  • Four-way valve

What is PID control?

PID control is closed loop control system used widely in industrial automation. PID stands for Proportional-Integral-Derivative control. PID control is the combination of these three controllers.

Conventional ON/OFF controllers are used only where we needed two-stage control operation, which always produces offset in the output. Oscillating nature of ON/OFF system between On and Off limits its usage and hence, it is replaced by PID controller.

What is Modbus?

Modbus is a serial communication protocol is developed by MODICON inc. Modbus devices use master-slave communication technique in which only one device(master) can initiate the transaction and other devices respond to the master request.

What is Modbus TCP/IP?

MODBUS/TCP is a communication protocol designed to allow industrial equipment such as Programmable Logic Controllers, computers, operator panels, motors, sensors, and other types of physical input/output devices to communicate over a network.