Tag: instrumentation and control
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Instrument Grounding: General Guidelines
Specific attention must be paid to instrument grounding, especially where field instruments are connected to a computer or microprocessor based control system. Where cable screens are used, ground continuity of screens must be maintained throughout the installation with the grounding at one point only such as that in the control room. At the field end…
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Valve Positioners: Function & Types
Basic Features of a Positioner Pneumatically operated valves depend on a positioner to take an input signal from the process controller and convert it to valve travel. In other words, a positioner is a motion control device made to actively compare the stem position against the control signal, adjusting the pressure to the actuator diaphragm…
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Directional Control Valves: Function & Principle of Operation
Directional control valves are used to regulate the flow rate of hydraulic fluid; they are also utilized in pneumatic systems for flow control. Directional control valve works by regulating the movement of the piston in the cylinder. It admits pressurized fluid to either end of the cylinder while providing a return path for fluid being…
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Instrument Manifolds: Function & Types
An instrument manifold also referred to as a valve manifold includes manual valves to isolate and equalize pressure from the process to the transmitter (in this case the DP transmitter) or to isolate a gauge or absolute pressure transmitter for maintenance and calibration purposes. Typically we have the following types of valve instrument manifolds:…
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Pneumatic System Components: Types & Functions
A pneumatic system utilizes air pressure to create mechanical motion. A basic pneumatic system consists of an intake filter that traps dirt before it enters the system, an air compressor that provides a source of compressed air, a dryer that removes the moisture in the air, a pressure tank that is a reservoir of compressed…
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Pressure Regulators: Function & Types
The main function of any gas pressure regulator is to match the flow of gas through the regulator to the demand for gas placed upon the system while maintaining the system pressure within certain acceptable limits. Generally, regulators are simpler devices than control valves. Regulators are self-contained, directed-operated control devices which use energy from the…
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PLC Instruction Set
An Overview of PLC Instructions Types There are various types of instructions that are available in a PLC. The instruction set will vary depending on the brand and type of processor you are working with. For example, the classic Allen-Bradley PLC-5 has 9 types of instructions: Bit Level Instructions This is the most common instructions…
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Demand Mode vs. Continuous Mode Safety Function
Demand Mode Safety Function Demand mode safety function is where a specified action is taken in response to process conditions or other demands. In the event of a dangerous failure of the SIF, a potential hazard only occurs in the event of a failure of the process of BPCS (Basic Process Control System). Demand mode…
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Input & Output Modules of a PLC – Types & Applications
The input/output modules act as the signal interface between the monitoring sensors and actuators, and the controller. Additional they provide electrical isolation, if needed, to convert the input signals into an electronic format appropriate for evaluation by the controller; the I/O modules provide the memory storage and format the output signals for displays and control…
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The IEEE-488 Instrumentation Bus (GPIB)
A bus in computer systems means a collection of unbroken signal lines that interconnect computer modules; these connections are usually made by taps on the lines. Examples of parallel bus architectures and protocols include: IBM PC bus (IBM PC/XT/AT), the Intel iSBX bus, the MicroVAX Q-bus, the Intel Multibus (IEEE-796 bus), the IEEE-488 instrumentation bus…