Railways NTPC (Technical Ability) Instrument Mechanical

Instrument Mechanical

Category : Railways

Instrument Mechanical


  • Instrumentation engineering is the engineering specialization focused on the principle and operation of measuring instruments that are used in design and configuration of automated systems in electrical, pneumatic domains etc.
  • They typically work for industries with automated

Processes, such as chemical or manufacturing plants, with the goal of improving system productivity, reliability, safety, optimization, and stability.

  • To control the parameters in a process or in a particular system, devices such as microprocessors, microcontrollers or PLCs are used, but their ultimate aim is to control the parameters of a system.
  • Instrumentation engineering is loosely defined because the required tasks are very domain dependent. An expert the biomedical instrumentation of laboratory rats has very different concerns than the expert in rocket instrumentation. Common concerns of both are the selection of appropriate sensors based on size, weight, cost, reliability, accuracy, longevity, environmental robustness and frequency response. Some sensors are literally fired in artillery shells. Others sense thermonuclear explosions until destroyed. Invariably sensor data must be recorded, transmitted or displayed. Recording rates and capacities vary enormously.

Transmission can be trivial or can be clandestine, encrypted and low-power in the presence of jamming. Displays can be trivially simple or can require consultation with human factors experts. Control system design varies from trivial to a separate specialty.

  • Instrumentation engineers are commonly responsible for integrating the sensors with the recorders, transmitters, displays or control systems. They may design or specify installation, wiring and signal conditioning. They may be responsible for calibration, testing and maintenance of the system.
  • In a research environment it is common for subject matter experts to have substantial instrumentation system expertise. An astronomer knows the structure of the universe and a great deal about telescopes - optics, pointing and cameras (or other sensing elements). That often includes the hard-won knowledge of the operational procedures that provide the best results. For example, an astronomer is often knowledgeable of techniques to minimize temperature gradients that cause air Turbulence within the telescope.
  • Instrumentation is the use of measuring instruments to monitor and control a process.
  • It is the art and science of measurement and control of process variables within a production, laboratory, or manufacturing area.
  • An instrument is a device that measures a physical quantity such as flow, temperature, level, distance, angle, or pressure. Instruments may be as simple as direct reading thermometers or may be complex multi variable process analyzers.
  • Instruments are often part of a control system in refineries, factories, and vehicles. The control of processes is one of the main branches of applied instrumentation. Instrumentation can also refer to handheld devices that measure some desired variable.
  • Diverse handheld instrumentation is common in laboratories, but can be found in the household as well. For example, a smoke detector is a common instrument found in most western homes.
  • Instruments attached to a control system may provide signals used to operate solenoids, valves regulators, circuit breakers, or relays. These devices control a desired output variable, and provide either remote or automated control capabilities.
  • A Transmitter is a device that produces an output signal, often in the form of a 4 - 20 mA electrical current signal, although many other options using voltage, frequency, pressure, or Ethernet are possible. .
  • Control instrumentation plays a significant role in both gathering information from the field and changing the field parameters, and as such are a key part of control loops.
  • Elements of industrial instrumentation have long histories. Scales for comparing weights and simple pointers to indicate position are ancient technologies. Some of the earliest measurements were of time.
  • In the early years of process control, process indicators and control elements such as valves were monitored by an operator that walked around the unit adjusting the valves to obtain the desired temperatures, pressures, and flows.
  • As technology evolved pneumatic controllers were invented and mounted in the field that monitored the process and controlled the valves. This reduced the amount of time process operators were needed to monitor the process.
  • The pneumatic and electronic signaling standards allowed centralized monitoring and control of a distributed process. The concept was limited by communication line lengths (perhaps 100 meters for pneumatics). Each pipe or wire pair carried one signal
  • The next evolution of instrumentation came with the production of Distributed Control Systems (DCS) which allowed monitoring and control from multiple locations which could be widely separated.
  • A process operator could sit in front of a scree (no longer a control board) and monitor thousands of points throughout a large complex. A closely related development was termed 'Supervisory Control and Data Acquisition' (SCADA).
  • These technologies were supported by personal computers, networks and graphical user interfaces.
  • A very simple example of an instrumentation system is a mechanical thermostat, used to control a household furnace and thus to control room temperature.
  • A typical unit senses temperature with a bi-metallic strip. It displays temperature by a needle on the free end of the strip. It activates the furnace by a mercury switch.
  • Any three phase load will be balanced when the loads (impedances) connected in three phases are same in magnitude as well as in phase.
  • Any three phase load will be unbalanced if impedances in one or more phases differ from the impedance (s) of the remaining phase (s).
  • Normally, unbalanced load is not employed on 3-phase, 3-wire ungrounded star-connected system because unbalanced loading may cause different voltage drops in lines. Consequently the three phase voltages are different (or unbalanced) in magnitude as well as in phase and it is quite possible that one phase voltage may exceed the line voltage. Such a condition is undesirable, since some loads may operate inefficiently due to lowering of the voltage and the other equipment may get damaged due to overvoltage.
  • Phase sequence is the order or sequence in which the currents or voltages in different phases attain their maximum values one after the other.

The given phase sequence can be reversed by interchanging any two terminals of the supply.

  • Non-interlinked three phase system will require 6 wires while interconnected 3-phase system will require 3 or 4 wires. So non-interlinked system will be very complicated and expensive.
  • In star-connected system similar (either start or finish) terminals of the three phases are connected together, to provide star or neutral point while in delta-connected system start terminal of one phase is connected to the finish terminal of the second phase and start terminal of second phase is connected to finish terminal of third phase and so on to provide a closed circuit 3-phase system.
  • Neutral point of a star-connected system can be connected to earth, so relays and protective devices can be provided in star-connected system for protection of the system against ground faults and it is usually done in practice. These are the reasons that 3-phase alternators are usually star-connected.
  • Delta-connected stem cannot provide 3-phase 4-wire system (i.e., neutral wire cannot be carried) which is essential for supplying lighting as well as power loads.
  • The most common motor control is the motor starter.
  • The low voltage release tripped the motor. The motor can be restarted by pusing the 'ON' button when the potential difference returns to normal.
  • Shading coil reduces vibration, chattering, noise wear and heat in the armature of a starter magnetic core.
  • When a contactor is in the open position, open positions the armature is at its greatest distance from the core and the impedance of the coil is low.
  • The 'ON' button of a starter should have at least on NO/ contact. (Normally open contact)
  • The 'OFF' button of a starter should have at least one N/C contact. (Normally Closed contact)
  • Thermal overload relay is provided in a starter to protet the motor against excess current.
  • Continuous chattering sound from the armature of an AC no-volt coil indicates open circuit in the shaded ring.
  • In a 3-phase induction motor started by a D.O.L. starter protection against the short circuit is given by the backup fuses.
  • Full load line current of a 3 HP, 3-phase, 415 volts. 50 Hz squirrel cage induction motor will be approximately 4.5 amps (\[1{\scriptstyle{}^{1}/{}_{2}}\] times the H.p.)
  • Kitchen appliances use sensors for control.
  • A refrigerator maintains a constant temperature by measuring the internal temperature.
  • A microwave oven sometimes cooks via a heat sense heat-sense cycle until sensing done.
  • An automatic ice machine makes ice until a limit switch is thrown.
  • Pop-up bread toasters can operate by time or by heat measurements.
  • Some ovens use a temperature probe to cook until a target internal food temperature is reached.
  • A common toilet refills the water tank until a float closes the valve. The float is acting as a water level sensor.

Other Topics

Notes - Instrument Mechanical

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