BLOG Meant for

This blog covers the following areas pertaining to instrumentation and control.

• Pressure

• Flow

• Level

• Temperature

• Neutron Flux

• Control

Pressure

• explain the basic working principle of pressure measuring devices, bourdon tube, bellows, diaphragm,      capsule, strain gauge, capacitance capsule;

• explain the basic operation of a differential pressure transmitter;

• explain the effects of operating environment (pressure, temperature, humidity) on pressure detectors;

• state the effect of the following failures or abnormalities: over-pressuring a differential pressure cell or  bourdon tube; diaphragm failure in a differential pressure cell; blocked or leaking sensing lines; and loss of  loop electrical power.

Flow

• explain how devices generate a differential pressure signal: orifice, venturi, flow nozzle, elbow, pitot tube, annubar;

• explain how each of the following will affect the indicated flow signal from each of the above devices: change in process fluid temperature; change in process fluid pressure; and erosion.

• identify the primary device, three-valve manifold and flow; transmitter in a flow measurement installation;

• state the relationship between fluid flow and output signal in a flow control loop with a square root extractor;

• describe the operation of density compensating flow detectors;

• explain why density compensation is required in some flow measurements;

• state the effect on the flow measurement in process with abnormalities: Vapour formation in the throat, clogging if throat by foreign material, Leaks in HI or LO pressure sensing lines;

Level

• explain how a level signal is derived for: an open vessel, a closed vessel with dry reference leg, a closed vessel with wet reference leg;

• explain how a DP cell can be damaged from over pressure if it is not isolated correctly;

• explain how a bubbler derives level signal for an open and closed tank;

• explain the need for zero suppression and zero elevation in level measurement installations;

• describe the effects of varying liquid temperature or pressure on level indication from a differential pressure transmitter;

• explain how errors are introduced into the DP cell signal by abnormalities: leaking sensing lines, dirt or debris in the sensing lines;

Temperature

• explain the principle of operation of temperature detectors: RTD, thermocouple, bimetallic strip & pressure cylinders;

• state the advantages and disadvantages of RTDs and thermocouples

• state the effect on the indicated temperature for failures, open circuit and short circuit;

Flux

• state the reactor power control range for different neutron sensors and explain why overlap is required: Start-up instrumentation, Ion Chambers, In Core detectors;

• explain how a neutron flux signal is derived in a BF3 proportional counter;

• explain the reasons for start-up instrumentation burn-out;

• explain how a neutron flux signal is derived in an ion chamber;

• state the basic principles of operation of a fission chamber radiation detector;

• state and explain methods of gamma discrimination for neutron ion chambers;

• explain how the external factors affect the accuracy of the ion chamber’s neutron flux measurement: Low moderator level, Loss of high voltage power supply, Shutdown of the reactor;

• describe the construction and explain the basic operating principle of in-core neutron detectors;

• explain reactor conditions factors can affect the accuracy of the incore detector neutron flux measurement: Fuelling or reactivity device movement nearby, Start-up of the reactor, long-term exposure to neutron flux, Moderator poison (shielding);

• explain the reasons for power control using ion chambers at low power and in-core detectors at high power;

Control

• identify the controlled and manipulated variables;

• sketch a simple block diagram and indicate set point, measurement, error, output and disturbances;

• state the difference between open and closed loop control;

• state the basic differences between feedback and feed forward control;

• explain the general on/off control operation;

• explain why a process under on/off control is not controllable at the set point;

• explain why on/off control is suitable for slow responding processes;

• explain the meaning of proportional control in terms of the relationship between the error signal and the control signal;

• explain why offset will occur in a control system, with proportional control only;

• choose the controller action for corrective control;

• convert values of PB in percentage to gain values and vice-versa;

• determine the relative magnitude of offset with respect to the proportional band setting;

• state the accepted system response, i.e., ¼ decay curve, following a disturbance;

• explain the reason for the use of reset (integral) control and its units;

• sketch the open loop response curve for proportional plus reset control in response to a step disturbance;

• state two general disadvantages of reset control with respect to overall loop stability and loop response if the control setting is incorrectly adjusted;

• calculate the reset action in MPR or RPM given a control system’s parameters;

• state, the purpose of rate or derivative control;

• state the units of derivative control;

• justify the use of rate control on slow responding processes such as heat exchangers;

• explain why rate control is not used on fast responding processes.

• sketch the open loop response curve for a control system with proportional plus derivative control modes;

• state which combinations of the contro