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MAY-JUN 2017

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INTECH MAY/JUNE 2017 41 Certification Review | association news The stator windings are wrapped around an iron core, thereby creating a rotating magnetic flux. The flux generates a magnetic field in the air gap between the stator and the rotor and induces a voltage, which produces current through the rotor bars. This creates a magnetic flux in the rotor, opposite to that of the sta- tor. Because opposite magnetic fields repel one another, the rotor begin to rotate, imparting a force (torque) on the motor shaft. Reference: Trevathan, Vernon L., A Guide to the Automation Body of Knowledge, Second Edition, ISA, 2006. charged from the end of a bubbler purge tube, the air pressure in the tube must be equal to (or higher than) the pressure ex- erted by the liquid head in the tank. As the tank level is decreased, the liquid head pressure at the tip of the purge tube decreases, and more bubbles per unit of time can escape. The corresponding reduction in pressure in the purge tube is proportional to the level in the tank. Therefore, the point at which the liquid head pressure and the purge tube pressure are equal is the highest level (URV = 100%) that the device will measure. Reference: Goettsche, L. D. (Editor), Maintenance of Instruments and Systems, Second Edition , ISA, 2005. CAP question The function of the rotor in an AC induction motor is to: A. reduce speed B. reverse the direction of the motor C. produce torque D. create a magnetic field CAP answer The correct answer is C, "product torque." An alternating current is passed through the stationary windings (stator) of an AC mo tor. CCST question In a bubbler (dip tube) level measuring system, for a bubble to be emitted at the open end of the purge pipe, the air pressure at that point is _______ the pressure exerted by the liquid at that point. A. twice B. equal to C. less than D. three times CCST answer The correct answer is B , "equal to." In order for air to be dis- ISA Certified Automation Professional (CAP) program Certified Automation Professionals (CAPs) are responsible for the direction, design, and deployment of systems and equipment for manufacturing and control systems. ISA Certified Control Systems Technician (CCST) program Certified Control System Technicians (CCSTs) calibrate, document, troubleshoot, and repair/replace instrumenta- tion for systems that measure and control level, temperature, pressure, flow, and other process variables.

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