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SACA C-202 ELECTRIC MOTOR CONTROL
SYSTEMS ACTUAL EXAM PAPER 2026
โ The operation of a thermistor is based on the _____ - hole theory. Answer: Electron โ _____ heated thermistors are used for precision temperature measurement and temperature compensation. Answer: Indirectly โ With a(n) _____ thermistor, an increase in temperature causes the resistance of the thermistor to decrease. Answer: NTC โ Cold resistance is measured at _____ ยฐC Answer: 25 โ A photoconductive cell (photocell) is a device that conducts current when energized by _____ Answer: Light โ A photocell is, in effect, a variable _____ Answer: Resistor โ _____ and contamination are the primary causes of photocell failure. Answer: Humidity
โ The primary difference between a photodiode and a regular diode is that a photodiode has an addition of a _____ in it's housing for focusing light on the PN junction. Answer: Lens โ Without light, the _____ of the photodiode is high. Answer: Resistance โ The _____ flowing through a photodiode increases as the resistance decreases. Answer: Current โ A voltage-output pressure sensor typically outputs 0 VDC to _____ VDC proportional to the rating of the pressure sensor. Answer: 10 โ A current-output pressure sensor typically outputs 4 mA to _____ mA proportional to the rating of the pressure sensor. Answer: 20 โ Pressure sensors are suited for a wide variety of pressure measurements on _____, pumps, and other similar equipment. Answer: Compressors โ A flow detection sensor is a sensor that detects the movement (flow) of liquid or gas using a(n) _____. Answer: solid-state device
โ A proximity sensor (proximity switch) is a solid-state sensor that detects the presence of an object by means of a(n) _____ sensing field. Answer: electronic โ A(n) _____ proximity sensor is a sensor that detects only conductive substances. Answer: inductive โ Inductive proximity sensors operate on the _____ principle. Answer: eddy current killed oscillator โ _____ sensors can detect materials such as plastic, glass, water, moist wood, etc. Answer: Capacitive โ Generally, any material with a _____ constant greater than 1.2 may be detected. Answer: dialectric โ The high-frequency sound waves of an ultrasonic sensor are typically in the _____ kHz range. Answer: 200 โ Materials such as foam, fabric, and _____ are difficult for ultrasonic sensors to detect and are better detected by photoelectric or proximity sensors. Answer: rubber
โ _____ mode is a method of ultrasonic sensor operation in which the emitter and receiver are placed opposite each other so that the sound waves from the emitter are received by the receiver. Answer: Direct โ _____ is a ratio of the amplitude of an output signal to the amplitude of an input signal. Answer: Gain โ Amplifiers connected together are called _____ amplifiers. Answer: cascaded โ A _____ device is a device in which both holes and electrons are used as internal carriers for maintaining current flow. Answer: bipolar โ The input of a common-_____ circuit is across the base and emitter, while the load is across the collector and emitter. Answer: emitter โ In any transistor circuit, the _____ junction must always be forward biased. Answer: base/emitter โ An op amp is often used in digital circuits that require the _____ amplification of a weak signal. Answer: analog
โ The main body of a(n) _____ MOSFET is composed of a highly resistive P-type material. Answer: enhancement โ Since a(n) _____ MOSFET does not conduct at zero gate voltage, it is often called a normally off MOSFET. Answer: enhancement โ The _____ resistance measurments taken when troubleshooting IGBT's are used to determine whether the resistance is too low and the device is defective. Answer: leakage โ One disadvantage of an IGBT is that the switching speed is inferior to that of a(n) _____ MOSFET. Answer: power โ Problems with IGBTs and other solid-state switches can be reduced by keeping their _____ clean for proper airflow movement. Answer: heat sinks โ Triacs, diacs, UJTs, and SCRs operate only as _____. Answer: switches โ When transistors are used as switches, a _____ can be mounted across the transistor to prevent damage from high-voltage spikes (transients). Answer: diode
โ The _____ region is the point at which the transistor is turned off and no current flows. Answer: cutoff โ A(n) _____ serves as the control point for an SCR. Answer: gate โ A gate current is used to reduce the level of _____ voltage necessary for an SCR to conduct or fire. Answer: breakover โ _____ control is the control of the time relationship between two events when dealing with voltage and current. Answer: Phase โ _____ is one of the most suitable industrial applications of SCRs. Answer: DC motor control โ A(n) _____ is needed to properly test an SCR under operating conditions. Answer: oscilloscope โ Triacs are the equivalent of two SCRs connected in a _____ arrangement with gates also connected to each other. Answer: reverse-parallel โ Triacs cannot replace SCRs in _____ applications. Answer: high- current
โ The "PIN" in PIN photodiode stands for P-type material, _____, and N-type material. Answer: insulator โ In a two-lead phototransistor, the _____ is replaced by a clear covering that allows light to fall on the base region. Answer: base lead โ In darkness, a phototriac is not triggered. The remaining leakage current is referred to as _____ current. Answer: peak blocking โ As electrons move across the _____ of a light-emitting diode (LED), they give up extra kinetic energy, which is converted to light. Answer: depletion region โ An optocoupler uses a glass _____ sandwich to separate input from output. Answer: dielectric โ _____ current is the amount of current drawn by a load when energized. Answer: Load โ Photoelectric sensors that switch DC circuits normally use _____ as the switching element. Answer: transistors
โ _____ current glow is the movement of electrons from positive to negative. Answer: Conventional โ Communication is the transmission of information from one point to another by means of _____ waves. Answer: electromagnetic โ A fiber optic receiver normally contains a(n) _____ that converts light back into electrical signals. Answer: photodiode โ The _____ is the first layer of protection for the glass or plastic core of an optical fiber cable. Answer: cladding โ _____ scan is a method of scanning in which the transmitter and receiver are housed in the same enclosure and the transmitted light beam is reflected back to the receiver from the reflector. Answer: Retroflective โ _____ scan distinguishes between shiny and nonshiny (matte) surfaces. Answer: Specular โ In a(n) _____ light source, the light source is turned on and off at a very high frequency, normally several kilohertz (kHz). Answer: modulated
โ One of the significant advantages of an SSR over an EMR is its _____. Answer: response time โ Even at full conduction, an SSR presents some residual resistance, which can create a voltage drop of up to approximately _____ V in the load circuit. Answer: 1. โ It is possible for small amounts of _____ (OFF-state leakage) to pass through an SSR because some conductance is still possible even though the SSR is turned off. Answer: current โ The _____ method is a method of SSR replacement in which a logical sequence is used to determine the reason for a failure. Answer: circuit analysis โ _____ is a phenomenon that occurs when a relay fails to turn off because the current and voltage in the circuit reach zero at different times. Answer: Half-waving โ An RC circuit is a circuit in which resistance (R) and capacitance (C) are used to help _____ the power in a circuit. Answer: filter โ A solid-state motor starter is an electronically operated switch (contactor) that uses solid-state components to eliminate
mechanical contacts and includes _____. Answer: motor overload protection โ _____ trip is the trio point after the overloads have tripped and have been reset (motor operating near or over nameplate rated current). Answer: Hot โ A typical solid-state _____ circuit consists of both start and run contractors connected in the circuit. Answer: starting โ _____ start is the most common solid-state starting method. Answer: Soft โ _____ stop is the most common solid-state motor starter stopping method. Answer: Soft โ The _____ starting method provides the highest possible starting torque per ampere of line current and is the most effective means of motor starting for applications where the inrush current must be reduced with a minimum sacrifice or starting torque. Answer: autotransformer โ _____ drives are the most common drives because they can easily vary the speed of a 3 phase motor. Answer: AC
โ Motor speed is controlled by controlling the _____ to a DC motor. Answer: voltage โ Motor torque is controlled by controlling the amount of _____ in the armature of a DC motor. Answer: current โ When AC power is from a 1 phase source (115/230 VAC), a _____ circuit should be used to smooth the DC waveform. Answer: filter โ A DC motor drive can provide _____ braking by connecting a resistor across the motor armature after the motor input power is removed. Answer: dynamic โ _____ braking requires a method to transfer the energy produced by a rotating motor shaft back to the main power supply. Answer: Regenerative โ The speed of an AC motor is determined by the number of stator poles and the _____ of the AC power supply. Answer: frequency โ A(n) _____ filters the voltage and maintains the proper DC voltage level in a motor drive. Answer: DC bus
โ _____ in electric motor drives are 1 phase full-wave rectifiers, 1 phase bridge rectifiers, or 3 phase full-wave rectifiers. Answer: Converters โ _____ to an AC motor drive is limited by the size of the conductors to the drive, fuse and circuit breaker sizes, and the transformer(s) delivering power to the system. Answer: Current โ Normally, a surge suppressor consists of _____ varistors, connected to the converter of a motor drive. Answer: metal-oxide โ _____ in a DC bud are changed from rectified DC voltage produced by the converter. Answer: Capacitors โ _____ in an AC motor drive are the most important part of the drive because they determine the voltage level, voltage frequency, and amount of current that a motor receives. Answer: Inverters โ A motor heats excessively and damage occurs to the windings if the voltage is not reduced when _____ is reduced. Answer: frequency โ _____ frequency is the frequency that controls the number of times solid-state switches in the inverted of a motor drive with pulse width modulation turn on and off. Answer: Carrier
โ Like PLCs, PLRs are designed to be programmed using _____ programming or function blocks. Answer: line โ In general, a _____ is considered the first choice for controlling industrial electrical circuits and systems. Answer: PLC โ A _____ can be used if a control system requires remote monitoring, HMIs, data acquisition of process conditions, motion control l, servo/stepped motor control, and/or vision control. Answer: PAC โ A programmable controller's power supply may provide power for the _____ modules. Answer: I/O โ _____ I/Os are the most common inputs and outputs. Answer: Discrete โ Examples of _____ inputs are potentiometers, rheostats, encoders, bar code readers, and temperature, level, pressure, humidity, and wind speed transducers. Answer: data โ The leakage current problem caused by using a two-wire thyristor output can be corrected by placing a load _____ across the input device. Answer: resistor
โ Electrical _____ is unwanted signals that are present on a power line. Answer: noise โ A(n) _____ circuit is used to suppress a voltage spike. Answer: snubber โ The _____ section is the brain of a programmable controller and can be referred to as the central processing unit (CPU). Answer: processor โ _____ time is the time it takes a programmable controller to make a sweep of the program. Answer: Scan โ In the _____ mode of a programmable controller, a circuit is monitored and the program is edited, changed, saved, and transferred. Answer: program โ _____ programming is the use of a PC to program a programmable controller that is not in the run mode. Answer: Off-line โ The first programmable controllers used _____ diagrams as a language to input information. Answer: line
