Motor Controls Level 2: The Search for More Controls
Off-Delay
A solid-state _______ timer requires constant power to operate electronics. When a signal is RECEIVED from the trigger circuit, the "contacts" will INSTANTLY CHANGE state. They will remain in this state the entire time the trigger signal is present. When the trigger signal is removed, the timing period is initiated. When the timing period has elapsed, then the contacts will return to their normal state.
Optocoupler
An _______ is used to provide a signal between two electrically isolated circuits (input and output). Signal flow is unidirectional or bidirectional depending on the type of device selected.
Open-loop
Another name for a Sensorless Vector Drive is the ______ vector drive. This means that the feedback loop comes from within the drive instead of an external encoder.
Open
A PN junction should exhibit a Low resistance when it is forward biased, and a High resistance when it is reverse biased. Given this, if a diode has high resistance at both polarities, it is _____.
High , Low
A diode exhibits a _____ resistance when it is reversed biased and a _____ resistance when it is forward biased
Dual Voltage
A part-winding starter is only used with a _____ ______ motor capable of part-winding starting. This motor has 2 sets of coils in each winding.
Ambient
A photocell is a photoelectric device that only reacts to _____ light.
Negative
Current-sinking outputs use the ______ side of the DC output circuit as the switch leg to the load device.
Positive
Current-sourcing outputs use the _____ side of the DC output circuit as the switch leg to the load device.
Pulsating
Diodes conduct current flow in only one direction and are commonly used to convert an AC voltage to a ____ DC voltage. This process is known as Rectification and is the most common application for silicon power diodes.
Injection
Dynamic, flux, injection, and regenerative are four types of electrical braking techniques. In _______ braking, a DC current is applied to two of the three windings in a three-phase motor.
Energize
Failure to _____ the load is a condition that occurs when the input control device is faulty.
De-ernergize
Failure to _______ the load is a condition that occurs when the load power is not present or too low, and the sensor input voltage never drops below SSR input drop value.
Forward, Reverse
For a BJT (Bi-Polar Junction Transistor) to operate as an amplifier, the base-emitter junction must be ______ biased and the base-collector junction must be ______ biased.
A1 and A2, 1L and 2T
For the IEC style SSR and the IEC style control wiring diagram, the inputs and outputs have standard number with ____ and ____ for inputs and ___ and ___ for the outputs.
Reverse
I put my thing down, flip it, and reverse it. Switching any two leads of a 3 phase will _____ it. Standard swap is L1 (A) with L3(C)
Solid State
In _____ _____ starters, a silicon-controlled rectifier (SCR) controls the voltage and current to the motor during acceleration. This technique provides the smoothest acceleration and greatest control of current and torque.
Converter
In a VFD, the ______ section of the VFD converts the incoming AC voltage into rectified DC voltage
Firing
In a single-phase motor speed control, the thyristor controls power in the circuit by changing the _______ angle of the AC sine wave that drives the motor.
Tin
In corrosive atmospheres, copper buses in MCCs are often coated with ______ to protect the bus from corrosion.
10%
Phase current to a VFD motor load should vary no more than _____ % in each phase.
Copper, Aluminum
Power buses in MCCs are typically ______ or ______.
Time Base
Programmable logic relay timing functions provide an adjustable ______ that allows precise timing with accuracy within a hundredth of a second and typical values are 0.01, 0.1, and 1 second.
Higher, Full
Reduced voltage starters apply a low voltage to a motor at startup and then _____ voltage when the motor is at running speed.
Lowers, Lessens
Reduced voltage starting ______ inrush currents and ______ the impact on the distribution systems
Sourcing
Sensors that use a PNP transistor to switch DC loads are current _____ devices.
Sinking
Sensors that use an NPN transistor to switch DC loads are current _____ devices.
Shorted
Test leads are placed across a diode first in one direction and then reversed. If a diode has low resistance at both polarities, it is _____.
Manufacturer's Manuals
The _____ ______ should be used to install, operate, or maintain an MCC. Use appropriate NEMA/IEC enclosures and maintain level surfaces.
Up
The ______ counter accumulates input pulses and provides an output after the preset count value is reached. These counters have a count input or a count input and a reset input.
Full Wave Bridge Rectifier
The converter section of the VFD with sometimes uses a ____________ to convert the incoming AC voltage to a pulsating DC voltage.
Lowest
The fault current withstand rating of an MCC is determined by the ______ rated device within the MCC
Beta
The ratio of collector current divided by base current is called ______, which is the current gain for the transistor.
Polarized Scan
What is the photoelectric scanning method in which the receiver responds only to the depolarized reflected light from a special reflector or polarized sensitive reflective tape? This scan is not affected by ambient light sources and is useful when detecting reflective materials.
Direct Scan
What is the photoelectric scanning method in which the transmitter and receiver are placed opposite each other? This method is for environments tends to have impurities in the air when monitoring over a large range.
Instant-On
_____ switching is used with reactive loads or combinations of resistive and reactive loads, where the voltage and current are out of phase, and there is no advantage to switching at any particular point in the cycle. This switching method is identical to the operation of an electromechanical relay. This SSR method is used for loads such as contactors, magnetic motor starters, small motors, lighting systems, and magnetic brakes.
Erratic Operation
______ _______ occurs due to loose terminal connections, power source not operating within specifications, or ambient temperatures are out of range.
Up/Down
______ counters accumulate input pulses from TWO inputs and provide an output after the preset count value is reached, one input adds counts and one input subtracts counts from the accumulated total.
Hardware
Intermittent problems or erratic operation with a programmable relay most likely indicates a _____ problem. This is also true if the installation fails after operating correctly for a number of complete cycles.
Shorted
Manual control for a wound rotor motor speed control is accomplished by inserting resistors in series with the 3 separate rotor windings (connected to slip rings). When the resistance is removed, the rotor windings are ______ together, and the motor is able to be operated at full speed.
On-Delay
NOTC and NCTO symbols on a control diagram represent what type of contact function?
Triac
Single-phase motor speed control circuits use SCR or ______ to control power to the motor for speed control
Pulse Width Modulation, Inverter
The VFD's AC output is a _______ waveform. The ______ controls the width (duration) and polarity (direction) of the pulsating DC waveform to produce the effective AC sine wave.
One-shot
The ______ solid-state timer is a timing device in which the "contacts" will instantly change state when the timer is powered on OR AN EXTERNAL trigger is applied. The contacts will remain in the activated state until the timing period has elapsed.
Accumulated
The ______ value is the current number of time units a programmed timer has counted after the timing period has been initiated
Preset
The ______ value is the number of time units a programmed timer is programmed to count before timed contacts change state (complete an operation).
Depletion
The area between the P-type materials and the N-type materials of a single junction PN diode is known as the ____ region. This region is an insulator (no free charge carrier present) with only ions present.
Coil Clearing
The coils of mechanically latching relays are NOT rated for continuous operation. ______ contacts contain contacts that prevent continuous power from being applied to the coil after it has been energized.
On-Delay
The solid-state ______ timer requires constant power to operate the electronics. When a signal is RECEIVED from the trigger circuit, the TIMING period is INITIATED. When the timing period has elapsed, the "contacts" change state. The contacts will remain in the activated state the entire time the trigger signal is present. The contacts will return to their normal state as soon as the trigger signal is removed
Metal-Oxide Varistor
Transient voltage spikes may damage a solid state circuit or cause false triggering of the output devices, for this, a ______ can be used to protect SSRs by adding it across its output terminals.
True
True or False: Braking of motors is used to reduce the time it takes a rotating motor to stop rotating after power is removed from the terminals.
True
True or False: Since solid-state sensors use semiconductor circuits instead of contacts to switch the attached load, the load must match the voltage and current specifications for the sensor.
True
True or False: Transistor circuits are identified by the terminal that is common to the input and the output.
True
True or false: The standard variable frequency drive or scalar drive outputs a PWM pattern that maintains a constant V/HZ pattern to the motor under ideal conditions.
Diffuse Scan
What is the photoelectric scanning method in which the transmitter and receiver are housed in the same enclosure and in which a specialized scanning technique is used not only to determine when an object is moved into position but also to identify the specific location of the object?
Retroreflective Scan
What is the photoelectric scanning method in which the transmitter and receiver are housed in the same enclosure and the transmitted beam is reflected back to the receiver from a reflector? This method is less likely to require recalibration due to excessive machine vibration.
Dynamic and Regenerative
What two types of braking are used with VFDs?
Photoelectric
What type of devices are non-contact solid-state devices that use light to detect the presence of objects?
Cuttoff, Saturation
When a transistor operates as a switch, it is in the _____ region (open switch) or _______ region (closed switch).
Reverse
When small signal and power diodes are in _____ bias, the diode resistance is very high with only leakage current flowing until the breakdown point (770V DC) is reached.
DC Bus
Which section of a VFD conditions the pulsating DC output voltage waveform from, filtering and smoothing the waveform, to produce a pure DC waveform?
Closed-Loop
More precise motor speed control can be accomplished using a vector drive, which uses feedback to modify the PWM output of the VFD. A(n) ______ vector drive uses a shaft encoder on the motor shaft to give shaft rotation data back to the drive.
True
True or False: Feeder power for a Motor Control Center (MCC) enters the unit from overhead or underneath.
Gate
An SCR is composed of a cathode, anode, and a gate. When a signal is applied to the ______, it acts as a "trigger" to turn the SCR on or off.
External
In general, _____ devices attached to the PLR are the cause for improper operation more than a failed PLR.
Part-Winding
_____ starters use a motor starting technique that applies power to part of the motor windings at startup and then connects the remaining coils for normal speed. However, full voltage is applied to the motor at all times through acceleration and up to normal speed with reductions being temporarily modified by the wiring configuration. Series for higher voltage and parallel for lower voltage.
Zero
_____ switching is preferred for resistive loads because voltage and current are in phase in a purely resistive load; this allows the load to be switched on and off when voltage and current are at or near zero. This type of method is used to control loads such as heating elements, soldering irons, and extruders for forming plastic products.
Peak
______ switching is preferred for highly inductive or capacitive loads where voltage and current are nearly 90° out of phase, by switching when load voltage is at peak and load current is near zero. This would be used to control loads such as transformers, larger motors, small DC motors, and heavy inductive devices.
Mechanical
_______ counters use shaft rotations to increment or decrement numerical wheels to display an accumulated count. Due to low cost of electrical timers, these devices have been forced into the legacy category.
Voltage Sensors
________ are electronic devices that monitor an AC or DC voltage and provide an output if that voltage is out of specification. Two commonly used sensors are the over voltage and under voltage relay and voltage band relay (protect equipment by operating within upper/lower voltage limit).
Phase Sequence
________ relays are solid-state devices that simultaneously monitor each phase of a 3-phase circuit for various failures such as out of sequence phases, a lost phase, or a too high or too low voltage level.
Triac
A _____ operates like a pair of SCRs connected in a reverse parallel configuration to control AC current flow to a load for both halves of an AC cycle and has terminal leads noted as the Gate, Main Terminal 1 (MT1), Main Terminal 2 (MT2). Current flows in either direction between MT1 and MT2.
Variable-Frequency Drive VFD
A ______ ______ is an electronic device for controlling the rotational speed of an AC motor by changing the frequency of the electrical power supplied to the motor.
Latching
A _______ relay is a relay that not only maintains its contacts in the last position without a continuously energized coil, but also with a mechanical mechanism or remnant magnetism until it resets electrically.
Frequency
A ________ relay is a solid-state device that monitors a single-phase voltage and will change output contact status when a deviation from nominal frequency is detected.
Solid-state
A starting rheostat or _____ starter provides a safer reduced voltage start.
3 Phase, full voltage
Reduced voltage starting is typically not used for single phase motors because they tend to be less than 5 HP and are started at full line voltage. It is important to note that smaller ______ motors can be controlled using ______ across the line starters as well.
Electronic
______ counters have a numerical readout and are programmed to count up, count down, or count up and down depending on application.
Autotransformer
______ starting is one of the most efficient and effective reduced voltage starting techniques. Its windings are typically tapped at 50%, 65%, and 80% of the line voltage value and are best suited for squirrel-cage motors.