Free USPS 955 Exam Flashcards

Digital logic gate whose output is HIGH (1) only when ALL inputs are HIGH. If any input is LOW (0), the output is LOW.

Digital logic gate whose output is HIGH (1) if AT LEAST ONE input is HIGH. Output is LOW (0) only when every input is LOW.

A single-input logic gate that outputs the opposite of its input: a HIGH input produces a LOW output, and a LOW input produces a HIGH output.

AND gate followed by an inverter. Output is LOW (0) only when ALL inputs are HIGH; for every other input combination the output is HIGH.

OR gate followed by an inverter. Output is HIGH (1) only when ALL inputs are LOW; for every other input combination the output is LOW.

Output is HIGH (1) only when the inputs DIFFER from each other. Output is LOW (0) when the inputs match (both HIGH or both LOW).

A semiconductor device that allows current to flow in only one direction (forward bias) and blocks it in reverse. Used to rectify AC to DC and to protect circuits from reverse current.

A three-terminal semiconductor device (base, emitter, collector on a BJT) used to amplify or switch electronic signals. The basic building block of digital logic and analog amplifier circuits.

A high-gain differential voltage amplifier with two inputs — inverting (−) and non-inverting (+) — and one output. Used for signal amplification, filtering, and comparator circuits.

V = I × R (Voltage = Current × Resistance). Rearranged: I = V ÷ R and R = V ÷ I. The foundation formula behind nearly every multicraft circuit calculation.

P = V × I (Watts = Volts × Amps). Also P = I² × R and P = V² ÷ R. Use whichever form matches the two values you're given.

Components connected along a single path. Current is the SAME through every component, voltage DIVIDES across each load, and total resistance is the SUM of all resistances (R_total = R1 + R2 + ...).

Components connected across multiple branches. Voltage is the SAME across every branch, current DIVIDES among branches, and total resistance is LESS than the smallest individual branch resistance.

Current that periodically reverses direction in a sine-wave pattern. Standard U.S. utility power runs at 60 Hz AC and is easily stepped up or down with transformers for transmission.

Current that flows in one constant direction only, without reversing. Powers batteries, control circuits, and most solid-state electronics; cannot be stepped up or down with a transformer.

Industrial power delivered as three AC waveforms offset 120° from one another. Drives large motors on USPS mail-processing and conveyor equipment with smoother torque and higher power density than single-phase.

Gear Ratio = number of teeth on the DRIVEN gear ÷ number of teeth on the DRIVER gear. A ratio greater than 1 means the driven gear turns slower with more torque; less than 1 means faster with less torque.

Gearing UP increases output speed but reduces output torque. Gearing DOWN decreases output speed but increases output torque. You trade speed for torque, or torque for speed.

A lever multiplies force around a pivot (fulcrum). Mechanical Advantage (MA) = output force ÷ input force = length of the effort arm ÷ length of the resistance arm. A longer effort arm gives more force but must move a greater distance.

A pulley redirects or multiplies force using a wheel and rope/cable; multiple pulleys sharing a load multiply mechanical advantage. A belt drive transfers rotational power between two pulleys, with the speed ratio inverse to the pulley diameter ratio.

Uses pressurized, incompressible LIQUID (typically oil) to transmit force and motion. Produces high force output with smooth, precise control — used in lifts, presses, and heavy actuators.

Uses pressurized, compressible AIR to transmit force and motion. Faster and lighter-duty than hydraulics, but less precise because air compresses under load.

Pressure applied to a confined, incompressible fluid is transmitted equally and undiminished in every direction throughout the fluid. This principle underlies hydraulic force multiplication: small piston force over a small area creates pressure that acts on a large piston area to produce a much larger force.

A closed, four-stage loop: the Compressor raises refrigerant pressure/temperature, the Condenser rejects heat and condenses vapor to liquid, the Expansion Valve drops pressure, and the Evaporator absorbs heat and boils the liquid back to vapor. The cycle then repeats.

Draws in low-pressure refrigerant vapor from the evaporator and compresses it into a high-pressure, high-temperature vapor, driving it toward the condenser. Functions as the 'pump' of the refrigeration cycle.

Rejects heat from the high-pressure refrigerant vapor to outside air or water, condensing it into a high-pressure liquid before it reaches the expansion valve.

Meters refrigerant flow and sharply drops its pressure (and temperature) just before the evaporator, allowing the refrigerant to boil at a low temperature.

Absorbs heat from the space being cooled as the low-pressure liquid refrigerant boils into a vapor, then sends that vapor back to the compressor to repeat the cycle.

Superheat is the temperature of refrigerant VAPOR above its boiling point, measured at the evaporator outlet, and confirms all liquid has vaporized. Subcooling is the temperature of refrigerant LIQUID below its condensing point, measured at the condenser outlet, and confirms all vapor has condensed.

A unique numerical label (e.g., 192.168.1.1) assigned to each device on a network, used to identify the device and route data to and from it.

The standard 8-pin connector used to terminate copper Ethernet (twisted-pair) cable for wired network connections — larger than the RJ11 connector used for telephone lines.

Transmits data as pulses of light through glass or plastic strands instead of electrical signals over copper. Offers higher bandwidth, longer transmission distance, and immunity to electromagnetic interference compared to copper Ethernet.

Temporary, volatile working memory a computer uses to hold actively running programs and data. Contents are lost when power is removed, unlike permanent storage such as an SSD or HDD.

The processor that executes program instructions, performs calculations, and coordinates data flow between a computer's components. Often called the 'brain' of the system.

An industrial computer that monitors inputs (sensors) and controls outputs (motors, valves, actuators) on automated equipment, such as USPS mail-sorting and conveyor systems, by running a stored logic program.

Mentally turning a 2D or 3D object around an axis to determine how it will appear from a different orientation without physically moving it — the object's shape and proportions stay the same, only the viewing angle changes.

A spatial-reasoning item type that asks you to predict where holes will appear when a folded, hole-punched piece of paper is unfolded. Trace each fold and punch in reverse order to find the final hole pattern.

A shape reflected so it is reversed left-to-right (or top-to-bottom) from the original, like a reflection in a mirror. A mirrored shape is NOT the same as a rotated version of that shape.

Mentally combining several separate 2D or 3D pieces to determine which finished shape or object they form when correctly assembled together.

A 3D drawing method that shows an object's three dimensions at equal angles (typically 120° apart) with no perspective distortion, commonly used in mechanical and technical drawings.

Counting the total number of cubes in a 3D stacked arrangement, including cubes hidden from direct view that can only be inferred from the visible structure.

Area of a rectangle = length × width. Used for calculating floor space, panel surface, or material coverage on maintenance job estimates.

Volume of a rectangular solid = length × width × height. Used for tank capacity, duct sizing, and material volume calculations.

°C = (°F − 32) ÷ 1.8. Subtract 32 from the Fahrenheit reading, then divide by 1.8 (equivalent to multiplying by 5/9) to get Celsius.

1 foot = 12 inches. Multiply a measurement in feet by 12 to convert it to inches; divide inches by 12 to convert back to feet.

1 horsepower = 746 watts. Divide a power value in watts by 746 to convert to horsepower; multiply horsepower by 746 to convert to watts.

A six-step energy-control procedure: (1) notify affected employees, (2) shut down equipment, (3) isolate the energy source, (4) apply lock and tag, (5) release stored energy, (6) verify zero energy before servicing. Prevents unexpected equipment startup during maintenance.

A standardized document, organized in 16 sections under OSHA's Hazard Communication Standard, listing a chemical's hazards, first-aid measures, handling/storage requirements, and required PPE. Must be accessible to employees who work with the substance.

An arc flash is an explosive release of energy from an electrical fault. NFPA 70E defines arc-flash boundaries (minimum safe approach distances from energized equipment) and required PPE categories based on incident energy.

Protective gear — safety glasses, gloves, hearing protection, arc-rated clothing, hard hats, and similar items — selected to match the specific hazard identified for the task being performed.