Reference
Glossary & Acronym Decoder
Aerospace electronics runs on acronyms. Search any term, or filter by category.
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Circuit Card AssemblyCCAAcronym
A populated printed circuit board — the unit a repair technician troubleshoots and repairs. The core deliverable of an aerospace board-repair shop.
Line Replaceable UnitLRUAcronym
A complete box or module that is swapped out at aircraft level, often containing one or more CCAs inside. A clipped lead or screw left inside an LRU becomes a flying short circuit.
Shop Replaceable UnitSRUAcronym
A subassembly or board pulled and repaired at the bench inside the shop, typically a CCA removed from a larger LRU. The repairable item that lands on your bench.
Unit Under TestUUTAcronym
The board being tested or repaired, the term used at the bench and on the test floor. Know its expected current draw from the test spec before powering it.
Device Under TestDUTAcronym
The board or part currently under test — used interchangeably with UUT on the Teradyne and bench. The thing the fixture and test program are measuring.
Automated Test EquipmentATETest & ATE
Computer-controlled test platforms (such as Teradyne testers) that decide what is 'failed' and hand you tickets. ATE includes in-circuit testers, functional testers, and flying-probe machines.
In-Circuit TestICTTest & ATE
A test that measures each component individually on the board using a bed-of-nails fixture — checking shorts, opens, and each R/C/L/diode in place. Great at finding assembly defects (missing, wrong, backwards, shorted, open) but blind to functional and parametric faults.
Bed-of-Nails FixtureTest & ATE
An ICT interface plate carrying hundreds to thousands of spring-loaded probes that press against test pads and vias on the board's underside, pulled down by vacuum or mechanical press. Unique to each board assembly.
Pogo PinTest & ATE
A spring-loaded probe in a bed-of-nails fixture that contacts a test pad or via. Worn, bent, or dirty pogo pins are a leading cause of false ICT failures — suspect the fixture when the same test fails on many boards.
GuardingTest & ATE
The ICT technique of driving the nodes surrounding a component to 0V through extra probes so parallel-path current cannot corrupt the measurement, electronically isolating a part without lifting a leg. It solves with math and extra pins the same problem you solve by hand with a DMM.
Boundary ScanJTAGTest & ATE
A test infrastructure (IEEE 1149.1, accessed via the TCK/TMS/TDI/TDO port) that commands ICs to wiggle and sense their own pins from inside the chip. It verifies BGA solder-ball connections that no probe can reach and no eye can see.
IEEE 1149.1Test & ATE
The standard defining JTAG boundary-scan test access. Lets ATE electrically test connections on dense and BGA packages that have no physical probe access.
Vectorless TestTest & ATE
A capacitive-plate opens test (such as FrameScan-type techniques) that detects whether each IC pin is actually soldered, without powering the part. Catches lifted leads on fine-pitch components that probing and vision miss.
Functional TestFTTest & ATE
A test that powers and exercises the board as it would run in the aircraft, measuring real responses often through the edge connector only. A functional ticket names a failed test step and a measured behavior — localizing it to a component is the technician's job.
Flying Probe TesterTest & ATE
An ICT-style tester with no fixture — a few robotic probes fly point to point across the board. Slower than bed-of-nails but fixture-free, common for low-volume work.
VectorTest & ATE
One step of a digital stimulus/response pattern that ATE drives into ICs to check outputs against truth tables. Vector tests catch dead gates, stuck pins, and missing, wrong, or backwards chips.
Shorts and Opens TestTest & ATE
The first-pass ICT check that verifies every net against every other for unintended connections and confirms expected connections. A shorts failure usually aborts the rest of the program and names two nets to investigate.
DatalogTest & ATE
The recorded measurements of every test, pass or fail, kept by the ATE. Used to review a unit's history and to build a fleet-wide failure Pareto for an assembly.
ParetoTest & ATE
A ranked failure-frequency chart for an assembly. A defect that sits at the top of the Pareto has a known cause and usually a known fix — tribal knowledge worth asking senior techs and test engineers about.
First-Pass YieldTest & ATE
The percentage of boards that pass test with no repair. A key health metric of a production or repair line.
Golden BoardTest & ATE
A known-good unit kept for comparison. Any measurement you cannot interpret on a suspect board, make on the golden board — diode-signature comparison against one localizes digital damage astonishingly fast.
Acceptance Test ProcedureATPTest & ATE
The test specification that defines pass/fail criteria for a board: expected voltages, currents, and waveforms with limits. After any repair you must re-run the full ATP, not just the failed step.
No Trouble FoundNTFTest & ATE
An outcome where a unit passes despite a reported failure — a result to be suspicious of, often an unreproduced intermittent or a fixture issue. Never ship NTF without a serious provocation effort.
Cannot DuplicateCNDTest & ATE
A reported failure that does not reproduce at the bench. Boards that bounce between failing at ICT and passing at the bench usually have an intermittent cracked joint or via — the fixture press flexes the board.
Re-Test OKRTOKTest & ATE
A unit that fails then passes on retest. Re-seat and re-run is legitimate once as a fixture check, never as a repair strategy — a part does not heal itself.
Digital MultimeterDMMMeasurement
The handheld instrument used a hundred times a day for voltage, current, resistance, continuity, diode, and capacitance measurements. Cardinal rule: voltage across, current through, resistance power-off.
OscilloscopeMeasurement
A voltage-versus-time grapher that shows the truth over time where a DMM only shows the average. Anything that moves — clocks, data, ripple, glitches, oscillation — is scope territory.
True-RMSMeasurement
A meter feature that reads the correct RMS value of any waveshape, not just clean sine waves. You want a true-RMS DMM for AC work such as 115VAC/400Hz aircraft power and transformer secondaries.
Root Mean SquareRMSMeasurement
The DC-equivalent heating value of an AC signal; for a sine wave, RMS equals peak divided by the square root of 2 (about 0.707 of peak). A DMM in AC volts mode reads RMS.
Equivalent Series ResistanceESRMeasurement
The internal resistance of a capacitor that rises as electrolytics dry out, causing ripple and instability. High ESR is the number-one switching-supply wear-out and needs an ESR meter or a scope-and-ripple judgment to detect — capacitance mode alone misses it.
Forward VoltageVfMeasurement
The voltage a diode junction drops when forward-biased, displayed by the DMM diode-test mode. Healthy silicon reads 0.5 to 0.7V, Schottky 0.15 to 0.45V, an LED 1.6 to 3.3V; low both ways means shorted, OL both ways means open.
ContinuityMeasurement
A DMM beeper mode that sounds below roughly 30 to 50 ohms, used for fuses, traces, connector pins, and verifying nets against the schematic. Fast but crude — it can beep through a 30-ohm fault, so confirm critical joints with ohms or a millivolt-drop test under load.
Diode TestMeasurement
A DMM mode that sources about 1mA and displays forward voltage — the secret weapon for checking diodes, BJT junctions, MOSFET body diodes, and IC protection diodes. Comparing pin-to-ground diode signatures between a good and bad board finds dead pins fast.
Millivolt-Drop MethodMeasurement
Measuring the few millivolts a current-carrying path develops to judge joint and contact quality, or to follow a gradient downhill toward a rail short. A clean 0-ohm path shows a few mV; a corroded one shows much more.
Volts per DivisionMeasurement
The oscilloscope's vertical scale setting. Set it so the expected signal fills 50 to 80 percent of the screen — for a 3.3V logic signal, 1V/div.
Time per DivisionMeasurement
The oscilloscope's horizontal scale setting, chosen to display a few cycles of the signal. For a 1MHz clock with a 1-microsecond period, use 0.5 to 1 microsecond per division.
TriggerMeasurement
The oscilloscope control that decides when to capture the waveform, producing a stable non-scrolling display. Auto mode always draws something while exploring, Normal shows only real events, and Single captures one-shot events like a glitch or power-up reset.
Probe CompensationMeasurement
The ritual of adjusting a 10:1 passive probe's trimmer on the scope's calibration terminal until the square wave has flat tops — not rounded (under) or spiked (over). A two-second habit to perform on any unfamiliar probe before trusting it.
Differential ProbeMeasurement
A scope probe that measures between two non-grounded points, required on floating or off-line circuits such as the mains side of a power supply. Never float a bench scope by defeating its earth pin — the ground clip is tied to mains earth.
Bandwidth LimitMeasurement
A scope setting (often 20MHz) that rejects ambient high-frequency hash, useful when measuring power-rail ripple. A scope only shows what is within its bandwidth — rule of thumb, bandwidth should be at least 5 times the highest frequency of interest.
Electrostatic DischargeESDDefect
Static you cannot feel (below about 3kV) that destroys or latently wounds modern semiconductors. The wounded part passes test and fails in flight, which is why aerospace ESD rules — wrist strap, dissipative mat, grounded iron, shielded bags — are absolute.
Foreign Object DebrisFODDefect
Any loose item — a clipped lead, solder ball, or screw — that becomes a flying short circuit inside an LRU. Aerospace discipline accounts for every tool and consumable, captures clipped leads, and inspects the work area before closing any assembly.
Moisture Sensitivity LevelMSLProcess & Standards
A rating of how readily a plastic IC package absorbs moisture; soldering a 'wet' part can popcorn it internally. MSL parts live in dry storage or dry packs with floor-life clocks that must be respected.
Conformal CoatingComponent
The clear protective layer (acrylic, urethane, silicone, or parylene) over aerospace boards that guards against humidity, condensation, and contamination at altitude. It hides defects, blocks probes, and must be removed for rework then restored and inspected (often under UV) per IPC-7711/7721.
Ball Grid ArrayBGAComponent
An IC package whose connections are solder balls hidden under the body, invisible to inspection and unreachable by probe. Cracked balls from thermal cycling cause intermittent flex-sensitive faults; verification needs X-ray or boundary scan, and replacement is specialist hot-air or IR rework.
Quad Flat No-leadQFNComponent
A leadless surface-mount IC package with pads under its edges, so joints are partly hidden and cannot be fully cleared by visual inspection — X-ray or boundary scan territory. Pin 1 is marked by a dot or notch.
Quad Flat PackageQFPComponent
A surface-mount IC with gull-wing leads on all four sides. Pin 1 is marked by a dot, notch, or beveled edge, with numbering running counterclockwise viewed from the top.
Small Outline Integrated CircuitSOICComponent
A surface-mount IC package with gull-wing leads on two sides, larger than TSSOP. Pin 1 is marked by a dot or notch, numbered counterclockwise from the top view.
Thin Shrink Small Outline PackageTSSOPComponent
A compact fine-pitch surface-mount IC package with leads on two sides. One of the standard packages a repair tech must identify on sight from the component gallery.
SOT-23Component
A small three-lead (or more) surface-mount package commonly housing transistors and diodes. Diode-test its junctions the same way you would a through-hole BJT.
Dual In-line PackageDIPComponent
A through-hole IC package with two rows of pins. Pin 1 is marked by a dot, notch, or beveled edge, with numbering counterclockwise from the top view.
Surface-Mount DeviceSMDComponent
A component soldered to pads on the board surface rather than through holes, the dominant mounting style on modern CCAs. Tiny 0201/0402 chip parts are often unmarked — rely on the BOM to identify them.
Surface-Mount TechnologySMTProcess & Standards
The assembly approach where components mount directly to the board surface. It enables dense fine-pitch boards whose joints may be hidden under packages like QFN and BGA.
Plated Through-HolePTHComponent
A hole with a plated barrel that both mounts a leaded component and connects board layers. Class 3 aerospace work requires high solder fill — typically 75 percent minimum vertical fill in plated through-holes.
ViaComponent
A plated barrel that connects board layers. Cracked via barrels from thermal cycling are a classic aerospace intermittent — works cold and fails hot (or the reverse) and responds to board flex; the via ranks as a suspect equal to any component.
Multilayer Ceramic CapacitorMLCCComponent
A tiny unmarked ceramic surface-mount capacitor used heavily for decoupling. It cracks from board flex or thermal shock — the crack can be invisible — and a shorted MLCC on a rail is the classic 'rail reads 0.5 ohm to ground' fault.
Tantalum CapacitorComponent
An orange or yellow polarized capacitor common on aerospace boards, with the stripe marking the POSITIVE lead (opposite of an electrolytic). It fails short and sometimes ignites — a burnt crater on a board is often a tantalum.
Aluminum Electrolytic CapacitorComponent
A polarized can capacitor with the stripe marking the NEGATIVE lead, and the number-one failing component class. It dries out with age and heat so capacitance drops and ESR rises; a bulged or vented top means it is dead.
Transient Voltage SuppressorTVSComponent
A protection diode across inputs or rails that clamps voltage transients and fails short once it has absorbed one. A shorted TVS saved the board — replace it and find the transient that hit it.
Metal Oxide VaristorMOVComponent
A voltage-dependent protection part that clamps surges across a line, degrading or failing after absorbing large transients. Like a TVS, a failed MOV is often evidence it did its protective job.
Ferrite BeadFBComponent
A small part that looks like an SMD resistor, rated in ohms at 100MHz, used to choke high-frequency noise on a rail. It is continuity at DC, so an open bead silently kills the rail it feeds — and opening one is a handy half-split point for short-finding.
MOSFETComponent
A voltage-controlled switching transistor dominant in power switching; gate voltage opens the drain-source channel. It typically fails drain-source shorted, and its gate oxide is ESD-fragile — gate-to-anything should read open since the gate is a capacitor.
Bipolar Junction TransistorBJTComponent
A current-controlled switch or amplifier (NPN or PNP) whose small base current controls a large collector current. It behaves as two back-to-back diode junctions, testable with DMM diode mode; a shorted collector-emitter is the common death.
Operational AmplifierComponent
A high-gain differential amplifier that, with negative feedback, amplifies, buffers, filters, or compares. Under feedback its two inputs sit at nearly the same voltage (the virtual short) and the output goes wherever the feedback math puts it — the basis of the three-measurement op-amp check.
ComparatorComponent
A part that looks like an op-amp but runs open-loop, so its inputs are NOT equal — that is normal for it — and it often has an open-drain output needing a pull-up. It outputs a high or low depending on which input is greater.
Low-Dropout RegulatorLDOComponent
A linear voltage regulator needing only about 0.1 to 0.5V of headroom above its output, versus roughly 2V for a classic linear part. Starved of headroom it is not broken — it just cannot regulate; a shorted regulator passes input straight to output, dangerous downstream.
Switching RegulatorSMPSComponent
A switched-mode power supply that chops the input at tens to hundreds of kHz through a MOSFET and inductor for efficiency. Bench checks follow the switch node, controller enable, feedback divider, and output caps; off-line primaries are at lethal, earth-referenced potentials.
CrystalComponent
A mechanically fragile resonator (designator Y or X) that sets an oscillator's frequency. A dropped board with a dead clock makes the crystal the prime suspect; it cannot be fully tested with a DMM, so scope the oscillation.
OscillatorComponent
A circuit or packaged module (often a 4-pin can: power, ground, output, sometimes enable) that produces the board's clock heartbeat. A flatline output means a dead oscillator — check its power and enable, then the crystal.
UARTUARTGeneral
A universal asynchronous serial interface that idles high and sends each byte as a low start bit, 8 data bits, and a high stop bit. Eyeball the bit width to confirm baud — 104 microseconds per bit is 9600.
Serial Peripheral InterfaceSPIGeneral
A fast push-pull serial bus using SCLK, MOSI, MISO, and an active-low chip select. On the scope it appears as bursts of clock with data lines and a chip-select dropping low around each transaction.
Inter-Integrated CircuitI2CGeneral
A two-wire open-drain serial bus (SCL and SDA) that idles high via pull-up resistors. A line stuck low forever means a hung device or a missing pull-up; rising edges are RC-rounded, which is normal.
ARINC 429General
A differential aircraft data bus with a distinctive bipolar waveform, common on civil avionics boxes. You repair around it by recognizing healthy versus dead activity and checking the transceivers, not by mastering the protocol.
MIL-STD-1553General
A transformer-coupled differential data bus used on military platforms. As with other avionics buses, the repair focus is recognizing live versus dead signaling and checking the transceivers and coupling transformers.
RS-422General
A differential serial interface common on aerospace boxes, more robust over distance and noise than single-ended RS-232. Verify healthy differential activity and check the transceivers when an interface fails.
RS-485General
A differential, often multi-drop serial interface related to RS-422 and common on aerospace equipment. Like RS-422, idle-high logic-level signaling that the technician checks for live versus dead activity at the transceiver.
Active-LowGeneral
A signal that does its job when at 0V, marked by a bar over the name or a leading slash, hash, or n (RESET-bar, /CS, WR#). A held-low active-low reset leaves the processor permanently in reset — a classic fault signature.
DecouplingGeneral
Placing a local energy-reservoir capacitor (typically 100nF) next to every IC power pin to supply instantaneous current and shunt high-frequency noise to ground. Lost decoupling can cause oscillation and instability.
RippleMeasurement
The small AC component riding on a DC power rail, measured by AC-coupling the scope at 10 to 50mV/div near the converter's switching period. A healthy switching rail shows low tens of millivolts; growing ripple points to a failing bulk or output capacitor.
DropoutGeneral
The minimum input-to-output voltage headroom a linear regulator needs to regulate — about 2V classic, 0.1 to 0.5V for an LDO. A regulator with insufficient headroom is starved, not broken.
Latch-UpDefect
A condition where a CMOS device enters a low-impedance state and draws excessive current, often heating the chip fast. At power-up, abnormally high supply current can signal latch-up or a short and prunes half the fault tree.
TombstoneDefect
A surface-mount chip part that has stood up on one end during reflow, lifting the other terminal off its pad. A visible-on-inspection assembly defect to hunt for under magnification.
Cold JointDefect
A solder joint that did not properly wet and reflow, showing a gray, lumpy, or dull disturbed texture. One of the most common assembly defect classes and a frequent cause of intermittent or open connections.
Cracked ViaDefect
A fractured plated via barrel, a classic aerospace intermittent that works cold and fails hot or responds to board flex. The fixture press flexing the board can reproduce it — a gift that tells you the fault is mechanical.
DendriteDefect
A conductive metal filament that grows between traces under humidity and contamination (salt, electrolyte, flux residue), bridging them into a short. A reason cleanliness per process matters and a suspect when adjacent nets short.
Tin WhiskerDefect
A conductive metal whisker that pure-tin finishes can grow over years, a known aerospace hazard causing mystery shorts on aged hardware. The reason part finishes are strictly specified — never substitute an unapproved finish.
Solder BridgeDefect
Unwanted solder connecting two adjacent pins or nets, often from rework. The first thing to check when ICT reports a short between adjacent nets — inspect rework areas first.
Bus ContentionDefect
Two outputs driving the same net at once, fighting each other. It shows as a mid-level (about half-rail) voltage, runt pulses, and a warm chip — confirm with a scope, since a DMM averages a toggling line into a similar mid-level reading.
Floating InputDefect
A logic input left undriven by a broken trace, cracked joint, or missing pull resistor, leaving its voltage drifting in the undefined region between thresholds. It picks up noise and is a defect signature in itself.
Runt PulseDefect
A digital pulse that fails to reach full height. Caused by bus contention, a weak driver, or a cracked joint making intermittent contact; persistence display modes help reveal rare runts in an otherwise healthy stream.
Hiccup ModeDefect
A switching supply output that pulses up and collapses repeatedly because it is current-limiting into a downstream short. The supply itself is often fine — go find the short on the output rail.
Material Review BoardMRBProcess & Standards
The formal body that dispositions nonconforming conditions a technician cannot resolve, including damage that exceeds repair limits. Routing a board to MRB is the quality system working, not a failure.
Do Not PopulateDNPProcess & Standards
A part shown on the schematic but intentionally left off the board (also DNI, do not install). Never write up a missing DNP part as a defect — it is supposed to be absent.
Bill of MaterialsBOMProcess & Standards
The authoritative list of every component, value, and part number for a specific board revision. The BOM is the truth when schematic value text lags revisions, and it identifies unmarked tiny SMD parts.
Reference DesignatorGeneral
A component's name on the schematic and silkscreen — a type letter plus a number, such as R47, C12, U3, Q8 (CR for diodes on aerospace drawings). It is how you cross from the schematic to the physical part on the board.
IPCIPCProcess & Standards
The industry association whose standards govern electronics assembly, acceptance, soldering, and rework. Its documents — A-610, J-STD-001, 7711/7721, WHMA-A-620 — define the rules an aerospace repair tech works to.
IPC-A-610Process & Standards
The visual inspection acceptability bible for electronic assemblies — what a good, acceptable, or defective solder joint, placement, and board condition look like. Aerospace work is judged to its strictest Class 3 criteria.
IPC J-STD-001Process & Standards
The standard governing the soldering process itself — materials, methods, and cleanliness — with a Space and Military Applications addendum adding requirements. Where A-610 judges the result, J-STD-001 governs the act, and certification to it is common.
IPC-7711/7721Process & Standards
The numbered procedures for rework (7711) and repair/modification (7721): component removal and replacement, pad and trace repair, laminate repair, and conformal coating removal and restoration. Aerospace shops require following them, not improvising.
IPC/WHMA-A-620Process & Standards
The acceptability standard for cable and wire harness assemblies. Relevant when a shop also builds or repairs harnesses and connectors.
ANSI/ESD S20.20Process & Standards
The standard defining ESD control programs — the framework behind a shop's wrist straps, dissipative mats, smocks, and audits. The reason ESD discipline is enforced and documented, not optional.
AS9100Process & Standards
The aerospace quality management system standard. The reason every repair step is documented, every part traceable, and every nonconformance formally dispositioned.
NASA-STD-8739Process & Standards
A NASA family of workmanship standards for soldering, crimping, and related processes used on space-flight hardware. Comparable in role to the IPC standards for high-reliability assembly acceptance.
Class 3Process & Standards
The high-reliability IPC acceptance category for the harshest environments where failure is not tolerable — the strictest criteria, used for aerospace. Conditions merely acceptable in Class 1 or 2 can be defects in Class 3, such as the higher plated-through-hole solder fill requirement.
Certified IPC TrainerCITProcess & Standards
An instructor certified to teach and certify others to an IPC standard such as A-610 or J-STD-001. CITs train and qualify the technicians (CIS) on the shop floor.
Certified IPC SpecialistCISProcess & Standards
A technician certified to an IPC standard such as A-610 Class 3 or J-STD-001, qualified to apply its acceptance criteria. The certification an aerospace repair tech is typically trained to hold.
VoltageVMeasurement
Electrical pressure between two points, measured in volts with a DMM across the points. Always a difference — saying 'the voltage at TP3' really means the voltage between TP3 and ground.
CurrentIMeasurement
The flow of charge through a path, measured in amperes with a DMM placed in series. Supply current is a diagnosis in itself — a board drawing far more than its spec has a short; far less means something is not starting.
ResistanceRMeasurement
Opposition to current flow, measured in ohms with the power off and capacitors discharged. In-circuit a reading can legitimately read low (parallel paths) but never high — a high reading means the part or its joint is genuinely open.
Zener DiodeComponent
A diode deliberately operated in reverse breakdown at a precise voltage, used as a reference or protection clamp. It tests like a normal diode forward, but verifying its reverse breakdown needs applied voltage above its rating.
Test PointTPGeneral
An exposed pad placed by the designer where someone was expected to need a probe. Test points are a guided tour of a board's important nets and the preferred probing spots on conformal-coated boards.
Half-SplitGeneral
The localization technique of measuring at a signal chain's midpoint — good there means the fault is downstream, bad means upstream — halving the suspect territory with each measurement. A 16-stage chain falls in four measurements.
Signal TracingGeneral
Applying a known stimulus at a chain's input and following it stage by stage with the scope until it disappears or corrupts. The fault lives between the last good node and the first bad one.
Diode-Signature ComparisonGeneral
Diode-testing from ground to every IC or connector pin on a suspect board and a known-good board, then comparing — a mismatch points to the damaged net. One of the fastest ways to localize digital damage, needing no schematic.
Decoupling CapacitorComponent
The local 100nF capacitor at each IC power pin that supplies instantaneous current and shunts high-frequency noise. A shorted one on a rail produces the classic low-ohms-to-ground fault; a lost one can cause oscillation.
TransceiverComponent
An interface driver/receiver chip on a serial bus or connector that is sacrificial by design when ESD or overvoltage enters there. Transceiver replacement is the most routine of digital repairs — check it first when I/O is dead on one connector.
Wrist StrapProcess & Standards
The grounded band worn whenever handling CCAs, carrying a ~1MΩ series resistor for operator safety — never substitute a plain wire. Daily strap testing is standard, and it goes on before the parts tote is even opened.
Peak-to-PeakVppMeasurement
The full vertical swing of an AC waveform from its lowest to highest point, one of the standard scope amplitude measurements alongside Vmax, Vmin, and Vavg. Counted as vertical divisions times volts-per-division or read directly from scope cursors.
AC CouplingMeasurement
A scope input mode that blocks the DC level so a small AC component can be magnified — the way to measure ripple riding on a power rail. DC coupling is the default since it shows the true level including DC.
TraceabilityProcess & Standards
The documented pedigree of every part and action — lot and date codes from controlled stock, recorded measurements, parts, procedures, and the technician's stamp. The defense against counterfeit parts and the reason you never use a personal parts bin on a flight article.