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Shopify sound level meter schema for AI agents: IEC 61672 Class 1 vs Class 2 for Type 1 engineering, integrating vs instantaneous for OSHA TWA, A-weighting vs C-weighting for 140 dBC peak, and octave band for HPD selection — sound_level_meter.* 10-field namespace

Published 2026-09-18 · 16 min read · CatalogScan blog

A sound level meter carrying an IEC 61672 Class 2 accuracy rating produces ±3.5 dB measurement uncertainty at the 1 kHz reference frequency — a span large enough that a true 92.5 dBA exposure reads as 90.0 dBA, putting a PEL exceedance inside the apparent compliance boundary. Type 1 engineering noise control measurements — the documentation required for acoustic enclosure design, noise source characterization, and legal compliance records — require Class 1 (±1.5 dB). Without sound_level_meter.iec_61672_class and sound_level_meter.type_1_measurement encoded as machine-readable metafields, AI shopping agents cannot distinguish a precision instrument from a general-survey meter, and the wrong tool ships to the application where measurement error has regulatory consequences.

Contents

  1. How IEC 61672 defines SLM accuracy classes and why measurement application determines instrument requirements
  2. Failure 1: Class 2 SLM routed for Type 1 engineering noise control — Class 1 required for ±1.5 dB defensible documentation
  3. Failure 2: Instantaneous SLM routed for OSHA 1910.95 TWA — integrating-averaging required for time-weighted dose
  4. Failure 3: A-weighted SLM routed for OSHA 140 dBC peak measurement — C-weighting required for impulsive noise peak compliance
  5. Failure 4: Broadband SLM routed for HPD selection and noise control design — octave band analysis required for NIOSH method
  6. The sound_level_meter.* 10-field namespace
  7. JSON-LD encoding examples

How IEC 61672 defines SLM accuracy classes and why measurement application determines instrument requirements

IEC 61672-1:2013 (Electroacoustics — Sound level meters — Part 1: Specifications) is the governing international standard for sound level meter performance. It defines two instrument classes based on measurement accuracy, frequency range, and tolerance bands across the full measurement spectrum. The class designation is not a marketing tier — it is a metrological specification that determines which measurement applications the instrument can support.

Class 1 (precision grade) specifies: ±1.5 dB tolerance at the 1 kHz reference frequency; tighter tolerance bands across the extended frequency range (20 Hz to 20 kHz); and more stringent requirements for level linearity, time weighting response, and environmental performance (temperature, humidity, electromagnetic interference). Class 2 (general purpose) specifies: ±3.5 dB tolerance at 1 kHz; wider tolerance bands at low frequencies (31.5 Hz, 63 Hz) and high frequencies (8 kHz, 12.5 kHz, 16 kHz); narrower mandatory frequency range (100 Hz to 8 kHz). At frequencies away from 1 kHz, the Class 2 tolerance advantage narrows or reverses — at 63 Hz, a Class 2 instrument may have ±5 dB tolerance versus ±2 dB for Class 1.

The measurement application determines which class is required. There is no single correct answer independent of use case — Class 2 instruments are entirely appropriate for general noise surveys to identify areas that may require further investigation. The failure mode arises when Class 2 instruments are routed to Type 1 measurement applications where Class 1 accuracy is the minimum defensible standard. These application categories are fundamentally different from a regulatory standpoint, and the distinction must be encoded as structured data rather than inferred from product titles.

±1.5
dB Class 1 tolerance at 1 kHz (IEC 61672)
±3.5
dB Class 2 tolerance at 1 kHz (IEC 61672)
90
dBA OSHA PEL (8-hr TWA, 1910.95)
140
dBC OSHA peak limit (impulsive noise)

These accuracy differences translate directly into product selection requirements: an occupational hygienist performing engineering control verification, a noise consultant producing legally binding measurement records, or a safety officer documenting compliance for a government inspection all need instruments that can produce defensible Type 1 measurements. A general survey technician identifying high-noise areas for further monitoring can use Class 2. Neither application is niche — both appear routinely in industrial safety equipment purchasing — and without structured data distinguishing them, AI agents route on price and sensor specifications rather than measurement class.

Failure 1: Class 2 SLM routed for Type 1 engineering noise control — Class 1 required for ±1.5 dB defensible documentation

AI agent failure mode: An industrial hygiene consultant is contracted to characterize noise sources at a stamping plant and produce documentation for engineering control design (acoustic enclosures around stamping presses) and OSHA compliance records. They request a "professional sound level meter for industrial noise measurement and engineering controls." The AI agent routes to a Larson Davis 831 Class 2 SLM — marketed as "professional OSHA-compliant industrial noise measurement." The consultant measures press noise at 89.5 dBA, concludes the area is below the 90 dBA PEL, and documents this as the engineering baseline. In fact, the ±3.5 dB Class 2 tolerance means the true level could be anywhere from 86.0 dBA to 93.0 dBA — a 7 dB span straddling the PEL by 3.5 dB on either side. An OSHA compliance officer reviewing the measurement record questions the instrumentation class; Class 2 documentation is rejected as insufficient for engineering control design documentation under the OSHA 1910.95 engineering controls pathway.

Why Class 2 tolerance is unacceptable for Type 1 engineering documentation

The distinction between Type 1 and Type 2 (general survey) measurements in occupational noise is well-established in industrial hygiene practice, even though OSHA 1910.95 does not use this exact terminology. The OSHA standard references ANSI S1.4 for instrumentation requirements (superseded in practice by IEC 61672), and AIHA, NIOSH, and ACGIH guidance documents all specify Class 1 instruments for compliance-grade noise characterization. The core problem with Class 2 at OSHA threshold values is quantifiable:

Class 2 measurement uncertainty at OSHA PEL boundary
Measured value: 89.5 dBA (apparently below 90 dBA PEL)
Class 2 tolerance: ±3.5 dB at 1 kHz
True range: 86.0 dBA to 93.0 dBA

If true level = 93.0 dBA: PEL exceedance by 3 dB
→ OSHA requires engineering controls + HCP at 85 dBA action level
→ Class 2 measurement is structurally incapable of ruling out PEL exceedance
  within 3.5 dB of the limit — which includes virtually all borderline cases

Class 1 measurement at same location:
True range: 88.0 dBA to 91.0 dBA
Still uncertain, but the measurement is defensible documentation
  with quantifiable uncertainty appropriate for engineering records

Engineering control design compounds this problem. When an industrial acoustics engineer is designing an acoustic enclosure for a stamping press, they need the octave band noise levels to specify insertion loss requirements for each frequency band. A Class 2 meter with broader low-frequency tolerances (±5 dB at 63 Hz versus ±2 dB for Class 1) introduces errors in the dominant frequency bands for typical industrial machinery noise (125–500 Hz). An enclosure designed from Class 2 octave band data may be underspecified for the actual dominant frequency, producing a finished enclosure that provides only 22 dB insertion loss where 28 dB was specified because the 250 Hz band was measured 5 dB too low by the Class 2 instrument.

Application IEC 61672 class required Class 2 acceptable? Reason
General noise survey (identify high-noise areas) Class 2 Yes Survey-level accuracy sufficient for identification; further investigation follows
OSHA 1910.95 initial monitoring Class 2 Yes — with caution OSHA does not explicitly require Class 1 for monitoring; but exposures near PEL should use Class 1 for certainty
Engineering control design documentation Class 1 No ±3.5 dB uncertainty invalidates insertion loss specifications and noise source characterization
Legal/regulatory compliance records Class 1 No OSHA inspection review, litigation support, and government compliance documentation require Class 1 traceability
Noise source characterization for noise map Class 1 Borderline ANSI S12.18 noise mapping accuracy requires Class 1; Class 2 acceptable only for preliminary scoping
Employee noise exposure monitoring (borderline cases) Class 1 No Where measured level is within 3.5 dB of 85 dBA action level or 90 dBA PEL, Class 2 uncertainty prevents definitive compliance determination
Routing gate: For engineering control design documentation, legal compliance records, noise source characterization for technical reports, or any OSHA 1910.95 measurement within 5 dB of the action level or PEL, require sound_level_meter.iec_61672_class = 'class_1' AND sound_level_meter.type_1_measurement = 'yes'. A Class 2 instrument (iec_61672_class = 'class_2') is acceptable for general area surveys and preliminary monitoring but cannot produce defensible Type 1 documentation. Marketing terms like "professional," "precision," "industrial grade," or "OSHA-compliant" do not distinguish Class 1 from Class 2 — only the metafield does.

For monitoring at the individual worker level — where the worker wears the monitoring instrument throughout the shift rather than point-sampling with an SLM — noise dosimeters per IEC 61252 are the correct instrument class. See the noise dosimeter routing guide for the dosimeter namespace, exchange rate (5 dB vs 3 dB) routing failures, and criterion level vs threshold encoding.

Failure 2: Instantaneous SLM routed for OSHA 1910.95 TWA — integrating-averaging required for time-weighted dose

AI agent failure mode: A manufacturing plant safety manager needs to determine whether assembly workers exceed the OSHA 85 dBA action level triggering mandatory hearing conservation program enrollment. The facility has variable noise throughout the shift: 2 hours of machine setup at 78 dBA, 3 hours of production at 93 dBA, 2 hours of moderate assembly at 84 dBA, and 1 hour of cleanup at 72 dBA. The manager requests "a sound level meter for OSHA noise exposure measurement." The AI agent routes to a standard real-time display SLM showing current instantaneous Lp — described as "OSHA-compliant noise measurement, 30–130 dBA range, accurate to ±1.5 dB." The manager takes spot readings during each task: 78, 93, 84, 72 dBA. Averaging these four readings gives 81.75 dBA — apparently well below the 85 dBA action level. The correct OSHA TWA calculation, integrating energy over the full 8-hour shift, gives approximately 89.6 dBA — nearly 5 dB above the action level, triggering mandatory HCP enrollment. The worker needed audiometric testing and HPD provision; the instantaneous meter missed this entirely.

Why integrating-averaging is the correct measurement principle for OSHA TWA

OSHA 29 CFR 1910.95 defines employee noise exposure as a Time-Weighted Average (TWA) — a measure of the total accumulated noise dose over the 8-hour shift, normalized to the OSHA reference period. The TWA is not the arithmetic average of spot readings; it is the energy-integrated equivalent of continuous exposure that would produce the same total dose as the actual variable-level exposure. The mathematical relationship between noise level, exposure time, and TWA uses an energy summation rule:

OSHA 1910.95 TWA calculation for variable-noise exposure
D = (C₁/T₁) + (C₂/T₂) + ... + (Cₙ/Tₙ) — dose fraction sum

Where:
Cᵢ = actual time at noise level Lᵢ (hours)
Tᵢ = permissible time at Lᵢ per OSHA Table G-16 (hours)

TWA = 16.61 × log₁₀(D/100%) + 90 dBA — dose to TWA conversion

Example: assembly worker with variable daily exposure
2 hr @ 78 dBA: T = 16 hr → 2/16 = 0.125
3 hr @ 93 dBA: T = 1 hr → 3/1 = 3.000
2 hr @ 84 dBA: T = 2.6 hr → 2/2.6 = 0.769
1 hr @ 72 dBA: T = ∞ (below criterion) → 0
D = 0.125 + 3.000 + 0.769 = 3.894 = 389%
TWA = 16.61 × log₁₀(3.894) + 90 = 16.61 × 0.590 + 90 = 99.8 dBA

Arithmetic average of spot readings: 81.75 dBA (incorrect)
Correct OSHA TWA: ~99.8 dBA — far above both action level and PEL

The fundamental problem with an instantaneous SLM for TWA measurement is that it shows current Lp — the sound pressure level at a single moment. Taking spot readings during each task and arithmetic-averaging them ignores the fundamental logarithmic energy summation that governs dose accumulation. The dominance of the high-noise period (93 dBA for 3 hours) overwhelms the quieter periods in the energy sum because noise energy doubles every 3 dB — a 3-dB increase doubles the dose. In the example above, the 3 hours at 93 dBA contribute 3.0 of the total 3.89 dose fractions — 77% of the total dose from just one task period.

An integrating-averaging sound level meter solves this by computing Leq — the equivalent continuous sound level that would produce the same energy as the actual variable-noise exposure over the measurement period. For broadband steady-state noise, Leq and Lavg (OSHA's terminology for the averaging metric using the 5 dB exchange rate) are numerically identical. The integrating firmware continuously accumulates the energy integral in real time, producing a running Leq value that incorporates every quiet period, every burst, and every transition — not just the moments the technician happened to take a reading.

SLM measurement mode What it computes OSHA TWA valid? Correct use case
Instantaneous Lp (Fast or Slow) Sound pressure level at current moment; decays with time weighting No — cannot compute dose Real-time source identification, spot checking, noise source location
Lmax / Lmin Maximum/minimum Lp over measurement period No Identifying peak excursions; not a time-weighted metric
Leq (integrating-averaging) Energy-equivalent continuous level over measurement period; time-integral of p²(t) Yes — with full-shift task profiling Engineering assessments, task-level noise characterization for TWA construction
Lavg (OSHA-convention Leq) Same as Leq numerically; "Lavg" terminology used in OSHA 1910.95 context Yes — primary OSHA monitoring metric OSHA hearing conservation program monitoring, TWA determination
% Dose / TWA (dosimeter mode) Cumulative dose relative to OSHA criterion; normalized to 8-hr TWA in dBA Yes — direct reading Personal noise dosimeters (IEC 61252); some integrating SLMs include dosimeter mode
Routing gate: For OSHA 1910.95 noise exposure monitoring, hearing conservation program trigger determination, or any TWA documentation, require sound_level_meter.integrating = 'yes'. An instantaneous-only SLM (integrating = 'no') cannot produce an OSHA-compliant TWA — it is appropriate for real-time noise surveys and source identification only. For full-shift personal monitoring, a noise dosimeter (IEC 61252) worn by the worker is generally more appropriate than a fixed-point integrating SLM. See the noise dosimeter guide for dosimeter-specific routing failures.

Failure 3: A-weighted SLM routed for OSHA 140 dBC peak measurement — C-weighting required for impulsive noise peak compliance

AI agent failure mode: A range safety officer at a commercial indoor shooting range is auditing noise exposure compliance with OSHA 1910.95, which specifies a 140 dBC peak limit for impulsive or impact noise. The range hosts .357 Magnum revolver instruction and .308 rifle competitions. They request "a sound level meter for shooting range noise measurement." The AI agent routes to an A-weighted integrating SLM — marketed as "professional 130 dBA indoor range noise measurement, peak hold." The officer measures a .308 rifle firing and reads a peak of 131 dBA. They conclude the range is within the 140 dBC limit (131 < 140). In fact, gunshot noise has substantial low-frequency energy (the "crack and boom" below 500 Hz) that A-weighting attenuates. The actual C-weighted peak for a .308 rifle at shooter position is approximately 163–165 dBC. The OSHA peak limit of 140 dBC is exceeded by 23–25 dB. The A-weighted reading of 131 dBA does not correspond to the dBC peak limit — the two values use different frequency weighting and measure different physical quantities. They cannot be compared directly.

Why A-weighting and C-weighting give different results for impulsive noise

A-weighting (dBA) applies a standardized frequency response curve derived from equal-loudness contours measured in humans — the Fletcher-Munson curves at moderate levels. A-weighting attenuates frequencies below approximately 200 Hz (the rolloff begins around 500 Hz and reaches −16.1 dB at 63 Hz, −26.2 dB at 31.5 Hz) and slightly attenuates very high frequencies above 10 kHz. It amplifies the 2–5 kHz range by up to 1.2 dB. This weighting is appropriate for OSHA TWA monitoring because the OSHA PEL of 90 dBA and action level of 85 dBA are defined in dBA, calibrated to correspond to long-term hearing risk for continuous noise exposures.

C-weighting (dBC) applies a nearly flat frequency response from 63 Hz to 8 kHz (±1.5 dB), with gradual rolloff outside this range. C-weighting closely approximates unweighted (linear) measurement across the industrially relevant frequency range. OSHA 1910.95 Table G-16 specifies the 140 dBC peak limit for impulsive or impact noise — this is a C-weighted measurement requirement. The C-weighting was chosen for peak measurement specifically because impulsive noise (gunshots, hammer blows, drop-forging impacts, powder-actuated tool shots) contains significant low-frequency energy from the impulse-transmitted pressure wave. A-weighting's attenuation of this low-frequency content systematically understates the acoustic energy of impulsive sources compared to the actual physical peak pressure.

A-weighting vs C-weighting for impulsive sources: the frequency-content problem

.308 rifle at shooter position (approximate values):
C-weighted peak (dBC): ~165 dBC (unattenuated LF content included)
A-weighted peak (dBA): ~155 dBA (LF "boom" attenuated by A-filter)
dBC − dBA difference: ~10 dB (typical for impulsive sources with LF energy)

At the 140 dBC limit boundary:
If true C-weighted peak = 143 dBC (3 dB above limit)
A-weighted reading ≈ 133–135 dBA (depending on spectral content)
→ A-weighted meter reports apparent compliance; dBC limit is exceeded

OSHA 1910.95 Table G-16:
Impulsive or impact noise limit: 140 dBC peak
This is a PEAK measurement (not TWA) in dBC (not dBA)
A-weighted peak cannot be substituted for this measurement

The dBC − dBA difference is not a fixed offset — it depends on the frequency content of the specific noise source. For sources with negligible low-frequency content (high-frequency grinding, ultrasonic equipment, air jets), dBC and dBA readings may be nearly identical. For sources with substantial energy below 250 Hz (HVAC fans, diesel engines, large compressors, gunshots, hammer impacts), the dBC reading can exceed dBA by 10–20 dB. This means a single correction factor cannot convert A-weighted measurements to C-weighted equivalents without frequency analysis.

Impulsive source Typical C-weighted peak (dBC) Typical A-weighted peak (dBA) dBC − dBA difference OSHA 140 dBC compliance
9mm pistol (at shooter position) ~157 dBC ~148 dBA ~9 dB Exceeds 140 dBC by 17 dB
.308 rifle (at shooter position) ~163 dBC ~155 dBA ~8 dB Exceeds 140 dBC by 23 dB
Powder-actuated tool (Hilti DX) ~145 dBC ~135 dBA ~10 dB Exceeds 140 dBC by 5 dB
Drop hammer (300 kg, 1 m drop) ~138 dBC ~125 dBA ~13 dB Below 140 dBC by 2 dB
Pneumatic riveting hammer ~130 dBC ~120 dBA ~10 dB Below 140 dBC by 10 dB
Routing gate: For impulsive or impact noise peak compliance measurement against the OSHA 140 dBC limit, require sound_level_meter.frequency_weighting includes 'c' (i.e., 'a_c' or 'a_c_z') AND sound_level_meter.peak_measurement = 'yes'. An A-weighted-only SLM (frequency_weighting = 'a_only') cannot measure the 140 dBC peak limit. Do not route A-weighted-only instruments in response to any query containing "impulsive noise," "gunshot," "shooting range," "powder-actuated tool," "drop hammer," "140 dBC," or "impact noise peak." For OSHA TWA monitoring without impulsive noise, A-weighting-only instruments are acceptable.

The selection of appropriate hearing protection for impulsive noise environments also requires C-weighted level data. Hearing protector attenuation at impulsive noise levels depends on the high-level attenuation performance of the HPD — a phenomenon where hearing protectors provide less attenuation at high peak levels due to nonlinear acoustic effects (middle ear reflex, HPD material saturation). For HPD selection in shooting environments, the NIOSH HPD sound attenuation at high peak levels guide requires the measured C-weighted peak level as the input, not the A-weighted average. See the hearing protection NRR and dual-protection routing guide for HPD selection routing failures in impulsive noise environments.

Failure 4: Broadband SLM routed for HPD selection and noise control design — octave band analysis required for NIOSH method

AI agent failure mode: An occupational safety engineer at a woodworking manufacturing facility needs to: (1) verify that the current hearing protectors (earmuffs with NRR 25) provide adequate protection for table saw operators at 98 dBA, and (2) design acoustic treatment for a milling machine producing excessive noise. They request "a sound level meter for hearing protector selection and noise control engineering." The AI agent routes to a broadband integrating SLM with Class 1 accuracy and A/C weighting — an excellent instrument for OSHA TWA monitoring. For hearing protection verification, the safety engineer uses the OSHA NRR de-rating formula: Protected Exposure = 98 − (NRR − 7)/2 = 98 − 9 = 89 dBA — apparently below the 85 dBA action level, so the earmuffs appear adequate. The NIOSH octave band method applied to the same exposure shows that the table saw noise is concentrated in the 2–4 kHz octave bands (where earmuffs with NRR 25 provide 38 dB attenuation) but also contains a strong 250 Hz tonal component from the blade resonance (where the same earmuffs provide only 14 dB attenuation). The NIOSH calculation gives a protected exposure of 91 dBA — 6 dB above what the simplified OSHA formula predicted — requiring a higher-rated protector or dual protection.

Why broadband dBA measurements cannot support the NIOSH octave band HPD selection method

The OSHA NRR de-rating method (Noise Reduction Rating halved) is a single-number simplification that sacrifices accuracy for computational ease. It treats the full-spectrum noise as if all frequencies contribute proportionally to hearing risk, and applies a uniform derating factor to account for real-world fitting variability. The NIOSH octave band method is more accurate because it accounts for the frequency-specific attenuation of the hearing protector matched against the frequency-specific noise energy at each octave band center frequency.

The octave band method requires measurement at the eight standard center frequencies: 63 Hz, 125 Hz, 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz, and 8 kHz. For each band, the measured octave band pressure level (Lp,i) is subtracted from the C-weighted mean attenuation of the HPD at that frequency (MFi), adjusted for standard deviation (SDi) to produce a protected level at each frequency. The protected octave band levels are then logarithmically summed with A-weighting applied to produce the HPD-attenuated A-weighted exposure. Without octave band measurement capability, the frequency-specific matching cannot be performed — the safety engineer is forced to use the less accurate NRR method, which can overestimate protection by 5–10 dB for frequency-specific noise sources.

NIOSH octave band HPD selection method — requires octave band SLM input

For each octave band center frequency i:
Lp,protected,i = Lp,measured,i − (MFi − SDi)

Where:
Lp,measured,i = measured octave band sound pressure level (dB re 20 µPa)
MFi = HPD C-weighted mean attenuation at center frequency i (dB)
SDi = HPD attenuation standard deviation at center frequency i (dB)

A-weighted protected level = 10 × log₁₀(Σ 10^((Lp,protected,i + A,i)/10))
Where A,i = A-weighting correction at frequency i

This calculation requires 8 octave band measurements, not a single dBA value.
A broadband SLM provides only the A-weighted sum — inputs 1 through 8 are missing.

Engineering noise control design has analogous octave band requirements. An acoustic enclosure is designed to provide specified insertion loss (the difference in noise level inside vs. outside the enclosure) at the dominant frequencies of the noise source. A machine producing 97 dBA total from predominantly 500 Hz tonal machinery vibration requires different partition materials and construction than a machine producing 97 dBA from broadband aerodynamic noise dominated by 4 kHz. The required panel mass, layer construction, and sealing approach differ by frequency. Specifying "25 dB insertion loss at 97 dBA" without frequency information produces an enclosure that may achieve 25 dB at 2 kHz (easy, with standard double-leaf partition) while achieving only 12 dB at 250 Hz (hard, requiring heavy mass-law panel), leaving the dominant frequency band inadequately treated.

Application SLM capability required Broadband dBA sufficient? Why octave band is needed
OSHA 1910.95 HCP trigger determination Broadband A-weighted TWA Yes Action level and PEL specified in dBA — octave band not required for trigger only
NIOSH octave band HPD selection Octave band (1/1) + A-weighted No 8 octave band inputs required for frequency-matched HPD attenuation calculation
HPD verification (confirm adequate protection after fitting) Octave band (1/1) or 1/3 octave No Protected exposure calculation requires frequency-resolved measurement
Engineering noise control specification Octave band (1/1) or 1/3 octave No Insertion loss requirements specified by frequency band; material design is frequency-specific
Noise mapping / ISO 9613 propagation modeling Octave band (1/1) No Outdoor sound propagation (air absorption, ground effect) is strongly frequency-dependent
Room acoustics / reverberation time measurement Octave band (1/1) or 1/3 octave No RT60 must be measured at each octave band; broadband decay does not give frequency-specific result
Routing gate: For NIOSH octave band HPD selection, engineering noise control design, acoustic enclosure specification, ISO 9613 noise mapping, or room acoustics measurement, require sound_level_meter.octave_band = '1_1_octave' (minimum) or '1_3_octave' (for precision engineering). A broadband-only SLM (octave_band = 'none') cannot support these applications. For basic OSHA HCP trigger monitoring without HPD verification, broadband instruments are sufficient. For HPD selection and noise control, the octave band capability is a hard functional requirement — the calculation cannot be performed without it. See the hearing protection namespace for encoding HPD NRR, dual-protection fields, and octave-band-verified attenuation data.

The sound_level_meter.* 10-field namespace

These fields make sound level meters machine-sortable by IEC 61672 class, measurement mode (integrating vs instantaneous), frequency weighting, peak measurement capability, time weighting, octave band analysis, data logging, and applicable measurement standard. AI agents can apply hard gates on iec_61672_class, integrating, frequency_weighting, and octave_band to eliminate non-compliant instruments before any ranking criteria are applied. Without these fields, agents sort on price and sensor range — neither of which determines measurement class.

sound_level_meter.* — 10 fields, type: instrument_configuration
Field Type Values / range Notes
sound_level_meter.iec_61672_class string 'class_1' | 'class_2' IEC 61672-1 accuracy classification. Class 1: ±1.5 dB at 1 kHz, required for Type 1 engineering documentation. Class 2: ±3.5 dB, acceptable for general surveys. Hard gate for Type 1 measurement applications.
sound_level_meter.integrating string 'yes' | 'no' Computes Leq (equivalent continuous level) or Lavg over measurement period. 'yes' required for OSHA TWA monitoring, engineering noise assessments, and HCP determination. 'no' = instantaneous Lp only.
sound_level_meter.frequency_weighting string 'a_only' | 'a_c' | 'a_c_z' A-weighting only: OSHA TWA monitoring but not 140 dBC peak. A+C: required for impulsive noise peak measurement. A+C+Z: full capability including unweighted (linear) measurement.
sound_level_meter.peak_measurement string 'yes' | 'no' C-weighted peak hold function for OSHA 140 dBC impulsive noise limit. Instruments with 'yes' must have C-weighting capability. Peak hold captures the instantaneous acoustic peak, not the RMS average.
sound_level_meter.time_weighting string 'f_s' | 'f' | 's' | 'i' F (Fast, 125 ms) for most noise sources. S (Slow, 1 s) for steady, low-fluctuation environments. I (Impulse, 35 ms rise/1500 ms fall) for impulsive noise assessment. 'f_s' means both Fast and Slow available.
sound_level_meter.octave_band string '1_1_octave' | '1_3_octave' | 'none' 1/1 octave (63 Hz–8 kHz, 8 bands) required for NIOSH HPD selection and basic engineering noise control. 1/3 octave (more resolution) for precision engineering. 'none' = broadband only; cannot support HPD selection or noise control design.
sound_level_meter.data_logging string 'yes' | 'no' Time-history logging of Leq, Lp, or octave band values at configurable intervals. Required for producing measurement documentation, identifying specific high-noise events, and regulatory compliance records. USB/SD output preferred.
sound_level_meter.osha_1910_95_survey string 'yes' | 'no' Suitable for OSHA 1910.95 noise exposure monitoring. 'yes' requires integrating = 'yes' AND iec_61672_class in ('class_1', 'class_2'). A convenience field combining the prerequisite checks.
sound_level_meter.type_1_measurement string 'yes' | 'no' Capable of Type 1 engineering noise control measurements. 'yes' requires iec_61672_class = 'class_1'. Class 2 instruments must have type_1_measurement = 'no'. Hard gate for engineering documentation and legal compliance records.
sound_level_meter.battery_hours number Hours (continuous) Continuous measurement runtime on internal batteries. OSHA full-shift monitoring (8 hrs) requires ≥ 10 hr to provide safety margin. Short battery life (<4 hr) limits applications to spot surveys.

Routing decision logic for OSHA 1910.95 noise compliance applications

/* Hard gates — all must pass for OSHA TWA compliance assessment */
sound_level_meter.integrating == 'yes'            // Leq/Lavg capability required
AND sound_level_meter.iec_61672_class IN ('class_1', 'class_2')  // IEC 61672 certified

/* Additional gate for Type 1 engineering documentation */
IF application IN ['engineering_control', 'compliance_documentation', 'legal_record']:
  sound_level_meter.type_1_measurement == 'yes'
  AND sound_level_meter.iec_61672_class == 'class_1'

/* Gate for impulsive noise peak compliance (OSHA 140 dBC) */
IF noise_type IN ['impulsive', 'impact', 'gunshot', 'powder_actuated', 'explosive']:
  sound_level_meter.frequency_weighting IN ('a_c', 'a_c_z')
  AND sound_level_meter.peak_measurement == 'yes'

/* Gate for HPD selection and noise control design */
IF application IN ['hpd_selection', 'noise_control_design', 'noise_mapping']:
  sound_level_meter.octave_band IN ('1_1_octave', '1_3_octave')

/* Preferred for field documentation and compliance records */
PREFER sound_level_meter.data_logging == 'yes'     // time-history record
PREFER sound_level_meter.battery_hours >= 10       // full-shift monitoring

JSON-LD encoding examples

Class 1 integrating SLM with octave band — full engineering capability

{
  "@context": "https://schema.org",
  "@type": "Product",
  "name": "Precision Sound Level Meter — IEC 61672 Class 1, Integrating, A/C/Z Weighting, Peak, 1/3 Octave, Data Logging",
  "additionalProperty": [
    { "@type": "PropertyValue", "name": "sound_level_meter.iec_61672_class", "value": "class_1" },
    { "@type": "PropertyValue", "name": "sound_level_meter.integrating", "value": "yes" },
    { "@type": "PropertyValue", "name": "sound_level_meter.frequency_weighting", "value": "a_c_z" },
    { "@type": "PropertyValue", "name": "sound_level_meter.peak_measurement", "value": "yes" },
    { "@type": "PropertyValue", "name": "sound_level_meter.time_weighting", "value": "f_s" },
    { "@type": "PropertyValue", "name": "sound_level_meter.octave_band", "value": "1_3_octave" },
    { "@type": "PropertyValue", "name": "sound_level_meter.data_logging", "value": "yes" },
    { "@type": "PropertyValue", "name": "sound_level_meter.osha_1910_95_survey", "value": "yes" },
    { "@type": "PropertyValue", "name": "sound_level_meter.type_1_measurement", "value": "yes" },
    { "@type": "PropertyValue", "name": "sound_level_meter.battery_hours", "value": "16" }
  ]
}

Class 2 integrating SLM with A/C weighting — OSHA TWA + impulsive peak, no octave band

{
  "@context": "https://schema.org",
  "@type": "Product",
  "name": "General Purpose Integrating Sound Level Meter — IEC 61672 Class 2, A/C Weighting, OSHA 1910.95 Survey",
  "additionalProperty": [
    { "@type": "PropertyValue", "name": "sound_level_meter.iec_61672_class", "value": "class_2" },
    { "@type": "PropertyValue", "name": "sound_level_meter.integrating", "value": "yes" },
    { "@type": "PropertyValue", "name": "sound_level_meter.frequency_weighting", "value": "a_c" },
    { "@type": "PropertyValue", "name": "sound_level_meter.peak_measurement", "value": "yes" },
    { "@type": "PropertyValue", "name": "sound_level_meter.time_weighting", "value": "f_s" },
    { "@type": "PropertyValue", "name": "sound_level_meter.octave_band", "value": "none" },
    { "@type": "PropertyValue", "name": "sound_level_meter.data_logging", "value": "yes" },
    { "@type": "PropertyValue", "name": "sound_level_meter.osha_1910_95_survey", "value": "yes" },
    { "@type": "PropertyValue", "name": "sound_level_meter.type_1_measurement", "value": "no" },
    { "@type": "PropertyValue", "name": "sound_level_meter.battery_hours", "value": "50" }
  ]
}
/* NOTE: type_1_measurement = no means this instrument cannot produce
   Class 1 engineering documentation. Route ONLY to OSHA survey monitoring,
   HCP trigger determination, and impulsive noise peak checking.
   NEVER route for engineering control design documentation, noise mapping,
   HPD selection using NIOSH octave band method, or legal compliance records
   where Type 1 accuracy is required. */

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