New article
Recently updated
Understanding metrological verification for sound level meters
Who is this article for?
Users who need to understand metrological verification.
No special access or permissions are required.
This article explains the metrological verification requirements and procedures for sound level meter measurement chains, including calibration, acoustic checks, and system monitoring in accordance with ISO 20906:2009/Amd.1:2013 and IEC 61672 standards.
Understanding the measurement chain components
The complete sound level meter measurement chain consists of:
- The measurement microphone with its weather protection
- The microphone cable
- The sound level meter unit with its display
The whole set is usually delivered with:
- A Calibration Certificate for the whole set (according to IEC 61672-3)
- A Calibration Certificate for the microphone itself, showing the frequency response and sensitivity (usually in mV/Pa)
In addition, a Type-Approval Certificate from a national accredited laboratory (PTB, METAS, LNE) may be initially requested with specific firmware versions on XL2.
Understanding microphone components and function
The Class 1 microphone set consists of two parts:
- The microphone capsule (or cartridge)
- The preamplifier
The role of the microphone is to transform the acoustic pressure waves into an electrical signal.
The role of the sound level meter is mainly to process the signal supplied by the microphone and to calculate all the required sound levels (LAeq, LAF, LAS, LCpeak), the spectra (1/3 Octave), and to make the audio signal available for possible listening.
Managing microphone sensitivity on NTi XL2-based systems
For NMTs based on NTi XL2, the microphone is factory calibrated and the microphone sensitivity is stored in the embedded electronic datasheet.
The microphone sensitivity is automatically loaded and displayed in the System log at each startup.
Understanding when sensitivity changes occur
The sensitivity of sound level meters is proper to each measurement chain. It is mainly linked to the microphone and will change in the following situations:
- The SLM chain (SLM + microphone) is swapped out with a replacement one (for instance, when the initial SLM chain is sent to the calibration laboratory)
- The microphone is swapped out with a replacement one
- An acoustic check with adjustment is performed
Note: Every time the applied sensitivity is changed, the daily calcheck reference values must be reset to allow proper monitoring of the system's performance.
On modern sound level meters, microphone sensitivity is a stable parameter with limited variations due to environmental conditions (temperature, humidity, atmospheric pressure) in accordance with the requirements of IEC 61672 for Class 1 instruments.
5. Following the metrological verification plan
The proposed metrological verification plan for Ideagen NMTs conforms to the requirements of the ISO 20906:2009/Amd.1:2013 standard.
|
Type of Operation |
Periodicity |
Validity conditions |
Remarks |
|
Factory calibration |
Initial |
Conformance to IEC 61672 Class 1 |
A calibration by an accredited laboratory is possible in addition. |
|
Acoustic check (onsite using a valid sound calibrator)
|
Initially for each deployment of a sound level meter chain Then 12 months or when needed |
Reading is within ±0.5dB around the calibrator's reference level. |
For permanent NMTs, performing a sensitivity adjustment shall only be conducted at reference ambient conditions (typically 22°C ± 4°C) in which the SLM chain must have been placed for at least three hours. The calcheck reference values shall be reset immediately after a sensitivity adjustment. |
|
Automatic system check (Calcheck) |
Daily |
Calcheck's reading is within tolerance around the reference level. |
In some circumstances, the result can be out of tolerance without having the noise levels affected. When the calcheck result is reported out of tolerance, a plausibility analysis must be conducted (comparison of actual noise levels with typical daily patterns, verification of spectral values, verification of the audio playback channel) to characterise a potential issue. If the issue remains for more than two to three days, an onsite inspection (including an acoustic check) must be performed. |
|
Onsite inspection |
When needed |
Acoustic check: reading is within ±0.5dB around the reference level. |
When an onsite inspection is triggered due to daily calcheck results being out of tolerance, a first acoustic check will be carried out, followed by a detailed inspection of the cable, connectors, and microphone membrane. Cleaning or repairing will be carried out when possible, followed by a new acoustic check (under reference ambient conditions if necessary). If at this stage the SLM chain still shows defaults, the faulty parts must be replaced with spare parts (SLM or microphone or cable), and the faulty parts shall be sent to the SLM manufacturer for diagnosis. |
|
Laboratory calibration (sound level meter complete chain) |
24 months or after repair |
Conformance to IEC 61672 Class 1 |
|
|
Laboratory calibration (sound calibrator) |
12 months |
Conformance to IEC 60942 Class 1 |
|
Cet article décrit les composants de la chaîne de mesure, le fonctionnement du microphone, la gestion de la sensibilité et le plan de vérification métrologique pour les systèmes basés sur NTi XL2.
Comprendre les composants de la chaîne de mesure
La chaîne de mesure complète du sonomètre se compose de trois éléments principaux :
- Le microphone de mesure, avec sa protection contre les intempéries
- Le câble du microphone
- L'appareil de mesure du niveau sonore avec son écran
L'ensemble est généralement livré avec deux certificats d'étalonnage :
- Un certificat pour l'ensemble de l'équipement (conformément à la norme IEC 61672-3)
- Un certificat pour le microphone lui-même, indiquant la réponse en fréquence et la sensibilité (généralement en mV/Pa)
Note : Un certificat d'approbation de type d'un laboratoire national accrédité (PTB, METAS, LNE) peut être initialement demandé avec des versions spécifiques du micrologiciel sur XL2.
Comprendre les composants et la fonction du microphone
Le microphone de Classe 1 est constitué de deux parties :
- La capsule microphonique
- Le préamplificateur
Le rôle du microphone est de transformer les ondes de pression acoustique en un signal électrique.
Le rôle du sonomètre est principalement de traiter le signal fourni par le microphone et de calculer tous les niveaux sonores requis (LAeq, LAF, LAS, LCpeak), les spectres (1/3 d'Octave), et de mettre à disposition le signal audio pour d'éventuelles écoutes.
Gérer la sensibilité du microphone sur les systèmes basés sur NTi XL2
Pour les NMTs basées sur le NTi XL2, le microphone est étalonné en usine et sa sensibilité d'origine est enregistrée dans une fiche électronique embarquée.
La sensibilité du microphone est automatiquement chargée et affichée dans le Journal Système à chaque démarrage.
Comprendre quand les changements de sensibilité se produisent
La sensibilité des sonomètres est propre à chaque chaîne de mesure. Elle est principalement liée au microphone et varie dans les situations suivantes :
- La chaîne SLM (SLM + microphone) est remplacée par une chaîne de remplacement, par exemple lorsque la chaîne SLM initiale est envoyée au laboratoire d'étalonnage
- Le microphone est remplacé par un microphone de remplacement
- Un contrôle acoustique avec ajustage est effectué
Important : Chaque fois que la sensibilité appliquée est modifiée, les valeurs de référence du contrôle quotidien doivent être réinitialisées afin de permettre un suivi correct des performances du système.
Sur les sonomètres modernes, la sensibilité du microphone est un paramètre stable, avec des variations limitées dues aux conditions environnementales (température, humidité, pression atmosphérique), conformément aux exigences de la norme CEI 61672 pour les instruments de classe 1.
5. Suivre le plan de vérification métrologique
Le plan de vérification métrologique proposé pour les NMT Ideagen est conforme aux exigences de la norme ISO20906:2009/Amd.1:2013.
|
Type of Operation |
Periodicity |
Validity conditions |
Remarks |
|
Factory calibration |
Initial |
Conformance to IEC61672 Class1 |
A calibration by an accredited laboratory is possible in addition. |
|
Acoustic check (onsite using a valid sound calibrator)
|
Initially for each deployment of a sound level meter chain Then 12 months or when needed |
Reading is within ±0.5dB around the calibrator's reference level. |
For permanent NMTs, performing a sensitivity adjustment shall only be conducted at reference ambient conditions (typically 22°C ± 4°C) in which the SLM chain must have been placed for at least 3h. The calcheck reference values shall be reset immediately after a sensitivity adjustment. |
|
Automatic system check (Calcheck) |
Daily |
Calcheck's reading is within tolerance around the reference level. |
In some circumstances, the result can be out of tolerance without having the noise levels affected. When the calcheck result is reported out of tolerance, a plausibility analysis must be conducted (comparison of actual noise levels with typical daily patterns, verification of spectral values, verification of the audio playback channel) in order to characterize a potential issue. If the issue remains for more than 2-3 days, an onsite inspection (including an acoustic check) must be performed. |
|
Onsite inspection |
When needed |
Acoustic check: reading is within ±0.5dB around the reference level. |
When an on-site inspection is triggered due to daily calcheck results being out of tolerance, a first acoustic check will be carried out, followed by a detailed inspection of the cable, connectors, and microphone membrane. Cleaning and/or repairing will be carried out when possible, followed by a new acoustic check (under reference ambient conditions if necessary). If at this stage the SLM chain still shows defaults, the faulty part(s) must be replaced with spare parts (SLM and/or microphone and/or cable), and the faulty parts shall be sent to the SLM manufacturer for diagnosis. |
|
Laboratory calibration (sound level meter complete chain) |
24 months or after repair |
Conformance to IEC61672 Class1 |
|
|
Laboratory calibration (sound calibrator) |
12 months |
Conformance to IEC60942 Class1 |
|
Dieser Artikel beschreibt die Komponenten der Messkette, die Funktion des Mikrofons, die Verwaltung der Mikrofonempfindlichkeit bei NTi XL2-basierten Systemen und den messtechnischen Verifizierungsplan gemäß ISO 20906:2009/Amd.1:2013.
Verstehen der Komponenten der Messkette
Die komplette Messkette des Schallpegelmessers besteht aus mehreren wesentlichen Komponenten, die zusammenarbeiten, um genaue Schallpegelmessungen zu ermöglichen.
Die Messkette umfasst:
- Das Messmikrofon mit seinem Wetterschutz
- Das Mikrofonkabel
- Dem Schallpegelmessgerät mit Display
Das gesamte Set wird in der Regel mit folgenden Dokumenten geliefert:
- Einem Kalibrierungszertifikat für das gesamte Set (gemäß IEC 61672-3)
- Einem Kalibrierungszertifikat für das Mikrofon selbst, das den Frequenzgang und die Empfindlichkeit angibt (normalerweise in mV/Pa)
Zusätzlich kann ein Bauartzulassungszertifikat von einem national akkreditierten Labor (PTB, METAS, LNE) angefordert werden (bei bestimmten Firmware-Versionen auf XL2).
Verstehen der Mikrofonkomponenten und -funktion
Das Mikrofon der Klasse 1 ist ein präzises Instrument, das aus zwei Hauptteilen besteht und eine spezifische Funktion in der Messkette erfüllt.
Das Mikrofon besteht aus:
- Der Mikrofonkapsel
- Dem Vorverstärker
Die Aufgabe des Mikrofons ist es, die Schalldruckwellen in ein elektrisches Signal umzuwandeln.
Die Aufgabe des Schallpegelmessers besteht hauptsächlich darin, das vom Mikrofon gelieferte Signal zu verarbeiten und alle erforderlichen Schallpegel (LAeq, LAF, LAS, LCpeak) sowie die Spektren (1/3 Octave) zu berechnen und das Audiosignal für eventuelle Abhörungen zur Verfügung zu stellen.
Verwalten der Mikrofonempfindlichkeit bei NTi XL2-basierten Systemen
Bei NMTs auf Basis des NTi XL2 ist das Mikrofon werkseitig kalibriert und die Mikrofonempfindlichkeit ist im integrierten elektronischen Datenblatt gespeichert.
Die Mikrofonempfindlichkeit wird somit automatisch geladen und wird außerdem bei jedem Start im Systemprotokoll angezeigt.
Hinweis: Bei modernen Schallpegelmessern ist die Mikrofonempfindlichkeit ein stabiler Parameter mit begrenzten Schwankungen aufgrund von Umgebungsbedingungen (Temperatur, Luftfeuchtigkeit, Luftdruck) gemäß den Anforderungen der Norm IEC61672 für Geräte der Klasse 1.
Verstehen, wann Empfindlichkeitsänderungen auftreten
Die Empfindlichkeit von Schallpegelmessern ist für jede Messkette spezifisch. Sie hängt hauptsächlich vom Mikrofon ab und ändert sich in bestimmten Situationen.
Die Empfindlichkeit ändert sich in den folgenden Situationen:
- Die SLM-Kette (SLM + Mikrofon) wird durch eine Ersatzkette ausgetauscht. Dies geschieht beispielsweise, wenn die ursprüngliche SLM-Kette zum Kalibrierungslabor geschickt wird
- Das Mikrofon wird durch ein Ersatzmikrofon ausgetauscht
- Es wird eine akustische Überprüfung mit Justierung durchgeführt
Wichtig: Jedes Mal, wenn die angewandte Empfindlichkeit geändert wird, müssen die täglichen Kalibrierungsreferenzwerte zurückgesetzt werden, um eine ordnungsgemäße Überwachung der Systemleistung zu ermöglichen.
5. Befolgen des messtechnischen Verifizierungsplans
Der vorgeschlagene messtechnische Verifizierungsplan für Ideagen-NMTs entspricht den Anforderungen der Norm ISO 20906:2009/Amd.1:2013.
|
Type of Operation |
Periodicity |
Validity conditions |
Remarks |
|
Factory calibration |
Initial |
Conformance to IEC61672 Class1 |
A calibration by an accredited laboratory is possible in addition. |
|
Acoustic check (onsite using a valid sound calibrator)
|
Initially for each deployment of a sound level meter chain Then 12 months or when needed |
Reading is within ±0.5dB around the calibrator's reference level. |
For permanent NMTs, performing a sensitivity adjustment shall only be conducted at reference ambient conditions (typically 22°C ± 4°C) in which the SLM chain must have been placed for at least 3h. The calcheck reference values shall be reset immediately after a sensitivity adjustment. |
|
Automatic system check (Calcheck) |
Daily |
Calcheck's reading is within tolerance around the reference level. |
In some circumstances, the result can be out of tolerance without having the noise levels affected. When the calcheck result is reported out of tolerance, a plausibility analysis must be conducted (comparison of actual noise levels with typical daily patterns, verification of spectral values, verification of the audio playback channel) in order to characterize a potential issue. If the issue remains for more than 2-3 days, an onsite inspection (including an acoustic check) must be performed. |
|
Onsite inspection |
When needed |
Acoustic check: reading is within ±0.5dB around the reference level. |
When an on-site inspection is triggered due to daily calcheck results being out of tolerance, a first acoustic check will be carried out, followed by a detailed inspection of the cable, connectors, and microphone membrane. Cleaning and/or repairing will be carried out when possible, followed by a new acoustic check (under reference ambient conditions if necessary). If at this stage the SLM chain still shows defaults, the faulty part(s) must be replaced with spare parts (SLM and/or microphone and/or cable), and the faulty parts shall be sent to the SLM manufacturer for diagnosis. |
|
Laboratory calibration (sound level meter complete chain) |
24 months or after repair |
Conformance to IEC61672 Class1 |
|
|
Laboratory calibration (sound calibrator) |
12 months |
Conformance to IEC60942 Class1 |
|