G.R.A.S. 42AG Instruction Manual

Instruction Manual

www.gras.dk

LI0196 – 19 July 2017

G.R.A.S. 42AG Multifunction Sound Calibrator

2

LI0196 – 19 July 2017

Revision History

Any feedback or questions about this document are welcome at [e-mail].

Revision Date Description

1 23 May 2017 First edition
2 19 July 2017 Caution about the speaker diaphragm added

Copyright Notice

© 2017 G.R.A.S. Sound & Vibration A/S

http://www.gras.dk

Any technical documentation that is made available by G.R.A.S. is the copyrighted work of
G.R.A.S. and is owned by G.R.A.S.

The content in this document is subject to change without notice. G.R.A.S. Sound & Vibration A/S
is not liable or responsible for any errors or inaccuracies that may appear in this document.

Trademarks

Any product names mentioned in this document may be trademarks or registered trademarks of
their respective companies and are hereby acknowledged.

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LI0196 – 19 July 2017

Contents

Introduction .................................................................................. 4

Main Features ........................................................................................... 4

About this Manual ...................................................................................... 4

Principles of Operation ................................................................................ 5

Description ................................................................................................ 6

Using the 42AG ............................................................................ 7

Microphone Calibration ............................................................................... 7

Calibration Considerations ............................................................... 9

Accuracy ................................................................................................... 9

Background Noise ...................................................................................... 9

Corrections ................................................................................................ 9

Maintenance and Calibration ......................................................... 11

Replacing Batteries .................................................................................. 11

Calibrating the 42AG Sound Calibrator ....................................................... 11

Adjusting the 42AG's Levels ...................................................................... 11

Delivered Items ........................................................................... 13

Technical Specifications ................................................................ 13

Warranty, Service and Repair ......................................................... 14

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LI0196 – 19 July 2017

Introduction

Main Features

The 42AG Multifunction Calibrator is a portable, battery operated precision instrument for cali­brating microphones and sound level meters. It produces an output level of either 94 dB or 114
dB at 250 Hz or 1 kHz.
It is designed for use in the field and comes with a protective casing. It provides display of
ambient calibration conditions, with pressure, temperature and humidity. It is delivered with an
individual calibration certificate. Its main features are:

• Specifications according to IEC Standard 60942 (2003), Class 1 sound calibrator.

• Calibration at two different frequencies:

•250Hzor1kHz.

• Calibration at two different levels:

•94dBor114dB.

• 1” microphones fit directly in the calibrator coupler. Adapters for ½", ¼" microphones and

⅛” microphones are included in the delivery.

• Green LED lights when calibration level is OK.

• Automatic compensation for ambient air pressure, temperature and humidity.

• Measurement of ambient air pressure, temperature (in ˚C or ˚F) and humidity.

• Automatic power off after 10 to 20 seconds.

• Automatic shut off when batteries are too low.

About this Manual

This manual contains the main sections listed below. When referring to 42AG's buttons, these
symbols are used:

dB Hz

Met

. See "Description" on page 6.

Introduction

This section outlines how the 42AG works. Also, the user interface, the battery compartment and
the location of the calibration button are described.

Using the 42AG

This section describes how 42AG is operated and discusses the factors that must be considered
to achieve a correct calibration result.

Maintenance and Calibration

This section explains how to change batteries and how to calibrate the 42AG.

Delivered Items and Specifications

These two sections list the items delivered with 42AG and its technical specifications.

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LI0196 – 19 July 2017

Principles of Operation

The 42AG consists of a sound source – a small loudspeaker – a reference microphone, and an
electronic control circuit. The special reference microphone is extremely stable and independent of
variations in barometric pressure, temperature, and humidity. Together, the reference microphone
and control circuit maintain a constant sound pressure level inside the calibration coupler, making
it possible to calibrate without separately accounting for the ambient calibration conditions and
changes to the load volume.

42AG can produce a sinusoidal signal of 250 Hz or 1 kHz at 94 dB or 114 dB. The environmen­tal conditions: air pressure, temperature and humidity can be displayed.

The calibrator complies with IEC 60942 (2003), Class 1 and has been designed to serve 1" and
smaller microphones and sound level meters equipped with such microphones.

42AG is designed for use in the field. The accuracy that can be achieved is within ±0.2 dB which
is more than adequate for field checks.

For proper laboratory calibration, we recommend the use of a pistonphone, or sending the micro­phone to a calibration laboratory.

Sinus generatorAmplifier

Feed-back and

Control Circuit

Coupler

Microphone

to be

calibrated

Venting

Sinus GeneratorAmplifier

Feed-back and
Control Circuit

Coupler

Microphone

to be

calibrated

Venting

Fig. 1. Simplified block diagram illustrating 42AG's principles of operation.

Caution. The loudspeaker inside the calibration coupler is not protected. Therefore, do not touch
the diaphragm and also take care to prevent any hard objects from entering the coupler as this
may deform or damage the diaphragm.