CASTLE GA112 User Manual

Thank you for buying a Castle product, I am sure you will find both
the goods and the service to be of the highest quality but if not, then
please feel free to write to me personally and I will ensure that your
needs are dealt with immediately.

This manual is designed to show you the operation of the goods you
have purchased and a very brief insight into acoustics itself. If you
would like to become a competent person in the eyes of the law, then
you may like to know more about our Competent persons training
course for the Noise at Work Regulations.

It is my intention for Castle Group Ltd to provide a complete range of
Noise and Vibration products and Services of the highest standard. If
you would like to know more about any of our other products and
services then please complete the reply paid card in this manual and
return it to us for prompt action or telephone on [phone].

Simon Bull

Sales and Marketing Director

Precautions

Operate the unit only as described in this manual.

• The GA112 is a precision instrument. Protect the instrument from shocks and
vibrations.

• Use only the microphone/preamplifier as supplied with the unit. Take special
care not to touch the microphone top as it can easily be damaged.

• Ambient conditions for operation of the unit are as follows : temperature
range - 10°C to +50 °C, relative humidity 30 to 90%.

• Protect the unit from water, dust, extreme temperatures, humidity, and direct
sunlight during storage and use. Also keep the unit away from air with high
salt or sulphur content, gases, and stored chemicals.

• Always turn the unit off after use. Remove the batteries from the unit if it is
not to be used for a long time (a week or more) . When disconnecting the ca­ble, always unscrew the plug and do not pull the cable.

• Clean the unit only by wiping it with a soft, dry cloth or, when necessary,
with a cloth lightly moistened with water. Do not use any solvents, cleaning
alcohol or chemical cleaning agents.

• Take care that no conductive objects such as wire, metal scraps, conductive
plastics etc. can get into the unit.

• Do not try to disassemble or alter the unit. Otherwise type certification will
become invalid. In case of an apparent malfunction, do not attempt any re­pairs. Note the condition of the unit clearl y and contact the supplier or Castle
Group direct.

NOTE
Castle Group sound level meters are electronic instruments and should be handled
accordingly. Damage caused by misuse, abuse and leaking batteries is not cov­ered by the warranty. If the instrument fails to function correctly, firstly check the
condition of the batteries. When changing the batteries, replace all three at any
one time. In order to conserve battery life do not leave the instrument turned on
when not in use.

CONTENTS

TITLE PAGE NO

Instrument Introduction 5

Battery Installation 6

Preparation of Equipment and Controls 7

Calibration 12

Measuring Sound Levels 13

Measuring Maximum Sound Levels 14

Use of Filters for Octave Band Analysis 15

Use of the Output Socket 16

Instrument Description 18

Circuit Description 19

Environmental Effects 19

Technical Specification 20

Warranty and After Sales Service 24

Instrument Introduction

The instrument covered by this handbook is an analogue sound level
meter built into our award winning, tough die-cast body, which is
both stylish and ergonomically designed. The instrument has ‘A’
weighting and ‘LIN’ (linear) frequency responses as well as a set of
ten octave band filters. The filter’s ‘AUTO’ facility allows a chart
recorder to display the results of a noise spectrum analysis. ‘SLOW’,
‘FAST’ and ‘PEAK’ responses are available. A maximum hold but­ton, ‘MAX’, allows the accurate recording of the ‘maximum rms’ of
a transient noise event. The instrument conforms to the relevant sec­tions of BS5969, IEC651, ANSIS1.4, BS2475 and BS EN60651
standards.

5

Battery Installation

To prepare the equipment for service batteries must first be fitted. Re­move the lower rear black plastic ‘clip in’ cover by pushing the locking
clip at the foot of the instrument upwards and push the cover out; this will
expose the battery compartment. Connect three new 6D22 type batteries,
preferably heavy-duty types which give greater economy and are less
prone to leakage, to the snap conductors ensuring correct polarity and
making sure that each stud is a firm fit. Replace the battery cover and
push the retaining clip firmly home. The instrument is now ready for cali­bration and use.

Re m o v e C o v er

to change B atter ies

Serial No. 012345

Release the spring catch
and remove the battery
compartment cove

r

Tel: [phone] Fax: [phone]

Castle Associates

Lim ite d

Salter Roa d, Scarborou gh,

England.

Serial No. 012345

6

Preparation of Equipment and Controls

Power/Weighting Switch

This is a three-position switch labelled OFF-A-LIN. In the OFF po­sition all power is removed from the instrument. The ‘A’ position
allows sound levels to be measured with ‘A’ weighting, (see figure

1). For a linear or ‘flat’ frequency response the LIN is used.

Figure 1 – ‘A’ weighting curve

Battery Check Button

A push button labelled BATT is provided to allow periodic check­ing of the battery condition. A meter deflection in the area marked
‘BATT’ shows the batteries are in good condition.

'A' AND LINEAR FREQUENCY WEIGHTINGS

-80

-70

-60

-50

-40

-30

-20

-10

0

10

10

100

1K

10K

Frequency/ Hz

SPL/d

B

'A' Weighting
Linear

7

Peak/Slow/Fast Switch

This three position slide switch, labelled SLOW-FAST-PEAK,
determines the damping coefficient of the analogue meter. The
SLOW position sets the instrument for the standardised ‘slow’ meter
response with a time constant of 1 second. In the fast setting the in­strument has a time constant of 125ms for the standardised fast meter
response. When the meter is used in the PEAK mode, the meter has
minimum damping and allows quick acting transient sounds to be
shown.

Maximum Hold Button

The MAX button is a momentarily acting push button which holds
the maximum sound level whilst the button is depressed. Once the
button is released the meter returns to normal operation. This facility
is very useful for capturing the maximum rms sound level of tran­sient sound events.

Filter Mode Switch

The octave band filters can be used by placing the switch in either
the MAN or the AUTO position. When in the OUT position the me­ter operates as a normal sound level meter with a ‘linear’ (‘flat’) or
‘A’ weighted response. When using the filters the ‘A’ weighted re­sponse can also be used if desired.

The filters can be used in two different modes, MAN or AUTO. In
the MAN (or manual mode), the centre frequency of the filters is
changed by depressing either of the select buttons, ‘frequency up’ or
‘frequency down’. The frequency of the filter currently in operation
is displayed by means of ten LED’s (light emitting diodes) ,
positioned on the front panel.

8