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CASTLE GA112 Manual

Sound level meter with octave filters
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Summary of Contents for CASTLE GA112

  • Page 2 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.
  • Page 3 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 re- pairs. Note the condition of the unit clearly and contact the supplier or Castle Group direct.

  • Page 4: Table Of Contents

    CONTENTS TITLE PAGE NO Instrument Introduction Battery Installation Preparation of Equipment and Controls Calibration Measuring Sound Levels Measuring Maximum Sound Levels Use of Filters for Octave Band Analysis Use of the Output Socket Instrument Description Circuit Description Environmental Effects Technical Specification Warranty and After Sales Service...

  • Page 5: Instrument Introduction

    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.

  • Page 6: Battery Installation

    Battery Installation To prepare the equipment for service batteries must first be fitted. Re- move 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.

  • Page 7: Preparation Of Equipment And Controls

    Preparation of Equipment and Controls Power/Weighting Switch This is a three-position switch labelled OFF-A-LIN. In the OFF po- sition all power is removed from the instrument. The ‘A’ position allows sound levels to be measured with ‘A’ weighting, (see figure 1).
  • Page 8 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 in- strument has a time constant of 125ms for the standardised fast meter response.
  • Page 9 Ten standard centre frequencies are used 31.5Hz, 63Hz, 125Hz, 250Hz, 500Hz, 1kHz, 2kHz, 4kHz, 8kHz and 16kHz. These allow the engineer to gain a clearer ‘picture’ of the frequency distribution of the noise. Typical responses of these filters are shown below (Figure 2). A memory facility is provided to allow the user to switch the filters ‘in’...
  • Page 10 To change the range ‘up’, depress the button marked with an up ar- row, to change the range ‘down’, the button marked with a down ar- row is depressed. The five base ranges on the GA112 are shown be- low (figure 3).
  • Page 11 Calibration Control This is a screwdriver-adjusted control, which alters the input sensi- tivity of the instrument. A small flat bladed screwdriver, no larger than 2mm, should be used when calibrating the instrument. Cali- bration should only be carried out in conjunction with a known sound source.

  • Page 12: Calibration

    Place the meter on its 70dB range and adjust the CAL control until the meter reads 94dB. If using the Castle GA607 calibrator, it is also possible to check the sound level meter on its 90dB range, switch the calibrator to the 104dB position and check that the reading is within 0.4 dB.

  • Page 13: Measuring Sound Levels

    Secondly by keeping the weighting in the LIN mode and putting the filter into the MAN mode (as detailed on pages 8 & 9), on its 1kHz centre frequency, the calibration should be within +0.5dB and –1dB. Measuring Sound Levels Use as a normal sound level meter Turn on the meter by selecting the ‘A’...

  • Page 14: Measuring Maximum Sound Levels

    Measuring Maximum Sound Levels Turn on the meter by selecting A weighting or LIN response, and switch the filters OUT. Check the battery voltage and the calibration of the sound level meter. Select a suitable range so that the maximum expected sound level would be registered on the meter without causing it to go off the scale.

  • Page 15: Use Of Filters For Octave Band Analysis

    Use of Filters for Octave Band Analysis Turn on the meter by selecting ‘A’ weighting or LIN response and switch the filters to MAN. Check the battery voltage and calibration of the sound level meter. Select the lowest filter frequency (31.5Hz) and the 100dB range.

  • Page 16: Use Of The Output Socket

    Use of the Output Socket The GA112 is equipped with a three-pin lemo connector on the right hand side of the instrument. The connector provides an AC and a DC signal output (see figure 4). The AC output is a logarithmic output and is direct representation of the sound present at the microphone.
  • Page 17 When using a chart recorder the following settings can be used as an initial guideline: - Paper speed (or X-axis travel) 0.5cm/sec. Sensitivity (or Y-axis travel) 200mV/cm (using 180mm paper) The following procedure can then be used: - Connect the chart recorder (or X-Y plotter) to the sound level meter. With the filters switched OUT measure the sound level .

  • Page 18: Instrument Description

    Instrument Description FILTER OFF, MAN. AUTO LED DISPLAY CALIBRATION AC OUTPUT RANGE CONTROL OCTAVE BAND WEIGHTING FILTERS FREQUENCY SELECT OVERLOAD LED DISPLAY OVERLOAD DETECTOR DC OUTPUT PRECISION METER RMS TO LOG DC HOLD CONVERTER BATTERY CHECK SLOW, FAST, PEAK Figure 5 – Block diagram of instrument...

  • Page 19: Circuit Description

    Environmental Effects The GA112 is designed for operation between the temperature limits of –10°C to +50°C. The unit may be stored, without batteries, be- tween –20°C and +60°C, but should not be subjected to temperatures beyond these ranges for long periods.

  • Page 20: Technical Specification

    Technical Specification Measuring Range Range Measuring Range Max. Peak Level 30-60dB 73dB 50-80d|B 93dB 70-100dB 113dB 90-120dB 133dB 110-140dB 153dB Detector Characteristics: Signal to noise ratio: >5dB at bottom scale Crest factor capability: 13dB at FSD Frequency weighting ‘A’ to BS EN 60651 to BS EN 60651 Time weighting Slow...
  • Page 21 Display Parameters Sound Pressure Level either ‘A’ or Linear weighted with or without Octave Band Filters. Battery condition indication. Filters Built in Octave Band Filters to BS EN 61260 : 1996 Filter centre frequencies 31.5Hz, 63Hz, 125Hz, 250Hz, 500Hz, 1kHz, 2kHz, 4kHz, 8kHz, 16kHz.
  • Page 22 Calibration Acoustic using GA607 (or GA602) at 94 dB or 104db at 1 KHz Potentiometer adjustment. Batteries Type: 3xPP3 Life: >40 hours at 3hrs/day >12 hours continuous Temperature Operating range: -10oC to +50oC Storage without batteries: -20oC to +70oC Effect of temperature: <0.5dB from –10oC to +50oC Humidity Operating range:...
  • Page 23 Overall Dimensions and Weight 280x85x60mm 800g with batteries Accessories available KA003 Attaché style carry case with tripod* KA005 Shoulder bag carrying Case GA607 Dual level acoustic calibrator 94dB and 104dB at 1kHz *Tripod purchased separately...

  • Page 24: Warranty And After Sales Service

    In the event of a fault occurring, during the warranty period, the instrument should be returned to Castle Group Ltd, in its original packaging, or to an authorised agent. Please enclose a clear description of the fault or symptom.

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