Casella CEL CEL-177 User Manual

Casella USA
17 Old Nashua Road #15
Amherst, NH 03031-2839

CEL-177

Precision Acoustic Calibrator

Handbook

www.casellausa.com Page 1 of 6 tel: [phone]
[e-mail]

28 Jan 2006 fax: [phone]

Casella USA
17 Old Nashua Road #15
Amherst, NH 03031-2839

Introduction

The CEL-177 is a convenient and accurate
device that allows the accuracy of the CEL
range of precision acoustic measuring
instruments to be checked. It my also be used to
calibrate sound level meters produced by other
manufacturars as long as they are fitted with the
industry standard dimension mcrophones. The
CEL-177 incorporates a continuous sound
source within a calibration cavity and tables are
provided of the sound pressure level developed
within the cavity when different types of
microphone are introduced. To facilitate the
calibration of noise dose rates the acoustic
output provided may be 'gated' to provide an
accurately known duration of calibration tone.
The product of this level and time function my
then be related to the noise dose count provided
by these instruments. A calibrated voltage is
also provided to allow vibration meters, or other
electronic measurement equipment to be
checked.

Description

The CEL-177 'Precision Acoustic Calibrator’
contains a high stability low distortion sine wave
oscillator, the amplitude and frequency of which
is factory adjusted to produce the required level
in the coupling cavity. The transducers are pre­aged and matched to the driving circuits to
ensure the long tem stability of the system The
frequency of operation is 1kHz. Pulses from the
oscillator are also needed to drive the counter
that provides the 66.5 sec gate for the dose
meter calibration function. A single 9 V 6F22
type battery provides the power for the device.

Acoustic calibration is performed within a closed
cavity within which the calibration pressure level
is generated. Microphones to be calibrated are
introduced into this cavity and are located
against a shoulder and held in place by the ‘0’
rings. It is inportant to ensure that the
microphone is correctly seated to avoid
calibration errors. The calibration cavity is
designed to accept 1 inch diameter microphones
whilst a range of couplers are available in order
to adapt it to acccomodate smaller diameter
types. Pressure equalisation is provided
between the calibration cavity and atmosphere,
however it is still recommended that the
microphone is inserted and withdrawn slowly
and a few seconds allowed for static pressures
to equalise before readings are taken.

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Schedule of Parts

The description CEL-177 refers to the following
items and upon receipt they should be checked
against this schedule:

CEL-177 Precision Acoustic Calibrator
CEL-2958 Leather case*
CEL-2835 1” to ½” coupler (13.7 mm)
6F22 9 V Battery
H1770682 Handbook

Accessory items, for use with this calibrator,
which must be specifically ordered and will be
shown separately on delivery notes and
invoices, include:

CEL-2834 1” to ½” coupler (12.7mm)
CEL-3379 Coupler (17mm)
RS591-089 Rechargeable battery
RS591-067 Battery Charger

* This item is not provided when the calibrator is
provided as part of a sound level meter kit as it
is then housed within the instrument's system
case.

Preparation of the Instrument

In order to commission the calibrator it is only
necessary to connect the battery. Although a
battery is provided with the unit it is not
connected in order to avoid accidental operation
in transit and to prevent damage due to leakage.
To connect the battery, first ensure that the unit
is switched off and then the black sleeve should
be unscrewed from the chromed head and
carefully slid off. The battery may than be
connected to the flying lead, ensuring correct
polarity, and the battery located in the battery
tray. It is held in position by the spring clip which
should be biased away to allow insertion of the
battery. On connecting the battery the calibrator
my run for a few seconds but will then switch
itself off.