CEL-283 Impulse Handbook Dec 2005

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

Introduction

Preparation of the Instrument

In line with the requirements of the new International Standard for sound level meters (IEC 651), the CEL-283 has been designed as a full specification type 2 instrument. It also meets the DIN Standard 46 633 and ANSI SIAM as well as other national standards. As an addition to the full range of facilities expected of a conventional sound level meter the CEL-283 also has long term integrating facilities enabling a direct readout of Leq values to be obtained. The instrument will therefore be found a valuable tool by all those charged with a responsibility to control either industrial or environmental noise.

The battery compartment is located in the rear of the instrument and is accessible when the two retaining screws have been removed. The batteries should be connected to the two flying leads and placed in the battery compartment before replacing the cover. To check the batteries the ON/OFF switch should be set to the battery position and the meter should then indicate within the scale banded 'batt' if they have sufficient charge to operate the instrument correctly. The batteries must be removed if either becomes discharged or if the instrument is not going to be used for some time. As an alternative to the primary cells provided, nickel cadmium rechargeable batteries type RS 591 089 may be used with this instrument. A suitable charger for these NiCad batteries is the type RS 691 067 which must be specified separately.

Schedule of Parts The instrument is normally provided as a complete measurement kit under the part number CEL-283/K1 and this comprises the following individual items: CEL-283 CEL-184 CEL-3379 CEL-3435 CEL-2962 6F22 D 3380 RS 1

Integrating Impulse Sound Level Meter Acoustic Calibrator Coupler Pistol grip and hand strap Foam windshield Batteries (3 off) Carrying Case Screwdriver

If the sound level meter only is required it is specified as CEL-283/X and, in this instance, the zip case type CEL-3341 is provided in place of the accessories listed above. It is also recommended that the windshield type CEL-3482 be used with the X version as it may be accommodated within the zip case. Another useful accessory for use with these instruments is the CEL-3435 pistol grip and hand strap that makes for more convenient use of the instrument.

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Calibration In line with current instrument practice all types of sound level meters should be regularly calibrated to ensure the accuracy of the reading obtained. For this purpose the CEL-184 Acoustic Calibrator is provided. To check the calibration of the CEL-283, the CEL-3379 coupler supplied with the kit should be placed over the microphone ensuring that it is correctly seated against the shoulder in the microphone coupler. The calibrator may then be placed over the coupler and microphone assembly, here again ensuring that both '0' rings are passed and the coupler and calibrator are correctly seated. Switch on both the calibrator and the sound level meter, the latter having its range selector set to the 60dB(A) range.

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The calibration level is 90dB(A) and this should cause a corresponding Indication on the scale. Should the instrument have drifted due to environmental influences it may be reset by means of the CAL control located through the aperture in the front panel of the instrument. Using the screwdriver provided the level maybe reset to the correct reading. If large changes in the calibration level are observed, the meter should be returned to our service department or your local agent.

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the International Standards - 125msec for FAST and 1 second for SLOW, The IMPULSE response provides a 35msec time constant for rising edges and 1.5 seconds for falling ones.

Controls and Indicators On front panel OFF/BATT/ON

FLAT/A

In the OFF position no functions are performed and the instrument draws no power. In the BATTERY position the meter indicates the on load voltage of the lower of the two batteries with the end of useful battery life shown as the lower mark on the scale; hence, when end of life is indicated both batteries must be changed. When in the ON position the instrument carries out its selected functions. MAX/SPL/LEQ (RESET) In the SPL position the instrument will display the current sound pressure level in accordance with the settings of the other controls. When the MAX mode is selected the meter display will lack onto the highest RMS level that occurs during the measurement sequence. In order to cancel the maximum hold store a general reset should be applied and this is achieved by switching the instrument from the MAX to the SPL position. In the LEQ mode the meter will display the accumulated average result from the time of the last general reset. The meter will be seen, therefore, to update each time a new answer is calculated and added to the cumulative result. Average results are, therefore, available over any time period from 1 second to 24 hours and are not limited to fixed time periods. To reset the LEQ calculation and the overload latch the instrument should be switched into the maximum hold mode and returned to the SPL position. A new LEQ measurement will commence as the instrument enters the SPL mode from MAX. The instrument may, therefore, be switched between SPL and LEQ modes without resetting the accumulated LEQ. The LEQ-Tm switches that are located in tire battery compartment will determine the actual operating conditions of the average mode. Results on the fast and slow time constant settings will be LEQ (Lm) as per the conventional definitions (BSI, ISO, etc) whilst the average will be impulse weighted if the impulse time constant is selected (see following section).

The standardised 'A’ weighting is provided in the 'A’ position of this switch giving results in dB(A). In the FLAT position the unweighted microphone signal is passed to the display giving results in dB(Flat/Lin). 90/60/30 This control selects the measurement range by setting the meter scale zero to the value selected; hence, the answer is given by reading the appropriate scale on the switch plus the meter. Measurement ranges provided are, therefore, 30-70, 60-100 and 90-130. It must be remembered, however, that on the top range the RMS levels are within specification over a span 90-120 whilst the additional 10dB is provided for the maximum hold function. This results from the use of a high sensitivity microphone to enable measurements to be made at 30dB(A) and it will, therefore, saturate at 135dB(A). In Battery compartment 3S-5S LTm These are located in the battery compartment and they set the operating conditions of the integrating mode. When in the LEO position conventional LEO results are obtained as per British and International regulations. Selecting the TM position on the right-hand switch will amplitude weight the average result in accordance with DIN and VDI requirements for LTm measurements. The left hand switch selects the 3 and 5-second periods required by these measurements. When in this mode of operation the results will be seen to up-date at the end of each 'takt'. The alternative method of amplitude weighting the results referred to in West German regulations, LAlm, may be accommodated by setting the right-hand switch to LEQ and the time constant switch to impulse.

SLOW/FAST/IMP This switch selects the time constants employed in the RMS detector and these are as defined in www.casellausa.com [email protected]

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OL This is the overload indicator and it is illuminated if the instrument is indicating an incorrect answer due to overloading of its circuits. When this occurs the measurement must be repeated on a higher range. The indicator is illuminated during an actual overload. When an overload occurs, an overload latch is set that causes the overload indicator to be illuminated when the instrument is in the LEQ mode, and this indicates to the operator that the instrument has been overloaded during the current measurement sequence. The overload latch is reset by the general reset function (see MAX/SPL/LEQ (Reset). OUTPUT SOCKET This 3.5mm miniature jack socket provides a feed of the conditioned AC output to ancillary instrumentation such as tape recorders, frequency analysers, etc. Technical Description The instrument covers the range of sound levels from 30-120dB(A) in three measurement ranges and has both fast and slow meter characteristics. In addition it is provided with the impulse time constant to facilitate the subjective assessment of transient sounds as well as a maximum hold circuit that is operational in conjunction with all three time constants. For broad band measurements the standard 'A: and Flat (Linear) frequency weightings are provided. The instrument employs a high sensitivity electret condenser microphone that has a proven record of calibration stability in respect of both its amplitude and frequency responses. Signals are fed through the preamplifier stages and onto the calibrated range changing attenuators and the frequency conditioning circuits. After additional amplification the signals are processed by a new design of wide dynamic range RMS detector. This provides a logarithmic output over a 40dB dynamic range enabling a clear indication of the sound level on a linear scaled meter. The wide dynamic range that this arrangement permits considerably improves the interpretation of the results as it eliminates the need for continual range changing that is necessary when the older style of instrument having a logarithmic scale is used. When the maximum hold mode is selected the RMS signal www.casellausa.com [email protected]

is fed to an analogue hold that is then connected to the meter via a buffer amplifier. For the LEQ result the RMS level is sampled every 10msec and this result is antilogged and fed to a digital integrator. This is then sampled every 300msec with the result being divided by time and the answer logged to give a result in dB for display on the meter. The instrument is powered by two standard 9V batteries and is housed within a pressed aluminium case that is contoured to provide the correct acoustic characteristics. Manufacturer's Servicing And Warranty Arrangements Each instrument has been carefully inspected and calibrated prior to dispatch from our factory in order to ensure its rigid conformity with the requirements of our specification. All technical information relating to individual instruments is filed under the instrument's serial number. It is important, therefore, to always quote this number in any correspondence with the manufacturers. The serial number is located on the back of the instrument. The manufacturers undertake to rectify any defect in the instrument that is directly attributable to faulty design or assembly and which becomes apparent during the first twelve months from the date of the initial calibration. Many of the specialized components used in the instrument are subject to separate warranties by their actual manufacturers and in all cases benefit of these undertakings will be passed onto the end user. However, Computer Engineering's (CEL’s) liability is limited to items of their own manufacture and they do not accept liability for any loss resulting from the operation or interpretation of the results from this equipment. In the event of a malfunction developing the instrument should be carefully packed and returned to either the manufacturer's agent in the territory or, in the case of domestic sales, to our Hitchin factory along with a detailed description of the fault. The necessary repairs will be undertaken and the instrument returned as soon as possible. After the warranty has expired, except on approved accounts, service work is undertaken against quotation and all packing and transit costs are charged extra. In the case of sales in the UK, service contracts are available for the instruments and full details of these are available on request.

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Specification

REFERENCE CONDITIONS FOR CALIBRATION

Accuracy Sound level meter: IEC 651, BS 5969 and ANSI S1.4 in the type 2 category. DIN 45 634 Maximum RMS hold and energy average as Leq, Lim or LTm (3 or 6 second), 40dB dynamic range linear scaled meter. Ranges 30 - 70 dB, 60 - 100 dB and 90 - 130 dB Overload indicator provided. Measuring Limits Self-noise less than 25dB(A) or less than 40dB(Flat). 135dB absolute maximum. Microphone 17 mm (0.67 inch) electret condenser type Frequency Response dB(A) or Flat Display 47 mm (1.9 inch) meter movement covering 40 dB dynamic range. Time Weightings Fast, Slow and Impulse as per standards. Maximum Hold Analogue hold of maximum RMS level with a decay rate of less than 1 dB/5 min at 20ºC. LEQ Calculation By means of 10msec samples of RMS level. Minimum measurement duration 1 second, maximum greater than 24 hours. Calibration Field calibration checks by means of CEL-184 or CEL-182 Acoustic Calibrators (NB coupler type CEL-3379 necessary for X version). Auxiliary Output 3.5 mm jack feed of conditioned AC output at 1.0V for FSD via 3k3 Ohms. Batteries 3 x 6 F22 (or equivalent) - 2 for sound level meter and one for calibrator. Temperature Range -10 to +50ºC operational. -15 to +60ºC storage. Humidity Range 30% to 90% for ±0.5 dB Electromagnetic Interference <MSD for 400 A/M Vibration Interference <62d B (Flat) for 1 m/sec/sec Dimensions 235mm x 75mm x 54mm (9.2in x 3in x 2.1in) Weight 425g (15oz)

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Type of sound field Free Reference incidence direction Microphone diaphragm Reference pressure level 94 dB relative to 0.00002 Pa Reference frequency 1 kHz Reference measurement range 60-100 Reference temperature 20ºC Date ........................ Calibration Certificate CEL-283 serial number ...................... .... ... . CEL-184 serial number ………………………. Date ……………………………………………. CEL Instruments are manufactured and serviced by: Casella CEL Inc. 17 Old Nashuia Road #15, Amherst, NH 03031 USA PHONE (800) 366-2966 FAX (603) 672-8053 [email protected] In line with our policy of continual design improvement we reserve the right to amend any of the details in this handbook.

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