Chapter 1 — Introduction
About 2238 Mediator™
2238 Mediator Integrating Sound Level Meter
Service Manual
Brüel&Kjær
2
1.1 About 2238 Mediator™
1.2 Standards
2238 Mediator Integrating Sound Level Meter complies with the draft of the IEC61672
Class 1 standard. This standard will supersede the IEC651 and IEC804 Type 1 stand-
ards. This implies that the Mediator also complies with current international and
national standards. The Mediator is categorized as a Group X sound level meter
according to IEC61672, i.e.; a self-contained, battery-operated instrument that re-
quires no external connections to other apparatus to measure sound levels.
1.3 Basic Configuration
Mediator comprises the following:
● l´ 2238 Mediator Integrating Sound Level Meter
● l´ Basic SLM Software BZ7126
● 1´ Microphone Preamplifier ZC0030
● 1´ Prepolarized Free-field 1/2² Condenser Microphone Type 4188
● l´ 9-pole cable with 25-pole Adaptor AO1386 or AO1442 Null-modem Cable for
Serial Interface
1.4 How Mediator Works
Mediator can be configured to a wide range of requirements with different software
packages or a combination of these packages. You can easily upgrade the software
via the serial RS –232 interface or it can be performed at a Brüel& Kjær service
centre. The Frequency Analysis Software option requires Type 2238-A-F (with filter
set) or a hardware upgrade (installation of filter set 2238MUF), that must be made at
a Brüel&Kjær service centre. If Mediator is ordered with Frequency Analysis Soft-
ware BZ7123, the filter set is part of the instrument.
Refer to the block diagram in Fig. 1.1 for an overview of how Mediator works. The
signal from the microphone is fed through the appropriate amplifiers, the desired
filters (“A”, “C”, “L” or octave filters (if fitted)) and correction filters (“Sound Inci-
dence”, “Windscreen”). The multiplexer switches two signals (either the same signal
or with different weightings) through to the RMS and the RMS/Peak detectors and
succeeding Time Weighting filters. At this point the signals are still in the analogue
domain. The signals are now converted in the D/A-converter and all subsequent sig-
nal processing is in the digital domain. Time weightings F and S are in the digital
domain. Finally the signals are fed through the D/A-converter and the buffered sig-
nals are output to the Aux1 and Aux2 connectors via the multiplexer.
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