Chapter 2 — Checking Procedure
Checking Procedure
2238 Mediator Integrating Sound Level Meter
Service Manual
Brüel&Kjær
18
2.3.9 Crest Factor Test (Crest Factor=3)
The 2238 must be in LCFP mode for this test. The signal is: Burst Duration: 5.5
milliseconds, Repetition Rate: 40Hz, Sine Wave Frequency: 2kHz.
● Press and use to set the range to 30 – 110 dB, then to OK, which also
returns you to the active display.
● Remount microphone 4188 to the 2238 and mount acoustic coupler onto it.
● On the Type 4226 Multifunction Acoustic Calibrator select “Test Level" on the
Function switch and turn power on. Set the Frequency on the 4226 to 2kHz and
use its thumbwheel to adjust output until the display on the 2238
reads
100.0 dB.
● Move the 4226’s Function switch to Crest Factor to start the test. See Table 2.8.
Table 2.8 Crest Factor Test
2.3.10 Tone Burst Test
● With the microphone and acoustic coupler still attached to the 2238, press
and set the range to 20 - 100 dB then to OK.
● On the 4226 select “Test Level" on the Function switch and adjust output until the
2238 display reads 96.0 dB. Switch the Function switch to “Time Weighting F" to
begin the “Fast (LCFP) Test".
● The 2238 display shifts between the high (correct) reading and a lower one (not
important) because of the pause between test signals. Check against Table 2.9
● To reset the 2238 for the “Slow (LCSP) Test", press , use and to select
Weightings, then until you get BB/S, then to OK. Press to Close and
return to the active display.
● On the 4226 move the Function switch to “Time Weighting S" (LCSP) to begin the
“Slow" test.
● Because the 4226 only generates a signal every 7–10 seconds, you must observe
the 2238 display for about 15 seconds while many readings flash by, and take the
absolute highest value as the “Actual" reading. The reading is highest just after
the signal is generated and the LED on the 4226 is lit.
Acceptance Criteria
in dB re 1µVRMS Actual
Reading
100dB±0.5dB
To Next Page
Loading...
