BRUEL & KJAER 1617 - Page 50

The recommended use of the various averaging control programs is as follows :
Sine for short duration signals where long averaging is undes irable because of the
sample length , and for periodic processes where a long period average is not neces-
sary
for statistical purposes.
Fast
Random for use with continuous signals where some short-term level varia-
tions could occur, but where the long averaging time at low frequencies does not
cause mis -representation of the signal.
Slow Random for the best possible confidence level when analyzing stationary ran-
dom signals .
Three
alternative shortest averaging times may be selected by the AVERAGING CON-
TROL
Minimum Time switch , to cater for signals with slowly repeating high frequency
components . Fig.4.4 shows the spectrum of a signal made with too short an averaging
time, and a spectrum of the same signal with correct averaging.
OrdinlllGOmm · Ab sc: I ... 5dehd.,. I 50nvn .
CClP)'righI .. OF 2005
Fig. 4. 4. Example of conditions where longer minimum averaging
times are required
45