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5.
USE WITH OTHER INSTRUMENTS
Since the Level Recorder is a virtually essential accessory in analogue analysis with the
201 0, its use was considered in detail in chapter 4. This chapter covers the principles of
use of other Bruel & Kjrer instruments together with the 2010 for particular measuring
applications. For detailed operating instructions for the instruments discussed, their own
Instruction Manuals should be consulted.
5.1. TRACKING FREQUENCY MULTIPLER 1901
The 1 901 is an accessory which effectively turns the 201 0 into a tracking analyzer for
examination of harmonic components of a signal. The 1901 receives the 1,2 MHz fixed
oscillator signal from the 201 0 and by operating on the periodic signal (of frequency f 1)
applied to the 1901 input, supplies the variable oscillator signal required to tune the
2010 to the frequency of that periodic signal. By means of the MULTIPLICATION FAC-
TOR N thumbwheels on the 1901, the 2010 can be tuned to any chosen harmonic of
the test signal between 1 and 999. The actual harmonic tuned is ten times the MULTI-
PLICATION FACTOR N because of a mis-match of the fixed oscillator frequency from the
1901 requirements (the 1 901
is
designed to operate with the Heterodyne Slave Filters
2020 and 2021, but in all but this respect is ideal for use with the 201 0 also).
The heteroydne filter section and the Nixie frequency display (not the BFO
section)
of the
201 0 are tuned to the 10 N .f
1
frequency by a variable frequency tuning signal from the
1901. The Heteroydne Analyzer can be tuned from 20Hz to 200kHz. As the BFO sec-
tion of the 201 0 will not be tuned to any particular frequency, pins 6 and 7 of the FRE-
QUENCY
C~NTROL
VOLTAGE "In" socket on the rear panel should be shorted.
Full details of the calibration of the 1901 and 2010 for combined operation are given in
the 1901 Instruction Manual. The 1901 manual also contains details of control of the
2010 frequency display and automatic bandwidth switching.
5.1.1. Analysis of Harmonic Contents of a Signal
A set-up for analysis of the vibration characteristics of a test motor using the Heterodyne
Analyzer in conjunction with the 1901 is shown in Fig.5.1. The 1901 input signal is
shown supplied by a Magnetic Transducer Type MM 0002.
When using the 1 901 to track a varying frequency, for example the fundamental or har-
monic of a test motor running up to full speed, a restriction is set on the rate at which
the frequency can be scanned
.
The minimum time spent scanning one decade is a func-
tion of the bandwidth set on the Heterodyne Analyzer and the MULTIPLICATION FACTOR
N set on the 1901. The minimum times for scanning one decade are shown in Fig.5.2.
57
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