10. Set the PEN DRIVE to "Off" and move the pen by hand to the thick line (50 dB) at
the top of the recording chart. This is printed with third octave frequency markings-w
spaced at 5 mm intervals.
11. Lift up the paper clip above the paper drive sprocket wheel and pull the recording
paper forward to a position where the pen is approximately 2,5 mm (third octave) or
7,5 mm (octave) before the centre of the frequency marking-w- corresponding with
the centre frequency of the third octave or octave frequency band in which analysis
is to commence.
12. If the pen is less (or greater) than 2,5 or 7.5 mm in front of the required centre fre-
quency marking on the paper, note the distance the paper is out of alignment and
turn the AUTOMATIC STOP wheel so that its white spot is a corresponding distance
below (or above) the white spot on the PAPER ADJUSTMENT wheel.
13. Push the PAPER ADJUSTMENT wheel upwards so that its white spot is near the top
of the opening on the front of the Recorder, and press the PAPER DRIVE "Start" but-
ton. The paper will start to move forward and should stop automatically at the re-
quired starting point on the chart. If not repeat items 12 and 13.
14. Set the PAPER DRIVE FUNCTION switch on the Level Recorder to "Stop" and on the
Band Pass Filter press the right-hand FILTER CONTROL MODE switch to "Run".
15. Slowly rotate the FILTER SHIFT SYNC. wheel on the Level Recorder downwards un-
til the digital display on the Band Pass Filter indicates a change in filter centre fre-
quency. Rotate the wheel a further distance just short of 5 mm downwards.
16. Set the right-hand FILTER CONTROL MODE switch on the Band Pass Filter to
"Stop" and on the Level Recorder set the PAPER DRIVE FUNCTION switch back to
its "Continuous F" position. The paper position is now synchronized with the filter
switching.
17. Turn the INPUT SECTION ATTENUATOR and GAIN CONTROL knobs of the Measur-
ing Amplifier to their extreme clockwise position and apply the signal to be analyzed.
18. Set the RANGE switch of the Band Pass Filter to "Lin" and step the INPUT SECTION
ATTENUATOR knob of the Measuring Amplifier to obtain a suitable meter deflection
without the INPUT OVERLOAD lamp flashing.
If the deflection is insufficient, even when the INPUT SECTION ATTENUATOR is in
its extreme anticlockwise position, then step the OUTPUT SECTION ATTENUATOR
knob until a suitable deflection is obtained without overload.
19. Set the PEN DRIVE switch of the Level Recorder to "On" and lower the pen lift cam.
20. Set the RANGE switch on the Band Pass Filter back to its "2 Hz — 20 kHz — A —
Lin."" mode and press the right-hand FILTER CONTROL MODE switch to "Run" to
commence recording.
The Level Recorder will start to run and will drive the recording paper forward one com-
plete chart length of 250 mm, so that the pen is at the start position for the next chart.
Each time the pen passes the chart position for a filter change, the Recorder causes a
band shift in the Band Pass Filter. Simultaneously, the signal level in the frequency
band is plotted out by the Recorder pen to give a frequency spectrogram of the whole fre-
quency range being scanned. At the end of the range, the Recorder pen is lifted, the
Type 1618 shifts back to its starting frequency and the recorder runs forward to the
starting point of the next chart.
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