knob of the Measuring Amplifier one step anticlockwise and adjust the GAIN CON-
TROL knob to obtain full scale pointer deflection on the indicating meter.
6. Keeping the reference source connected, calibrate the Level Recorder so its pen def-
lection corresponds with the meter indication of the Measuring Amplifier. This de-
pends on the record mode selected and may be performed as follows:
"AC and DC Log" record modes: Adjust the SENSITIVITY knob of the Level Recor-
der to move the pen to the thick line ("50 dB") at the top of the recording chart.
"DC Lin" record mode: Disconnect the cable from the SIGNAL INPUT socket of the
Level Recorder and adjust the DC LIN. POSITION knob to move the pen to the thick
line ("0 dB") at the bottom of the recording chart. Reconnect the SIGNAL INPUT
socket cable and adjust the SENSITIVITY knob to move the pen to the thick line
("50dB") at the top of the chart. If the pen position cannot be adjusted, then carry
out the adjustment with the POLARITY REVERSER switch of the Level Recorder set
to its opposite polarity. To improve the accuracy of the calibration, turn the INPUT
SECTION ATTENUATOR knob of the Measuring Amplifier two steps clockwise (i.e.
decrease sensitivity by a factor of 10) and adjust the DC LIN. POSITION knob to
move the pen to a level graduation on the chart corresponding with the level indi-
cated by the indicating meter. Finally, return the INPUT SECTION ATTENUATOR
knob to its original position and adjust the SENSITIVITY knob so that the pen is im-
mediately over the thick line (50dB) at the top of 'the chart.
Once correctly adjusted avoid touching the DC LIN POSITION and SENSITIVITY
knobs of the Level Recorder or calibration will be lost.
7. Disconnect the reference source and set Band Pass Filter controls:
SELECTIVITY
RANGE
FILTER CONTROL MODE
MANUAL FILTER CONTROL
"Bandwidth" and "Record Step" as required
"2 Hz - 20 kHz - A - Lin"
"Recorder" — "Stop"
To centre frequency of the octave or third octave
band in which analysis is to commence.
8. Set the PAPER DRIVE button of the Level Recorder to "On" and press the right hand
FILTER CONTROL MODE switch of the Band Pass Filter to "Run", letting the paper
driye forward until it stops automatically. The 1 /3 OCTAVE light on the level Recor-
der should now be lit, indicating that the paper drive was stopped at the instant the
Band Pass Filter was stepped to the start of the octave or third octave in which ana-
lysis is to commence. To maintain this exact starting point, keep the PAPER DRIVE
and POWER push-button set to "On" (inner position)
9. On the Level Recorder, set the PEN DRIVE button to "Off" and slide the pen by hand
to the thick line (50dB) at the top of the recording chart. This is printed with third
octave centre frequency markingsw spaced at 5 mm intervals.
10. For third octave or octave analysis in third octave steps, use the PAPER ADJUST-
MENT wheel to advance the paper to a position where the pen is 2,5 mm before the
centre of the frequency marking T corresponding with the centre frequency of the
third octave band in which analysis is to commence.
For octave analysis in octave steps, move the recording paper forward to a position
where the pen is 7,5 mm before the frequency marking-r corresponding with the
centre frequency of the octave band in which analysis is to commence.
18
To Next Page
Loading...
