Operating Instructions; Switching On The Instrument; Preliminary Settings Of The Controls; Input Coupling (Ac/Dc, 0) - Philips PM 3214 Anleitung

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2.3
2.3.1
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2.3.2
OPERATING INSTRUCTIONS
Switching on the instrument
Before connecting the instrument to any supply, the instructions given in section 2.1 Installation, should be
carefully carried out.
The oscilloscope will meet specifications (see section 1.2) normally after awarming-up period of approximately
15 minutes. However, if the instrument has been subjected to an extremely cold environment (e.g. left in a
car overnight in freezing conditions) and is then brought in for use in a warm room, awarming-up period of
sufficient length should be allowed (see 1.2.11).
Preliminary settings of the controls
This procedure is a general indication of whether the oscilloscope is functioning correctly and provides a suit-
able starting point before any measurements are made.
Refer to Fig. 2.2 for location of controls.
Set INTENS and FOCUS controls in mid position.
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Depress AUTO and select an average time coefficient between 10µs/div and 10 ms/div with the TIME/DIV
switch. With all other pushbuttons normal (not depressed► channel A and channel B traces can be positioned
on the screen with the relevant POSITION controls. Set the INTENS control for a display of medium bright-
ness and adjust FOCUS control for well focused traces.
2.3.3
Input coupling (AC/DC, 0)
AC coupling (pushbutton depressed) is useful to block the d.c. component of a signal. Choice of AC limits the
lower frequencies, causing low repetition rate sinewave signals to be attenuated and low repetition rate square-
waves to be distorted. The degree of attenuation is determined by the input RC time (0.1s). Input RC time is
extended by 10 if 10:1 passive probes are employed.
When switching to AC coupling it will take approximately five input RC times before the trace is stabilised to
the average value of the input signal.
AC position measurements cannot be made with respect to ground.
0 position disconnects input source and short-circuits input of amplifier to provide zero signal check.
DC coupling (pushbutton released) provides for full range frequency input, i.e. down to d.c.
2.3.4 Use of probes
1:1 passive probes should only be used for d.c. and low frequencies.
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Capacitive loading attenuates high frequencies or increases the rise-time of measurement signals (dependent on
source impedance►.
10:1 passive probes have less capacitive loading; usually about 10pF to 20pF. FET probes are superior,
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especially when measurements are to be taken from high impedance test points or at the upper frequency
limit of the oscilloscope bandwidth.
10:1 passive probes must be properly compensated before use. Incorrect compensation leads to pulse distortion
or amplitude errors at high frequencies.
For correct adjustment, the CAL output connection can be used (see Fig. 2.3.)
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2.3.5
Selection of chopped or alternate modes
(A ALT CHOP ADD B)
In dual channe! operations (CHOP or ALT depressed) the chopped mode (depress CHOP) must be selected for
relatively slow sweep speeds (from .1 ms/div to .5 s/div) or at low repetition rates of sweeps occuring, even at
high sweep rates. Selection of the ALTernate mode under these circumstances would make comparisons between
waveforms difficult because traces would actually appear to be written one by one. However, when the display
is fast enough to be interrupted by the chopping frequency the alternate mode must be selected (depress ALT),
usually at sweep rates faster than .1 ms/div.