2-6.
TYPICAL OPERA T I N G PROC EDURES
a.
Low-Pass or High-Pass Filter
The operating made of each channel of the i nstrument is se lected with the
H I PASS!LO PASS switch . The position of this switch determi nes whether the
channel is operating
as
a Low Pass ( I N) or High Pass ( OUT) fi Iter.
In the Low Pass mode of operation the passband of the fi l ter extends from DC
to the cutoff frequency whi ch is defined by the settings of the three CUTOFF
FREQUE NCY dials and the MULT I PL IE R. In the High Pass mode of operation the
passband extends from the cutoff frequency setting to the upper 3-dB point of
the i nstrumenl (opproximately
2
MHz for Model
452
and 1 MHz for Mode l
852).
b.
Response Selection
The desired type of response for each channel is selected with the FLAT AMPL!
FLAT D E LAY switch. The position of this switch determi nes whether the response
of-the channel is a Butterworth response (OUT) or L i near Phase response ( I N) .
The Butterworth characteristic provides a maxima l l y flat amplitude response which
is 3 dB down at the cutoff frequency . Beyond the cutoff frequency the ampl itude
response ral ls off at a rate of
24
dB/octave
( 8
0
dB/decade) for the Madel
452
and
48
dB/octave
(160
dB/decade) for the Model
852.
The L ow-Pass or High-Pass Butterworth response for either model may be deter
mined by Ical i ng the norma l i zed plots given i n Figures
2
-3
,
2-4, 2-5
and
2-6.
To determine the frequency response for a particular Cutoff Frequency setti ng,
the normal ized scale on these plots should be multi plied by the cutoff frequency .
For example, if the cutoff frequency is set to
500
Hz Low-Pass, then "1 " on the
normalized scale represents
500
Hz,
"2"
represents
1000
Hz and
"S'
represents
250
Hz,
The Flat Delay characteristic provides a response which is useful for fil tering
SquQrewave or pulsed waveforms with minimum overshoot and ringing . While
thi s response is availab l e in either Low-Pass or High-Pass modes of operation, its
primary usefulness is in Low-Pass mode .
Normalized Delay characteristics are given in Figures
2-7,2-8,2-9
and
2-10.
For comparison, these figures include Phase and Delay characteristics for the
Bulterworth response.
The procedure for determining the Phose or Delay response for a particular Cut
off Frequency from the norma l i zed p l ats is the same as outl ined for the ampl itude
response . The actual D e l ay i n seconds is equal to the value obtained from the
p l ot divided by the value of cutoff frequency.
2-7
Summary of Contents for 452
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