HP 400F, Руководство по эксплуатации и обслуживанию, Страница: 14 / 54

Section
ill
a. Perform the steps listed under Paragraphs
3-5 and 3-7.
b. Set the meter RANGE switch to the approxi�
mate
range of
the voltage to be measured.
DO
NOT APPLY MORE THAN 600
VOLTS TO INPUT. DO NOT OVER­
LOAD THE
•
1 MV THROUGH . 3
VOLT RANGES WITH MORE THAN
300 VOLTS AT FREQUENCIES BE­
LOW 300 kllz OR WITH MORE THAN
64 VOLTS AT FREQUENCIES ABOVE
300 kllz. IF ANY OF THESE OVER­
LOADS
ARE EXCEEDED, THE IN­
STRUMENT MAY BE DAMAGED.
c. If the signal to be measured is a frequency
less than 100 kHz, the 100 kllz L. P. FILTER
may
be
switched in to filter out all frequency
components above 100 kHz.
d. Connect the signal to be measured to the
INPUT terminals. The RMS voltage amp­
litude
of
the input will be indicated on the
meter.
3-9. DB MEASUREMENTS.
3-2
a. Perform the steps listed under Paragraphs
3-5 and 3-7.
b. The dB measurement is equal to the algebraic
sum
of
the meter indication
and
the RANGE
setting. For example: if the RANGE setting
is +20 dB. and the meter reading is -3 dB.
the actual dB measurement is +17 dB.
c. The dB scale of the 400F/FL is calibrated
in dBm. 0 dBm is equivalent to 1 milliwatt
dissipated by a 600 ohm load. Therefore.
all measurements in dBm must be made
across a total impedance of 600 ohms.
Measurements across all other impedances
will be in dB. but not in dBm.
d. A reading in dB may
be
converted to dBm
by using the Impedance Correction Graph
(Figure 3-3). For example: to convert a
40
dB
reading across 100 ohms to dBm. lo­
cate the 100 ohm load impedance onthe bottom
of the graph. Follow the impedance line to
the heavy black line, and read the meter
correction at that point. The correction for
100 ohms is +7.5 dBm, and the corrected
reading is +47. 5 dEmo
Model 400F /FL
3-10. WIDE BAND AC AMPLIFIER.
EXTREME CARE SHOULD BE
TAKEN TO AVOID COMMON
GROUND PATHS BETWEEN THE
INPUT
AND
OUTPUT SIGNALS.
BECAUSE O F THE HIGH GAIN O F
THE INSTRUMENT ON THE MORE
SENSITTVE RANGES
(SO
DB ON . 1
MV RANGE, ETC.), COMMON
GROUND PATHS CAN CAUSE
OSCILLATIONS AT HIGHER
FREQUENCIES.
a.
Perform the steps listed in Paragraphs 3-5
and 3-7.
b. Set the meter RANGE switch to the approxi­
mate range
of
the input signal.
c. When signals of frequencies less than 100 kHz
are being amplified, the 100 kllz. L. P. FIL­
TER may
be
switched in to reduce high fre­
quency noise and lessen the possibility of
oscillations.
d. Connect the input signal to the INPUT
terminals.
e.
Table 3 -2 shows the gain factor for each
range
of the 400F/FL into an open circuit.
Table 3-2. AC Amplifier Gain Factors
RANGE GAIN RANGE GAIN
300 V -50 dB lOOmV +20 dB
100 V
-40 dB
30mV
+30 dB
30 V
-30 dB 1 0 mV +40 dB
1 0 V -20 dB 3 mV +50 dB
3 V -10 dB 1 mV +60 dB
lV
o dB .3mV +70 dB
.3 V +10 dB .1mV +SO dB
3-11. 400F WITH OPTION 01.
3-12. Operating procedures forthe 400F with Option
01 are the same as the operating procedures for the
standard 400F. The only difference between the two
models is the scale layout. The 400F with Option 01
has a dB scale which reads from -15 to +2. instead
of from -12 to +2. The dB scale is placed at the top
of
the meter face for better resolution.
01795-2