
THEORY
1864-1644 Positive Polarity Megohmmeter
20
A unity-gain FET-input ampli
fi
er (+1) follows the
standard resistors in the circuit con
fi
guration. R210
and C203 comprise a low-pass
fi
lter input to FET
Q204. The ampli
fi
er components include a differ-
ential ampli
fi
er (Q202, Q203), a coarse
∞
control
(R244), the SET
∞
control (R242) and an output
transistor (Q201). The signal then enters the series
combination of R135 and R134 back to the GUARD
terminal.
Resistors R221 through R223 (R
B
) are meter-sensi-
tivity resistors that are ganged to the voltage resistors
R124 through R127 (R
A
). R222 is used for both the
50 V and 500 V ranges, while the 200 V range uses
the circuit resistance and has no added resistor. The
remaining two resistors, R221 and R223, are used
for the 250 and 100V ranges, respectively. Potenti-
ometer R243 is an adjustable control in the meter
sensitivity circuit.
5.2.3 Type 1864 Megohmmeter (Figure 7.9)
The circuit of the 1864 Megohmmeter is basically
the same as that of the 1863 (paragraph 5.2.2). The
exceptions are explained in the following paragraphs.
In the 1864 the second dc power supply is a qua-
drupler. This supply establishes the plate voltage of
V101 with the use of resistors R109 through R114.
The regulator circuit has a slightly different input
when the
TEST VOLTAGE
switch is switched
from V (1) to 0 V (10). Resistors R124 and R125 are
switched out of the circuit in the 0V (10) position.
Voltage-selection resistors for the 1864 are R126
through R133 and the meter sensitivity resistors are
R221 through R228. An additional range resistor,
R220, is in the 1864.
Figure 5-1 Megohmmeter block diagram
Содержание 1864-1644
Страница 10: ...CONTENTS FIGURES AND TABLES 1864 1644 Positive Polarity Megohmmeter vi This page intentionally left blank...
Страница 16: ...INTRODUCTION 1864 1644 Positive Polarity Megohmmeter 6 This page intentionally left blank...
Страница 22: ...OPERATION 1864 1644 Positive Polarity Megohmmeter 12 This page intentionally left blank...
Страница 28: ...APPLICATIONS 1864 1644 Positive Polarity Megohmmeter 18 This page intentionally left blank...
Страница 38: ...SERVICE AND MAINTENANCE 1864 1644 Positive Polarity Megohmmeter 28 This page intentionally left blank...
Страница 39: ...1864 1644 Positive Polarity Megohmmeter 29 PARTS LIST AND DIAGRAMS Chapter 7 PARTS LISTS AND DIAGRAMS...
Страница 40: ...1864 1644 Positive Polarity Megohmmeter 30 PARTS LIST AND DIAGRAMS...
Страница 43: ...1864 1644 Positive Polarity Megohmmeter 33 PARTS LIST AND DIAGRAMS Figure 7 4 Type 1864 switching diagram...
Страница 44: ...1864 1644 Positive Polarity Megohmmeter 34 PARTS LIST AND DIAGRAMS Figure 7 5 Type 1864 schematic diagram...
Страница 45: ...1864 1644 Positive Polarity Megohmmeter 35 PARTS LIST AND DIAGRAMS Figure 7 6 Complete cabinet assembly...
Страница 46: ...1864 1644 Positive Polarity Megohmmeter 36 PARTS LIST AND DIAGRAMS...