HP 4262A Operating And Service Manual page 228

A12 BOARD CIRCUIT DESCRIPTION.
Table A below shows the relationship of selected range
resistors to 4262A FUNCTION, CIRCUIT MODE and
RANGE settings. Range selector switches (active switches)
Q3 through Q10 and associated switches Q1, Q2, Q11 and
K1 (relay) are controlled to select the range resistance which
will provide an appropriate full scale range (see table with
circuit schematic). Two switches concurrently act to enable
detection of an exact voltage drop across the range resistor
regardless of the resistance of the range selection switch
through which the range resistor current flows. For example,
both Q3 and Q4 turn on to sense the voltage drop and to
simultaneously route the DUT current flow through range
resistor R4 (1022). R4 and Q4 compose a feedback loop in
the Range Resistor amplifier on the selected range. The exact
voltage drop across R4 is routed through Switch Q3 (K1:
ON, Q11: OFF). The selectable 1022, 1002, 1kQ and 10kQ
range resistances are always placed in parallel with the
permanent 100k range resistance (R9 plus R10). The
100k$2 range resistance alone is selected by causing Q11 to
turn on, K1 to deenergize, and its contacts to open. The open
contacts of K1 also interrupt the error current flowing
through the stray capacitance in the range resistor circuit.
This eliminates any error current effect on the circuit being
used (R9, R10 and C3) on this range. In addition, to further
reduce the error current, Q1 and Q2 conduct the current
flowing through the stray capacitance of the relay contacts to
ground.
Table A. Range Resistor (Rr) and Source Resistor (Ro) Selections.
Range
1 2 3 4 5 6 1 8
Function
Full. 120Hz | 1000xH | 10.00mH|100.0mH | 1000mH | 10.00H | 100.0H | 1000H
scale 1kHz | 100.0xH| 1000uH {10.00mH {100.0mH | 1000mH| 10.00H | 100.0H
L 10kHz [ 10.00uH | 100.00H | 1000pH |10.00mH |100.0mH| 1000mH | 10.00H
Rr, Ro SER 10Q 10092 1kQ 10kQ 100kQ
PARA 10Q 100Q 1kQ 10kQ
120Hz | 1000pF | 10.00nF | 100.0nF | 1000nF | 10.00uF| 100.0xF | 1000uF |10.00mF
SF;';lllé 1kHz | 100.0pF { 1000pF | 10.00nF | 100.0nF | 1000nF | 10.00uF { 100.0uF | 1000uF
C 10kHz | 10.00pF | 100.0pF | 1000pF | 10.00nF | 100.0nF| 1000nF |{10.004F | 100.0uF
Rk, Ro PARA| 100kQ 10kQ 1kQ 100Q 10Q
SER 100k 10k 1kQ 100Q 100
Ful- | 120/
scale 1kHz/] 1000m& | 10.00©2 | 100.0©2 | 100092 |10.00k$2| 100.0kQ2 { 1000k | 10.00MQ2
R 10kHz
Rz, Ro SER 10Q 1002 1kQ 10k 100k
PARA 100 1000 1kQ 10k 100k
8-50