Unity Gain - Keithley 616 Instruction Manual

THEORY OF OPERATION
d . Zero Check Operation.
25764E). The front panel ZERO CHECK switch (S102)
operates a relay solenoid (KIal) when set to ZERO
CHECK. In the energized state (as shown on the
schematic) the relay contact is closed.
contact makes a connection between the FET amplifier
(Jl19)
input and GUARD
1.
In this mode, a connection is
made between resistor R124 and input LO.
that the input HI terminal is shunted to LO by a
10 8 Q resistor (Rl12).
2. Fast Mode. In this mode, a connection is
made between resistor R124 and GUARD.
that the input H I terminal remains connected to
the electrometer amplifier input.
or COULOMB functions , the feedback element is
shorted out so that no voltage can be generated
across the amplifier feedback.
Remote zero check capability is provided
when the Model 6162 is connected to the
616. The connection at Pl13D is in para­
llel with the front panel switch.
front panel ZERO CHECK switch should be off
when using the remote zero check feature.
e.
in Figure 24. (Refer to schematic 257 7 6D).
ond stage variable-gain amplifier is composed of a
FET stage ( Q 301A. Q 301B) and an integra,ed circuit
Q A301.
Gain is determined by resistors RN301 (A to
F) where :
INPUT
22
(Refer to schematic
The closed
as follows:
Notice
Notice
In AMPERE, OHMS,
NOTE
The
This amplifier A 2 is shown
The sec­
R
Gain F (See Table 4 - 1 . )
=
R I

UNITY GAIN

BUFFER
FIGURE 24 . Simplified Diagram of Amplifier Section .
TABLE 4-l.
Voltage Gain
Sensitivity R
V
. 0 1000 500K Q
V
500KO
. 1000
1. 000 V 500KO
500K O
10.00 V
500KO
100. 0 V
1. Gain Setting. Resistors RN30LA to RN301F
are connected in parallel combinations to achieve
the proper gain. On the 10 mV sensitivity set­
ting, the gain is determined by the series com­
bination of resistors RN30lB and R303.
meter R303 is a calibration adjustment for the
10 mV sensitivity setting.
sensitivity, the resistors are switched into the
circuit as shown in Table 4 - 2.
R304 is a calibration adjustment for the
sensitivity setting.
TABLE 4-2.
Gain Switching
Sensitivity F eedback Resistors Used For Gain Set.
50 MQ (RN301B
. 01000V
V
(RN301B + R303//RN30lC)
5 MQ
. 1000
500 KQ (RN30lB
1. 000 V
(RN301B
10.00 V 50 Kn
KQ
(All above//RN301F + R304)
5
100. 0 V
SENSITIVITY
SETTING
MODEL 616
�
Gain
r
50 Mn
100
10
5 M O
500 KQ 1
50 KQ 0 . 1
5 K n
0.01
Potentio­
For each succeeding
Potentiometer
lOOV
+
R303)
R303//RN301C//RN30lD)
+
R303//RN30 1C//RN301E)
+
1
VOLT
OUTPUT
11 7 5