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MODEL 616
4 - 1 .
GENERAL.
This s e c tion contains information to
describe the Model 616 circuit operation.
cuitry i s located on five print�d circuit boards .
The circuits are arranged in functional modules to
facilitate troubleshooting and servicing.
shielded input section houses the elec trometer ampli
fier and range switch .
4- 2 .
ANALOG C IRCUITRY
a .
simplified form in Figure 2 4 .
25764E) .
The input signal applied be tween HI and La
(Jl20) is amp lified by the input MOS - FET amplifier
composed o f transistors QlOlA and Ql01B.
QI02A and QI02B are used for over-voltage protection
(base-emi tter connected ) .
provides high gain (approx.
meter amplifier section.
internal zero adjus tment used for calibration pur
poses.
Potentiometer Rl19 is a front panel ZERO
control with adjus tment capability of approximately
3 mV .
Transistors Ql05 and Ql06 are complementary
output s tages which provide a maximum of ±200 volts
(JI18 ) .
a t the "Xl" terminal
lifier is connected in a unity-gain configuration.
�
Input r
sis tance between HI and LO is greater than
2 x 10
ohms in "VOLTS" function.
IN
INPU T
A MP
RA NGE
1175
4 .
S E CT I O N
The cir
The 6 16 ' s
This amplifier A l is shown in
(Refer to schematic
Trans istors
Integrated circuit QA101
1 0 0 , 0 0 0 ) for the electro
Potentiometer Rl23 is an
The elect rome ter amp
L SI
CHIP
FIGURE 2 3 .
Overall Block D i agram of Model 6 1 6 .
T H E O R Y O F
O P E RAT I O N
b.
Shunt (NORMAL ) Mode Operation.
schematic 25764E ) .
trometer amplifier is connected as a unity-gain
buffer amplifier with an input resis tance greater
than 2 x 1 0 14 ohms .
ed in decade steps from lO l l ohms to 10 ohms by
selecting the desired ahudt resistor on the AMPERE
positions of the RANGE switch.
through RIll are switched into the cir-cuit shunting
the HI and LO termina l s .
nected in the circuit is numerically the reEiprocal .
of the AMPERE posit ion selected (that is 1 0 l l A
10 1 1 0 resistor ) .
c .
Feedback (FAST) Mode Operation.
schematic 2576 4 E ) .
meter amplifier is connected in a feedback amplifier
configurat i o n .
the range element
ed between HI and GUARD .
function is det ermined by the f eedback resistor and
the open-loop gain, whe r e :
R i
For example , on IO -ll A range , R i
voltage drop for full range input current would be
less than 20 microvo l t s .
PO L A RI T Y
DE TE C TOR
DRIVERS
THEORY OF OPERATION
(Refer to
In the IINORMAL" mode,
Input resistance may be decreas
Resistors RlOl
The shunt resistor con
(Refer to
In the "FASTII mode,
In AMP ERE , COULOMB , or OHMS functions,
(resistor or capacitor) is connect
Input resis tance on AMPERE
R F (K =
50 , 000 minimum)
=
2 x 10 6 1L
A -D
CONVERTOR
DISPLA Y
the elec
�
the electro
Input
21
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