HP 3478A Technical Manual page 95

7-F-1. INTRODUCTION 7-F-1. INTRODUCTION
7-F-2. The following Service 7-F-2. The following Service Group has the
detailed description of the operating circuitry of the -hp- detailed description of the operating circuitry of the -hp-
Model 3 Model 3478A M 478A Multimeter. ultimeter. The genera
plains the purpose of each operating block of the 3478A plains the purpose of each operating block of the 3478A
Simplified Block Diagram (show Simplified Block Diagram (shown in
detailed description explains the circuitry in each detailed description explains the circuitry in each
operating block. operating block.
7-F-3. 7-F-3. GENERAL BLOCK GENERAL BLOCK DIAGRAM
OPERATION OPERATION
7-F-4. 7-F-4. Refer Refer to to Figure 7-F-1 Figure 7-F-1 for the following discussion
of the 3478A's General Block Diagram Theory Of of the 3478A's General Block Diagram Theory Of
Operation. Operation.
7-F-5. 7-F-5. The 3478A The 3478A can be can be separated
areas, Floating areas, Floating Common an Common and Cha
Floating Common has the cicuitry which does the ac, dc, Floating Common has the cicuitry which does the ac, dc,
and and ohms ohms measurements. measurements.
Circuitry, A/D Converter, A/D Controller, Ohms Cur- rent Circuitry, A/D Converter, A/D Controller, Ohms Cur- rent
Source, and Source, and AC AC to to DC
Common is used to calculate and display readings, Common is used to calculate and display readings,
controls the Floating Common Circuitry, and sends and controls the Floating Common Circuitry, and sends and
receives remote in receives remote information. formation.
Controller (the main CPU used with the Control ROM) Controller (the main CPU used with the Control ROM)
and associated and associated circuitry. circuitry. Communications bet
Chassis Common and Floating Common is done by the Chassis Common and Floating Common is done by the
Isolation Circuitry. Isolation Circuitry.
7-F-6. 7-F-6. The following The following paragraphs
measurement sequence. measurement sequence.
a a . . S S e e t t - - u u p p . . The 3478A receives range and function The 3478A receives range and function
in- formation from the front panel (local) or over the in- formation from the front panel (local) or over the
T T i i t t l l e e
Introduction ......... Introduction
General Block Diagram Theory Of Operation..... General Block Diagram Theory Of Operation..... ...7-F-3
Theory Of Theory
General General ........
Input Circuitry................................................. ... ... 7-F Input Circuitry.................................................
Ohms Current Ohms
AC AC to to DC
A/D Converter A/D
3478A Logic Circuitry..................................... 3478A Logic Circuitry..................................... ... ... 7-F
Chassis Common Circuitry Chassis Common
Isolation Logic.............. Isolation
Floating Common Circuitry Floating Common
Power Supplies.............. Power
Group has the general and general and
The general description l description ex-
n in Figure 7- Figure 7-F-I). F-I). The
DIAGRAM THEORY THEORY OF
for the following discussion
separated into tw into two major
d Chassis Common. ssis Common. The
It It consists consists of of the the Input
DC Converter. Converter. The Ch The Chassis
It It consists of consists of the M
Communications between th
paragraphs explain explain a a typical
SERVICE GROUP F SERVICE GROUP F
THEORY OF OPERATION THEORY OF OPERATION
Service Group F Contents Service Group F Contents
.................. .................. ..................
Of Operation Operation ........ ................. ..................
................. .................. .................. ..................
Current Source............ Source.....................
DC Converter........... Converter....................
Converter........ ................. .................. ..................
Circuitry ........
Logic....................... ..................
Circuitry ........
Supplies....................... ..................
HP-IB (remote). HP-IB (remote). The information is received by
Controller which then passes the information over the Controller which then passes the information over the
Isolation Isolation Circuitry
Controller then sets up the measurement circuitry to do Controller then sets up the measurement circuitry to do
ex- the the desired desired measurement.
sends information to the display to show the selected sends information to the display to show the selected
function and ra function
The
3478A's different functions. 3478A's different functions.
b. b. DC
DC Volts Function is selected. DC Volts Function is selected.
OF
configuration by t configuration
depends on the range selected. depends on the range selected.
(dependent on the range) to IOV (for full scale in- puts) (dependent on the range) to IOV (for full scale in- puts)
o major
which is then applied to the A/D Converter. which is then applied to the A/D Converter.
The
Input
digital information and transfers it to the A/D Controller. digital information and transfers it to the A/D Controller.
The A/D Controller then processes the information and The A/D Controller then processes the information and
assis
transfers it over the isolation transformers to the Main transfers it over the isolation transformers to the Main
Controller. Controller.
the Main ain
calculates calculates the corr
ween the e
calculated by using the zero measurement (see step f) calculated by using the zero measurement (see step f)
and the calibration constant(s) (which are stored in the and the calibration constant(s) (which are stored in the
Calibration RAM). Calibration RAM).
typical
panel to be displayed and sent over the HP-IB (if the panel to be displayed and sent over the HP-IB (if the
3478A is in remote and addressed to talk). 3478A is in remote and addressed to talk).
7-F-1 7-F-1
P P a a r r a a g g r r a a p p h h
.................. .................. ............ ... ...7-F-1 ...7-F-1
...7-F-3
.................. ................ ....... ....7-F-7 ....7-F-7
.................. ............... ...... ....7-F-8 ....7-F-8
7-F-10
.................. ............... ...... ... ... 7-F 7-F-17
.................. .................. .......... . .. ... . 7-F 7-F-25
.................. ............. .... .. ... . 7-F 7-F-31
7-F-50
................. .................. .......... . .... .... 7-F- 7-F-55
.................. ................ ....... ... ... 7-F 7-F-71
................. .................. ........... .. ... ... 7-F 7-F-75
.................. ............. .... .... .... 7-F-8 7-F-83 3
The information is received by the Main
Circuitry to to the the A/D A/D Controller.
measurement.
and range. nge. The following takes place The following
DC Vo Volt lts Fu s Func ncti tion on. . The following occurs if the
1. 1. The Input Circuitry The Input Circuitry is set up to a cert
by the A/D he A/D Controller circuit Controller circuitry.
2. The input voltage is amplified or attenuated 2. The input voltage is amplified or attenuated
3. 3. The A/D The A/D Converter Converter changes t
4. The Main Controller takes the information and 4. The Main Controller takes the information and
the correct reading ect reading. . The correct
5. 5. The corrected reading is t The corrected reading is then sent to the front
TM 11-6625-3071-14 TM 11-6625-3071-14
-10
-17
-25
-31
-50
55
-71
-75
the Main
Controller. The A/ The A/D D
The Main Cont The M ain Controller a roller also
takes place in the in the
The following occurs if the
is set up to a certain gain ain gain
ry. The gain The gain
changes the volt he voltage to age to
The correct reading is reading is
hen sent to the front
lso