Functions
1-1
IM 755601-01E
1
1.1 Block Diagram
Block Diagram
H
CUR
CPU
H
POT
L
POT
L
CUR
+
-
Constant current source
for measurement
A/D
converter
D/A
converter
Pre-amp
Comparator
Constant current source
for contact check
Diff. amp.
Analog section Digital section
A/D
interface
Display
interface
Printer
interface
Handler
interface
Communication
interface
Memory
Measurement Principle
A constant current is fed through the resistor under measurement from the H
CUR
terminal
to the L
CUR
terminal, and the voltage difference between the H
POT
and L
POT
terminals is
measured. Because the electric potential at the H
POT
terminal is controlled so that it is
equal to the circuit’s common electric potential, the resistance can be determined by
dividing the voltage at the L
POT
terminal by the current.
In the contact check that is performed before or after the measurement, a constant
current is fed from the H
CUR
terminal to the H
POT
terminal and from the L
POT
terminal to
the L
CUR
terminal. The voltage that appears across these terminals is compared with the
reference voltage that was set by the D/A converter to check the connection to the
resistor under measurement.
Since the analog section is insulated from the digital section (electric potential of the
case), the circuit is robust against noise, resulting in a stable measurement. In addition,
the handler interface is also insulated from the case in order to minimize noise influence.
Chapter 1 Functions
LOCAL key
GP-IB connector
