Fluke 76 - Measuring Low Resistance (Lo-Ohms)

76
Service
2-8
A/D
CONTROL
131.072 kHz
CLOCK
MICROCOMPUTER
CONTROL
SWITCH
NO.
1
2
3
4
5
AUTO
ZERO
ON
ON
INTE-
GRATE
ON
READ
+INPUT
ON
ON
READ
–INPUT
ON
ON
HOLD
ON
ON
+
–
VOLTAGE
REFERENCE
+
BUFFER INTEGRATOR COMPARATOR
3
4
5
1
INPUT
VOLTAGE
2
+
+
–
REFER TO WAVEFORM
COMPARE
8 MINOR CONVERSIONS, 200 mS
(1 FULL RESOLUTION CONVERSION)
AS SEEN AT INTEGRATOR OUTPUT
SAMPLE #1
SAMPLE #2 SAMPLE #8
REPEAT
HOLD
READ
RAMP
INTEGRATE
RAMP
ZERO
BASELINE
AUTO ZERO
16.7
mS
8.33
mS
–
l4f.eps
Figure 2-4. A/D Converter
Microcomputer Control 2-14.
A microcomputer, integrated within U4, controls the various instrument functions and
drives the display. The position of the rotary switch, S1, is decoded by the
microcomputer from the three inputs F0, F1, and F2. All function modes, input ranging,
signal routing, active filter enable, a/d timing and mode are controlled by the
microcomputer.