Fluke PM3082 Service Manual page 59

5.1 -4
Calibrator
This circuit is used for probe adjustment. It is built up around triple analog multiplexer D1151. The
sections D1151/1,2,10,15 and D1151/3,4,5,9 form a 2 kHz oscillator. The third section
D1151/11,12,13,14 switches in the 2 kHz rate of the oscillator. The oscillation principle is now
explained with the simplified diagram in the figure.
Figure 5.11 Simplified diagram of CAL generator
The start is in the situation as given in the figure. C1151 charges from +12V via R1151 and the switch
contacts 15 and 2. After some time the voltage across C1151 reaches the digital "High" level and the
switch contacts go to the opposite position. This causes C1151 to discharge to 0V via switch contacts
3 and 4 and R1152. Via switch contacts 15 and 1 and R1153 a gap is created between the switching
moments. The charging/discharging process makes pin 11 high and low at a 2 kHz rate. This
connects voltage divider R1156/R1157 and R1158, R1159 with + 10VREFor leaves it floating in the
2 kHz rate.
5.1.1.3 Preamplifiers
Diagram 6, 7
The preamplifiers for channel 1 and 2 and associated current sources are given in diagram 6.
Diagram 7 gives this for channel 3 and 4. Channel 1,2, 3 and 4 are identical, therefore only channel
1 is explained.
The output signals AT 10UT 1 and AT1OUT0 from the channel 1 attenuator are applied to pin 3 and
5 of amplifier IC D1201. The balanced output signal of this IC is available at pin 18 and 19. This signal
is routed to the Y-functions section via the level shifters V1201 and V1202.
+12V
UNIT DESCRIPTIONS