is applied to U14 a BCD to 7 Segment Converter/Driver and to the display driver transistors Q1-
Q5.
7.3.5.2
Watts Display
The Analog to Digital conversion in the Model 2105 is allowed by U15 and its associated
components. The reference voltage applied to U15-2 is 1Volts. 1.2Volts are generated by D11
and adjusted by RV23. X1 generates a 100 kHz clock signal for U15-22; the frequency of the
oscillator allows the 2105 a conversion rate of 3 readings per second. The digital portion of U15
is applied to U16 a BCD to 7 Segment Converter/Driver and to the display driver transistors Q6-
Q10.
7.3.6 Decimal Point Positioning
Schematic 2105-070 sheet 8
The decimal points for both displays are selected by U17
7.3.7 Analog Multiplier
Schematic 2105-070 sheet 5
Analog multiplier U12 receives the output of voltage amplifier U9-6 and the output of either
U7-1, U7-7 or U8-6, depending on the selected current range.
The output from U12, which is proportional to the product of the signals at its two inputs, is
then scaled according to the selected voltage range by R44, R45, R46, R47, RV19, RV20 and
RV21.
RV18 adjusts the offset of the analog multiplier.
7.3.8 Range Selection
Schematic 2105-070 sheet 2-5 & 2105-072
The Ranges for both current and voltage are selected by U1 of the switch board, by configuring
relays RL1-RL8.
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