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62
VII-3.
VII-3.1.
VII-3.2.
VII-3.3.
PM 2522
The anodes of the indicators are controlled via 4 electronic switches (TS303 up to TS306).
Via e.g.
R312 the negative scan pulse (in this case "SCAN 103") is applied to the base of
TS308, which converts the pulse into a T.T.L. level.
By 1C302 the pulse is inverted. The negative going edge of the pulse turns on TS303, thus
the anode of the indicator LED is connected to the +5 V supply and the LED will light up.
Senn
ee)
If the read-out exceeds
1999
two signals are supplied to the overrange detector.
These signals are:
DATA OUT
B = logical 1
SCAN
103
=
logical 0
Then the output of the detector becomes eo!
1 and blockes (via R311, TS307, IC302,
GR301 // GR303), SCAN 100, 10! and 103.
Only indicator LED 302 lights up and shows a 0 because the maximum display is 2046.
SUPPLY
The circuit diagram of the supply is shown
inFig. 20.
+5 V source
This source serves to supply the indicator
LED's and the digital IC's.
It is stabilized by a series-stabilisation circuit.
+ and
- 12 V sources
These sources serve to supply the analog section and the reference voltages for the ADC.
Stabilisation is performed by series-resistors and parallel zener diodes.
- 19 V source
The principle of stabilisation in this circuit is the same as that of the + and
- 12 V sources.
This voltage is used to supply IC104 and IC105.
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