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Les langues disponibles
РМ 2522
59
VII. Circuit description
SERVICE DATA
VII-1.
Vile 1: 1.
МЕ! 2
УЗ.
ANALOG
SECTION
The analog section of the instrument serves to convert all modes to be measured into a voltage
level of + or - 2 V in order to obtain a maximum display.
This voltage is supplied to the digital section, which has a constant input - sensitivity of 2 V
for maximum display.
DC voltage circuit
The input circuit for direct voltage measurements is shown in Fig. 28.
The attenuation for the various ranges is given in the table below.
Range
Attenuation
Input amplifier at end-of-range
200 mV
lx
02 V
я
1х
2
V.
20V
100 x
O2
200
V
100 x
2
V
1000
V
10,000 x
(ORY
The attenuated input voltage is supplied to an amplifier, the gain of which is switchable
between 1 x and 10 x by means of the range switches. The output of the amplifier is always
2 V at end-of-range and is supplied to the analog digital converter.
AC voltage circuit
The circuit for alternating voltage measurements is shown in Fig. 28 and is in principle equal
to the circuit for direct voltage measurements.
However, for a.c. behaviour the attenuator resistors are shunted by capacitors.
After being amplified 1 x or 10 x the a.c. voltage (always 2 V at end-of-range) is supplied
to an a.c. - d.c. converter.
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The direct voltage output of this converter is supplied to the analog-to-digital converter.
Direct and alternating current circuit
The circuit of current measurements is shown in Fig. 28.
The current to be measured is converted into a voltage by means of shunts (R201 ... R205).
The voltage across the shunt is 0.2 V at end-of-range, thus the 1 x/ 10 x amplifier is set to
its 10 x position in all ranges. For alternating currents the a.c. - d.c. converter is switched
in after the 10 x amplifier.
The current ranges are protected by a 2.5A
fuse (VL2). If the voltage across the shunts,
caused by a too high current or by supplying an excessive voltage to the current input, is
larger than 1.4 V the diodes GR118- 119 or GR120- 121, depending on the polarity, become
conductive. The current through the diodes is restricted by R113 up to R116.
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