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1. . Safety instructions
The measurement amplifier conforms to all safety regu-
lations for electrical measuring, control, monitoring
and
laboratory
equipment,
DIN EN 61010, Section 1, and the equipment has been
designed to meet protection class I. It is intended for
operation in a dry environment, suitable for the opera-
tion of electrical equipment and systems.
Safe operation of the equipment is guaranteed, pro-
vided it is used correctly. However, there is no guaran-
tee of safety if the equipment is used in an improper or
careless manner.
If it may be assumed for any reason that non-hazardous
operation will not be possible (e.g. visible damage), the
equipment should be switched off immediately and
secured against any unintended use.
In schools and other educational institutions, the op-
eration of the AC/DC power supply unit must be super-
vised by qualified personnel.
•
Before using the AC/DC power supply unit for the
first time, confirm that the specifications printed
on the rear side of the housing are compatible with
the local mains voltage.
•
Before using the AC/DC power supply unit for the
first time, check the housing and the mains lead for
any damage. In the event of any malfunc-
tion/operational defect or visible damage, switch
off the unit immediately and secure it against unin-
tended use.
•
The instrument may only be connected to the
mains via a socket that has an earth connection.
•
Before making any connections, check the experi-
ment leads for damaged insulation and exposed
wires.
•
Never cover the air vents in the housing. This is
necessary in order to ensure sufficient circulation of
air required for cooling the internal components of
the equipment.
•
The equipment may only be opened/repaired by
qualified and trained personnel.
2. Description
The measuring amplifier can be used for measuring
very small voltages, currents and charges.
The design involves a highly sensitive DC amplifier
utilising the modulation principle and featuring silicon
varicap diodes. The voltage to be measured is con-
nected to a bridge composed of varicap diodes along
with a constant high-frequency voltage. The modulator
then outputs a high-frequency signal that is propor-
tional to the voltage being measured. This signal is then
amplified by a high-frequency amp. The signal is de-
modulated by a rectifier that is controlled from the
modulation generator by means of an in-phase control
as
specified
under
signal. Additional amplifiers output the signal to termi-
nals for a display instrument. Due to having been in-
verted twice, the input and output signals are in phase.
The direct input of the amplifier (terminal "I Q") can
handle voltages of up to 300 V for a prolonged period,
so that no damage due to overvoltage need be expected
in the course of normal operation. Caution: voltages in
excess of 300 V may only be applied to terminal "U"
(10) with a measuring range of 100 V/1 V and under no
circumstances to terminal "I Q".
Changes in the measuring range alter the feedback by
decades. This also changes the gain factor (and the
measuring range) in decade steps.
The input signal may be positive or negative. The out-
put voltage is in-phase with the measured voltage. A
toggle switch (6) can be used to alter the polarity of the
output. For a positive input voltage, set the switch to
the right, for a negative input set it to the left.
Any DC instrument can be used to display the results.
An output of 1 V to the display instrument corresponds
to the value given by the range setting of the amplifier.
Generally instruments with 10 V or 3 V ranges will be
used for display purposes. The limit of the scale thus
corresponds to 10 times or 3 times the number indi-
cated on the front panel of the amplifier. Display in-
struments with ranges of 1 V or less should only be used
when utmost sensitivity is required (e.g. for 100 μV or
-11
10
A). Using 10 V or 3 V instruments allows a finer
granulation of ranges to be achieved (1 : 0.3). It is not
necessary to adapt the display.
The maximum output to the display is 12 V so that
instruments in the range 10 V/3 V should not be sub-
jected to damage due to overvoltage. Overloading or
short circuits across the output will not damage the
amplifier.
In highly sensitive ranges there may some drifting of
the zero point. This can be corrected using the "Offset"
knob (7). For this terminal "U" (10) must be connected to
the ground terminal (11) (via a conductor or a zero-
voltage generator).
The "Discharge" button (12) can be used to short circuit
the amplifier.
The operating voltage of the amplifier is +15 V and -15
V. This is supplied by a built-in stabilised power supply.
The supply voltage can be connected to external cir-
cuitry (e.g. measuring bridges) via the +15 V and –15 V
sockets. They have a common zero connected to
ground. Resistors (10 kilohms) limit the load capacity of
the voltage output (no short circuit hazard).
The apparatus U8531401-115 is for operation with a
mains voltage of 115 V (±10%), and the unit U8531401-
230 is for operation with a mains voltage of 230 V
(±10%).
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