Jeulin 282009 Manuel D'instructions page 9

Measurements
Power level indicator
Réf :
282 009
ENGLISH
1.3 Technical characteristics
1.3.1 Operating principle
The input voltage is compared with a reference voltage and displays the result
by lighting up LEDs (from 1 to 11), proportionally to the ratio between the input
voltage / reference voltage.
The reference voltage is corrected to zero in order to obtain a significant
illumination.
The input signal, rectified by diodes and then amplified, is input into two
special integrated circuits installed in cascade. This signal is amplified using a
potentiometer (adjustable with a screwdriver) to obtain a full scale adjustment.
A variation of the input voltage causes LEDs to light up or go off according to a
linear scale.
The last LED remains lit up to show the maximum level that was reached. A
reset (RAZ) linearly reduces the maximum voltage reached to 0 V.
Therefore, the result is an analogue display device capable of displaying the
variation of the input voltage.
The power level indicator is not a wattmeter. It is a simple instrument that
qualitatively provides information about power concepts.
1.3.2 Usage conditions
The power level indicator is specifically used for experiments carried out with
the associated equipment: reversible demonstration alternator (ref. 292 075),
demonstration alternator model (ref. 292 077), water and air turbine kit (ref.
282 006), ecological lamp (ref. 332 016), hydroelectric power station (ref.
282 005), etc. It can also be used for other voltage sources less than 30 V AC
and 15 V DC.
The advantage of the power level indicator is that it can make a comparison of
electrical powers available at different alternator terminals or at alternators
moved by different mechanical actions.
Thus, the comparison is only meaningful if the power level indicator is
connected to the terminals of each alternator at no load (the current that
passes through the power level indicator is of the order of a few micro-
amperes). The electrical power available at the alternator terminals is thus
proportional to the induced e.m.f.
In the case in which the power level indicator is used under load (for example
incandescent lamp), the electrical power actually output to the circuit is
displayed. This is less than the available power due to Joule effect losses in
the circuit (load and resistance of the alternator winding).
In conclusion :
The power level indicator displays:
- at no load, the available power (potential).
- under load, a real power.
These two powers cannot be compared.
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