V. Cl and C2 provide relay drivers U2 and U3 with +10 VDC
and -10 VDC. These voltages are used for controlling the relays
on the Load Board.
2. Load Resistances
There are two load resistances on the Load Board, seen from
the ESU being tested. The first has a fixed load of 200 ohms,
and is used to measure the current leakage. The other is a vari-
able load resistance, which varies in steps of 25 ohms, from 10
ohms to 5200 ohms.
3. Fixed Load Resistance
The fixed load resistance is based on the two 100 ohms non-in-
ductive resistances (R17 and R18) connected in series. The total
load can be 350 W continuously.
4. Variable Load Resistance
The variable load resistance is also based on a non-inductive re-
sistance (R3 - R16). In addition, relays (K2 - K10) have been
used to offer the choice between different combinations of re-
sistances. You can therefore obtain any value between 10 and
5200 ohms.
5. Measuring Resistance and Attenuator
The measuring signal transmitted to the Sampling Unit is
drained over a 2.0 ohms resistance (R1) in series with the vari-
able load resistance (R3 - R16). Before the signal is transmitted
to the measuring device, it passes through a variable attenuator,
based on a 10 dB attenuator (R20 - R22) and a 20 dB attenuator
(R26 - R30). By connecting these attenuators in series, you can
obtain an attenuation of 30 dB.
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