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At DC, output currents up to 18 A can be obtained without the temper-
ature trip operating but the output transistor heat-sink thermostats will
close at 88°C (190° F) and trigger the TEMPERATURE protective circuit-
ry.
4.5.4. Exciter
The EXCITER protection circuitry is triggered by:
a) Failure of fuses protecting the cooling fan or field windings,
b) Activation of the Exciter Body over-temperature thermostat (the
thermostat is set to close at 99°C (210° F)),
c) Attempted operation with the Exciter Head separated from the
Exciter Body,
d) Opening of an external pair of contacts connected to the shaker
system using the ACCESSORY connector.
4.6.
METERING AND MONITORING
The meter
rectifiers
used have a quasi- RMS characteristic. This gives
correct reading for sinusoidal and Gaussian distributed signals.
4.6.1. Voltage Metering
The output voltage of the 2707 is applied to the meter via a three-posit-
ion range selector switch. The ranges available are 3, 10 and 30 V RMS.
From the range selector the signal is applied via a unity gain isolating ampli-
fier to the quasi-RMS
rec.
t ifier. The output of the rectifier drives the VOLT-
AGE METER.
4.6.2. Current Metering
The voltage across the current feedback resistor is applied via a rarige
selector switch (3, 10, 30 A RMS and
±
10 A DC) to a voltage amplifier
with a gain of approximately 50. The measuring amplifier's output is recti-
40
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