Chapter 6 – Maintenance
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6.2.4.2
On-Off Logic
Once the on-off logic senses a press of the ON/OFF key, it
powers up the battery-driven 12V power supply. This supply, in
turn, powers two additional supplies, 5V and -12V.
6.2.4.3
Power Supplies
All power supplies reside on the main PCB. There are three, as
explained in this section.
Power Supply, 12V - The 12V supply powers the other
supplies, the Velocimeter sensors and, through a microprocessor-
controlled power switch, the photocell probe.
The photocell power switch allows the microprocessor to turn
off the photocell when it is not needed, saving power and
extending battery life. The 12V supply also powers the analog
filters, azimuth conditioning, and contrast circuitry.
Power Supply, 5V - The 5V supply runs the screen display
and digital circuitry, including the microprocessor and memory.
Power Supply, -12V - The -12V supply powers the
Velocimeters and analog filters, azimuth conditioning, and the
contrast circuitry. The -12V sensor power currently has a limit of
20 mA. It can take a continuous short without damage. The
effect of a short circuit on the microprocessor and display
depend on the battery voltage.
6.2.4.4
Short-circuit Protection
All supplies help operate the serial communications hardware.
Fuses protect the batteries and sensor power from short circuit
damage.
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