Tektronix WFM5250, Руководство по обслуживанию

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Theory of Operation
Fan Control
There are multiple temperature sensors in different locations in the instrument.
The control processor reads the temperature sensors and sets a target speed for
the fans. The fan circuit holds the fan speed at the target by measuring the fan
tachometer output, allowing reliable operation at low speed. If a fan is not
turning, the circuit senses the stall and turns on a red LED (DS2 or DS3 on the
CPU board). The fans are tested at power on. If a fan fails, a message is shown on
screen and also entered into the diagnostic log.
Power Supply and Distribution
External power may be supplied by either the provided power module or a
customer-supplied 11-17 V DC power source. Protection circuits include a
self-resetting fuse, transient
fi ltering, and limiting, over- and under-voltage
protection and current limiting. A latching relay controls standby mode. The
nominal 12 V DC input powers 5 V and 3.3 V supplies. All three voltages are
distributed to the CPU and FPGA boards to power circuits as well as lower
voltage local regulators.
WFM5250 Waveform Monitor Service Manual 7