1261B User Manual
Racal Instruments
Ó
1995
Understanding The 1261B 6-5
Cooling air is exhausted through the top of the mainframe in the
1261B Bench Top mainframe.
Cooling The Power
Supply
The power supply assembly contains a speed controlled fan for
its own internal cooling. Filtered air enters through the one side
of the mainframe and exits at the opposite side after passing
through the power supply.
Standard
Monitoring System
The Standard Monitoring System (SMS) performs temperature
monitoring on each slot, fan speed sensing and control, power
supply voltage and current monitoring. System status is
reported via a front panel annunciator for Voltage, Current,
Airflow and Temperature alarm conditions.
SMS Fan Speed
Monitor
A TTL pulse train at the speed (RPM) of each fan is output to
rear panel Monitor Connector J410. The fans output 2 pulses
per revolution.
The front panel AIRFLOW LED is green under normal conditions
and red during a fault. A fault is indicated when the fan
speed is < 15 Hz or > 300 Hz.
SMS Fan Speed
Control
The speed of the module cooling fans is controlled by either the
slot with the highest absolute temperature or the highest
temperature rise.
If the absolute temperature of any slot e40
E
, the fans
operate at full speed. If the temperature rise across any module
slot exceeds 10
E
C, the fans operate at full speed.
SMS Fan Speed
Switch
Switch S3 mounted on the SMS rear panel allows user to select
between
maximum
fan speed or
variable
fan speed.
SMS Temperature
Monitor
The exhaust air temperature
of each slot is measured by 13
passive thermistors. An additional thermistor monitors the intake
air temperature.
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