Thermo Scientific 7451 Operating And Maintenance Manual page 29

Section 2
Set-Up and Operation
Temperature Tracking
2-16 Controlled Rate Freezer
During a Run when the chamber temperature is higher or lower than the
programmed temperature by a pre-determined amount for a pre-
Alarm
determined time period (as set in Section 3), the controller will:
• Sound a tracking alarm,
• Light the Alarm LED,
• Sound the audible alarm at a 75% On duty cycle (2 second period),
• Show "Temperature is High" or "Temperature is Low" depending on
conditions, (compared to the programmed temperature) on the fourth
line of the display, alternated with the normal fourth line display
contents at a 2 second rate,
• Mark the strip chart recorder and thermal printer at 50°C to document
on paper where the alarm occurred,
• Continue the profile run without interruption.
This is a "self clearing" alarm. When in the alarm condition, the audible
alarm can be silenced by one depression of the Silence key but the Alarm
LED will continue to flash and the alarm message be displayed while the
alarm condition is present. When the alarm condition is resolved, the
Alarm LED will stop flashing and the audible alarm will silence (if the
Silence key has not already been pressed). However, the alarm message will
remain on the fourth display line until the Silence key is pressed a second
time.
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