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CALIBRATION PROCEDURES
The recommended calibration interval for the ALT-621 and ASP-621 indicators is
one year. If at any time during regular use the unit becomes unreliable or out of correct
operating calibration, it must be repaired and/or re-calibrated before continuing its use.
The ALT-621 is easy to calibrate. There are 4 set points used in the calibration of the
altimeter (the ALT-621-50 has 7 set points). This enables the altimeter to have a greater
degree of accuracy, allowing it to self-correct to the nearest calibrated set point.
Note: the calibration factors are stored in the microcontroller's EEPROM memory. This
memory does not need battery back-up. The calibration will not be lost when power is
removed.
1. Apply power to the ALT-621. Go to the mBar display, and allow the unit to warm up
for a minimum of 15 minutes.
2. Connect a known altitude pressure standard to the Vacuum Port.
3. Press the Exit and Leak Check buttons simultaneously. The display will change to:
Cal? No Yes
4. Press the Leak Check button to proceed with calibration, or select the Exit button to
exit out of the calibration mode without any changes being made.
5. At this point the display will read:
Goto
0 Feet
This is to notify the technician that the current calibration point is 0 feet. To select a
different calibration point, press the backlight button (the button will not activate the light
while in Cal mode).
There are 4 calibration points: 0, 10,000, 20,000, 30,000 (the ALT-621-50 has 3
additional set points at 40,000, 45,000, 50,000) feet. When the desired calibration point is
displayed, press the Units button.
The display will read:
CHAPTER 3
Altimeter Calibration Procedures
7
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