Preston PS-425 - Operation; Preliminary Information; Error Codes; Pre-Testing

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CHAPTER 3
OPERATION
• Preliminary Information
Prior to using the PS-425 tester, the user should become familiar with the unit by reading
this manual and operating the tester independently of any other attached devices.
For greater accuracy, the indicator should be powered on for 15 minutes before use.
The test procedures described in this manual are general in nature, for reference
use only. The operator may substitute these procedures with others, as applicable to the
tests to be performed, the aircraft to be checked, or according to other documentation.
Error codes display as follows:
• The display will blink if altitude exceeds 35,200 feet, or if sensor temperature is
below 32F or 0C, or above 122F or 50C. Beyond these limits the accuracy should not
be trusted.
• Altitude displays “High Alt” if it exceeds 40,000 feet.
• “InverseP” will be indicated on the airspeed side if the static pressure exceeds the
pitot pressure by more than approximately 0.1 mbar. Due to its independent pressure
and static sensors, no damage will occur to the tester due to inverse pressure.
However, damage could occur to any system attached to the tester, therefore the
warning is to alert the user of the condition.
• “Over Pressure” will be indicated on the airspeed side if the pressure exceeds the
equivalent of 500 knots. Due to independent pressure and static sensors, no damage
will occur to the tester due to this condition. However, damage could occur to any
system attached to the tester, therefore the warning is to alert the user of the
condition.
Be very gentle with the precision metering valves. Do not close these valves with
unnecessary force, or internal damage to valve seating will occur. Normally, the valves
are closed when the operator senses resistance near the bottom of the internal stem travel.
Repeated over-torqueing of the valve will eventually cause damage to the valve seat.
• Pre-Testing
Pre-test the static system of the PS-425 test box according to the following steps:
1. Ensure the PS-425 is not connected to any external hoses or devices.
2. Close the Vacuum Control, Vacuum Vent, Crossbleed, Pressure Control, and
Pressure Vent valves.