CM170407AMA
2. command an altitude value equal to ambient pressure;
3. reach the ambient pressure with controlled rates. Rate values are set as follows:
• the altitude rate is set from the Settings Menu; refer to the Calibration and
Adjustments manual for information;
• the airspeed rate is set to the current maximum airspeed rate limit;
• the AoA rate is set to the current maximum AoA rate limit.
When the ambient pressure is reached, the message: “Ambient pressure reached” will be
displayed, and the MPS49 will switch to “Ambient pressure reached” mode.
NOTE the VENT/SEAL valve on the case, if present, must be in the “VENT” position.
To interrupt the venting procedure, the Operator can press the MEAS, CNTR or HALT
keys.
For more information about the “Ambient Pressure Reached” mode, refer to chapter 4.2.3.
The airspeed value for step 1. is zero knots by default. For more information, refer to the
MPS49 Calibration and Adjustment Manual.
7.4 PRECISION MEASUREMENTS
7.4.1 OPERATION ON LARGE OR VERY SMALL VOLUMES
A precision measurement can only be obtained when the test lines pressures are stabilized.
Even though the stability of the controlled values in the CONTROL mode are very good, the
MEASURE mode should be used whenever a very precise measurement is required.
The MEASURE mode function should always be used if large test volumes are being
measured, such as with an older aircraft.
On the other hand, if the volumes are very small, the pressure changes could generate
thermal effects that may lead to long settling times.
The suggested procedure to follow in these cases is the following:
1. set the commanded values and wait for the MPS49 to reach them;
2. remain in CONTROL mode for some minutes, to allow the MPS49 to “actively”
stabilize thermal effects and other transients;
3. enter MEASURE mode by pressing the MEAS key;
4. remain in MEASURE mode for some minutes, to allow further stabilization;
5. measure the values;
6. return to CONTROL mode, by pressing the CTNR key.
7.4.2 DIFFERENTIAL PRESSURE ZERO ADJUSTING AND ULTRA-LOW SPEED FUNCTION
For the most accurate low Airspeed and AoA measurements, it is recommended that the
MPS49 differential pressure readings should be zeroed at the start of each new test
sequence, where a precision airspeed measurement is required. Zeroing ensures the best
accuracy of low airspeed and AoA measurement.
The Altitude channel of the MPS49 is not affected.
Zeroing is accomplished by setting the pressure differential between the pitot and static
lines (or Ps2 and static lines) to zero at the ambient pressure.
The procedure will be activated only at the following conditions:
D.Marchiori Copyright 31
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