PRESSURE CONTROLLER CPC21 WITHOUT HAMILTON STANDARD SB 21-66PRESSURE CONTROLLER CPC22 AND CPC21 WITH HAMILTON STANDARD SB 21-66NO. 2 AIR DATA COMPUTER ON AIRPLANES WITH SB 21-1119
521  Pressure Controller Test Pin Function Chart 
May 01/99  Figure 501  21-31-0 
Page 508A 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

B.  Equipment and Materials
(1)  
A specific voltage and tolerance range is provided for the tests. All tests shall be conducted using the most accurate meter available. A Simpson meter 260, model 4M is acceptable for all readings with the exception of voltage readings in the millivolt level. For outputs in the millivolt level, a portable vacuum tube voltmeter or digital voltmeter should be used (accuracy + 0.020 volts dc).

(2)  
When checking test pin M, step N.(l), the use of an instrument other than a Simpson meter 260 4M may result in ac voltage readings significantly lower than the specified tolerance, due to the filtering characteristics of the instrument.

(3)  
A breakout box (P/N F80206-l) may be used on Model CPC-22 Cabin Pressure Control Unit with the above meters.

C.  Standby Rate Potentiometer Wiper (Test Pin A or Test Jack 1)
(1)
Place CABIN RATE control on pressurization control panel at the pip mark (

 ). Check that voltage between test pin A and test pin N is 0.024 +0.010 volt dc or between test jack 1 and test jack 13 is 0.056 ±0.010 volt dc.

(2)  
Slowly move control knob from DECR to INCR and back to DECR. Check that there is a smooth linear change in voltage between test pin A and test pin N, ranging from 0.005 +0.005 volt dc (DECR) to 0.165 +0.050 volt dc (INCR) or between test jack 1 and test jack 13, ranging from 0.008 ±0.005 volt dc (DECR) to 0.350 ±0.050 volt dc (INCR).

D.  Flight Altitude Potentiometer Wiper (Test Pin B or Test Jack 2)
(1)  Set FLT ALT control on pressurization control panel to the following settings and check for the corresponding voltages.
Altitude (feet) Volts dc (± 0.1)
 +4,000 +16.65 +12,000 +12.26 +20,000 +8.86 +36,000 +4.33
NOTE:  Check that FLT ALT control knob releases after it is pushed in to make a new setting. It should rotate freely without changing the counter numbers.
E.  Land Altitude Potentiometer Wiper (Test Pin C or Test Jack 3)
(1)  
Rotate LAND ALT control on pressurization control panel from -990 thru 000 feet and check for a smooth linear change in voltage.

(2)  
Set LAND ALT control on pressurization control panel to the following settings and check for the corresponding voltages.

565 
Jun 20/91  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  21-31-0 Page 509 

Altitude (feet)  Volts dc (± 0.1)
-500 +8.31 +400 +7.68 +1,400 +7.00 +2,400 +6.34 +3,400 +5.70 +4,400 +5.08 +5,400 +4.48
F.  Auto Mode Barometric Correction Potentiometer Wiper (Test Pin D or Test Jack 4)
(1)  
Rotate CABIN PRESS BARO SET knob through its range and check for a smooth and continuous voltage change. Set knob at 29.92 in. Hg (1013 mbs).

(2)  
Measure and record the voltage at test pin D or test jack 4.

(3)  
Obtain and record the current field pressure for the day.

(4)  
Refer to Fig. 502 and read the barometric correction potentiometer voltage for the field pressure.

(5)  
Check that voltage at test pin D or test jack 4 is within + 0.025 volt of the voltage that you read from Fig. 502.

G.  Cabin Altitude Potentiometer Wiper (Test Pin E or Test Jack 5)
(1)  
Rotate CAB ALT control on pressurization control panel from -990 feet through 000 feet and check for a smooth and continuous voltage change.

(2)  
Set CAB ALT control on pressurization control panel to the following settings and check for the corresponding voltages.

Altitude (feet) Volts dc (± 0.05)
Test Pen E Test Jack 5
+400 -5.76 -7.68 +1,400 -5.25 -7.00 +2,400 -4.76 -6.34 +3,400 -4.28 -5.70 +4,400 -3.81 -5.08 +5,400 -3.36 -4.48 +6,400 -2.92 -3.89 +7,400 -2.50 -3.33
H.  Standby Mode Barometric Correction Potentiometer Wiper (Test Pin F or Test Jack 6)
(1)  
Select STBY mode and place FLT-GRD switch to FLT. Rotate CABIN PRESS BARO SET knob through its range and check for smooth and continuous voltage change. Set knob at

29.92 in. Hg (1013 mbs).

(2)  
Record field pressure and determine the corresponding voltage from chart (Fig. 502). 
　
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