Piper Aircraft Corporation Malibu Mirage PA-46-350P, Airplane Maintenance Manual

Page: 1465 / 1956

PAGE 7
Feb 28/07 7H19
77-20-00
PIPER AIRCRAFT, INC.
PA-46-350P, MALIBU MIRAGE
MAINTENANCE MANUAL
3. Cylinder Head Temperature (CHT) Scanner
The following information describes the Cylinder Head Temperature Scanner used in the Malibu Mirage.
This scanner, when connected to the cylinder head temperature gauge and six resistive temperature
probes, scans the six probes, determines the hottest cylinder, connects that probe to the gauge and
outputs a signal that can be used to indicate which cylinder is the hottest.
A. Description
(1) Electrical
The Cylinder Head Temperature Scanner gives a discrete output to indicate which cylinder out
of six is the hottest. The scanner, momentarily disconnects the CHT gauge and connects all of
the probes to measuring circuits that measure the resistance of each probe. The scanner then
makes appropriate determinations based upon those measurements, reconnects the gauge to
a selected probe, and outputs a discrete output.
An external cycle switch may be used to manually select which cylinder head temperature
probe is connected to the gauge. Momentarily grounding the proper pin will step the scanner to
Cylinder No. 1. Cylinder No. 1 will be displayed on the gauge for approximately 8 seconds (the
"heartbeat" period). Upon the next heartbeat the gauge will again display the hottest cylinder.
Again momentarily connecting this pin to ground before the heartbeat will step the scanner to
Cylinder No. 2. Now Cylinder No. 2 will be displayed on the gauge for the heartbeat period.
Upon the next heartbeat the gauge will again display the hottest cylinder. Continuing to
momentarily connect this pin to ground before the heartbeat will step the scanner to the next
cylinder in rotation (3, 4, 5, 6, etc.). By maintaining a ground on this pin, any particular cylinder
being displayed will continue to be displayed until the ground is removed and the heartbeat
cycle occurs. Heartbeat will not occur so long as this pin is grounded.
Six discrete lamps are used to display the hottest cylinder (1 through 6), and are mounted
adjacent to the external cycle switch.
An alarm output is also generated when any cylinder is over the preset limit for a "Hot"
cylinder. This alarm output is interfaced with the Exceedance Audio Alert Horn. When the
external cycle control is in use, the alarm will maintain the last condition displayed when in the
automatic mode, regardless of the current condition during the manual external cycling.
(2) Physical
The Cylinder Head Temperature Scanner is a single unit with an integral heat sink and requires
no forced cooling. The internal circuits are arranged on two printed circuit boards mounted
parallel to the each other. All connections between boards are made by means of two part
connectors.
B. Troubleshooting
In the event of a detectable scanner failure, the scanner will automatically connect the gauge to the
probe for cylinder number 3.