56-101-00930 Revision H
Page 8
D.
Hot Engine Testing
A hot engine causes thermocouples to generate a small potential which produces errors in
measured resistance values. This effect is natural for any type of resistance measuring
instrument.
The effect, however, can be avoided by taking two measurements:
1. With test leads connected in one polarity;
2. Reversing the lead connections for the second measurement.
Add the two readings and divide by two. (The true value is equal to the average of the two
readings.) The two readings must be taken in quick succession so that the thermocouple
temperature will be the same for both readings. If the thermocouples are too hot, the readings
will be too far from nominal to provide sufficient accuracy. In this case, wait for the engine to
further cool.
E.
Setting the System Resistance
1. Short the test lead clips together.
2. Set the FUNCTION switch to RES MEAS.
3. Set the RANGE switch to 200
Ω.
4. While pressing in the PTS pushbutton in, rotate the SYS RES knob to set the required
system resistance for the specific aircraft-under-test (refer to the specific AMM).
Note:
While the PTS button is held in, the TT1200A
shows the message “PTS”
on the
right of the display.
5. Release the PTS button.
Note:
The TT1200A replaces the message “PTS” with “SET” on the display.
3. POWER UP (INITIALIZATION)
A. At power up, the TT1200A displays a series of informational messages (refer to Figure 5),
including the unit’s software version (Ver ##.##.##.X); the available battery power percentage
(Battery ###%) and the calibration due date (Cal. Due, mm/yyyy).
Note:
If the calibration due date is less than 30 days before the calibration is needed, the
mess
age “Cal. In ## Days” displays. If the calibration due date has been exceeded,
the
unit displays “Cal Required”.
B. If no errors are detected during power up, the instrument enters normal mode. If the function
switch is in the RES MEAS or INS MEAS position, the message “Push PTM” displays.