barfield DC400A - Conductance to Megaohm Conversion

61-101-00802.EF2 (REV. G) CH. 2
January 7, 2015 Page 6 of 44
Test Set Display Reading Equivalent MΩ
1. Less than 1
1000 1.
500 2.
200 5.
100 10.
050 20.
020 50.
010 100.
005 200.
002 500.
001 1,000.
000 Greater than 1,000
Example: 1000/50 = 20 MΩ
Table 1 Conductance to Megaohm Conversion
(4) Rotate the INS TEST POINTS switch through each remaining
position.
(5) Allow test set to stabilize. Sometimes the reading never completely
stabilizes. If the reading is in the acceptable range after 30 seconds it
should be considered OK.
(6) Verify T/S reading is less than 50 nS at each position except
SIG/RTN.
(7) With switch rotated to SIG/RTN, verify an “over range” test set
reading of “1”.
Note: If P/N 114-389001-17 probe (Gull Airborne) is installed in the
collector tank, an “over range” reading also appears when the
switch is placed in the LO-Z/RTN position.
(8) Connect the aircraft battery.
(9) Close circuit breakers.
(10) If testing 1900C/1900D, UC and UE aircraft, set the aircraft fuel panel
select switch to AUX and maintain.
Note: The fuel quantity select relay shorts the signal lead to return
lead of “MAIN/TOTAL” or “AUX/NAC” that is not selected.
Also, due to continuity through diodes inside the probe, a short
on “RTN/GND” shows as a short on “SIG/GND”.
(11) Rotate INS TEST POINTS switch through remaining positions.