G SERIES PILOT’S GUIDE .
INSIGHT
INSTRUMENT CORPORATION BOX 122, FORT ERIE, ONTARIO, L2A 5M6
30
PROBE DIAGNOSTIC Screen
Left is positive resistance
Right is negative resistance
EGT 6 turned red because
the resistance is greater
than the MAX setting of 20
CHT 4 turned red because the
resistance difference between
positive and negative leads is
greater than the DIF setting of
10
Typical single engine 8 foot harness display setting on G3 above.
The probe diagnosis page indications are in green for normal readings and red for readings that fail the criteria set at the
bottom of the screen.
Each temperature probe consists of two wires, a positive lead and a negative lead. The two numbers next to each identifier
show the resistance in Ohms of each lead.
For example, the line EGT1 8 3 means the positive lead of the EGT1 probe has 8 Ohms resistance, and the negative lead
has 3 Ohms resistance.
When the probe is new, it will have relatively low resistance.
As the probe ages, it’s resistance will slowly go up. Eventually, the probe will measure outside the pass/fail criteria you set
at the bottom of the screen, and change from green to red, indicating that the probe should be replaced before it fails and
leaves you with no temperature reading at all.
One other point to consider is that the longer the wiring to the probes, the higher its resistance.
Every foot of EGT wire adds 1.7 Ohms/ft for the + lead and 0.8 Ohms/ft for the - lead. Every foot of CHT wire adds 0.2
Ohms/ft for the + lead and 0.7 Ohms/ft for the - lead.
A 24 ft harness will fail the criteria that an 8 ft harness will pass with. That is why we allow the user to modify the pass/fail
criteria on the bottom of the screen.
The meaning of the pass/fail criteria is as follows:
R MAX sets the maximum resistance (in Ohms) that any single lead may have. If the R MAX is set to 20 Ohms a probe with
either the positive or negative leads measuring greater than 20 Ohms will be annunciated in RED, otherwise its displayed
in GREEN.
R DIF sets the maximum resistance (in Ohms) that the positive lead may differ from the negative lead. If R DIF is set to
10 Ohms, the positive and negative leads need to measure within 10 Ohms of each other to be annunciated in GREEN,
otherwise its RED.
Proper setting on G1234 with 8, 10, 14 foot harness should be R MAX 20 R DIF 10
Proper setting on G1234 with 20, 24 foot harness should be R MAX 25 R DIF 15
Proper setting on G1234 with 30, 35 foot harness should be R MAX 30 R DIF 20
