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a) Action: Remove the Flow Transducer from the aircraft. Lightly blow into the transducer
and check for the rotor to spin freely. Check for a Fuel Flow reading on the
CGR when the rotor is spinning.
If the rotor in the Flow Transducer does not spin, hold the transducer over white
paper and tap at all angles. Debris can lodge in the transducer and block the
rotor.
7.7 Amp Problem:
Amps are measured on the aircraft using a Shunt. A Shunt has very low resistance and produces a differ-
ential voltage on the two signal wires connected to the Shunt. The differential voltage is proportional to
the amperage flowing through the Shunt (50 mV at 50 Amps for the S-50 Shunt). In series with the two
signal wires are two fuses to protect the wires form catching fire in case of a short. These fuses should be
located a short distance from the Shunt. The wires are then routed to the EDC Amp input.
Symptom:
Symptom:
Symptom:
Symptom:
Symptom: Inaccurate, jumpy or zero reading.
1. Problem: A wire, fuse or fuse connection is open, shorted or mis-wired.
a) Action: Remove one of the signal wires on the Shunt and connect it to the other signal
wire. This will short the two signal wires together. The CGR should read 0.0
amps. A common problem is with the fuses or fuse holders in line with each Amp
signal wire from the Shunt to the EDC. The fuses should be located a short
distance from the shunt. Inspect the wires, fuses and fuse holders.
7.8 Resistive Fuel Level Problem:
Fuel can be measured in a fuel tank using a Resistive Float Sensor. The sensor must be connected to a
RFLM (Resistive Fuel Level Module). This module provides a pull-up resistor to produce a voltage as the
float changes resistance with changes in the fuel level. A signal wire connects the float to the RFLM and a
wire connects the RFLM to the EDC. The RFLM requires bus voltage to provide the pull-up.
As the float sensor arm moves up, the resistance will change, creating a higher or lower voltage (depend-
ing on the float type) on the signal wire. The EDC monitors the signal and produces a digital value (called
sensor counts) based on the signal voltage. The sensor counts can be viewed in the “Fuel Tank Calibra-
tion” screen. The sensor counts are then converted to a fuel level based on the calibration data in the
“Fuel Tank Calibration” screen.
Resistive floats are notoriously inaccurate and inconsistent. Floats move up and down millions of times
during their lives. They can move even when the aircraft is parked. The metal-to-metal contact of the
wiper to the coil wears and corrodes. The wiper force weakens. The bearing surfaces wear. It’s not
uncommon to even find new floats that work poorly. The CGR can calibrate out non-linearity, but incon-
sistency will always cause reading problems. It will cause you to perform the fuel tank calibration proce-
