Electronics International MVP-50T - Manual (Page 58)

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Rapidly tap the White transducer wire to ground. A small fuel flow reading should
show on the MVP.
2. Problem: The rotor in the Fuel Flow Transducer is blocked.
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 MVP 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 7.7 7.7 7.7 7.7 Amp Problem: Amp Problem: Amp Problem: Amp Problem: Amp Problem:
Amps are measured on the aircraft using a Shunt. A Shunt has very low resistance and produces a differential
voltage on the two signal wires connected to the Shunt. The differential voltage is proportional to the amper-
age 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.
A. Symptom: A. Symptom: A. Symptom: A. Symptom: A. 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 MVP 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 7.8 7.8 7.8 7.8 Resistive Fuel Level Problem: Resistive Fuel Level Problem: Resistive Fuel Level Problem: Resistive Fuel Level Problem: 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 (depending 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 Calibration” screen.
The sensor counts are then converted to a fuel level based on the calibration data in the “Fuel Tank Calibra-
tion” screen.
Resistive floats are notoriously inaccurate and inconsistent. Floats move up and down millions of time 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 find
even new floats that work poorly. The MVP can calibrate out nonlinearity, but inconsistency will always cause
reading problems. It will cause you to perform the fuel tank calibration procedure over and over with little or
no long-term improvement. Consider using a capacitive probe or our magnetic float sensor if at all possible.