Download Manual CFS1

Printed in Switzerland
Copyright  2004 by Arrow Group GmbH., Switzerland
All rights reserved. No part of this Manual may be reproduced or transmitted in
any form or by any means without the written permission of Arrow Group GmbH
Contents of this Manual are subject to change without notice. Arrow Group
GmbH assumes no responsibility for errors or omissions in this Manual nor for
improper installation of the CAPACITIVE FUEL SENSOR. It is the responsibility
of the Installing Agency to assure that the details expressed within this Manual
conform to industry standards and practice for the installation and acceptance
of the CAPACITIVE FUEL SENSOR.
WARRANTY
Arrow Group GmbH warrants that the CAPACITIVE FUEL SENSOR if properly
used will be free from defects in material and workmanship for one (1) year
following the date of shipment by Arrow Group GmbH
THE ABOVE WARRANTY IS IN LIEU OF ANY OTHER WARRANTY,
WHETHER EXPRESS, IMPLIED OR STATUTORY, INCLUDING, BUT NOT
LIMITED TO, ANY WARRANTY OF MERCHANTABILITY, FITNESS FOR ANY
PARTICULAR PURPOSE, OR ANY WARRANTY OTHERWISE ARISING OUT
OF ANY PROPOSAL, SPECIFICATION OR SAMPLE. ARROW GROUP GMBH
NEITHER ASSUMES NOR AUTHORIZES ANY PERSON TO ASSUME FOR IT
ANY OTHER LIABILITY.
CAPACITIVE FUEL SENSOR
If the CAPACITIVE FUEL SENSOR fails to conform to the above warranty,
Arrow Aviation´s sole and exclusive liability will be to replace such CAPACITIVE
FUEL SENSOR which fails during the applicable warranty period. The warranty
excludes all costs of shipping, customs clearance, duty, import and or taxes and
other related charges. Arrow Group GmbH will have a reasonable time to
replace the CAPACITIVE FUEL SENSOR.
LIMITATION OF LIABILITY
INSTALLATION MANUAL
IN NO EVENT WILL ARROW GROUP GMBH BE LIABLE FOR ANY LOSS OF
PROFITS, LOSS OF USE, INCIDENTAL, CONSEQUENTIAL, OR SPECIAL
DAMAGES, IRRESPECTIVE OF WHETHER ARROW GROUP GMBH HAS
ADVANCE NOTICE OF THE POSSIBILITY OF SUCH DAMAGES.
Arrow Group GmbH
Capacitive Fuel Sensor
__________________________________________________________
Capacitive Fuel Sensor
Arrow Group GmbH
__________________________________________________________
SECTION I - General Information
TABLE OF CONTENTS
1.1 Introduction
SECTION I - General Information ....................................... 2
The information contained within this Manual describes the technical aspects,
features and components of the CAPACITIVE FUEL SENSOR. The first section
serves as an introduction. It describes the technical specification of the product.
The following section describes the installation and checkout procedures.
Proper techniques must be followed to ensure correct operation.
1.1
Introduction ............................................................. 2
1.2
Product Description................................................ 3
1.3
Principal of Operation ............................................ 4
1.4
Security Analysis .................................................... 4
1.5
Technical Specification .......................................... 7
TANK
VENT
MAXIMUM FUEL LEVEL
FUEL
TANK
SECTION II - Installation Instruction .................................. 8
2.1
General .................................................................... 8
2.2
Unpacking and Inspecting Equipment.................. 8
2.3
Harness and Cable Fabrication ............................. 9
2.4
Connection Wire Description................................. 9
2.5
Installation and Setup............................................. 9
FUEL
QUANTITY
INDICATOR
CAPACITIVE
FUEL
SENSOR
MINIMUM FUEL LEVEL
The CAPACITIVE FUEL SENSOR is installed in a fuel tank and converts the
fuel level into a voltage between 0 and 5 volts which is delivered to an adequate
fuel quantity indicator instrument. As an alternative methode of installation the
CAPACITIVE FUEL SENSOR can be connected with a tube.
TANK
VENT
CAPACITIVE
FUEL
SENSOR
FUEL
QUANTITY
INDICATOR
MAXIMUM FUEL LEVEL
FUEL
TANK
MINIMUM FUEL LEVEL
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Arrow Group GmbH
Capacitive Fuel Sensor
__________________________________________________________
Capacitive Fuel Sensor
Arrow Group GmbH
__________________________________________________________
1.2 Product Description
1.3 Principal of Operation
The CAPACITIVE FUEL SENSOR consists of an aluminium pipe which builds a
capacitor and a head on top of the pipe which contains an electronic circuit to
convert the change in capacitance into a voltage change when the fuel level
inside the pipe changes.
The following block diagram show the electrical circuit of the CAPACITIVE
FUEL SENSOR:
A reference oscillator with a frequency of about 55 kHz drives two symmetrically
built integrators synchronously to its clock and its phase. The capacitors CX1
and CX2 determine the amplitude of the two driven integrators where CX1 is the
reference capacitor and CX2 is the variable capacitor in the fuel tank. The
EMPTY ADJUST trimmer PCX1 is used to adjust the constant current to the
reference capacitor CX1 when the tank is empty to zero the difference. The
difference of the integrator amplitudes gives the relative change of the
capacities CX1 and CX2 to each other with high common mode rejection and high
resolution. The difference signal is conditioned by a lowpass filter with a corner
frequency of about 800 Hz. The gain of it can be adjusted with the FULL
ADJUST trimmer PL. The output of the lowpass filter is connected to an
instrumentation amplifier and an output stage. These two stages transform the
signal into an voltage in the range of 0 to 5 volts.
1.4 Security Analysis
According to the Federal Aviation Administration (FAA) Advisory Circular
25.981-C1 “FUEL TANK IGNITION SOURCE PREVENTION GUIDELINES”
Fuel Quantity Indicating System Probes (FQIS Probes) are intrinsically safe, if
the following conditions are fulfilled:
1. Laboratory testing has shown that the minimum ignition energy required to
ignite hydrocarbon fuel vapor is 200 micro joules during the duration of the
spark. Therefore, for electrical or electronic systems that introduce electrical
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Capacitive Fuel Sensor
Arrow Group GmbH
__________________________________________________________
energy into fuel tanks, such as fuel quantity indicating systems, the energy
introduced into any fuel tank should be less than 200 micro joules during
either normal operation or operation with failures. To ensure that the design
has adequate reliability and acceptable maintenance intervals, a factor of
safety should be applied to this value when establishing a design limit. For
example, a maximum energy of 20 micro joules is considered an
intrinsically safe design limit for fuel quantity indicating systems.
2. Analyses and testing indicate a small piece of steel wool will ignite jet fuel
when a current of approximately 60 milli amperes root-mean-square (RMS) is
applied to the steel wool. Therefore, for electrical or electronic systems that
introduce electrical energy into fuel tanks, such as fuel quantity indicating
systems, the electrical current introduced into any fuel tank should be limited.
Because there is considerable uncertainty associated with the level of
current necessary to produce an ignition source from filament heating, a
factor of safety should be applied to this value when establishing a design
limit. A maximum of steady-state current of 10 milli amperes RMS is
considered an intrinsically safe design limit for fuel quantity indicating
systems.
During normal operation of the CAPACITIVE FUEL SENSOR the current to the
fuel capacitor CX2 is driven by a constant current source in the voltage/current
reference circuit. This current is adjusted to be 6.67 µA and the voltage can be
max. 2 volts. The capacitance of the tank capacitor CX2 is about 50 pF if the
tank is completely filled.
Capacitive Fuel Sensor
Arrow Group GmbH
__________________________________________________________
If that voltage is the maximum rated voltage of 35 volts, the energy in the
capacitor will become 0.06 µJ which is much less than the value stated in the
FAA Advisory Circular 25.981-C1 for an intrinsically safe design criteria.
U
I=
35 V
=
R
= 1.75 mA
20 kΩ
If at the same time the capacitor in the tank has a short circuit, the current is
limited by the series resistor of 20 kΩ to a value of 1.75 mA which is also much
less than the value stated in the FAA Advisory Circular 25.981-C1 for an
intrinsically safe design criteria.
Sensor
Head
Aircraft Power max 35V
Output 0..5V to Instrument
Aircraft Ground
Short circuit in Sensor head
20 kΩ
E = U2 • C = 2V2 • 50 pAS/V = 200 pJ
Thus the energy in the capacitor is limited to 200 pJ during normal operation of
the sensor. In case of a short circuit in the sensor head between the input
voltage terminal and the resistor driving the tank capacitor, the tank capacitor is
loaded to the input voltage.
Short circuit in Capacitor
E = U2 • C = 35V2 • 50 pAS/V = 0.06 µJ
As a result, the CAPACITIVE FUEL SENSOR can be
viewed as an intrinsically safe device according to the
FAA Advisory Circular 25.981-C1
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Arrow Group GmbH
Capacitive Fuel Sensor
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Capacitive Fuel Sensor
Arrow Group GmbH
__________________________________________________________
1.5 Technical Specification
SECTION II - Installation Instruction
The CAPACITIVE FUEL SENSOR is designed to meet TSO specifications. The
following table shows the characteristics in detail:
SPECIFICATION
Temperature Range:
Altitude:
Humidity Range:
Electromagnetic
Compatibility:
Random Vibration:
Weight:
Physical Dimension:
CHARACTERISTIC
-35°C to +70°C
-1,200 feet to 20,000 feet
up to 95% at +55°C for 12 hours,
non condensing
according to RTCA DO-160 A specification
according to MIL-STD-810E specification
0.063 kg
Width: 40 mm
Height: 350 mm
Depth: 20 mm
Mounting:
10 mm whole in fuel tank
CAUTION: Do not drill wholes in the sensor
head or serious internal damage will result.
Ventilation Fitting:
6 mm
Connection wires:
3 x AWG22 shielded:
white/orange:
power input
white/blue:
aircraft ground
white:
signal output
Supply Voltage:
11 VDC to 35 VDC
protection for reverse polarity
Quiescent Current:
typical 1.6 mA, max. 2.7 mA
Output Voltage Range:
0VDC to 5 VDC
Output Current:
max. 10 mA
Output Load Resistance:
2 kΩ
Output Load Capacitance: 500 nF
Accuracy:
± 0.5% full scale from +10°C to +30°C
± 1% full scale from -10°C to +30°C
± 2% full scale whole operating range
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2.1 General
This section contains considerations and recommendations for installation of
the CAPACITIVE FUEL SENSOR. Interconnect harness wiring and final testing
are discussed as well as guidelines to setup the CAPACITIVE FUEL SENSOR
for proper operation together with a Fuel Quantity Indicator. Adherence to the
instruction contained herein should ensure a satisfactory installation.
Where connection with other manufacturer’s equipment are considered,
the Installing Agency must verify that the information provided is correct
and properly understood. Arrow Group GmbH assumes no responsibility
for miss wiring to represented equipment or to other equipment.
2.2 Unpacking and Inspecting Equipment
After unpacking the CAPACITIVE FUEL SENSOR a through visual inspection
should be conducted for evidence of any damage which may have occurred
during shipment. If damage is observed, a claim should be promptly filed with
the transportation company. The shipping carton must be retained in order to
substantiate the claim. It is recommended that the recipient retain all
shipping cartons and material for future requirements.
2.3 Harness and Cable Fabrication
The following section describes the necessary connections of the CAPACITIVE
FUEL SENSOR and the other aircraft systems. FAA Federal Air Regulation,
Part 43 and practice expressed within FAA Advisory Circular 43.13-1A and
43.13-2A, must be adhered to in order to ensure proper alteration to the
airframe. Use MIL-W-22759-Tefzel wire or equivalent and MIL-C-27500-Multiple
Conductor shielded cable or equivalent to fabricate the harness.
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Arrow Group GmbH
Capacitive Fuel Sensor
__________________________________________________________
2.4 Connection Wire Description
COLOR
white/blue
NAME
aircraft
ground
white/orange supply
power
white
output
signal
shield
shield
DESCRIPTION
Must be connected to the aircraft ground at the
connector of the fuel quantity instrument.
Must be connected to the avionic bus at the
connector of the fuel quantity instrument.
Must be connected to the fuel probe input of the
fuel quantity instrument.
This shield is left unconnected inside the sensor
head. It can be connected to the supply cable
shield if this cable is routed near high energy
wires.
2.5 Installation and Setup
1. Install the CAPACITIVE FUEL SENSOR in the fuel tank or connect it at
the lower end to the fuel tank with a tube, so that 10 mm of the bottom of
the sensor is inside the fuel when only unusable fuel is contained in the
tank.
2. Connect a 12 volt battery to the supply
wires and a volt meter to the output signal.
3. Using a small screw driver and turn “Empty
Tank Adjustment” clockwise until the volt
meter reads 1V. Then turn counterclockwise until the volt meter reads less than
0.1V.
4. Fill the tank to its max. level.
5. Adjust “Full Tank Adjustment”
until the volt meter reads 5V.
Note: The maximum fuel level must not be higher than 25
cm measured from the bottom of the sensor.
6. Connect wires of the CAPACITIVE FUEL SENSOR to the fuel quantity
instrument according to section 2.4. If the manufacturer of this instrument
offers a special connector for the fuel probe on his instrument this
connector should be used. Do not route wires to other equipment then the
CAPACITIVE FUEL SENSOR.
Revision A
February 6, 2004
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ARROW GROUP GMBH
Switzerland
[email protected]
_______________________________________________________
Dealer: