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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 Revision A February 6, 2004 Page 1 Page 2 Revision A February 6, 2004 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 Revision A February 6, 2004 Page 3 Page 4 Revision A February 6, 2004 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 Page 4 Revision A February 6, 2004 Page 6 Revision A February 6, 2004 Arrow Group GmbH Capacitive Fuel Sensor __________________________________________________________ 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 Revision A February 6, 2004 Page 7 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. Page 8 Revision A February 6, 2004 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 Page 9 ARROW GROUP GMBH Switzerland [email protected] _______________________________________________________ Dealer: