1 Title of the Invention

The Title of Invention is “Testing Method for Multiplexing Electronic Board for Sensor Measurement Unit”.

2 Field of the Invention

The present Invention generally relates to Industrial applications and military Helicopters for Automatic Flight Control System and in particular relates to the design and development of testing methodology for multiplexing electronic board of Sensor Measurement Unit (SMU) in Attitude Heading Reference System (AHRS).

3 Background of the Invention

AHRS is a type of sensor system used in aerospace and aviation applications to determine the orientation and movement of an aircraft, helicopter, spacecraft etc. It works by combining data from different sensors to calculate the aircrafts attitude (pitch, roll and yaw) and its heading (direction of travel). AHRS consists of Attitude Heading Reference Unit (AHRU), Magnetometer and Removable Memory Module. SMU is the heart of AHRU which consists of three axis Fiber Optic Gyroscope (FOG), single axis Micro-Electro-Mechanical-System (MEMS) based Accelerometers (3 Nos), processing boards and multiplexing electronic board. Multiplexing electronic board used to convert analog signals into digital data (ADC) conversion from 3 accelerometers through flexible printed circuit board (flex PCB) and 3 channels magnetometer. Processing board includes erasable programmable read only memory (EPROM), random access memory (RAM) and electrically erasable programmable read only memory (EEPROM).

The present testing methodology for multiplexing electronic board covering 70% of the components are tested functionally without assembly in SMU. After assembly in SMU, during good functional checks the board is tested 100% and verified the functionality of the board for 3 channel
accelerometers and 3 channels magnetometer. During good functional checks observed some of the channel from accelerometer and magnetometer, the output parameter varies due to the failure of components in multiplexing board which needs to be identified. The removal of multiplexing board from SMU assembly is very difficult and it damages the flex PCB. The problem is limited test parameters in the multiplexing electronic board before assembly in the sensor measurement unit.

The proposed testing methodology for multiplexing electronic board covering 100% of the components to be tested functionally without assembly in SMU and to prevent the damage of flex PCB.

3.1 Prior Art

The present testing methodology covering 70% of the components are tested functionally in the multiplexing electronic board without assembly in SMU. During good functional checks of SMU, the multiplexing electronic board is tested 100% and verified the functionality of the board for 3 channel accelerometers and 3 channels magnetometer. Due to this testing parameter limitation, some components related to accelerometer and magnetometer causes failure in good functional checks. The removal of the multiplexing electronic board fortroubleshooting causes the damage in flex PCB. The proposed testing methodology covering 100% functional testing of the multiplexing electronic boards without assembly in SMU and to prevent the damage of flex PCB.

4 Brief Summary of the Invention

The 100% functional testing of the multiplexing electronic board before assembly in SMU is the challenging task. The board is not designed by us. Knowing the schematic diagram of the board, the complete functions of the board was studied. The challenging task is without soldering the multiplexing electronic board to the flex PCB, the complete functional
testing to be carried out to verify the 3 channel accelerometers and 3 channels magnetometer output.

The multiplexing electronic board consists of 6 different sections; the details are power supply, comparator, modulation and demodulation excitation, 3 channels Accelerometer, 3 channels Magnetometer, Multiplexer and AOC section. The board tested in In-circuit tester for passive components check and limited level of functional testing. The proposed testing methodology to test the board for all functional tests in the six sections and verify the accelerometer and magnetometer output for 3 channels. The present invention enables to check the complete functionality of the multiplexing electronic board without soldering to the flex PCB.

5 Detail Description of the Drawings

Figure 1: is the assembly of Sensor Measurement Unit [10 - Axis 1 Gyroscope, 11 - Axis 2 Gyroscope, 12 - Axis 3 Gyroscope, 13 - Axis 1 Accelerometer, 14 - Axis 2 Accelerometer, 15 - Axis 3 Accelerometer, 16 - Processing Board, 17 - Multiplexing electronic Board, 18 - Gyro processing board, 20-Mechanical block for sensor assembly]

Figure 2: is the assemblies of multiplexing electronic board with flex PCB and 3 accelerometers [13 - Axis 1 Accelerometer, 14 - Axis 2 Accelerometer, 15 - Axis 3 Accelerometer, 17 - Multiplexing electronic Board, 19-flex PCB].

Figure 3:is the functional block diagram of multiplexing electronic board [21 -Power supply section, 22 -Comparator section, 23 - Modulation and demodulation excitation section, 24 -3 channels Accelerometer section, 25-3 channels Magnetometer section, 26 - Multiplexer and ADC section, 27 -Flex PCB connector, 28 -Magnetometer connector, 29 - Processor board connector]
Figure 4: is the proposed test method for multiplexing board [21 -Power supply section, 22 -Comparator section, 23 - Modulation and demodulation excitation section, 24 -3 channels Accelerometer section, 25-3 channels Magnetometer section, 26 - Multiplexer and ADC section, 27 -Flex PCB connector, 28 -Magnetometer connector, 29 - Processor board connector, 30 -Digital Power Supply, 31 - Function Generator, 32

- Digital Multimeter, 33 - Digital Oscilloscope, 34 - Junction Box, 35 -Interconnection box]

Figure 5: is the flowchart for SMU assembly and calibration testing on two axis rate table [36 - Assembly components verification for multiplexing electronic board, 37 - Multiplexing electronic board assembly, 17 -Multiplexing electronic board test {70% of the components are verified functionally), 38 - flex PCB (19) soaking at lOS'C for 8 hours, 39 - flex PCB (19) cambering at 80°C for 45 minutes as per accelerometer position, 40 - cambered flex PCB soldered with 3 accelerometers (13, 14, 15) , 41

- accelerometer assembled flex PCB is soldered with multiplexing electronic board, 42 — mechanical assembly (20) of sensor measurement unit, 43 - sensor measurement unit good functional checks, 44 - failure of SMU good functional checks due to multiplexing board (17) and accelerometers (13, 14, 15), 45 - Multiplexing electronic board (17) desoldering from flex .PCB (19), 46 - Accelerometer (13 or 14 or 15) desoldering from flex PCB (19), 47 - SMU calibration test on two axis rate table after validating SMU good functional checks, 48 - carry out SMU finishing by applying adhesive on the required places of SMU assembly]

6 Detail Description of the Invention

Testing a multiplexing electronic board can be a complex and time-consuming process, but it is essential to ensure that the board meets the required performance and safety standards for its intended use. The complexity of the board can vary depending on the number and type of sensors it is designed to work with, as well as the processing capabilities
required to handle the data from these sensors. Developing a testing methodology for a multiplexing electronic board can be challenging due to the complexity of the board and the need to test multiple inputs and outputs simultaneously.

Figurel shows the assembly of sensor measurement unit, it consists of 3 axis fiber optic gyroscopes, 3 single axis accelerometers, processing boards and multiplexing electronic board. The flex PCB is soaked at 105°C for 8 hours and cambering carried out as per the accelerometer assembly position. After cambering the flex PCB, three accelerometers are soldered with flex PCB. The accelerometers assembled flex PCB is soldered with multiplexing electronic board as shown in Figure 2. The functional block diagram of multiplexing electronic board is shown in Figure 3. It consists of 6 different sections: Power supply section (21), comparator section (22), Modulation and demodulation excitation section , (23), 3 channels Accelerometer section (24), 3 channels Magnetometer section (25), Multiplexer and ADC section (26). The multiplexed output from accelerometers is communicated through the flex PCB connector (27). The output from 3 channel magnetometers is received from the connector (28). The processed output from accelerometers and magnetometers are sent through the connector (29) to the processing boards.

The present testing methodology for multiplexing electronic board covering 70% of the components are tested functionally without assembly in SMU. After assembly in SMU, during good functional checks the board is tested 100% and verified the functionality of the board for 3 accelerometers and 3 channel magnetometer. The proposed testing methodologies for the multiplexing electronic board to test 100% of the components functionally without assembly in SMU and to prevent the damage of flex PCB. The proposed testing methodology is shown in Figure 4. Testing a multiplexing electronic board typically requires specialized equipment, such as test
fixtures, digital power supply, function generator, digital multimeter, digital oscilloscope etc. Figure 5 shows the flowchart for the complete assembly of the sensor measurement unit and functional calibration testing and performance of the SMU on two axis rate table. The good functional check of the SMU (43) shows the performance of the gyroscope, accelerometer and magnetometers from 3 channels. In case any performance issue from accelerometers and magnetometers, the multiplexing electronic board de-soldered (45) from accelerometer assembled flex PCB and it causes the damage of flex PCB.

In summary, designing a testing methodology for a multiplexing electronic board requires a systematic approach and the goal is to ensure that the board meets the desired performance criteria and is reliable and robust in operation.