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Studies On Direct Sensor Interface Technology For Launch Vehicle Applications

Electronic Theses of Indian Institute of Science

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Field Value
 
Title Studies On Direct Sensor Interface Technology For Launch Vehicle Applications
 
Creator Sirnaik, M N
 
Subject Sensors
Launch Vehicles
Direct Sensor Interface Technology
DSiT System
Signal Processing
Signal Conditioning
Satellites
Satellites - Control Systems
Satellite Launch Vehicle
Sensor Detectors
Detectors
Instrumentation
 
Description In a process monitoring/control applications tens to thousands of sensors are used for monitoring system parameters. To achieve overall system goals, their reliable performance is critical. Generally a sensor’s output signal is too small or too noisy and may not be compatible with the input requirements of a Data Acquisition System. The sensor is interfaced to Data Acquisition System, through cabling, junction boxes and Interface Electronics like excitation circuitry, multiplexers, signal-conditioning circuitry etc. An interface or signal conditioning circuit does impedance matching, filtering, multiplexing, pre-amplification, amplification and digitization to make the sensor’s output signal compatible with the Data Acquisition System.
Conventional Signal Conditioning includes Multiplexers, Anti aliasing filters, Operational Amplifier, Instrumentation Amplifiers, Isolation Amplifiers and Charge Preamplifiers etc. Operational Amplifiers e.g. voltage followers with High input impedance and low output impedance are used for impedance matching between the sensor and processing electronics. Anti aliasing filters remove noise from the sensor’s output signal. Normally the sensor is located away from the processing electronics and data is transmitted through wires/cables. During transmission, interference from external fields’ especially strong Audio Frequency, Radio Frequency and 50Hz power line fields affects the sensor’s output signal. To minimize the effect of external field twisted pair shielded cables are used. Amplifiers with Differential input configuration are used to suppress the effect of interfering signals. Differential input Instrumentation Amplifiers with High input impedance, high CMRR; are most widely employed. Isolation Amplifiers isolate the input and output circuits by an extremely high impedance. Galvanic, optical isolations are most common. The conditioned data is transmitted to Data Acquisition System (DAS) and at the DAS the signal is multiplexed, filtered and digitized using Analog to Digital Converters (ADCs), followed by Digital Filtering and processing. For Control applications, the processed data is converted back to analog form using Digital to Analog Converters (DACs) for interfacing to external world. The transmission distance varies from tens of centimeters to few meters. Depending upon the distance twisted pair cables, IR transmission and Optical transmission is employed. During transmission, the data is prone to interferences from EMI, EMC, Noise and Signal to Noise ratio (SNR) degradation with distance. This affects the reliability of the system and increases the overall system cost.
To eliminate the effects due to the environmental disturbances during transmission and to maintain signal integrity, it is preferred to have a unique and compact solution for each sensor where signal conditioning (excitation, filtering, amplification, compensation and digitization) is carried out and digital data can be transmitted to Data Acquisition System. Here each sensor has its own signal conditioning module.
Directly interfacing sensors with micro controller yields simple and compact design solutions. Direct Sensor interface Technology (DSiT) is one of the state of the art technologies for sensor interfaces where an unconditioned, uncompensated, raw output signals from sensors are interfaced directly to a single-chip solution. The sensors’ output are multiplexed using Multiplexer; Amplified using Programmable Gain Amplifier (PGA), digitized using ADC, filtered using Digital Filters and transmitted using Digital Interfaces (SPI, I2C, UART) in a single chip. DSiT scheme incorporates all the elements necessary in an instrumentation system creating a balanced combination of features, to create truly intelligent sensor systems.
The sensors are interfaced directly to a single DSiT chip, without any additional circuitry and the direct digital data transmission is achieved with the help of Digital Interfaces SPI, UART, SMBus/I2C. As this involves onchip signal conditioning and digital data transmission, expenditure on additional signal conditioning circuitry, analog interfaces for analog data transmission, separate Analog to Digital Converter for each sensor is reduced. This reduces the overall system cost and as the count of discrete components is reduced the system reliability is improved. In addition, as the data is transmitted digitally the effects of noise, S/N degradation and electromagnetic interferences are eliminated. The accuracy level achieved is sufficiently good for monitoring and control applications.
In Launch Vehicles/Satellites number of sensors are used for performance evaluation, monitoring and control purposes. Harnessing, signal conditioning of the sensors’ output and onboard processing of the sensor data is carried out individually for each sensor. Implementation of the DSiT system will reduce the total weight of the launch vehicles and satellites, resulting in reduced overall system cost, increased reliability and reduced onboard processing overhead. In addition, the reduction in weight allows incorporation of larger payloads/ more propellant loading in payloads which increases the life of the Satellites.
As it is compact, it can be readily used for facility parameter measurements during the ground testing of liquid engines and stages at LPSC/ISRO. Implementation of DSiT for facility parameter measurements will reduce the cabling cost and improve the reliability of the chain.
 
Contributor Rao, G Mohan
 
Date 2016-09-26T11:56:35Z
2016-09-26T11:56:35Z
2016-09-26
2012-01
 
Type Thesis
 
Identifier http://etd.iisc.ernet.in/handle/2005/2575
http://etd.ncsi.iisc.ernet.in/abstracts/3338/G25113-Abs.pdf
 
Language en_US
 
Relation G25113