3 research outputs found
Advanced electronics for fourier-transform ion cyclotron resonance mass spectrometry
With the development of mass spectrometry (MS) instruments starting in the
late 19th century, more and more research emphasis has been put on MS related
subjects, especially the instrumentation and its applications. Instrumentation
research has led modern mass spectrometers into a new era where the MS performance,
such as resolving power and mass accuracy, is close to its theoretical
limit. Such advanced performance releases more opportunities for scientists to
conduct analytical research that could not be performed before.
This thesis reviews general MS history and some of the important milestones,
followed by introductions to ion cyclotron resonance (ICR) technique
and quadrupole operation. Existing electronic designs, such as Fourier-transform
ion cyclotron resonance (FT-ICR) preamplifiers (for ion signal detection) and
radio-frequency (RF) oscillators (for ion transportation/filtering) are reviewed.
Then the potential scope for improvement is discussed.
Two new FT-ICR preamplifiers are reported; both preamplifiers operate at
room temperature. The first preamplifier uses an operational amplifier (op amp)
in a transimpedance configuration. When a 18-k
feedback resistor is used, this
preamplifier delivers a transimpedance of about 85 dB
, and an input current
noise spectral density of around 1 pA/
p
Hz. The total power consumption of
this circuit is around 310 mW when tested on the bench. This preamplifier has a
bandwidth of fi3 kHz to 10 MHz, which corresponds to the mass-to-charge ratio,
m/z, of approximately 18 to 61k at 12 T for FT-ICR MS. The transimpedance
and the bandwidth can be adjusted by replacing passive components such as the
feedback resistor and capacitor. The feedback and bandwidth limitation of the
circuit is also discussed. When using an 0402 type surface mount resistor, the
maximum possible transimpedance, without sacrificing its bandwidth, is approximated
to 5.3 M
. Under this condition, the preamplifier is estimated to be able
to detect ~110 charges.
The second preamplifier employs a single-transistor design using a different
feedback arrangement, a T-shaped feedback network. Such a feedback system
allows ~100-fold less feedback resistance at a given transimpedance, hence preserving
bandwidth, which is beneficial to applications demanding high gain. The
single-transistor preamplifier yields a low power consumption of ~5.7 mW, and
a transimpedance of 80 dB
in the frequency range between 1 kHz and 1 MHz
(m/z of around 180 to 180k for a 12-T FT-ICR system). In trading noise performance
for higher transimpedance, an alternative preamplifier design has also
been presented with a transimpedance of 120 dB
in the same frequency range.
The previously reported room-temperature FT-ICR preamplifier had a voltage gain of about 25, a bandwidth of around 1 MHz when bench tested, and
a voltage noise spectral density of ~7.4 nV/
p
Hz. The bandwidth performance
when connecting this preamplifier to an ICR cell has not been reported. However,
from the transimpedance theory, the transimpedance preamplifiers reported in
this work will have a bandwidth wider by a factor of the open-loop gain of the
amplifier.
In a separate development, an oscillator is proposed as a power supply for
a quadrupole mass filter in a mass spectrometer system. It targets a stabilized
output frequency, and a feedback control for output amplitude stabilization. The
newly designed circuit has a very stable output frequency at 1 MHz, with a frequency
tolerance of 15 ppm specified by the crystal oscillator datasheet. Within
this circuit, an automatic gain control (AGC) unit is built for output amplitude
stabilisation. A new transformer design is also proposed. The dimension of the
quadrupole being used as a mass filter will be determined in the future. This
circuit (in particular the transformer and the quadrupole connection/mounting
device) will be finalised after the design of the quadrupole.
Finally, this thesis concludes with a discussion between the gain and the noise
performance of an FT-ICR preamplifier. A brief analysis about the correlation
between the gain, cyclotron frequency, and input capacitance is performed. Future
work is also suggested for extending this research
Single-ended traveling wave fault location on radial distribution lines
In this thesis a single-ended traveling wave fault location algorithm is developed for autonomously locating short circuit faults on a radial distribution line using the high frequency traveling wave transients. The traveling wave pattern observed at the sub-station is correlated with the traveling wave pattern predicted using time tree analysis for different fault locations and fault resistance. Genetic search techniques are used to evolve an initial population of possible fault locations to determine the most likely fault location. It is shown through extensive EMTP simulations that the scheme is capable of finding the location of three phase faults, inter-phase faults and single-phase faults for fault resistances ranging from 0 - 1000 ohm on a radial distribution line with five sub-feeders.
A new high speed FPGA based data acquisition system is developed suitable for capturing traveling wave fault data from a radial distribution line with the necessary fidelity for the proposed fault location algorithm. The data acquisition system is deployed on a Medium Voltage distribution line in the Santa Caterina region of Brazil.
A branched communication network is constructed out of RG-58 coaxial cable and a Time Domain Reflectometry device is used to capture the reflection pattern under different fault conditions. The fault location algorithm is adapted to work with TDR a opposed to fault generated traveling waves. The location algorithm is capable of locating faults with resistance between 0 and 75 ohm up to three zones away from the injection point
Single-ended traveling wave fault location on radial distribution lines
In this thesis a single-ended traveling wave fault location algorithm is developed for autonomously locating short circuit faults on a radial distribution line using the high frequency traveling wave transients. The traveling wave pattern observed at the sub-station is correlated with the traveling wave pattern predicted using time tree analysis for different fault locations and fault resistance. Genetic search techniques are used to evolve an initial population of possible fault locations to determine the most likely fault location. It is shown through extensive EMTP simulations that the scheme is capable of finding the location of three phase faults, inter-phase faults and single-phase faults for fault resistances ranging from 0 - 1000 ohm on a radial distribution line with five sub-feeders.
A new high speed FPGA based data acquisition system is developed suitable for capturing traveling wave fault data from a radial distribution line with the necessary fidelity for the proposed fault location algorithm. The data acquisition system is deployed on a Medium Voltage distribution line in the Santa Caterina region of Brazil.
A branched communication network is constructed out of RG-58 coaxial cable and a Time Domain Reflectometry device is used to capture the reflection pattern under different fault conditions. The fault location algorithm is adapted to work with TDR a opposed to fault generated traveling waves. The location algorithm is capable of locating faults with resistance between 0 and 75 ohm up to three zones away from the injection point