5 research outputs found
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A predictive model for time domain reflectometry soil water content and salinity measurements
Soil water content and water potential are two important parameters in
determining the status of water in the soil. Improvement in the ability to measure these
parameters by way of increased speed, accuracy, resolution, imaging volume, ease of
automation, as well as reduced calibration requirements and reduced soil disturbance
would be of utility to many applications in agriculture and engineering. To make the
measurements economically and without the use of hazardous materials or methods would
also be of value. A brief review is given on most of the existing water content and water
potential measurement techniques with focus given on electromagnetic and quantum
mechanic techniques due to their potential for best balancing the design goals. A review of
the theories of electromagnetics and quantum mechanics are presented with applications to
soil water content and water potential measurements. One electromagnetic method, Time
Domain Reflectometry, or TDR, shows great promise in balancing all the desired design
goals. A mathematical model is proposed to be able to predict TDR water content and
electrical conductivity (or salinity) measurement results over wide ranges of those
parameters. Preliminary validations were performed on the model for both invasive and
potentially non-invasive TDR probes in a sandy soil with the results showing good
agreement between predictions and actual results but with some model refinements still
needed. A proposal for ongoing research is given to refine the models and address the
question on the feasibility of using the models in a field grade TDR instrument to measure
water content and electrical conductivity (or salinity)
Dual frequency master oscillator generation and distribution for ALS and ALS-U
The ongoing work to upgrade ALS to ALS-U demands strict RF requirements such
as low jitter and low spurs frequency reference to meet its accelerator and
science goals. A low phase noise dual frequency Master Oscillator (MO), where
the two frequencies are related by a fractional ratio of 608/609 and flexible
divide by four frequency outputs has been consolidated into a single chassis.
Optical fiber clock distribution system has been selected over the old coax
system used in ALS to distribute these signals to various clients across the
facility, providing high electrical isolation between outputs and therefore
lower phase errors. A Xilinx FPGA ties the MO chassis together by providing a
RS-485 interface to monitor and control the system. The new system aims to
deliver phase-continuous frequencies with a phase noise (integrated RMS jitter)
from 1 Hz to 1 MHz of less than 200 femtosecond per output. This paper will
discuss the design, implementation, performance and installation of the new MO
generation and distribution system.Comment: Poster presented at LLRF Workshop 2023 (LLRF2023, arXiv: 2310.03199
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Water content and electrical conductivity profile measurements for dispersive media using enhanced time domain and frequency domain models
Water conservation and water quality are rapidly increasing in importance in all areas of the world. The ability to accurately measure soil water content and salinity, over a wide variety of conditions, is key to meeting this need. A set of forward prediction models and waveform interpretation algorithms to extract Volumetric Water Content (WC) and Electrical Conductivity (EC) profiles vs. position and time for electrically lossy and dispersive geophysical and biological media are presented. These are applicable to both Time Domain and Frequency Domain Electromagnetic Wave Propagation Transmission and Reflection measurements. These forward prediction models are developed using physically based First Principles models from the Theory of Electromagnetics together with Scattering (S) Parameter and Transmission (T) Parameter network modeling techniques applied to wave propagation in various media with cascaded domains of different properties. The interpretation algorithms fit the pre-derived Forward Prediction models to the measurement data via lookup tables, interpolation and optimization methods. Presented applications include the transmission line methods of Time Domain Reflectometry, Time Domain Transmission, Frequency Domain Reflectometry and Frequency Domain Transmission including high dynamic range Frequency Domain Vector Network Analysis. Other applications include Ground Penetrating Radar and Microwave Remote Sensing. The models account for temporal and spatial heterogeneity to obtain WC and EC vs. time and position. Models are introduced for composite media with multiple constituents of varying Ohmic (EC) and dielectric (electric permittivity) properties accounting for dispersive frequency dependence and loss. These models interpolate between the physical upper and lower bounds of parallel and serial influences of each of the capacitive and conductive constituents. New models are also introduced accounting for charged interfaces and resulting bound and semi-bound water constituents within the pore spaces of soils containing clay or organic matter fractions resulting in a transition zone from bound to free water (via a semi-bound water zone) impacting the frequency dependence on electric permittivity. Validations of the models are presented via comparisons to actual measured data over wide ranges of water content, electrical conductivity and soil types
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Digital Low-Level RF control system for Accumulator Ring at Advanced Light Source Upgrade Project
Currently ALS is undergoing an upgrade to ALSU to produce 100 times brighter
soft X-ray light. The LLRF system for Accumulator Ring (AR) is composed of two
identical LLRF stations, for driving RF amplifiers. The closed loop RF
amplitude and phase stability is measured as < 0.1\% and < 0.1^\circ
respectively, using the non-IQ digital down conversion together with analog
up/down conversion, under a system-on-chip architecture. Realtime interlock
system is implemented with < 2 \mus latency, for machine protection against
arc flash and unexpected RF power. Control interfaces are developed to enable
PLC-FPGA-EPICS communication to support operation, timing, cavity tuning, and
interlock systems. The LLRF system handles alignment of buckets to swap beams
between AR and Storage Ring by synchronous phase loop ramping between the two
cavities. The system also includes an optimization routine to characterize the
loop dynamics and determine optimal operating point using a built-in network
analyzer feature. A cavity emulator of 31 kHz bandwidth is integrated with the
LLRF system to validate the performance of the overall system being developed