Thesis (Ph. D.)--University of Minnesota, 1928. / Cover title. Vita. Caption title: Active glucose, by Charles E. Clifton and John M. Ort. "Read before the American Chemical Society, Swampscott, Massachusetts, September, 1928." Bibliography: p. 862.

No description available.

No description available.

Thesis (Ph. D.)--Columbia University, 1930. / Vita. Bibliography: p. 21.

Thesis (M. Phil.)--University of Hong Kong, 1980.

published_or_final_version / Chemistry / Master / Master of Philosophy

In this paper, four methods to simulate or generate electric resistance at high resolution have been developed, tested and evaluated. Each method is called a Resistor Simulator and are numbered from one to four.  Resistor Simulator one is based upon a set of digital potentiometers configured to achieve increased performance over a single 8-bit potentiometer. There were many issues with calibration and control over the individual potentiometers leading to a decent but uneven characteristic.  Resistor Simulator two tests the setup of an encapsulated LED a photoresistor pair where output resistance is controlled by the light output of the current controlled LED. Although the output was purely resistive, and the resistance was controllable. This method has big issues with non-linearity and very poor repetitivity were the same input could give resistances several kiloOhms apart.  Resistor Simulator three uses an ADC in combination with a DAC to measure the current going through the simulator over a shunt-resistor and regulate the voltage output to match the voltage-drop that the set resistance would generate. There were some issues with working in the extreme ends of the analog electronics in the circuit limiting how low currents that could be properly measured. This problem could be bypassed to evaluate the rest of the system with good results. The limiting factor of the simulator was the resolution of the DAC at high resistances. Resistor Simulator four was the largest and costliest of them all, but performance was also the best. It is built as a resistance ladder with a set of 16 binary matched resistors and bypass switches for each resistance. This way, output resistance is set just like a binary number. The performance of the simulator was equally good throughout the entire resistance span. The only thing that limited performance from great to good was that it was hard to get precisely matched resistors of odd values and low tolerance making for some deviation from the theoretical resistances. All four resistance simulators were realized on a single Arduino shield PCB, designed with Altium Designer and assembled by the student. Although an Arduino was used for this project, any microcontroller could be used as all communication with the PCB is done via SPI.  Resistance performance was evaluated with an automated test system for inaccuracy, resolution and repetitivity. Furthermore, practicality parameters such as size and cost were evaluated to further determine the suitability of each resistor simulator.  The outcome from this work is intended to be used as basis to design systems for test and evaluation of alarm systems. / Denna rapport beskriver fyra metoder för att simulera eller generera elektisk resistans med hög upplösning och noggrannhet. Metoderna har identifierats, utvecklats, testats och utvärderats. Varje metod benämns som en Resistor Simulator och är numrerade från ett till fyra. Resistor Simulator ett bygger på en uppsättning av digitala potentiometrar konfigurerade i en krets för att utöka dess upplösning och prestanda jämfört med en enkel 8-bitars potentiometer. Dock så stöttes en hel del problem på i samband med kalibrering och styrning av de individuella potentiometrarna med hyffsad men ojämn karaktäristik. Resistor Simulator två utvärderar konceptet med en inkapslad LED och fotoresistor där resistansen styrs genom att kontrollera ljusflödet med strömstyrning av dioden. Denna lösning var den enda med rent resistiv utgång och resistansen var kontrollerbar. Dock så har metoden stora problem med icke-linjärt beteende och variationer mellan test där samma styrsignal kan ge resistanser flera kiloOhm från varandra. Resistor Simulator tre använder en ADC tillsammans med en DAC för att mäta strömmen genom simulatorn och reglera spänningen för att motsvara det spänningsfall som den valda resistansen skulle generera. Denna lösning stötte på en del problem med för höga spänningsnivåer på den analoga elektronik som användes vilket begränsade hur låga strömmar som kunde mätas. Detta problem kunde förbigås för att utvärdera resten av systemet med goda resultat. Den begränsande faktorn för simulatorns upplösning låg dock i upplösningen på DAC vid höga resistanser. Resistor Simulator fyra var den största och dyraste av dem alla, men också den som presterade bäst. Den är byggd som en resistorstege med en uppsättning av 16 binärt matchade resistorer som alla försetts med en kortslutande styrbar brytare vilket gör att resistans kan beräknas på samma sätt som ett binärtal räknas. Prestandan var genomgående bra i hela mätområdet med enda baksida att det var svårt att införskaffa resistorer av udda värden med mycket låga toleranser varav mindre avvikelser från den teoretiska upplösningen uppkom. Alla simulatorer realiserades på ett tilläggskort till en Arduino som designats med Altium Designer och byggdes ihop av studenten. Även om en Arduino användes för just detta projekt skulle vilken annan mikrokontroller kunna användas då all kommunikation på kretskortet sker via SPI. Prestandan av simulerad resistans testades med ett automatiskt testsystem och utvärderades för onoggrannhet, upplösning och repeterbarhet. Utöver detta utvärderades praktiska parametrar som storlek och materialkostnad för att kunna utvärdera i vilka sammanhang respektive simulator passar bäst till. Utfallet från detta arbete avser att ligga till grund för utveckling av utrustning för test och utvärdering av larmsystem.

The data acquisition system COMET developed by Saab AB contains a unit for signal conditioning and A/D conversion, called KSM. The varieties in signal conditioning constitutes of a number of specific PBAs and maintenance as well as reconfiguration of these are complicated not to mention costly. This thesis has aimed to investigating whether the signal conditioning circuits can be replaced by a general purpose, programmable solution. If so, how can this be done? The development has been carried out by evaluating ideas through the use of a laboratory environment and has resulted in an analog design for laboratory purpose. A reconfigurable design is the result of this thesis as an alternative to the solution used today. In the proposed design mainly digital otentiometers, switches and MUXes are used. In that way signal path and overall behaviour can be selected. Some extensions have been made in comparison to the current functionality, but additional development is necessary to make the design complete. Future versions of the COMET system could be significantly improved by considering the result of this thesis when developing the signal conditioning circuitry.

<p>The data acquisition system COMET developed by Saab AB contains a unit for signal conditioning and A/D conversion, called KSM. The varieties in signal conditioning constitutes of a number of specific PBAs and maintenance as well as reconfiguration of these are complicated not to mention costly. This thesis has aimed to investigating whether the signal conditioning circuits can be replaced by a general purpose, programmable solution. If so, how can this be done? </p><p>The development has been carried out by evaluating ideas through the use of a laboratory environment and has resulted in an analog design for laboratory purpose. A reconfigurable design is the result of this thesis as an alternative to the solution used today. In the proposed design mainly digital otentiometers, switches and MUXes are used. In that way signal path and overall behaviour can be selected. Some extensions have been made in comparison to the current functionality, but additional development is necessary to make the design complete. </p><p>Future versions of the COMET system could be significantly improved by considering the result of this thesis when developing the signal conditioning circuitry.</p>

ITC/USA 2013 Conference Proceedings / The Forty-Ninth Annual International Telemetering Conference and Technical Exhibition / October 21-24, 2013 / Bally's Hotel & Convention Center, Las Vegas, NV / Cobham Electronic Systems, Inc. has developed a digital potentiometer circuit to allow for digital compensation of frequency and temperature variations in the VCO/PLL frequency control loop of a telemetry transmitter. The ability to reprogram the RF center frequency of a telemetry transmitter is a useful feature and is required on many telemetry programs. When setting the frequency modulation deviation (FM Modulation Index) of a telemetry transmitter, the exact setting will change with RF center frequency due to the variation of the transfer function of the VCO (Kvco). Typically, a resistor divider is used to set the frequency modulation deviation level by setting the output data signal amplitude. However, since Kvco varies with respect to RF center frequency, a method of adjusting frequency modulation deviation for each frequency setting is required. The shunt resistor in the resistor divider is replaced with a digital potentiometer to provide the necessary adjustment, using the on-board microprocessor to store a look-up table of settings versus frequency. A key feature of the digital potentiometer circuit is a method to increase the frequency bandwidth of the potentiometer. Digital potentiometers typically have frequency bandwidths measured in kiloHertz to MegaHertz, which limits their use in setting the frequency modulation deviation of high data rate telemetry transmitters. The circuit consists of a 256 position digital potentiometer and several resistors that are used to adjust the slope of the resistance vs. digital code curve and to translate the curve up and down along the Y-Axis. Adding external resistors to the digital potentiometer helps to increase the frequency bandwidth of the digital potentiometer. The selection of the maximum resistance range of the digital potentiometer is also important, as the potentiometer bandwidth is greater when a small portion of the total resistance is used. This paper will explore various methods of increasing the effective bandwidth of a digital potentiometer, with the goal of making them suitable for use in dynamically setting the frequency modulation deviation via digital control.