Methods to simulate resistance at high resolution and accuracy

Sammanfattning: 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.