Homework 2 solutions_1

Homework 2 solutions_1 - Homework 2 12 1. Give two...

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Homework 2 1. Give two completely different examples of sensors and their associated transducers. For each of them, identify the physical element undergoing the change and how the transducer converts this change into a measureable output. Example 1 Cell-based sensor for pathogens. The sensor is a layer of adherent cells in culture that die in response to the presence of a pathogen. The transducer is an array of capacitance sensors that detect changes in cell adherence. (Cells that adhere to surfaces have a flattened-out morphology when healthy, and they ball up and/or detach from the surface when they die.) Example 2 Strain gauge. The sensor is a material whose electrical resistance changes with strain (the electrons move through the material differently). The transducer is a bridge circuit that converts a change in resistance to a change in voltage. Example 3 Pressure sensor. The sensor is a membrane that deflects under pressure. The transducer is circuit that includes a capacitor with one electrode on the membrane as one plate and a fixed electrode a small distance away as the second plate. When the membrane moves, the capacitance changes, which the circuit converts to a voltage or current. 2. a) What is a calibration curve? b) What is it’s purpose? c) Is loss of calibration due to random or systematic errors? Give an example of something that could lead to loss of calibration. a) A calibration curve is a plot of the output of a measurement system for a series of known inputs, typically standards. b) It is only by comparing the outputs to what they should be at known input values that systematic errors, such as offsets, can be identified and the accuracy of device determined. Calibration records are useful diagnostics, and provide a valuable record. Calibration should be performed routinely to ensure that your data are trustworthy. c) Systematic errors, such as room temperature changes, sensor drift, the corrosion of connecting wires. 12 points (6 each) 12 points
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3. a) How can one determine the precision of a measurement? b) Is poor precision a result of random or systematic errors? c) Give an example of such errors. d) How does precision differ from reproducibility? e) Give an example of errors that would lead to poor reproducibility.
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This note was uploaded on 11/28/2010 for the course ENES enes100 taught by Professor Staff during the Spring '10 term at Maryland.

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Homework 2 solutions_1 - Homework 2 12 1. Give two...

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