## Instrumental Ch1-3,5

 Data Domain
 way of encoding an Analytical response in electrical or non electrical signals
 Detector
 device that indicates change in environment
 Transducer
 device that converts non electrical signals to electrical data
 Sensor
 device that is capable of monitoring a specific chemical species continuously and reversibly
 Examples of non electrical domains
 light, color, scale position, number(objects)
 Examples of electrical domains
 current, voltage, charge, frequency
 Analog domains
 record the magnitude of electrical quantities
 Time domains
 record things that vary with time frequency, phase, pulse width
 Digital domains
 record discrete values count,serial, parallel
 Precision
 is a measure of random of indeterminate error associated with an analysis
 Accuracy
 measure of determinate errors (operator, method)
 Detection limit
 the minimum concentration or mass of analyte that can be detected at a known confidence level-which is dependent on the ratio of magnitude of analyte signal to the size of the statistical fluctuations of the blank
 Figures of merit
 A numerical quantity based on one or more characteristics of a system that represents a measure of the systems efficiency or effectiveness
 On a calibration plot the ________ the slope the more sensitive the machine
 Higher
 Two things that can limit sensitivity
 slope of the calibration curve and the reproducibility or the precision of the measure device
 Selectivity
 degree at which the method is free from interference by other species in the sample matrix
 Circuit
 a closed path that may be followed by and electrical current
 Kirchhoff’s current law
 sum of current around any point in a circuit is zero
 Kirchhoff’s voltage law
 sum of voltages around closed electrical loop is zero
 Power
 the amount of work done by an electrical current
 Voltage divider
 a device that provides potentials that are variable functions of an input voltage
 Potentiometer
 a device that provides potential that’s continuously variable
 A/D converter
 a device that converts the input analog signal to a number proportional to the magnitude of input voltage
 Sinusoidal wave
 the most common periodic electrical signal
 Dielectric
 A substance that contains no current carrying or charged species, it resists a change in voltage
 Impedance
 expression which in applied to any electrical system which impedes the flow of current
 Operational Amplifiers
 a device used in precise measurement of voltage, current, and resistance- can also be used to provide a constant current and constant voltage
 Feed back circuit
 A special type of OP amp- the output signal is connected to one of its inputs reading a signal feed back
 Signal
 Noise
 degrades accuracy and precision -can limit amounts of analyte detected
 Chemical noise
 A type of noise that is caused by temperature, pressure variations, changes in humidity, and light
 Types of Instrumental noise
 Thermal noise, Shot noise, Flicker noise
 Thermal noise
 a noise that is random and periodically produces voltage fluctuations that appear as readout noise
 Thermal noise is dependent on what? and independent on what?
 dependent on frequency bandwidth independent of frequency
 Thermal noise is also known as
 white noise or Johnson noise
 Shot noise
 A noise that is caused when electrons or other charge particles cross a junction
 Flicker noise
 A noise whose cause is not understood but is characterized by the fact that its magnitude is inversely proportional to the frequency of the signal observed
 Environmental noise
 a noise that occurs when parts of the instrument act as an antenna which can pick up electromagnetic radiation and convert it to an electrical signal
 Ways to improve signal to noise
 Analog filtering, Modulation, signal chopping, lock in amplifiers, various software programs…… add math ways
 Analog filtering
 uses a low pass filter to remove high frequency components of the signal- this includes thermal and shot noise
 Modulation
 a process where the signal is either brought up or down- in an effort to separate it from noise- the noise filtered out and then the signal brought back to its original place
 Signal chopper
 Converts the signal into a square wave
 lock in amplifiers
 can be used when the S/N ratio is bad- but requires a reference signal with the same frequency and phase to work
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