Lecture Midterm Flashcards
(67 cards)
Components of a measurement system
Measuring (measured variable) -> Sensor -> Variable Conversion Element -> Signal Processing -> Signal Transmission -> Remote intermediate -> Signal presentation/Recording -> Output display
gives an output that is a function of the measurand
sensor
if the output of the sensors is in an inconvenient form, converts it to a more convenient one
variable conversion element
improve the quality of the output of the measuring system
signal processing element
give an output based on the modulation of the magnitude of an external power source like electricity
active instruments
give an output based on internal changes (entirely by the quantity of the measurand) in the system that do not need an external power source, output resolution dependent on the measurand
passive instruments
instrument whose measurements are based on weights placed on top until the system is balanced (more accurate), point of ref, output is a result of a type of equilibrium
null-type instrument
instrument whose measurements are based on the deflection of a pointer connected to a spring that changes level with the measurand, how much a point moves from another
deflection-type instruments
output varies cts. as the quantity of the measurand changes in an infinite number of steps, more sensitive/dynamic, cts, proportionality
analog instruments
output varies in discrete steps as the quantity of the measurand changes, commonly used in modern instruments thanks to computing and micro-processors
digital instruments
gives an indication of the physical quantity measured, output is proportional, easier to visually detect
indicating instruments
gives a measurement signal output that is proportional to the magnitude of the measured quantity, typically parts of automatic control systems
signal instruments
the measure of how close the output reading of the instrument is to the correct value
accuracy - common to report inaccuracy as % f.s.
an instrument’s degree of freedom from random errors, samples are close together
precision
the closeness of output readings when the same input is applied repetitively over a short period of time with the same measurement conditions
repeatability
the closeness of output readings for the same input when there are changes in the measurement conditions
reproducibility
What is more accurate, repeatability or reproducibility?
reproducibility
the maximum error that is to be expected in some value
tolerance
the min and max values of a quantity that the instrument is designed to measure
range
when the output reading is linearly proportional to the quantity being measured
linearity
the minimum level of input before the change in the instrument output reading is of enough magnitude to be detectable
threshold
lower limit on the magnitude of the change in the input measured quantity that produces an observable change in the instrument output; how small of a change in input is needed for a change; presented as either an absolute value of fs
resolution
the difference between loading and unloading curves of measurement, dependent on each curve, error to both sides of the curve
hysteresis
range of different input values over which there is no change in output value, happens in digital output instruments
dead space
