Quiz 1 Topics Flashcards
Accuracy
Closeness of the reading to the actual quantity being measured.
Calibration Error
Type of systematic error
Can be caused by assuming a nonlinear response when in reality the response is not perfectly linear
Error in the calibration process
Intrusive Device
Ex: a thermometer
Can have significant loading error due to the energy exchange between the device and the measured value
Non intrusive Device
Ex: infrared sensor
Does not “intrude” on the measured value. Negligible loading error.
Random Error
Caused by lack of repeatability in the output of the measuring system.
Usually caused by uncontrolled variables in the measurement process.
Hysteresis
Time based dependence of the output on present and past inputs
Different output for the same input depending on if the measurement was creasing or decreasing prior to taking the reading
Span
Difference between the upper and lower range limits of a measuring device
Repeatability
Instruments ability to produce the same output repeatedly under the same conditions
Sensitivity
Ratio of change in output over to change in input. Determined during calibration.
Ex: rise of fluid in thermometer /change in temp
Short variable (Length, type, range)
2 bytes
Integer
+/- 32000
Long
Length, type, range
4 bytes
Integer
+/- 2,000,000,000
Unsigned short (Length, type, range)
2 bytes
Integer
0 to 64,000
Unsigned long
4 bytes
Integer
0 to 4,000,000,000
Float / double
Length, type, range
4 bytes
Floating point number
1x10^(+/-38)
Double double
8 bytes
Floating point number
1x10^(+/-308)
Short*
Int*
Double*
Pointer
Size depends on the OS
Type var[#]
Array size = type size * #
ISO
NIST
Standards organizations
Primary standards
Mass, length, time, temp, current, moles, light intensity
Secondary standards
Often kept in labs for calibration, they must be traceable to a primary standard (meaning they were compared to the standard at one point).
Bias
A systematic error that favors a particular result
LVDT
Linear variable differential transformer
1 primary coil centered between 2 secondary coils
Ferromagnetic core moves back and forth through coils, causes a voltage difference.
Coils are connected in such a way that their signs are inverted, so they will have opposite phases when the core is closer to one or the other.
Wheatstone Bridge
1/4 bridge
3 resistors of the same resistance value and one strain gage. If the bridge is balanced at first, the voltage output corresponds to the change in resistance due to strain.
Potentiometer
Resistance varies as a function of the position of a slider
Variable voltage divider
Inexpensive, readily available, require no signal conditioning
Capacitive Displacement Sensors
Based on either the distance between the capacitor plates (non linear relationship with voltage)
Or
Change in overlapping area of the plates (linear relationship with voltage)
Systematic Error
Repeatable error in a measurement that doesn’t vary with replication.
Estimated by the difference between the true value and average of many readings.
