Semester 2 Flashcards
What is the relationship between precision and significant figures?
The higher the significant figures, the higher the precision.
What does precision refer to?
The limit of error in a measurement or variable.
What does accuracy refer to?
Closeness to the true value of a variable.
How is precision/uncertainty preserved in a calculation?
When multiplying, dividing or using other functions, the answer should have the same number of significant figures as the smallest in the calculation.
How is precision/uncertainty preserved when adding or subtracting?
The answer should have the same number of decimal places as the smallest used in the calculation.
Ideally, what is the relationship between the input and output of and an instrumentation system?
Linear and is defined by the sensitivities.
How do you find sensitivity, k, from a output range/input range graph?
It is the slope of the graph:
k = slope = Δo/ΔI
What is sensitivity in terms of the output?
k(I - Imin) + Omin = O
O = output
What “other inputs” can affect a system?
Modifying input and interfering input
What does modifying input (Im) do?
Modified the linear sensitivity I.e temperature in strain gauges.
What does interfering input (Ii) do?
Interferes with the zero condition, therefore changing the static reference.
What does an error band do?
Defines for a particular input, the output will be within +- ΔO
What combines to give an overall statistical behaviour?
Random effects in I, Im and Ii.
The random fluctuations in Im, Ii and I (overall statistical behaviour) can be assumed to have what kind of function?
Gaussian probability density function around the mean value
How is accuracy of a measurement system quantified?
Using measurement error E
E = measured value - true value
What does the error band centred around the ideal output represent?
The accuracy of the system
When does a bridge become more linear?
When r»_space; 1
What Is the bridge ratio when maximum sensitivity occurs?
r = 1
How can bridges be linearised?
A combination of sensors (with equal characteristics) and negative feedback.
What is the force given by Newtons 2nd law, Hooke’s law and resistive damping?
F = ma +rv + ky
How can non-linearity be removed in a bridge?
- 2 strain gauges to be used in an adjacent arm (R1 and R2)
- R1 in tensile (+) and R2 in compressive (-) strains.
What is stress?
σ = force/area
What is the effect of stress called?
Strain, which is defined as the fractional change in length.
ε = Δl/l
What is Youngs modulus (E)?
E = σ/ε
