Flashcards in Semester 2 Deck (31):

1

## What is the relationship between precision and significant figures?

### The higher the significant figures, the higher the precision.

2

## What does precision refer to?

### The limit of error in a measurement or variable.

3

## What does accuracy refer to?

### Closeness to the true value of a variable.

4

## 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.

5

## 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.

6

## Ideally, what is the relationship between the input and output of and an instrumentation system?

### Linear and is defined by the sensitivities.

7

## How do you find sensitivity, k, from a output range/input range graph?

###
It is the slope of the graph:

k = slope = Δo/ΔI

8

## What is sensitivity in terms of the output?

###
k(I - Imin) + Omin = O

O = output

9

## What "other inputs" can affect a system?

### Modifying input and interfering input

10

## What does modifying input (Im) do?

### Modified the linear sensitivity I.e temperature in strain gauges.

11

## What does interfering input (Ii) do?

### Interferes with the zero condition, therefore changing the static reference.

12

## What does an error band do?

### Defines for a particular input, the output will be within +\- ΔO

13

## What combines to give an overall statistical behaviour?

### Random effects in I, Im and Ii.

14

## 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

15

##
How is accuracy of a measurement system quantified?

###
Using measurement error E

E = measured value - true value

16

## What does the error band centred around the ideal output represent?

### The accuracy of the system

17

## When does a bridge become more linear?

### When r >> 1

18

## What Is the bridge ratio when maximum sensitivity occurs?

### r = 1

19

## How can bridges be linearised?

### A combination of sensors (with equal characteristics) and negative feedback.

20

## What is the force given by Newtons 2nd law, Hooke's law and resistive damping?

### F = ma +rv + ky

21

## 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.

22

## What is stress?

### σ = force/area

23

## What is the effect of stress called?

###
Strain, which is defined as the fractional change in length.

ε = Δl/l

24

## What is Youngs modulus (E)?

### E = σ/ε

25

## When a material extends in length due to strain, there is a decrease in cross sectional area, what does this result in?

###
Two opposing strains are produced; longitudinal and transversal, which are related by Poissons ratio.

26

## What damping ratio gives optimum response and settling times?

### 0.7

27

## What is a major limitation of a hydrophone?

### It has a very high output impedance, effectively making it a current source.5

28

## How should the strain gauges in a bridge be arranged to eliminate interfering inputs?

### The strain gauges under longitudinal strain in opposite arms and similarly for compressive strain.

29

## How do you determine the static error in a measurement system?

### Assume all of the statistical variations may be combined as a linear sum of the component variances. In addition the variances must be scaled using the partial derivatives of the model equations.

30

## How is an error band use to analyse a system?

### The statistical variation takes into account any modifying, interfering, offset, non-linearities, hysteresis, parameter variations and defines the behaviour via a derivation from the linear relationship.

31