1。 Briefly define the following terms
1)Transducer
A transducer is a device that converts a signal from one physical form to a corresponding signal having a different physical form .
2)Sensor
A nsor converts a physical signal into an electrical signal （i.e。， a microphone)。
3)Actuator
An actuator is a device that converts electrical energy into physical energy （i。e., a loudspeaker）。
4)Linearity
The linearity describes the cloness between the calibration curve and a specified straight line.
5)Sensitivity
The nsitivity is defined in terms of the relationship between input physical signal and output electrical signal。 It is generally the ratio between a small change in electrical signal to a small change in physical signal。 The nsitivity is the slope of the calibration curve。
6)Hysteresis
The hysteresis refers to the difference between two output values that correspond to the same input, depending on the direction （increasing or decreasing） of successive input values. That is， similarly to the magnetization in ferromagnetic materials, it can happen that the output corresponding to a given input depends on whether the previous input was higher or lower than the prent one。
Some nsors do not return to the same output value when the input stimulus is cycled up or down。 The width of the expected error in terms of the measured quantity is defined as the hysteresis。
7)Repeatability The repeatability is the cloness of agreement between successive results obtained with the same method under the same conditions and in a short time interval。
δ—sample standard deviation
8)Strain （mechanical)
Fractional change in length ΔL/L.
9)Gage factor
The gage factor is defined as the fractional change in resistance divided by the strain.
10)Piezoresistive effect
The change in resistivity as a result of a mechanical stress is called the piezoresistive effect.
11)direct piezoelectric effect.
the phenomenon of generation of a voltage under mechanical stress is referred to as the piezoelectric effect。
12)conver piezoelectric effect。
The mechanical strain produced in the crystal under electric stress is called the conver piezoelectric effect.
13)Numerical Aperture
The ”acceptance cone” defines how much light will be accepted into the fiber and ultimately how much remains in the fiber， and is referred to as the numerical aperture.
14)Extrinsic nsor
The optical fiber plays no part in achieving the modulating but simply acts as a transmission medium ; the are extrinsic nsors.
15)Intrinsic nsors （fiber optic nsor)
The optical fiber plays a major role in modulating the energy from the source; the are referred to as intrinsic nsors.
16)Humidity
a quantity reprenting the amount of water vapor in the atmosphere or a gas
17)Absolute humidity
Absolute humidity is the mass of water vapor per unit volume of air.
18)Relative humidity
The ratio of the actual vapor density to the theoretical maximum (saturation） vapor den
sity at the same temperature, expresd as a percentage。 The relative humidity is the ratio of the actual vapor pressure to the saturation vapor pressure at given temperature.
19)Peltier effect
When two dissimilar metals are connected together, a small voltage called a thermojunction voltage is generated at the junction。 This is called the Peltier effect.
20)Law of Homogeneous Conductors
For a given pair of homogeneous conductors forming a clod loop， the Seebeck emf depends only on the temperatures of the junctions， and not on the temperature distribution along the length of the conductors。
21)Law of intermediate metals
A third (intermediate） metal wire can be inrted in ries with one of the wires without changing the voltage reading （provided that the two new junctions are at the same temperature).
If there is a third metal introduced into the thermocouple circuit ， it will not adverly effect the reading， if and only if the two junctions of the third metal are at the same temperatures .
22)Bernoulli's theorem
Bernoulli’s equation states that energy is approximately conrved across a constriction in a pipe.
Bernoulli’s equation: P/(ρ•g) + ½v2/g + y = constant （ρ=density； g=acceleration of gravity ; v=fluid velocity； y=elevation ）
2。 Describe the following devices and how they work
1)Strain gage
The strain gauge usually consists of wire, baking, thinpaper， and lead welded。 The wire is arranged in the form of a grid in order to obtain higher resistances。
2)Parallel plate Capacitive Sensor
The parallel plate Capacitive Sensor is a function of the distance d (cm） between the electrodes of a structure， the surface area A （cm2) of the electrodes， and the permittivity ε0 (for air) of the dielectric between the electrodes; therefore：
