253 Quiz 13 14 15

Front 1

Capacitive sensors consist of two parallel plates in which the dielectric between the plates is non-conductive medium such as air. The capacitance C is given by C = (er e0 A)/d. Using your course material (module 10), A is ______________, d is _____________, er is ________________ and e0 is _______________________.

Back 1

e0 is the absolute permittivity, er is the relative permittivity of the dielectric medium between the plates,
A is the area of the plates
d is the distance between the plates.

Front 2

Capacitive sensors consist of two parallel plates in which the the dielectric between the plates is non-conductive medium such as air. The capacitance C for a two parallel plates with surface area A and distance d between them is given by

C = (er e0 A)/d. Assume e0 =1 and unitless. What is the units of er ? _______________________.

Back 2

Farad/m

Front 3

Capacitive sensor probes are often used to measure physical quantities (measurands) that cause changes to the dielectric constant of the medium between the plates. This principle is used in devices to measure ___________________ and ____________________.

Back 3

Humidity, Surface level, Moisture content

Front 4

Capacitive probes are typically used to measure changes in the gap between the probe and a metallic surface. The changge in the gap is typically due to changes in applied pressure or due to variations in the thickness of the surface under test. Although the change in the gap results in a change in the capacitance value, the measurands are ______________ or ______________.
Question 4 answers

Back 4

pressure, thickness.

Front 5

To measure the changes in the capacitance value of the capacitor sensor, we typically use the following variable conversion element (VCE) ________________. This kind of VCEs convert the change in capacitance value into a change in a more convenient physical quantity such as voltage.

Back 5

Deflection-type AC Bridge

Front 6

In the case of variable inductance sensors, the current through the inductor I equals the voltage across the inductor V divided by the impedance of the inductor ZL. I = V/ZL where ZL = w L, that is I =V/(w L). If we are to fix the values of V and w, then I = Constant/L. That is, a change in the value of L results in a change in the value of the current through the inductor. This principle is used to measure change in _______________________. Hint: See Fig. 13.1 in the course materials.

Back 6

displacement

Front 7

In the case of variable inductance sensor, the following type of VCE _______________________ is typically used.

Back 7

Deflection-type AC bridge

Front 8

In the case where a variable reluctance sensor (VRS) is used to measure the speed of a shaft, a ferromagentic gearwheel is placed on the shaft. Assume that the rotational speed of the shaft is 20 rotations per second and the number of teeth on the gearwheel is 10. Determine the frequency of the periodic output voltage measured across the pick up coil. the frequency is ______________ cycle per second. Hint: see Fig. 13.2.

Back 8

200 cycles per second

Front 9

In the case where a variable reluctance sensor (VRS) is used to measure the speed of a shaft, a ferromagentic gearwheel is placed on the shaft. Assume that the rotational speed of the shaft is 20 rotations per second and the number of teeth on the gearwheel is 10. Determine the frequency of the periodic output voltage measured across the pick up coil. the frequency is ______________ cycle per second. Hint: see Fig. 13.2.

Back 9

200 cycles per second

Front 10

The physical principle behind eddy current sensor is the fact that the exposure of a metal surface to a ________________ frequency magnetic flux results in the creation of surface circular currents (known as eddy currents) on that metal surface. The eddy currents on the metal surface generate a magnetic field that is _________ in direction to that of the applied magnetic flux.

Back 10

high
opposite

Front 11

The eddy currents alter the inductance of the probe coil and this alteration can be translated into an output voltage that is proportional to the _____________ between the probe and the target. Hint: See Fig 13.3 in the course material (module 10).

Back 11

distance

Front 12

Hall effect sensors are based on a principle known as_____________ law which states that a magnetic field would exert a force on an electric charge only if it is moving. The force on the moving electric charge is proportional to the strength of the magnetic field and the speed of the charge. The direction of the force is always perpendicular to both the magnetic field and the velocity of the charge.

Back 12

Lorentz Force

Front 13

In Fig. 13.4 (principles of Hall-effect sensor), the excitation current I provides the moving electric charges. The relationship between I, the magnetic field strength B and the output voltage V generated due to Lorentz force is V= K*I*B, where K is known as the Hall constant.

You have a sample of silver in the form of a rectangle block used in a Hall-effect probe. The Hall constant for silver

K=7.98x10-7 m2/C (C=Coulomb is the unit of charge). The sample is placed in a magnetic field B of 2.18 Tesla, and an excitation current of I=10.00 A is applied through the sample. Determine the Hall effect output voltage in uV (with 2 digits afetr the decimal point).

Back 13

17.40 uV

Front 14

List two applications for Hall Effect sensors.

Back 14

Keyboard button
Automobile ignition system

Front 15

Barium Titanate (ferroelectric ceramics) has piezoelectric properties and is used in constructing sensors for meauring pressure, force and acceleration. For a rectangular block of material, the induced voltage is given by V= (k*F*d)/A, where F is the applied force in N, A is the area of the material in mm2, d is the thickness of the material in mm and k is the piezoelectric constant.

Given that Barium Titanate has a piezoelectric constant of 140 mV mm/N, determine the output voltage when a force of 2 Newtons is applied on a rectangular block of Barium Titanate with thickness (d) of 1 mm and surface area (A) of 200 mm2. Express the output voltage in mV with 2 digits after the decimal point.

Back 15

1.40 mV

Front 16

List two applications of piezoelectric sensors.

Back 16

ultrasound revievers
Microphones

Front 17

Strain gage is based on the physical principle that the change in the resistance of a thin conductive wire is inversely proportional to _____________ of the wire

Back 17

cross-sectional area

Front 18

Strain gage sensor is typically used with the following VCE circuitry_______________.

Back 18

Deflection-type DC Bridge

Front 19

A strain gage with Ru of 120 ohms (without stress applied) is used to measure the strain experienced on a metal beam. The VCE Wheatstone bridge used with the strain gage has R1=R2=R3= 1000 ohms with an excitation voltage of 10 volts. Assume that the output voltage of the bridge is 54 uV, determine the corresponding change in Ru, that is, deltaRu. Assume deltaRu <<< Ru. Express delta R in milli-ohms with 2 digits after the decimal point.

Back 19

6.05 m-ohms

Front 20

Biosensor is a sensor that includes two key elements. These are: [a] and [b].

Back 20

biological recognition element
transducer

Front 21

For a home blood glucose meter that is based on measuring current (Amperometric measurement), the biological recognition element is ______________________________.

Back 21

glucose oxidase

Front 22

The transducer part of a Biosensor converts the biological response into [a] signal.

Back 22

electrical

Front 23

Reduction/oxidation (Redox) reactions involve the transfer of electrons from one compound to another. Specifically, one reactant is oxidized (loses electrons) and one is reduced (gains electrons). For a home blood glucose meter that is based on measuring current, the electrons that cause the measurable current come from the oxidation of __________________.

Back 23

FADH2

Front 24

The reason why high altitude results in inaccurate readings on home glucose meters is because at high altitude there is a much lower concentration of ___________________ which is a crucial part of the reduction/oxidation (Redox) reaction resulting in hydrogen proxide H2O2.

Back 24

oxygen

Front 25

When blood is collected, whether at the lab, or using home blood glucose monitoring, it is whole blood. However, when the laboratory measures glucose, it processes the blood into plasma (a clear pale yellow color). Because the red blood cells are absent from plasma, there is more room for glucose to occupy this space. Plasma Glucose is generally about ____________ than Whole Blood Glucose.

Back 25

11% higher

Front 26

The range of the home blood glucose meter we talked about in class was from [a] mg/dl of glucose to [b] mg/dl of glucose.

Back 26

20
600

Front 27

An example of biological recognition element is [a], while an example of physical transducer is [b].

Back 27

Antibodies
Optical

Front 28

Enzymes are proteins. Although they are not living things, they are made by living things. Different enzymes have different types of [a].

Back 28

job

Front 29

In Clark oxygen electrode device, the concentration of Glucose is determined by the rate of change in the concentration level of [a] which is converted into a change in the current level flowing between the [b] and [c] of the device.

Back 29

oxygen
cathode
anode

Front 30

pH meter measuring electrode converts hydronium ions concentration [H3O+] (that is equivalent to the hydrogen ions concentration [H+]) into ____________________.

Back 30

voltage drop

Front 31

In a pH meter, the measuring electrode is _____________ to the hydronium ions concentration [H3O+] (that is equivalent to the hydrogen ions concentration [H+]). However, the reference electrode is _______________ to the hydronium ions concentration [H3O+] (that is equivalent to the hydrogen ions concentration [H+]).

Back 31

sensitive, insensitive

Front 32

What is the sensitivity of the pH meter expressed in terms of mV per pH unit (2 digits after the decimal point) at
(1) 0 degree C
(2) 25 degree C
(3) 50 degree C
(4) 100 degree C

Back 32

(1) - 54.20 mV/pH unit at 0 degree C
(2) - 59.16 mV/pH unit at 25 degrees C
(3) - 64.12 mV/pH unit at 50 degrees C
(4) - 74.04 mV/pH unit at 100 degree C

Front 33

What is the value of pH (expressed with 2 digits after the decimal point) corresponding to a measured potential difference of 128.00 mV at 50 degrees C? The mV/pH level slope at 50 degrees C is - 64.12 mV/pH.

Back 33

5.00 pH units

Front 34

What would be the potential difference (expressed in mV with 2 digits after the decimal point) at 100 degrees C between the measuring electrode and the reference electrode for a pH of 9.50 pH units?

Back 34

- 185.10 mV

Front 35

Using the linear relationship between the pH level and the corresponding potential difference between the measuring and reference electrodes at 25 degree C, calculate the voltages (in mV with 2 digits after the decimal point) measured between the measuring and reference electrodes of a pH meter for a solution with pH of 0 and another with pH of 14 . Assume that neutral pH is 7 at 25 degrees C.

Back 35

414.12 mV for a pH value of 0
-414.12 mV for a pH value of 14

Front 36

What would the potential difference (express with 2 digits after the decimal point) be between the measuring electrode and the reference electrode at the operational amplifier if the pH of a solution is 2.00 pH units at 100 degrees C? Assume that neutral pH is 7 pH units.

Back 36

370.20 mV

Front 37

One very important environmental correction that pH meters must be capable of performing is ______________________ compensation.

Back 37

temperature

Front 38

The circuitry in a pH meter, converts the potential difference between the measuring and reference electrode into pH level reading.

For example, at 25 degrees C,
(a) the first stage op amp acts as a decoupler with a gain of 1,
(b) the second stage op amp multiplies the potential difference (expressed in V) by a multiplier (known as the ionization constant and equals the inverse of the sensitivity expressed in V/pH ) = ____________ and
(c) the third stage op amp (differential op amp) applies an offset of ______________.
Note that the sensitivity at 25 degrees C is - 0.05916 V/pH.
Express all numeric values with 2 digits after the decimal point.

Back 38

-17
7

Front 39

There are two main types of smoke detectors: _______________ detectors and __________________ detectors.

Back 39

ionization
light scattering

Front 40

n the light scattering smoke detector, there is a T-shaped chamber with a light-emitting diode (LED) that shoots a beam of light across the horizontal bar of the T. A photodiode, positioned at the bottom of the vertical base of the T, generates a current when it is exposed to light.

Under smoke-free conditions, the light scattering smoke detector generates ____________ current. When smoke is present, the light is ________________ by smoke particles, and some of the ______________is directed down the vertical part of the T to strike the photodiode generating current. When sufficient light hits the cell, the current triggers the alarm.

Back 40

no
scattered
light

Front 41

In the ionization smoke detector, the ionization chamber is basically two metal plates a small distance apart. Between the two plates, air molecules-made up mostly of ___________ and ____________ atoms, are ionized when electrons are knocked out of the molecules by alpha particles radiated from the __________________ material (be specific).

Back 41

Oxygen
Nitrogen
Americium

Front 42

In the ionization smoke detector, the positively charged ions of oxygen and netrogen flow toward the ___________ charged plate, while the freed electrons flow toward the ______________ charged plate, resulting in a steady flow of current.

Back 42

negatively
positively

Front 43

In the ionization smoke detector, when smoke enters the ionization chamber, the current is disrupted as the smoke particles attach to the ___________________ and restore them to a neutral electrical state. This reduces the flow of ________________ between the two plates in the ionization chamber. When the electric ______________ drops below a certain threshold, the alarm is triggered.

Back 43

oxygen and nitrogen ions
electricity or electrons
current

Front 44

Both ionization and light scattering detectors are effective smoke sensors. Ionization detectors respond more quickly and are more sensitive to ______________ fires with smaller combustion particles (smaller than 1 micrometer); while light scattering detectors respond more quickly to _______________ fires with large combustion particles (greater than 1 micrometer)

Back 44

flaming
smoldering

Front 45

Carbon monoxide (CO) is produced in the case of incomplete combustion reaction which happens when there is not adequate amounts of _____________________ to produce carbon dioxide.

Back 45

oxygen

Front 46

The oxidation reaction at the anode of a CO detector converts CO + H2O into carbon dioxide, hydrogen ions and _______________________

Back 46

electrons

Front 47

The reduction reaction at the cathode of a CO detector combines the hydrogen ions, the electrons (delivered by the external power supply - potentiostat) with __________________ and produces ___________________, which then returns to the medium to undergo the process again.

Back 47

oxygen
water

Front 48

The overall reduction/oxidation reaction in a CO detector produces 2 CO2 molecules for every 2 CO and 1 O2 molecules used. The detector gas permeable membrane is constructed so that the following gas __________________can diffuse out from the detector into the room, leaving the sensor unchanged.

Back 48

carbon dioxide

Front 49

Electrons are generated by the oxidation process at the anode of a CO detector. For the electrons to be transferred to the cathode where the reduction process takes place, ____________ must be applied externally between the _________ and ___________.

Back 49

a power supply
anode
cathode

Front 50

Electrons are generated by the oxidation process at the anode of a CO detector. For the electrons to be transferred to the cathode where the reduction process takes place, ____________ must be applied externally between the _________ and ___________.

Back 50

a power supply
anode
cathode

Front 51

Carbon monoxide binds very strongly to the iron atoms in hemoglobin, the principal oxygen-carrying compound in blood. The affinity between CO and hemoglobin is ___________ times stronger than the affinity between hemoglobin and oxygen. When CO binds to the hemoglobin it cannot be released nearly as readily as oxygen would do. The preferential binding of _________________ to the iron in hemoglobin is the main reason for carbon monoxide poisoning.

Back 51

200 to 240
CO

Front 52

Thermocouples convert a change in temperature into a ________________________

Back 52

emf

Front 53

Name the two alloys that make up a K-type thermocouple.

Back 53

Alumel (Nickel Aluminum)
Chromel (Nickel Chromium)

Front 54

Two of the main disadvantages of thermocouples are:

Back 54

are relatively expensive
have low output level

Front 55

Thermistors operate on the principle that the semiconductor material exhibit a change in resistance with a change in temperature . Unfortunately, that relationship is not linear, in fact, it has __________________________, which necessitates the need for special signal conditioning.

Back 55

negative temperature coefficient

Front 56

Thermistors are used in physical chemistry, physiology, ecology and environment temperature measurements because of the following advantages:

Back 56

high precision (resolution of 0.0001 0C)
small size

Front 57

Your basic fever digital thermometer today uses a thermistor to measure the change in body temperature. To display digitally the correct temperature, the change in the thermistor resistance is converted into voltage using ________________ (be specific about the type of conversion element)
Question 18 answers

Back 57

voltage divider

Front 58

RTD Resistance Temperature Devices relay on the principle that the ___________ of a metal varies with temperature.

Back 58

resistance

Front 59

Your basic fever digital thermometer today uses a thermistor to measure the change in body temperature. To display digitally the correct temperature, the following electronic components are used in its construction :

Back 59

a) op amp for signal gain and offset
b) A-D-C for dignal digitizition
c) Code converter for signal lineraization and inversion