1. What is air core inductance ?
The inductance that would be measured if the core had unity permeability and the
flux distribution remained unaltered. (A measure of the inductance of a coil
without a core).
2. What do you mean by Balance?
A weighing machine. The terms scale and balance are often used
interchangeably. a balance was a device that determined mass by balancing an
unknown mass against a known mass as with a 2 pan assay balance.
3. Define Viscosity.
It is a measure of fluidity of the system. Many fluids undergo continuous
deformation with the application of shearing stress.
4. Define Newtonian fluids
If the force flow relation is linear then the fluid is Newtonian .
5. Define Non Newtonian fluids
If the force flow relation is non linear then the fluid is Newtonian .
6. Define Kinematic Viscosity.
Ratio of absolute viscosity to the density of the fluid. V= μ cm2 /V sec
7. Define Specific Viscosity.
Ratio of absolute viscosity of the fluid to the absolute viscosity of a standard fluid at
the same temperature. μs = μ / μh
8. Define Relative Viscosity.
Ratio of absolute viscosity of the fluid at a given temperature to the absolute
viscosity of a standard fluid at 20°c.
9. Define Viscosity index
It is an empirical number that indicates the effect of change of temperature on
viscosity if a fluid.
10. Define fluidity.
It is the reciprocal of viscosity. It is unit is 1/ poise.
11. Define Humidity.
It is basically moisture content in air or it is the quantity of water vapour retained by
gas.
12. Define Absolute Humidity.
Weight of water vapour in unit wait of gas.
1. H=Wr / Wg
13. Define Specific Humidity.
It is weight of vapors in unit weight of mixture.
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14. Define Relative Humidity.
This is the ratio of moisture content of gas to maximum moisture content of the gas
at that temperature.
15. Define various units of Humidity.
Vppm = parts per million / volume.
G/ kg = weight concentration
Relative humidity = in %
Dew point in °C.
16. Define Hygrometer.
Used to measure the moisture content in air. It also used to measure humidity.
17. What is the basic principle of Hygrometer.
It consist of mechanical device measuring the dimension change of humidity
sensitive materials like animal hair, animal membrane , paper etc.
18. Define Moisture.
Defined as the amount of water absorbed by solids or liquids.
19. What are the different types of viscometer?
Say bolt viscometer
Rotameter type
Consistency meters.
20. What is Psychrometer?
Psychrometer is a device that uses the bulb thermometers to measure humidity. It is
also used in air conditioning systems for maintaining humidity.
21. What are the different types of hygrometer?
Hair hygrometers
Wire electrode hygrometers
Electrolysis type hygrometers
Resistive type
Capacitive type
Microwave reflector
22. Explain the principle of saybolt viscometer.
As the viscosity of the fluid varies , the flow rate and hence time taken to drain the
fluid through the capillary tube varies. The time indicates the viscosity and is
denoted by say bolt number.
23. What is meant by consistency?
General term for viscosity and more often used in connection with Non-Newtonian
fluids.
24. What is Celsius or Centigrade?
A temperature scale defined by 0°C at the ice point and 100°C at the boiling point of
water at sea level.
25. Define Absolute Zero
Temperature at which thermal energy is at a minimum. Defined as 0 Kelvin,
calculated to be –273.15°C or –459.67°F.
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26. What is Ambient Temperature?
The average or mean temperature of the surrounding air which comes in contact with
the equipment and instruments under test.
27. Define Boiling Point
The temperature at which a substance in the liquid phase transforms to the gaseous
phase; commonly refers to the boiling point of water which is 100°C .
28. What is Calorie?
The quantity of thermal energy required to raise one gram of water 1°C at 15°C.
29. Define Exothermic process?
A process is said to be exothermic process when it releases heat.
30. What is Dissipation Constant?
The ratio for a thermistor which relates a change in internal power dissipation to a
resultant change of body temperature.
31. What is Fahrenheit?
A temperature scale defined by 32° at the ice point and 212° at the boiling point of
water at sea level.
32. Define Freezing Point
The temperature at which a substance goes from the liquid phase to the solid phase.
33. What is Kelvin?
Kelvin is the unit of absolute or thermodynamic temperature scale based upon the
Celsius scale with 100 units between the ice point and boiling point of water. 0°C =
273.15K. Symbol K.
34. What is Joule?
The basic unit of thermal energy.
35. Define Heat
Heat is thermal energy. Heat is expressed in units of calories or BTU’s.
36. What is Heat Sink?
A body which can absorb thermal energy.Practicaly, A finned piece of metal used to
dissipate the heat of solid state components mounted on it.
37. What is Heat Transfer
The process of thermal energy flowing from a body of high energy to a body of low
energy. Transfer by Means of :conduction; the two bodies contact. Convection; a
form of conduction where the two bodies in contact are of different phases, i.e. solid
and gas. Radiation: all bodies emit infrared radiation.
38. What is Latent Heat?
The amount of heat needed to convert a pound of boiling water to a pound of steam.
39. State Limits of Error
A tolerance band for the thermal electric response of thermocouple wire expressed in
degrees or percentage defined by ANSI specification MC-96.1 (1975).
40. What is Loop Resistance?
The total resistance of a thermocouple circuit caused by the resistance of
thermocouple wire.Usually used in reference to analog pyrometers which have
typical loop resistance requirements of 10 ohms.
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41. What is Maximum Operating Temperature?
The maximum temperature at which an instrument can be safely operated.
42. What is Mean Temperature?
The average of the maximum and minimum temperature of a process equilibrium.
43. Define Melting Point
The temperature at which a substance transforms from a solid phase to a liquid
phase.
44. What is Negative Temperature Coefficient?
A decrease in resistance with an increase in temperature.
45. Define Resistance Temperature Characteristic
A relationship between a thermistor’s resistance and the temperature.
46. What is Specific Heat?
The ratio of thermal energy required to raise the temperature of a body 1° to the
thermal energy required to raise an equal mass of water 1°.
47. What is RTD?
Resistance temperature detector.
48. What is Thermal Coefficient of Resistance?
The change in resistance of a semiconductor per unit change in temperature over a
specific range of temperature.
49. What is Thermal Conductivity?
The ability of a material to conduct heat in the form of thermal energy.
50. What is a Thermistor?
A temperature-sensing element composed of sintered semiconductor material which
exhibits a large change in resistance proportional to a small change in temperature.
Thermistors usually have negative temperature coefficients.
51. What is a Thermocouple?
The junction of two dissimilar metals which has a voltage output proportional to the
difference in temperature between the hot junction and the lead wires (cold junction)
52. What is Zero Power Resistance?
The resistance of a thermistor or RTD element with no power being dissipated.
53. what is Pressure?
Pressure is the amount of force applied to a unit area; Force divided by Area =
Pressure; the SI unit for pressure is the Pascal (Pa) which is derived from Kilogram
per Metre Squared (kg/m2).
54. what isAbsolute Pressure?
Absolute Pressure is one which is measured relative to a perfect vacuum.
55. define Barometric Pressure
Barometric Pressure or Atmospheric Pressure is the total outside air pressure
measured with reference to absolute vacuum. The pressure varies depending on
geographical location, altitude and local weather conditions.
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56. what is Bar?
Bar is a widely used metric unit of measure for pressure and 1 bar converts precisely
to 100000 Pascals.
57. what is Bonded Foil Strain Gauges ?
Bonded Foil Strain Gauges are metal based foil elements that are incorporated into
a flexible electrically insulating material which can then be bonded to a diaphragm
with adhesives. As pressure is applied to the diaphragm the strain gauge will deform
and its resistance will change.
58. what is Burst Pressure is a design safety limit which should not be exceeded. If
this pressure is exceeded it may lead to mechanical breach and permanent loss of
pressure containment.
59. what is Ceramic Pressure Sensors typically use diaphragms made from
Alumina (Al2O3) with a screen printed thick film strain gauge circuit. Ceramic
diaphragms are very inert and provide a high level of protection from aggressive
chemicals.
60. Compound Pressure Ranges are ones that combine positive and negative
pressure ranges into one pressure measurement device.
61. what is Differential Pressure is the difference between two separate pressure
points.
62. Digital Compensation is the process of collecting many measured points at
different pressures and temperatures and using this data to correct the output of a
pressure transducer so that the pressure accuracy and thermal errors can be
improved beyond what is practically achieved with analogue compensation.
63. Full Range Output or FRO is the maximum electrical output signal for an
analogue output pressure sensor.
64. Full Scale Output or FSO is the maximum electrical output signal for an
analogue output pressure sensor.
65. Gauge Reference Pressure is a pressure measured relative to atmospheric or
barometric pressure.
66. Hydrostatic Pressure is what is exerted by a liquid when it is at rest. The height
of a liquid column of uniform density is directly proportional to the hydrostatic
pressure.
67. what is Inch of Water Gauge or Inches of Water Column is an english and
american unit for measuring liquid level. 1 inch of water column at 4 degrees
celsius equals 249.089 Pascals.
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68. what is Long Term Stability or Long Term Drift is the amount of change of a
measured reading at exactly the same pressure and ambient conditions over a
given period of time which is typically quoted as an annual figure.
69. Measurement Precision is used to describe how close together a set of results
are and it means the same as non-linearity.
70. what is Negative Gauge Pressure or Suction Pressure is the difference in
pressure between any vacuum pressure and atmospheric pressure.
71. what is Non-Linearity is how much a set of recorded pressures deviate from the
best straight line and it is expressed as a percentage of full scale.
72. what is Overpressure or Proof Pressure is the maximum pressure that can be
applied to a pressure instrument without significantly affecting its reading
accuracy. Some manufacturers will state a maximum calibration shift following
an over-pressure condition where others will state that the specification is
unaffected.
73. what is Pressure Accuracy defines the limit that any pressure measurement
reading will deviate from the ideal point.
74. what is Pressure Transducer is any device that can convert a change in pressure
into a varying electrical signal.
75. Pressure Transmitter is a pressure transducer which has been combined with an
amplification circuit to allow the electrical signal to be sent over longer distances
without degradation.
76. Primary Pressure Standard are instruments that can measure pressure very
accurately by deriving a pressure reading from the fundamental components of
mass, acceleration and area.
77. what is PSI, Pounds per Square Inch or Pound Force per Square Inch is a
widely used British and American unit of measure for pressure.1psi converts to
6,894.76 Pascals.
78. what is Reference Pressure is the pressure present on the reverse or negative
side of a sensing diaphragm. For example the pressure reading will be zero when
the total pressure measured on the positive side of the diaphragm equals the
reference pressure.
79. what is Secondary Pressure Standards are instruments that cannot be used to
measure Force and Area directly to derive a measurement of pressure but are still
used as a traceable standard for calibrating other pressure instruments, e.g. an
Electronic Pressure Calibrator that uses a Pressure Transducer inside would be
classed as a Secondary Pressure Standard.
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80. what is Semiconductor Strain Gauges?
These are typically made from Silicon and have very high gauge factors
compared to metal foil strain gauges. Ions are implanted into the n type Silicon
substrate to create p type regions which are significantly more conductive than the
surrounding n type Silicon. A p-n junction,created which provides electrical
isolation for p-type region when reverse voltage is applied, thus creating isolated
resistive region that will change with applied stress.
81. Sealed Gauge Reference Pressure is a pressure measured relative to an
atmospheric or barometric pressure which has been sealed in a fixed closed
volume.
82. Span Output is the difference between the minimum and maximum output
signals of a pressure sensor.
83. Span Offset is the amount of deviation in maximum span output signal of a
pressure sensor from the ideal value at full scale pressure. The span offset is
normally expressed as percentage of full scale pressure or electrical units, e.g.
±0.5% FS or ±3mV.
84. what is Standard Atmosphere is a universally adopted standardized pressure
reading for barometric pressure at sea level and equals precisely 1013.25mb
absolute. Standard atmosphere is a particularly useful datum point in altitude
measurement since all altimeters are calibrated to this pressure.
85. Static Line Pressure is the total pressure present at a particular point along a
pressurized pipe. It is often quoted on the specifications for differential pressure
sensors as an indicator of the maximum pressure that can be applied to both the
high and the low side pressure ports at the same time. This should not be
confused with the over-pressure limit which is related to the differential pressure
range rather than the static line pressure.
86. what is Suction Pressure or Negative Gauge Pressure is the difference in
pressure between any vacuum pressure and atmospheric pressure.
87. Traceable Pressure Calibration means that the equipment which was used to
calibrate a pressure measuring device has been regularly calibrated by another
more accurate instrument for which its own calibration can be traced back either
indirectly or directly to a National Standards Laboratory e.g. National Physical
Laboratory in the UK.
88. Transducer is a device that converts a non-electrical change into an electrical
change.
89. Vented Gauge Reference Pressure or VG is a pressure measured relative to
"actual" atmospheric or barometric pressure.
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90. Wheatstone Bridge Strain Gauge circuits are used extensively inside pressure
transducers to convert mechanical stress into an electrical output signal.
91. Zero Offset is the deviation in output or reading from the ideal point at zero
pressure.
92. Zero Tare is the operation of removing any Zero Offset to obtain the optimum
measurement at zero pressure.
93. Factory calibration: The tuning or altering of a control device by the
manufacturer to bring it into specification
94. Range: The limits within which a device or circuit operates or the distance over
which a transmitter operates reliably.
95. pH: An indication of the acidity or alkalinity of a solution. Units range from 0
(most acidic), to 7 (neutral), to 14 (most alkaline).
96. Linearity: The degree to which performance or response approaches the
condition of being linear. Expressed in percent.
97. Impedance: The opposition in an electric circuit to the flow of an alternating
current. It consists of ohmic resistance, inductive reactance, and capacitive
reactance.
98. what is Inch of Mercury?
It is a British and American unit of measure for pressure. 1 inch of Mercury at 0
degrees Celsius (32 deg F) equals 3386.39 Pascals.
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