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Instrumentation, Measurement and Control > Measurement of composition > Flashcards

Measurement of composition Flashcards

1
Q

Two systems used for measuring composition

A
  • Photometric
  • Electrochemical
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2
Q

Importance of composition measurement

A
  • standard way of measuring dissolved solids
  • ## we cannot always measure composition directly
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3
Q

Photometric methods

A
  • absorbance
  • turbidity
  • refractive index
  • Brix
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4
Q

Electrochemical methods

A
  • Conductivity
  • pH
  • REDOX
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5
Q

A light source emits radiaiton through the medium
Transmitted radiation is measured on the detector side
A photodiode determines the intensity of the light and converts it to a photoelectric current
The intensity of light received is proportional to the concentration of the substances

A

Absorbance

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6
Q

The cloudiness of haziness of a fluid caused by suspended particles

A

Turbidity

Measurement via the light absorbing and light scattering propoerties of the fluid
Most suspended solids are made up on inorganic materials, though bacteria and algae can also contribute to the total solids concentration

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7
Q

Sources of turbidity

A

Anything drifting or floating in the water

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8
Q

Measure turbidity by using a lamp which emits a beam into the medium which scatters as it hits the particles.
The detector converts the received light intensity into an electric signal

A

Nephelometric turbidity sensors

They feature an LED lamp and a light detector that is positioned in a 90o angle. The lamp emits a beam into the medium which scatters as it hits the particles. The detector converts the received light intensity into an electric signal

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9
Q

Absorption equation

A

Absorption = extinction coefficient * concentration * OPL

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10
Q

Amount of oxygen needed to fully oxidise all the oxidisable substances in a sample and can be determined via absorbance.

The sample is first prepared by being heated and adding digesting reagents. After digestion process has occured, the sample changes colour. This colour change is proportional to the concentration of carbon compounds. It is measured photometrically and the final value is determined using preset absorption curves

A

Chemical oxygen demand measured via absorbance

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11
Q

FNU are measured with …

A

infrared light

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12
Q

NTU are measured with …

A

white light

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13
Q

Use the back scattered light method. LED lamp and two light detectors positioned at 90 and 135o. Solid particles in the medium cause the incident light emitted by the lamp to scatter

A

Total solids sensors

Optical so not a direct measure

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14
Q

refractive index formula

A

speed of light in vacuum/speed of light in the substance

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15
Q

The ….. the refractive index, the slower the light travels in that material

A

larger

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16
Q

The larger the refractive index, the ….. the light travels in that material

A

slower

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17
Q

The speed of light in a vacuum is fixed, but when light moves through any other medium, it ….. since it is constantly being absorbed and re-emitted by atoms in the material

A

slows

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18
Q

When light changes speed as it crosses a boundary from one medium into another its direction of travel ……….

A

changes

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19
Q

Work by measuring the angle of critical refraction

A

Refractometers

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20
Q

Evaluate the amount of dissolved substances in solutions. They measure a wide range of liquid systems from low to hgh viscosity. Portable devices are available that can be used on location. Up to in line process devices which are relatively expensive.

A

Refractometers

21
Q

Amount of sucrose by mass in a pure water solution

A

Brix scale

One degree Brix is 1 gram of sucrose in 100 grams of solution.
Dissolution of sucrose and other sugars in water changes not only specific gravity but also optical properties in particular refractive index

22
Q

Refractive index changes with …

A

Temperature

23
Q

Instruments measure the process stream
temperature and refractive index and … the Brix value to what it would be at 20°C

A

correct

24
Q
  • based on the presence of ions
  • analysis of water based systems
A

Electrochemical methods

25
Q

Conductivity is linked directly to the ………………………

A

total dissolved solids

26
Q

Works by determining the resistance of the solution between two flat or cylindrical electrodes separated by a fixed distance

A

Conductivity

27
Q

Conductivity of solutions ……. as temperature changes

A

changes

28
Q

measure of transfer of hydrogen ions between chemical species in an aqueous solution

A

pH

29
Q

Measures of transfer of electrons between chemical species

A

reduction potential

30
Q
  • Glass or non glass electrodes
  • The pH electrode uses a hydrogen ion selective glass in contact with the solution which develops a potential proportional to the pH of the solution
  • A reference electrode is designed to maintain a constant potential at any given temperature and serves to complete the pH measuring circuit within the solution
  • REF electrode provides a known reference potential for the pH electrode. The difference in the potentials of the pH and reference electrodes provides a millivolt signal proportional to pH
A

pH potentiometric principle

31
Q

Remove electrons from another substance and are reduced themselves

A

Oxidisers

32
Q

Transfer electrons to another substance and are oxidised themselves

A

Reducers

33
Q

Measure in volts of the affinity of a substance for electrons, its electronegativity is then compared with Hydorgen (which is set at 0).

A

Redox potential

34
Q

A measure (in mV) of the tendency of a chemical substance to oxidise or reduce another chemical

A

Oxidation Reduction Potential

35
Q

A positive ORP indicates that a substance is ….

A

an oxidising agent

36
Q

A negative ORP indicates that a substance is ……

A

a reducing agent

37
Q

ORP potential is … dependent

A

temperature

38
Q

Determined by measuring the potential of a chemically inert electrode which is immersed in the solution. The sensing electrode potential is read relative to the reference electrode and the value is presented in millivolts (mV)

A

ORP measurement

39
Q

What is used to measure ORP

A

ORp sensor
REDOX sensor

40
Q

Usage of conductivity

A

Monitoring desalination

41
Q

Nephelometric Turbidity Units

A
  • NTU
  • FNU
42
Q

Brix measurement usages

A
  • food industry for quality contro
43
Q

Usages of ORP

A
  • Water which contains a relatively high concentration of a redox active species.
  • ORP measurements are used often to control disinfection
  • detect metallic pollution in groundwater or surface water or to determine the content of wastewater effluent
  • ORP to detect arsenic levels in drinking wells
44
Q
A
44
Q
A
45
Q

measured potential is reflection of the combination of the effects of the dissolved species in the medium

A

non specific measurement

46
Q

ORP is a ____ measurement

A

non specific

Because of this factor, the measurement of ORP in
relatively clean environmental water (ground, surface,
estuarine, and marine) has only limited value unless a
predominant redox-active species is known to be
present

47
Q

Digital multiparameter transmitter (4-20mA) which can be used for multichannel simultaneous monitoring of: conductivity, disinfection, ORP, oxygen, sludge level, turbidity & pH

A

Multiparameter field device

48
Q
A

Instrumentation, Measurement and Control (12 decks)

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