Chemical sensors

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Lecture 13

• Chemical sensors

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pH sensor

• pH indicates how acidic or alkaline a solution is
• pH term translates the values of the hydrogen ion
  concentration
• Solutions with pH lt 7 are acidic, with pH gt 7
  alkaline (basic), pH 7 is said to be neutral.

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pH sensor

• pH is defined as the negative logarithmic value
  of the Hydrogen ion (H) concentration

pH Ion Concentration (gram equivalent per liter) Type of Solution
0 1.0 Acid Solution - Hydrogen ions - H
1 0.1 Acid Solution - Hydrogen ions - H
2 0.01 Acid Solution - Hydrogen ions - H
3 0.001 Acid Solution - Hydrogen ions - H
4 0.0001 Acid Solution - Hydrogen ions - H
5 0.00001 Acid Solution - Hydrogen ions - H
6 0.000001 Acid Solution - Hydrogen ions - H
7 0.0000001 Neutral Solution
8 0.000001 Basic (alkaline) Solution - Hydroxide ions -OH-
9 0.00001 Basic (alkaline) Solution - Hydroxide ions -OH-
10 0.0001 Basic (alkaline) Solution - Hydroxide ions -OH-
11 0.001 Basic (alkaline) Solution - Hydroxide ions -OH-
12 0.01 Basic (alkaline) Solution - Hydroxide ions -OH-
13 0.1 Basic (alkaline) Solution - Hydroxide ions -OH-
14 1.0 Basic (alkaline) Solution - Hydroxide ions -OH-
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Examples of substances
Product pH
Battery Acid 0
HCl in stomach acid 1
Lemon juice, vinegar 2-3
Orange juice 3-4
Acid rain 4
Black coffee 5
Urine, salvia 6
Pure water 7
Sea water 8
Baking soda 9
Ammonia solution 10-11
Soapy water 12
Bleach 13
Oven cleaner 13-14
Drain cleaner 14
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pH sensor
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pH sensor - properties

• electrical resistance of the circuit is very high
  (around 400M O)
• Temperature dependent
• Requires regular calibration

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pH sensor
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Density - tanks
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Density - pipes
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Density vibrating fork
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Oxygen sensor (Lambda sensor)
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Oxygen sensor (Lambda sensor)
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Blood glucose sensor
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Blood glucose sensor
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Heated alcohol sensor
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Heated alcohol sensor
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Pyroelectric infrared-detector for Gas Analysis