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 < 7 are acidic, with pH > 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

pHIon Concentration (gram equivalent

per liter)Type of Solution

0 1.0

Acid Solution 

- Hydrogen ions - 

H+

1 0.1

2 0.01

3 0.001

4 0.0001

5 0.00001

6 0.000001

7 0.0000001 Neutral Solution

8 0.000001

Basic (alkaline) Solution 

- Hydroxide ions -OH-

9 0.00001

10 0.0001

11 0.001

12 0.01

13 0.1

14 1.0

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Examples of substancesProduct 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 Ω)• 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 sensorglucose oxidase

2 2 2 2Glucose + 2H O+O Gluconic Acid + 2H O

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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