Biomedical Engineering Reference
In-Depth Information
Fig. 1.7
pH scale
Solutions with a higher [H
+
] ions than water (pH less than 7) are acidic;
solutions with a lower [H
+
] than water (pH greater than 7) are basic or alkaline.
Measuring pH evaluates the potential of solutions with unknown [H
+
]toa
known reference potential. PH meters alter the voltage ratio between a reference
half-cell and a sensing half-cell to pH values. In acidic or alkaline solutions, the
voltages on the outer membrane surface vary proportionally to changes in [H
+
].
The pH meter classifies the change in potential and determines [H
+
] of the
unidentified by the Nernst equation:
unknown H
þ
=
internal H
þ
E
¼
E
o
þ
2
:
3 RT
ð
Þ=
nFlog
f
½
½
g
where E = full potential difference (measured in mV); E
o
= reference potential;
R = gas
constant;
T = temperature
in
Kelvin;
n = number
of
electrons;
F = Faraday's constant; [H
+
] = hydrogen ion concentration.
pH measurement is measured by using pH meter. A pH measurement system
consists of three parts:
1. Basic electrode
2. Reference electrode
3. Impedance measurement meter
The actual pH of the solution changes with the temperature change.
1.9.8 Rotational Motion Measurement
The various devices available for measuring rotational displacements are: Rota-
tional displacement transducers measure the angular motion of a body about some
rotation axis. Circular and helical potentiometers, rotational differential trans-
former, incremental shaft encoders, coded-disk shaft encoders, the resolver, the
synchro, the induction potentiometer, and the rotary inductosyn, Gyroscopes.
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