Biomedical Engineering Reference
In-Depth Information
8.2.2 Methods
David Tinwin describes four types of breath alcohol devices which include
semiconductor models (Breathalyzer), fuel cell models (alcosensors), infrared (IR)
spectroscopy models (intoxilyzers), and Gas Chromatography (GC) models (in-
toximeters) [ 51 ].
Taking blood to check alcohol on the road is difficult and almost impossible, so
the simple and feasible method is to check the extent of the gas breathed by a
driver. The E-nose can test the alcohol quantity of a driver conveniently and save
important data at any time.
8.2.2.1 Sensor
The wide-ranging selectivity of the chemical sensors in an E-nose is remunerated
by advanced information processing, although the sensor is a key design parameter
for the system. These design parameters include sensitivity, speed of operation,
cost, size, manufacturability, ability to operate in diverse environments, and the
ability to be automatically and quickly cleaned.
MQ-3 (Hanwei electronics: www.hwsensor.com ) gas sensor has good sensi-
tivity to alcohol, and has high quality resistance to disturbance from gasoline,
smoke, and vapor. The sensor could be used to detect alcohol at different con-
centrations; it is low cost and suitable for different applications. Basically, it has
six pins, the cover, and the body. Of the six pins, only four can be used. Two are
for the heating system, called H, and the other two are for connecting power and
ground, called A and B in Fig. 8.14 .
Also, TGS -822 (Figaro) can be used as breath alcohol detectors [ 47 ]. The
Figaro sensor developed using a tin dioxide (SnO 2 ) semiconductor as sensing
element of sensor has low conductivity in clean air. The sensor's conductivity
increases depending on the presence of detectable gas concentration in the air. As
shown in Fig. 8.13 a simple electrical circuit can convert the change in conduc-
tivity into an output signal which corresponds to the gas concentration.
The main characteristic of the sensor (TGS 822) is high sensitivity to the vapors
of organic solvents as well as other volatile vapors. Note that it also has sensitivity
to a variety of combustible gases such as carbon monoxide, making it a good
general-purpose sensor.
It is also available with a ceramic base which is highly resistant to severe
environments as high as 200 C (model# TGS 823) Fig. 8.15 .
TGS sensor complies with the above electrical characteristics when the sensor
is tested in standard conditions as specified:
Test Gas Conditions: 20 ± 2 C, 65 ± 5 %R.H.
Circuit Conditions: V C = 10.0 ± 0.1 V (AC or DC),
V H = 5.0 ± 0.05 V (AC or DC),
R L = 10.0 kX ± 1%
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