Figaro TGS2442-B00 TGS 2442 Gas Sensor For Carbon Monoxide Carbon monoxide (Ø x H) 9.2 mm x 12.7 mm TGS2442-B00 Data Sheet

2

GENERAL INFORMATION FOR TGS SENSORS

The sensing material in TGS gas sensors is metal
oxide, most typically SnO

2

.  When a metal oxide

crystal such as SnO

2

 is heated at a certain high

temperature in air, oxygen is adsorbed on the crystal
surface with a negative charge.  Then donor electrons
in the crystal surface are transferred to the adsorbed
oxygen, resulting in leaving positive charges in a
space charge layer.  Thus, surface potential is formed
to serve as a potential barrier against electron flow
(Figure 1).

Inside the sensor, electric current flows through the
conjunction parts (grain boundary) of SnO

2

 micro

crystals.  At grain boundaries, adsorbed oxygen
forms a potential barrier which prevents carriers from
moving freely.  The electrical resistance of the sensor
is attributed to this potential barrier.  In the presence
of a deoxidizing gas, the surface density of the
negatively charged oxygen decreases, so the barrier
height in the grain boundary is reduced (Figures 2
and 3).  The reduced barrier height decreases sensor
resistance.

The relationship between sensor resistance and the
concentration of deoxidizing gas can be expressed
by the following equation over a certain range of gas
concentration:

Rs = A[C] 

−α

where:

Rs

 = electrical resistance of the sensor

A

  = constant

[

C

] = gas concentration

α 

= slope of Rs curve

Fig. 1 - Model of inter-grain potential barrier

(in the absence of gases)

Fig. 2 - Scheme of the reaction between CO and adsorbed

oxygen on SnO

2

Fig. 3 - Model of inter-grain potential barrier

(in the presence of gases)