TGS2442 Datasheet, PDF (4/25 Pages) List of Unclassifed Manufacturers – Detection of Carbon Monoxide

TECHNICAL INFORMATION FOR TGS2442
1. Specifications
1-1 Features
* Miniature size and low power consumption
* High sensitivity/selectivity to carbon monoxide
(CO)
* Low sensitivity to alcohol vapor
* Reduced influence by various interference gases
* Long life and low cost
1-2 Applications
* Residential and commercial CO detectors
* Air quality controllers
* Ventilation control for indoor parking garages
1-3 Structure
Figure 1 shows the structure of TGS2442. The sensor
utilizes a multilayer structure. A glass layer for thermal
insulation is printed between a ruthenium oxide (RuO2)
heater and an alumina substrate. A pair of Au electrodes
for the heater are formed on a thermal insulator. The gas
sensing layer, which is formed of tin dioxide (SnO2), is
printed on an electrical insulation layer which covers the
heater. A pair of Pt electrodes for measuring sensor
resistance is formed on the electrical insulator. An activated
charcoal filter is used for the purpose of reducing the
influence of noise gases.
1-4 Basic measuring circuit
Figure 2 shows the basic measuring circuit of the TGS2442.
Circuit voltage (Vc) is applied across the sensing element
which has a resistance (Rs) between the sensor’s two
electrodes (pins No. 2 and No. 3) and a load resistor (RL)
connected in series. The sensing element is heated by the
heater which is connected to pins No. 1 and No. 4.
The sensor requires application of a 1 second heating cycle
which is used in connection with a circuit voltage cycle of
1 second. Each VH cycle is comprised by 4.8V being applied
to the heater for the first 14ms, followed by 0V for the
remaining 986ms. The Vc cycle consists of 0V applied for
995ms, followed by 5.0V for 5ms. For achieving optimal
sensing characteristics, the sensor's signal should be
measured after the midpoint of the 5ms Vc pulse of 5.0V
(for illustration, see the timing chart in Fig. 3).
NOTE: Application of a Vc pulse condition is required to
prevent possible migration of heater materials into the
sensing element material. Under extreme conditions of high
humidity and temperature, a constant Vc condition could
result in such migration and cause long term drift of Rs to
higher values. A 5ms Vc pulse results in significantly less
driving force for migration than a constant Vc condition,
rendering the possibility of migration negligibly small.
Non woven fabric
Metal cap
Charcoal filter
Metal gauze (double layer)
Lead wire
Substrate
3
2
Metal base
Lead pin
4
1
Top view of the sensor
without cap
Noble metal
electrode
Figure 1 - Sensor structure
Figure 2 - Basic measuring circuit
(including equivalent circuit)
Revised 03/00
2