Riken Keiki GD-3EC, Technical Manual

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11. Appendix 11-1 Detection principle
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11-1-2 New ceramic type
<Sensor overview>
This uses an ultrafine particle (new ceramic) oxidation catalyst to detect gas concentrations over a wide range,
from low concentrations (ppm) up to the lower explosive limit (LEL). This revolutionary gas detection sensor was
developed by Riken Keiki and specifically designed to detect combustible gases.
<Sensor structure and principle>

Structure
The new ceramic sensors consist of a detecting element and a compensating element. (Some sensors do
not have a compensating element.) The detecting element consists of an ultrafine particle oxidation catalyst
(new ceramic) that reacts with combustible gases sintered on top of a precious metal coil. This undergoes a
combustion reaction in the presence of the detection target gas.
The compensating element consists of a material inert to combustible gases sintered on top of a precious
metal coil. This compensates for atmospheric effects.

Principle
When combustible gas burns on the surface of the detecting element heated to between 300 °C and 450 °C
by the precious metal coil, this increases the temperature of the element. This temperature variation results in
changes in the resistance of the precious metal coil that makes up the element. These variations in
resistance are essentially proportional to gas concentrations. The resistance variation can be extracted as a
voltage using a bridge circuit to calculate the gas concentration.
<Sensor element diagram>
<Bridge circuit>
Compensating element
・・・ Compensates for atmospheric effects.
Precious metal coil
0.8 mm - 1.4 mm
Glass +
alumina carrier
0.5 mm - 1.4 mm
Detecting element
・・・
Detects gas.
Precious metal coil
Oxidation ca
alumina carrier
0.5 mm - 1.4 mm
0.8 mm - 1.4 mm
Element temperature
increases.
Resistance increases.
Element temperature
decreases.
Resistance decreases.
Detecting
element
Resistance of
rheostat arm R
Sensor voltage Vs
V
+
-
Compensating
element
Sensor output