Hot Wire Type Semi-Conductor
Stationary sensor
Method Sensor: SH
Example: SHF-8603

Stationary sensor
Example: SH-8616

1. Brief description

Category

This sensor uses a metal oxide semiconductor, which changes in resistance when it
comes into contact with a detectable gas. The sensor detects this change in resistanceas the gas concentration. It is a high-sensitivity gas sensor for low concentrations.

2. Structure and principles

Portable sensor
Example: SH-8641

Detectable gas
Combustible

SolidToxic[Conceptual rendering of the sensor elements][Structure]

The sensor consists of a detector element, which consists of acoil of a precious-metal (e.g., platinum) wire and a metal oxide
semiconductor sintered on the coil, and a compensation elementwith a material inactive against detectable gases sintered on it.

Inactivematerial

Precious-metal
wire coil

Metal oxide
semiconductor

Precious-metal
wire coil
0.5-1.4 mm

0.5-1.4 mm[Principles]

The resistance (R) of the detector element is the combined
resistance of the resistance (RS) of the semiconductor and theresistance (RH) of the precious-metal wire coil. The detector
element is heated 300℃ to 400℃ by the precious-metal wire
coil and keeps a constant resistance. Then, methane gas or the
like comes into contact with the detector element and separates
the oxygen adsorbed on the surface of the metal oxide
semiconductor. This increases the number of electrons that canfreely move inside the semiconductor, reducing the resistance ofthe semiconductor. This results in the reduced resistance of theentire detector element. By allowing the bridge circuit to detect
the change in resistance, the sensor determines the gas
concentration.

0.8-1.4 mm

0.8-1.4 mm

Detector element

Compensation element[Bridge circuit]
Metal oxide semiconductor=> Change in resistance

Detector element＋V－

Compensation element
Sensor output

Sideresistance RSensor voltage Vs

3. Features (of the sensor SH-8616 as an example)○ Output characteristics

The sensor detects changes in
the resistance of thesemiconductor, meaning that it
detects even low concentrations(ppm level) that cannot bedetected by new ceramic-basedsensors.
The sensor is highly sensitive
with a high sensor output level for
low concentrations.

○ Miniaturization and power saving

100

The precious-metal wire coil for the heater can be downsized
to provide a smaller sensor that requires less power.

Outputratio(%)
00

Gas concentration(ppm)○ Aging characteristics

2000○ Gas selectivity

The sensor maintains stability over the long term with a longlife. Compared with the catalytic combustion-based sensor,
this type sensor is highly resistant to toxicity and severe
atmosphere.

Adding an impurity to the metal oxide semiconductorchanges the interference effect. This characteristic allows thesensor to selectively detect some gases.

4. Detectable gas, molecular formula, model, and detection
range (examples)
Molecularformula

Model #Methane

CH4

SHF-8601

0-5000ppm

Hydrogen

H2SHF-8603

0-500/1000/2000ppm

HydrogenH2SH-8612

City gas-

Detectable gas

Combustible
gases in general-Detection
range

SH-8640
SH-8641○Stationary products... SD-3SP, SD-3DSP, GD-84D-EX,
GD-A80S, GD-A80DS○Portable products... SP-220, GX-2012GT
GX-2012GT

SH-8616
SH-8639

5. Products of this type (examples)

0-20 00 ppm