Potentiostatic Electrolysis
Stationary sensor
Method Sensor: ES
Example: ESF-A24R

C O ( - H 2)

Stationary sensor
Example: ES-23 series

1. Brief description

This sensor electrolyzes detectable gas using an electrode with the potential kept constant toallow a current to be generated, and then measures the current to determine the gas
concentration. It is the gas sensor most suitable for detecting toxic gases. You can specify aparticular potential to detect a particular gas.

Portable sensor
Example: ESR-A1 series

Category

Detectable gas

ElectrochemicalToxic

2. Structure and principles[Structure]

The sensor is structured with an electrode (action electrode)—a gas-permeable film with a catalyst (e.g., gold or platinum)
placed over it—along with reference and counter electrodes;
these electrodes are housed in a plastic container filled with anelectrolytic solution.

[Principles]

The sensor uses a potentiostatic circuit to keep the potential
between the action and reference electrodes constant. The
action electrode directly electrolyzes detectable gas. If thedetectable gas is H2S, the following reactions occur:Action electrode: H2S + 4H2O -> H2SO4 + 8H++ 8eCounter electrode: 2O2 + 8H+ + 8e- -> 4H2O
The current generated by the reactions is proportional to thegas concentration. By measuring the current that flows between
the action and counter electrodes, the sensor determines thegas concentration.

[Structure]

Potentiostatic circuit
Gas-permeable film

R (Resistance)

Detectable gas
Electrolyticsolution

Gas release

Referenceelectrode
Counterelectrode

Action electrode3. Features (of the sensor ES-237iF (H2S sensor) as an example)○Output characteristics○Aging characteristics

For approximately two years, the sensor keeps its
sensitivity at a level approximately 80% of the originallevel. Since humidity slightly affects the sensitivity, thereading may vary depending on the season.

Sensor output

The gas concentration is
proportional to the current value.
The sensor outputs the current
value without any change andthe gas concentration is,therefore, proportional to thesensor output.

(μA)
300
Gas concentration (ppm)○Responsiveness(ppm)0With almost stable readings athigh temperatures, the sensor is
likely to decrease its sensitivity
with a decrease in temperature.
100
Even at 0℃, the sensor
maintains its sensitivity at a level
not lower than 80%. By
performing temperature
(%)
40
020
corrections, it minimizes reading
Temperature (℃)
fluctuations.
Span output ratio

1.6
Reading

The response curve is as shownin the right figure.
The sensor makes gas react
based on catalysis reaction todetermine the current value.
Since H2S does not alter theelectrode catalyst, the sensor
excels in accuracy andreproducibility.

○ Temperature
characteristics

02Time (min.)4. Detectable gas, molecular formula, model, and detection
range (examples)
Detectable gas

Molecularformula

Model #Detection
range

Carbon monoxide/
Hydrogen sulfide

CO/H2S

ESR-A1DP

CO:0-500ppm
H2S:0-30ppm

Carbon monoxide(Reduce H2interference)CO

ESR-A1CP

0-500ppm

Hydrogen sulfide

H2S

ESF-A24R

0-100ppm

Carbon monoxide

COES-23

0-75/150/300ppm

Hydrogen sulfide

H2S

ES-1827iF

0-3 ppm

5. Products of this type (examples)○Stationary products... SD-3EC, SD-3DEC, GD-84D-EX,
EC-600, GD-70D, SD-1EC○Portable products... CO-04, CX-04, HS-04,
GX-3R, GX-3R Pro,
CO-FL1, GX-2012,
GX-8000
GD-84D-EX