Technical materials

Gas detectors incorporate various sensors based on the target gas type and concentrations, and discussed here are the main sensor principles adopted by Riken Keiki gas detectors. It also provides technical information explaining the explosion-proof construction required of combustible gas detectors.

Sensor principles

New Ceramic Catalytic Method

This sensor relies on detecting the heat produced when a combustible gas burns on an ultrafine particle oxidation catalyst (new ceramic). The sensor measures over a broad range, from several thousand ppm to the LEL.
(Main detection target gas: Combustible gases) More Information

Interferometer Method

This optical sensor offers accuracy and outstanding long-term consistency. The sensor also has an extensive history as a key product in Riken Keiki’s history.
(Main detection target gas: Combustible gases) More Information

Catalytic Combustion Method

This sensor relies on detecting the heat produced when a combustible gas burns on an oxidation catalyst. Ideal for detecting the lower explosive limit (LEL)
(Main detection target gas: Combustible gases) More Information

Semi-Conductor Method

This general-purpose sensor is designed to detect a wide range of gases, from toxic gases to combustible gases. The sensor offers high sensitivity, with high output in the low concentration range.
(Main detection target gas: Combustible gases, toxic gases) More Information

Hot Wire Type Semi-Conductor Method

This high-sensitivity combustible gas sensor is ideal for detecting low-concentration gas. Low power consumption and compact dimensions also make it ideal for portable gas detectors.
(Main detection target gas: Combustible gases, toxic gases) More Information

Thermal Conductivity Method

This sensor detects concentrations of target gases based on differences in thermal conductivity of these gases. Ideal to detecting high-concentration gas (vol%)
(Main detection target gas: Combustible gases) More Information

Potentiostatic Electrolysis Method

This sensor is capable of selectively detecting a target gas. Ideal for detecting toxic gases
(Main detection target gas: Toxic gases) More Information

Membrane Type Galvanic Cell Method

This sensor applies the galvanic cell principle to detect oxygen. It does not require an external power supply and offers outstanding consistency in performance over the long term.
(Main detection target gas: Oxygen) More Information

Non-Dispersive Infrared Method

This sensor relies on the unique infrared absorbing characteristics of the detection target gas. The optical sensor offers outstanding consistency in performance over the long term.
(Main detection target gas: Combustible gases, toxic gases) More Information

Membrane-Separated Electrode Method

Relying on electrochemical principles, this toxic gas sensor incorporates a configuration in which the gas permeable membrane (diaphragm) is completely separated from the working electrode to achieve excellent selectivity.
(Main detection target gas: Toxic gases) More Information

Chemical Tape Method

This sensor detects extremely low concentrations of gas based on the color of the tape when the detection target gas reacts with color developer impregnated into the tape.
(Main detection target gas: Toxic gases) More Information

Photo-Ionization Detector

This sensor detects gas concentrations based on the ionization current generated when the detection target gas is irradiated and ionized by ultraviolet light.
(Main detection target gas: Toxic gases) More Information

Pyrolysis-Particle Detection Method

This sensor detects gas by measuring concentrations of the oxide particles produced when the detection target gas is heated. It offers outstanding consistency in performance over the long term, interference characteristics, and response characteristics.
(Main detection target gas: Toxic gases) More Information

Flame Detector

This device detects the presence of flames by detecting the intense ultraviolet and infrared light emitted from the gas when a substance ignites.
(Detection target: Flame detection) More Information

Differential Optical Absorption Spectroscopy

This method for measuring gas concentrations relies on the fact that light of certain wavelengths is absorbed by different gases. Open-path gas detectors rely on this method.
(Main detection target gas: Combustible gases) More Information

X-ray diffractometer equipped with an X-ray fluorescence spectrometer

This system incorporates an angular drive mechanism in an energy dispersion X-ray fluorescence analyzer detector to enable single unit analysis of both X-ray diffraction and fluorescence.
(Detection target: X-ray diffraction and fluorescence measurement) More Information

Open Countor for Low Energy Electron Counting

This is the world’s only surface analysis sensor capable of counting low-energy electrons emitted within air. This proprietary RIKEN product was developed and commercially introduced by Riken Keiki.
(Detection target: Substance surface analysis) More Information

Explosion-proofing

What explosion-proof means

In (hazardous) locations where gas, vapor, or powder posing explosion risks is present or is assumed to be present in the air—for example, oil refineries and chemical plants—the technical measures (explosion-proof construction) implemented to prevent explosions are collectively referred to as explosion proofing, and devices incorporating such measures are referred to as explosion-proof devices.

The conditions required to ignite an explosion

An ignition source, combustible material (e.g., combustible gas), and combustion-supporting gas (e.g., oxygen) are referred to as the three factors required for combustion and explosion. No explosion can occur if even one of these factors is missing.

lgnition source

+

Combustibles

+

Oxygen

=

Explosion and fire

* Ignition source: fire, static electricity, impact, temperature, sparks, or electromagnetic radiation, etc.
* Combustible materials: dust (solid), vapor (liquid), gas, etc.

Hazardous location・Non-hazardous location

Locations where an explosive atmosphere is present at levels requiring special preventive measures for the construction, installation, and use of electrical equipment or not present:

① Present (or potentially present)
⇒ Hazardous location (explosion-proof area)
② Not present
⇒ Non-hazardous location (non-explosion-proof area)

Types of explosion-proof construction

Riken Keiki gas detectors incorporate one of the following three explosion-proof design approaches.

・ Intrinsic safety “ i ”: Design intended to eliminate the risk of arcing or sparks caused by electrical circuits igniting gas or vapor when the device is in a normal state or when it is in a specified failure state The electricity used is limited to prevent sparks or fires. The construction is classified as “ia” for up to two possible failures and “ib” for one possible failure.



・Flameproof enclossures “d”: This refers to a design intended to withstand internal explosions without sustaining damage in the event of explosive atmospheres entering the device and to prevent the ignition of external gas or vapor.


・Type of protection “n”: A construction designed to ensure that there is no risk of igniting surrounding explosive atmospheres when the device is in a normal state.

Other types of explosion-proof construction include the following:


Pressurized enclosures “p”, Oil-immersion “o”, Increased safety “e”, Encapsulation “m”, Dust ignition protection by enclosure “t”, and Special “s”

Explosion-proof certification in different countries

  • International ⇒ IECEx
  • European ⇒ ATEX
  • North America ⇒ UL/cUL, FM/cFM * “c” corresponds to Canadian standard
  • Brazil ⇒ INMETRO
  • Japan ⇒ Certificate of conformity for electrical equipment used in potentially explosive atmospheres (Japan Ex)
  • China ⇒China Ex
  • Taiwan ⇒ TS
  • Republic of Korea ⇒ KCs

Classification of hazardous locationz (areas)

Special hazardous location (Zone 0)

Locations in which explosive atmospheres are present continuously or for extended periods
Example:
① Inside combustible gas containers or tanks
② Spaces above liquid surfaces in inflammable liquid containers or tanks

Type 1 hazardous location (Zone 1)

Locations in which explosive atmospheres are produced under normal conditions
Example:
① Locations where combustible gas or vapor may be emitted under normal operating conditions
② Locations where combustible gas or vapor is prone to leaking during maintenance or repairs
③ Indoor or poorly ventilated locations where combustible gas or vapor accumulates around openings

Type 2 hazardous location (Zone 2)

Locations free of explosive atmospheres or where explosive atmospheres are present under normal conditions only for short periods
Example:
① Locations where combustible gas or vapor may leak if a container or plant is damaged by corrosion, deterioration, or damage
② Locations where combustible gas or vapor may be released in the event of an operating error or an abnormal reaction
③ Indoor locations surrounding or adjoining Type 1 hazardous locations associated with a remote possibility of combustible gas or vapor ingress

Explosion-proof construction types suitable for each type of hazardous location
Hazardous location Kind of gas-explosion protection Remarks
Special hazardous location (Zone 0) Intrinsic safety (ia)
Encapsulation (ma)
Class 1 hazardous location (Zone 1) Flameproof enclosures (d) Explosion-proof structures used in special hazardous location (Zone 0) can also be used.
Pressurized enclosures (px, py)
Increased safety (e)
Oil-immersion (o)
Intrinsic safety (ib)
Encapsulation (mb)
Special (s)
Class 2 hazardous location (Zone 2) Intrinsic safety (ic) Explosion-proof structures used in special hazardous location (Zone 0) and Class 1 hazardous location (zone 1) can also be used.
Type of protection 'n' (nA, nC, nR)
Encapsulation (mc)
Pressurized enclosures (pz)
Explosion-proof class
Gas groups

Gas groups are defined as Group I or Group II, depending on the usage environment. (See Table 1)

Group I
Electrical devices used in mines where explosive mine gas may be present

Group II
Electrical devices used in explosive gas atmospheres other than mines where explosive mine gas may be present
Category

These are categorized 1G to 3G depending on the presence of an explosive atmosphere. (See Table 1)

Table 1 Correlation between group and category

Group Category
(94/4/EC)		 Zone Existence of explosive atmosphere
Group Ⅰ
(Coal mine)		 M1 Exists (methane,dust)
M2 May exist (methane,dust)
Group Ⅱ 1G Zone 0 Exists continuously, frequently,or for a long time
2G Zone 1 Exists intermittently during normal operation (possible)
3G Zone 2 Only exists occasionally or for a short period of time (Does not exist during normal operation)

Explosion-proof symbol
Symbol indicating explosion-proof construction

Explosion-proof construction type
Indicates the type of explosion-proof construction.(See Table2)

Table 2 The type of explosion-proof construction

Intrinsic safety i(ia, ib)
Flameproof enclosures d(da, db)
Pressurized enclosures p
Increased safety e
Encapsulation m
Type of protection 'n' n
Oil-immersion o
Special s

Explosion-proof electrical device groups

Depending on whether they feature flame-proof enclosures or intrinsically safe explosion-proof construction, respectively, explosion-proof electrical device groups (IIA, IIB, IIC) are classified as maximum safety gap or minimum ignition current. (See Table 3)

Table 3 Explosion-proof devices and explosion-proof class

Explosion
class		 Flameproof enclosures Intrinsic safety
Maximum experimental safe gap range
for gas or steam		 Minimum ignition current ratio
for gas or steam
ⅡA Equal to or more than 0.9mm Over 0.8
ⅡB Over 0.5mm and less than 0.9mm Equal to or more than 0.45 and equal to or less than 0.8
ⅡC Equal to or less than 0.5mm Less than 0.45

*The minimum ignition current ratio is shown based on the minimum ignition current of methane.

Maximum safety gap
This is the maximum joint gap that prevents the propagation of a flame to an external gas mixture through a 25 mm long joint in a flame-proof test container when the gas mixture with the highest flame propagation is ignited inside the specified test container.

Minimum ignition current
This is the minimum current for an inductive or resistive circuit used to ignite the most easily ignitable gas mixture in a spark ignition test.

Temperature grade

This is categorized based on the maximum surface temperature of the electrical device and the ignition temperature of the combustible gas or vapor. Combustible gases and vapor have their own specific ignition temperatures. The methods for measuring ignition temperature are internationally stipulated in IEC 60079-20-1 “Gas and vapour classification - Test methods and data”. Values measured by these measuring methods are often used. (See Table 4)

Table 4 Temperature grade and ignition temperature

Maximum surface temperature of
electrical equipment (°C)		 Temperature
class		 Ignition temperatures of combustible gases or vapors (°C)
Less than 450°C T1 Over 450°C
Equal to or less than 300°C T2 Over 300°C and less than 450°C
Equal to or less than 200°C T3 Over 200°C and less than 300°C
Equal to or less than 135°C T4 Over 135°C and less than 200°C
Equal to or less than 100°C T5 Over 100°C and less than 135°C
Equal to or less than 85°C T6 Over 85°C and less than 100°C

Ignition temperature
This refers to the minimum temperature of a heated surface leading to ignition when the heated surface is in contact with a mixture of combustible gas or vapor and air under specified conditions.

EPL (Equipment Protection Level)

EPL (IEC 60079-26:2006) conceptualizes explosion-proof performance in terms of protection level by identifying and indicating the specific ignition risks posed by that device. This facilitates the selection of devices suitable for specific hazardous locations. EPL is classified Ga, Gb, or Gc. (See Table 5)

Table 5 Explanation of EPL

EPL Protection performance Normal operation zone
Ga "Very high degree of protection"
Doubly protected by two independent explosion-proof structures, or maintains explosion-proof performance even when two failures occur independently of each other.
・Equipment that is Ga on its own: Intrinsically safe explosion-proof structure"ia"
・Two independent explosion-proof structures: Combines two Gb pieces of equipment		 Zone 0
Gb "High degree of protection"
Maintains explosion-proof performance in normal operation,and maintains explosion-proof performance even when severe disturbances occur frequently in terms of explosion-proof performance or when considering failures that can occur during nomal use.
・Intrinsically safe explosion-proof structure "d",etc.		 Zone 1
Gc "Improved protection"
Maintains explosion-proof performance only during normal operation.
・Type n device		 Zone 2

Gas detector groups and temperature grades for typical combustible gases and vapor

Gas detector groups and temperature grades for typical combustible gases and vapor

Temp. Class
Exp-proof Class		 T1 T2 T3 T4 T5 T6
ⅡA Acetone
Ammonia
Isobutane
Ethane
Acetic acid
Ethyl acetate
Toluene
Benzene
Methane		 Isopentyl
acetate
Acetic anhydride
Butane
Propane
Methanol		 Hexane Acetaldehyde
ⅡB Carbon
monixide		 Ethanol
Ethylene
Ethylene oxide
ⅡC Water gas
Hydrogen		 Acetylene Carbon disulfide

Reference:
Technical recommendations of the National Institute of Occupational Safety and Health JNIOSH-TR-No.44: 2012 (published by National Institute of Occupational Safety and Health, Japan)