Terminology

The glossary explains major terms related to gases and gas detectors.
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E F G H I J K L M N O P Q R S T U V W X Y Z
A

ACGIH

Acronym for American Conference of Governmental Industrial Hygienists.
ACGIH recommends allowable concentrations for harmful substances for each specific substance.

Alarm Setpoints

Preset value at which an alarm is issued when the gas concentration reaches that value.

Aging Characteristics

Variations in readings that occur due to changes in the characteristics of a gas detector over extended periods.

ATEX

This European explosion protection directive applies to devices used in potentially explosive environments. ATEX is an acronym derived from the French words ATmospheres EXplosibles.
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Auto Reset

Configuration in which an alarm stops automatically after being triggered once the conditions triggering the alarm are no longer present.

C

Calibration

Determining the correlation between device readout values and actual gas concentrations using calibration gas.
Calibration does not cover error corrections made by adjusting the instrument.

Calibration Curve

Curve representing correlation between readings and gas concentrations.

Calibration Gas

Gas used to calibrate and adjust gas detectors. Used for zeroing, span adjustments, scale calibration, and other procedures.

CE Marking

System designed to promote the free distribution of products within the European region, with the CE marking used to indicate that specified products sold within the EU comply with EU standards. The CE marking indicates that products comply with essential requirements stipulated by EU directives and regulations, according to product category.
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Combustible Gas

In general, gases that ignite or combust in air or oxygen. Gas or vapor forming an explosive atmosphere when mixed with air at a certain ratio.
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D

Daily Maintenance

Device maintenance and cleaning that can be performed relatively easily by the user before work begins.
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Degrees of protection provided by enclosures(IP code)

Protection levels are stipulated under IEC 60592 and JIS C 0920. The IP (International Protection) Code indicates the degree of protection provided by enclosures against the ingress of solid foreign objects and water.

Detection Target Gas

Gas to be detected by a particular gas detector.

Detection Principle

Physical or chemical principle by which the presence of a gas is detected and converted into an electrical signal.

Detection Range

Concentration range for a detection target gas at which gas concentrations can be displayed and alarms issued.

Detector Head

Unit that detects gas concentrations and converts them to electrical signals.
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Diffusion Method

The diffusion method is a detection principle whereby a detector is installed or worn in the location where the gas is to be detected and detects leaking gas that comes into contact with the sensor due to convective diffusion.

E

EN

This is an abbreviation for European Norm (European Standards). These European standards facilitate trade between EU member nations and ensure that products distributed within the EU meet specific standards.
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Explosion Protected Construction

Engineering technique applied to electrical devices to ensure that they do not become ignition sources if placed/used in explosive atmospheres.

Explosive Range

Range of concentrations of a combustible gas mixed in air in which ignition will result in explosion.
Concentrations between the upper explosive limit and lower explosive limit.
Example: The explosive range for hydrogen is 4.0 vol% - 75 vol%.

F

Flameproof Enclosures

Construction designed to withstand damage due to internal explosion caused by the ingress of explosive gas within the device and to prevent the ignition of external gas or vapor.
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Full Scale

Maximum value within the measurable range that can be displayed as a gas concentration when gas is detected.

F Sensor

Series of new sensors developed for use in fixed gas detectors. High-reliability sensor offering smaller dimensions and better performance than previous sensors.

G

Gas Detection

Quantitative determination of the concentrations of various gases in air, etc.
Typically detects concentrations of combustible gases such as methane and hydrogen, toxic gases such as carbon monoxide, and oxygen in air.

I

IEC

Established by the IEC (International Electrotechnical Commission), these international standards apply to electrical, electronic, and related technologies.
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IECEx

IECEx (IEC System for Certification to Standards Relating to Equipment for Use in Explosive Atmospheres). IECEx eliminates the need for multiple national certifications for the safety of electrical devices used in explosive atmospheres. It establishes one international certificate and helps promote distribution of products across participating countries.
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Indication Range

Range within which a gas detector can detect gas and display the concentration.

Indicator Alarm Unit

Unit that receives signals from a gas detector and displays the gas concentration and outputs alarms and contacts.
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Inhibit

This temporarily suspends the gas detection function during product maintenance. This is also called "point skip," which has the same function.

Interference Gas

Gases other than the detection target gas occurring alone or together with the detection target gas and affecting device readings.

Intrinsic Safety

Design to eliminate risk of arcing or sparks from electrical circuits igniting gas or vapor, both under normal operating conditions and in specific failure states. The electricity used is restricted to prevent flames. "ia" for two assumed failures and "ib" for one.
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ISO

These international standards are established by the ISO (International Organization for Standardization).
They cover mining, agriculture, and pharmaceuticals, and various other industries (excluding electrical and electronic technologies) and stipulate a wide range of requirements, not just for products, but for how such organizations operate. Standards for electrical and electronic technologies are issued as IEC standards.
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L

Linearity

Extent to which a linear relationship is maintained between an input signal and the corresponding output signal.

Lower Explosive Limit

Minimum concentration of a combustible gas mixed in air at which explosion will occur in the presence of an ignition source.

LEL

Acronym for lower explosive limit.
Minimum concentration of a combustible gas mixed in air at which explosion will occur in the presence of an ignition source.
Example: The LEL for hydrogen is 4.0 vol%.

M

Mean Value

Value equal to the sum of all gas concentration measurements divided by the number of measurements. This value is the arithmetic mean of the measurements.

mg/m³

The mass of a specific gas in 1 m³ of measured gas, expressed in units of milligrams.

O

Operating Temperature Range

Temperature range within which the specified performance and functionality of a gas detector is maintained.

OEL

Acronym for occupational exposure limits. Threshold limit values for determining levels of chemical substances to which workers are exposed from a health standpoint.

P

Peak Value

Maximum and minimum values measured during a specified period.

ppm

Expresses gas concentrations as parts per million. While this is not an SI unit, it is used as a legal unit of measurement.
1 ppm = 1 × 10⁻⁴ vol%

ppb

Expresses gas concentrations as parts per billion. While this is not an SI unit, it is used as a legal unit of measurement.
1 ppb = 1 × 10⁻³ ppm

%LEL

Concentration of a combustible gas expressed as a percentage of its lower explosive limit.

Expresses gas concentrations as parts per thousand. This is used only in limited circumstances--for example, isotopic ratios.

R

Response Time

Time taken for the reading to reach a stipulated percentage (e.g., 90 %) of the final reading with respect to the gas after instantaneously switching from clean air to the test gas (or vice versa).

Regular Maintenance

Sensitivity adjustments and other maintenance tasks carried out periodically (e.g., every six months) by Riken Keiki service engineers or other trained maintenance personnel to maintain the performance of a gas detector as a safety device.
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Repeatability

Extent to which individual measurements match when clean air and the test gas are repeatedly measured over a relatively short timeframe under identical conditions.

R Sensor

Series of new sensors developed as compact sensors for portable gas detectors. High-reliability sensor offering outstanding durability and better performance than previous sensors.

S

Self-latching

Configuration in which an alarm persists, once triggered, unless reset, even when the conditions triggering the alarm are no longer present.

Sensitivity

Extent to which gas detector readings vary in response to changes in gas concentrations.

Sensitivity Check

Confirmation of sensor output (gas detector reading) using gas of known concentration.

SIL

This is an acronym for Safety Integrity Level. An indication of safety performance. Degree of safety. Consisting of seven parts (Parts 1 to 7), IEC 61508 is the international standard for electrical, electronic and programmable electronic (E/E/PE) safety systems used in the process industry. SIL is comprised of levels 1 to 4, with SIL4 indicating the highest safety.
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Suction Type

The suction method is a detection principle whereby an internal or external pump is used to draw in gas from the measurement location for measurement.

T

TLV

Concentrations of harmful substances deemed to have no adverse health effects for virtually all workers, even with repeated daily exposure; values recommended by organizations such as the ACGIH in the USA.
TLV is further divided into TLV-TWA, TLV-STEL, and TLV-C.

TLV-TWA

The time-weighted average concentration of a harmful substance deemed to have no adverse health effects, even with repeated exposure during normal work for 8 hours per day or 40 hours per week. Acronym for threshold limit value time weighted average.

TLV-STEL

Concentration of harmful substance deemed to have no adverse health effects on workers, even with continuous exposure for 15 minutes, provided daily exposure does not exceed the TLV-TWA. Acronym for threshold limit value short term exposure limit.

TLV-C

Concentration of a harmful substance that must not be exceeded, even momentarily, during work. Acronym for threshold limit value ceiling.

Type of protection"n"

Design to eliminate risk of ignition in surrounding explosive atmospheres under normal operating conditions.
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U

Upper Explosive Limit

Maximum concentration of a combustible gas mixed in air at which explosion will occur in the presence of an ignition source.

UEL

Acronym for upper explosive limit.
Maximum concentration of a combustible gas mixed in air at which explosion will occur in the presence of an ignition source.
Example: The UEL for hydrogen is 75 vol%.

V

vol%

Expresses gas concentrations as percentage values.
While this is not an SI unit, it is used as a legal unit of measurement.

W

Warm-up Time

Time required to reach acceptable performance tolerances after a gas detector is turned on.