GB/T 20936.4-2017Gas detectors for explosive atmospheres -- Part 4: Performance requirements of open path detectors for flammable gases (English PDF)

Foreword

GB/T 20936 Gas detectors for explosive atmospheres is divided into several parts:

-- Part 1: Performance requirements of detectors for flammable gases;

-- Part 2: Selection, installation, use and maintenance of detectors for flammable

gases and oxygen;

-- Part 3: Guidance on functional safety of fixed gas detection systems;

-- Part 4: Performance requirements of open path detectors for flammable gases;

...

This part is Part 4 of GB/T 20936.

This part was drafted in accordance with the rules given in GB/T 1.1-2009.

This part is modified in relation to IEC 60079-29-4:2009 Explosive atmospheres - Part

29-4: Gas detectors - Performance requirements of open path detectors for flammable

gases with the use of the redrafted method.

Compared with IEC 60079-29-4:2009, the following structural adjustments have been

made in this part:

-- 4.3.1 General rule is added, and the numbers of subsequent articles are postponed.

The main technical differences between this part and IEC 60079-29-4:2007 and their

reasons are as follows:

-- Regarding normative references, adjustments with technical differences have

been made in this part to adapt to Chinese technical conditions. The adjustments

are reflected in Chapter 2 "Normative references". The specific adjustments are

as follows:

lambda IEC 60079(all parts) is replaced with GB/T 3836(all parts). The degree of

consistency between the parts of the two standards is shown in Appendix

B;

lambda IEC 60079-0 is replaced with GB 3836.1, IEC 60825-1 is replaced with

GB 7247.1, IEC 61000-4-1 is replaced with GB/T 17626.1, IEC 61000-4-

3 is replaced with GB/T 17626.3, and IEC 60079-29-1 is replaced with

GB/T 20936.1-2017.

The following editorial changes have been made to this part:

Gas detectors for explosive atmospheres - Part 4:

Performance requirements of open path detectors for

flammable gases

1 Scope

This part of GB/T 20936 specifies performance requirements of equipment for the

detection and measuring of flammable gases or vapours in ambient air by measuring

the spectral absorption by the gases or vapours over extended optical paths, ranging

typically from one metre to a few kilometres.

Such equipment measures the integral concentration of the absorbing gas over the

optical path in units such as LEL.m for flammable gases.

NOTE 1: Actual values of concentration can be deduced only where it can be established that the

concentration is uniform over the optical path, for example in very short optical paths (< 100 mm). In

such cases, the equipment is within the scope of GB/T 20936.1-2017.

NOTE 2: This part is based on present absorption techniques using infrared radiation. Other techniques

and applications may require additional test considerations (e.g., pressure test).

Equipment falling within the scope of this part is classified by the following types:

Type 1: an optical transmitter and receiver, located at either end of a path through the

atmosphere to be monitored.

Type 2: an optical transceiver (i.e., combined transmitter and receiver) and a suitable

reflector, which may be a topographic feature or a retroreflector, located at either end

of a path through the atmosphere to be monitored.

This part is also applicable when an equipment manufacturer makes any claims

regarding any special features of construction or superior performance that exceed the

minimum requirements of this part. All such claims shall be verified and the test

procedures should be extended or supplemented, where necessary, to verify the claimed

performance. The additional tests shall be agreed upon between the manufacturer and

the test laboratory and identified and described in the test report.

This part does not apply to any of the following:

a) equipment intended to provide range resolution of gas concentration (e.g.,

Light direction and ranging (LIDAR));