组用字母标明，标记在类性和类别之后，表示危险区域内的气体或蒸汽环境。
The groups indicated by letters, which follow the type class, indicate the gas or vapor atmospheres within the hazardous locations.
应根据IEC证书和GB证书选择危险区域内的仪表。采购仪表前应事先取得这两样证书。
Instruments shall be selected for hazardous areas on the basis of IEC and GB certification. Certificates shall be obtained prior to any order placement.
在NEMA类型7和9定义中以加以说明。组(用字母标明)，标记在类性和类别之后，表示危险区域内的气体或蒸汽环境。
As explained in the definitions of the NEMA Types 7 and 9. The groups (indicated by letters), which follow the type class, indicate the gas or vapor atmospheres within the hazardous locations.
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