BS 6705:1987

This standard BS 6705:1987 Specification for electrical measuring instruments for use on intrinsically safe circuits in coal mines is classified in these ICS categories:

• 29.260.20 Electrical apparatus for explosive atmospheres

This British Standard specifies limiting parameters for input/output circuits of portable electrical measuring instruments for testing intrinsically safe circuits used in coal mines. It applies to the following types of test circuits when connected to intrinsically safe circuits having a voltage not exceeding 60 V peak at the point of test.

1. Voltage dependent circuits. These are high impedance circuits contained in instruments such as voltmeters, oscilloscopes, frequency meters and similar instruments that depend upon voltage for their operation.
2. Current dependent circuits. These are low impedance circuits contained in instruments such as ammeters, and similar instruments that depend upon current for their operation.
3. Current injection circuits. These are circuits which inject a current into the circuit under test generally for the purpose of measuring resistance or impedance.

This standard is not applicable to intrinsically safe instruments that provide a high voltage for testing insulation nor to instruments used to measure the resistance or continuity of shot-firing circuits. Nor does it specify operational performance requirements of testing instruments.

Instruments specified in this standard are intended for use in accordance with BS 6704 and with any condition of the applicable certification to either the instrument or the circuit to which it is connected for test purposes.

NOTE The titles of the publications referred to in this standard are listed on the inside back cover.

Specifies limiting parameters for test instruments intended for use in accordance with certification documents relating to both the instrument and the intrinsically safe circuit to be tested; and applies to voltage dependent, current dependent and resistance measuring instruments.