Test Instrument Guide.pdf

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Test Instruments
Standards & Requirements
Instrument Standard
BSEN61010 is the basic safety standard for
all electrical test instruments.
The basic instrument standard is BSEN61557
(Elec safety in low volt distribution systems).
HSE guidance notes GS38 recommends
certain requirements for all instuments, leads,
probes and accessories.
Instrument Accuracy
Basic accuracy of 5% is usually adequate. In the
case of analogue instruments 2% of fsd.
Basic accuracy is an
‘ideal’
and accuracy in the field can
differ due to:-
Instrument errors:-
operator ability; battery condition;
ambient temp; instrument orientation.
Loss of calibration:-
need for regular calibration using
standards traceable to national standards. Checks after
mishandling.
Field errors:-
contact resistance, lead resistance etc.
Low Resistance Ohm Meters
This can take the form of a specialised low-ohm meter or
the continuity range of an IR/continuity tester.
Test current may be a.c or d.c.
The test current must be derived from a source with a
no-load voltage of between 4v & 24v and capable of
delivering a short circuit current not less than 200mA
(0.2A).
Measuring range must cover a span of at least 0.2Ω to
2Ω.
Digital resolution must be 0.01Ω.
Instruments to BSEN61557-4 will satisfy the above.
IR Ohm-meter
Must be capable of developing the test voltage across
the load:-
250v SELV-PELV
500v Circuits rated up to 500v excluding ELV
1000v Circuits rated between 500v & 1000v
Instruments to BSEN61557-2 will satisfy the above.

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