Safety hints to consider when selecting a digital multimeter

By Elizabeth Latham, Journalist
Thursday, 08 March, 2007

When choosing a digital multimeter, not only is it important to look at basic specifications, features, functions and overall value of the meter but it also needs to meet the latest and most demanding safety standards.

What are the company's requirements?

Before selecting a digital multimeter, you need to be aware of your company's test procedures and safety requirements.

Consider Australian Standards

The Australian Standard AS61010 was introduced in 2006. It specifies the minimum design safety and testing requirements for electrical equipment for testing, measurement and control.

A key area that is addressed by the standard is 'overvoltage installation categories'. The categories vary according to what the tool is being used for and where it is being used.

A common mistake made by people when choosing a digital multimeter is to pick a tool that has a high-enough voltage rating; however, it is often the case that when engineers analyse multimeter safety they discover many units fail and may become dangerous because they have had a much higher voltage put through them than they were designed for, Henk van Velze, distribution account manager at Fluke Australia, manufacturer and distributor of electronic test tools, said.

Look for the safety symbol

According to Henk, independent testing is the key to safety compliance.

He advises users to look for a symbol and listing number of an independent testing lab and to beware of wording such as 'designed to meet specification...'

"The symbol CE (Comformite Europeenne), a European Commission directive, can be misleading. Manufacturers are permitted to self-certify that they have met their own Declaration of Conformity and mark the product 'CE', however this does not guarantee that the tool has been independently tested," he said.

How is the battery?

Don't forget the battery's condition. Before using the meter, make sure the battery has sufficient power in it. To ensure it is in good condition, replace it immediately when the 'low battery' indicator is displayed. A low battery may cause inaccurate readings.

Test leads

Before using the meter's test leads, they should be shortened together in low ohm range to check their continuity.

Also, make sure the leads are in the correct input jack and that the correct range and meter setting has been selected because reading a voltage measurement while leads are in the 'amp' input jacks will cause instrument damage and damage the operator.

Be certain that the correct range is selected before connecting the test leads to the voltage source to be measured. When in doubt about which range to use, switch to the highest possible range and work down.

Calibration up to date?

To keep a meter in good working condition, regular calibration is required. This means before using the meter make sure it has a valid calibration sticker. Typically, meters are calibrated once a year; however, some companies may require calibration more frequently.

Visible give-aways

Check for any visible signs that the meter is not in good condition by looking for any visible signs of damage or malfunction.

Ensure the test leads are in good condition by making sure there are no signs of ageing such as cracks or splits in the insulation. To prevent high-voltage leakage and failure, consider yearly lead replacement.

Don't work alone

Try to avoid working alone when measuring high voltages. B&K Precision advises having someone nearby who can give first aid if necessary. It is recommended that that person has training in CPR and general first aid.

Finally, digital multimeters are precision devices that require knowledge and acre to get the best out of them. Always remember the manual is there to be read.

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