Boating NZ : FREE TO READ April 2014
subscribe online at www.mags4gifts.co.nz/boating-nz 43 HOW IT WORKS In simple terms, electricity flows from the meter, along the red lead, through the bulb/wire/fuse being tested, and back to the meter along the black lead. If there is a break, the electricity can’t get back to the meter – there is no continuity, and no reading. Ergo, you’ve found the culprit. All parts of the circuit must be de-energised during a continuity test. The boat’s 12-volt DC source is switched off, or the circuit isolated. Powell says it’s important to understand that a multimeter generates its own, small pulse of electricity for the test and measures the resistance it meets. “If it can’t get around the circuit, we test the components individually until we find the break.” NO-SHOW NAV LIGHT – A THREE-STEP CHECK 1. Select the multimeter’s Ohms setting – marked with the omega (Ω) symbol. 2. Disconnect the ends of the two wires leading to the light. This is easiest to do at the circuit board. 3. Place a multimeter probe on each wire end – any way, the test isn’t polarity sensitive. If you get a reading, the circuit’s OK; if the screen shows “0L” (open loop) there is no continuity. This could be because there’s a break in the wire, the bulb’s blown, the bulb socket in the light fitting is faulty – often corroded, or the wiring connections are loose. Testing each of these segments independently establishes the cause of the dead light. The integrity of a fuse is also checked in this way. A particular advantage of a continuity check is the ability to test difficult-to-access components – a masthead light, for example. The integrity of the circuit can be first checked from the saloon. Continuity checks are also useful for checking the integrity of a VHF’s aerial connection. Poor or no reception is often caused by dodgy connectors at the back of the radio. VOLTS As with Ohms, a modern multimeter’s volt scale is auto-ranging, but you have to choose either DC or AC volts on the instrument’s selector dial. The DC volts symbol is a flat line over three dashes (V ), while AC volts is a sine wave ( V ). The selection is usually indicated on the screen as well. ABOVE: Test a bulb’s integrity – part of a process of elimination to find a fault. TOP LEFT: A simple check to confirm that the fuse is OK. BELOW LEFT: Placing the probes directly onto the posts is a reliable way to check the battery’s health. NOTE • High output 500 watts + • Extremely quiet operation • Unparalleled low wind performance • Corrosion resistant • Vibration free Locations: • 5G Miro Place, Albany, Auckland • Gulf Harbour Marina, Whangaparaoa, Auckland www.enertecmarinesystems.com email: email@example.com • Most automated, low maintenance, easy-to-use watermaker ever • Consumes less than 1/3 the power of conventional systems • As fitted to 95% of the Volvo fleet • Manual operation mode if required Locations: • 5G Miro Place, Albany, Auckland • Gulf Harbour Marina, Whangaparaoa, Auckland www.enertecmarinesystems.com email: firstname.lastname@example.org 0414-48 REGULAR_PB_Mulitimeters_April14.indd 43 18/03/2014 5:18:45 p.m.
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