Electrical Projects Since the VOM has a multitesting capability and is handy to carry around, it's a popular piece of equipment in the workshop. This means frequent changing of selector-switch function and range settings which can often be inconvenient and lead to meter damage if not done carefully. The test probes themselves often make accurate measurement of an operation requiring three hands. One way to make continuity checks quicker and more efficient is to build a separate checking device for this purpose. The continuity checker is ideal for this purpose and can be built inexpensively.

Electrically, the device is quite simple. The key component is isolation relay FR-101 (available from ALCO Electron Products, Inc., North Andover, Mass.), which combines an isolated stepdown transformer and a sensitive low-voltage relay in a single unit. With 110V ac applied to terminals 3 and 4 of the four-terminal barrier strip, 30V is induced into the isolated circuit as measured at test receptacle J and across terminals 1 and 2 of the terminal board. When an appliance with its power switch in the on position is plugged into test receptacle J, a continuous circuit is created. This

shorts the isolated circuit of the checking device, allowing current to flow through relay coil K and activate the low-voltage relay. Lamp I (a low-wattage lamp available in electrical-supply stores) in the relay's primary winding circuit will then light, indicating good continuity in the appliance. It can be seen that the test leads applied across the plug prongs of the appliance cord, or across isolated portions of the circuit, will achieve the same result.




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Home > Electrical Projects > Tools And Components > Bench - Type Continuity Checker

Febuaury 11, 2012