Updated on 19 October, 2021
A tester, test light, mains fuse, or voltage tester is an essential piece of electrical testing equipment utilized to test the electrical condition of a specific component under controlled conditions. Using a variety of different techniques, these instruments can test for voltage, current and level changes as well as a host of other characteristics. Many different models are available on the market today and include different features. Regardless of what your testing needs may be, there is an instrument for you.
One type of testing equipment that is used by many people is a multimeter. These tools are used for measuring voltage levels, current, and even the resistance of conducting metallic materials. Because these devices require direct contact with the circuit in order to obtain readings, they must often be held up by insulation or a barrier to prevent the device from being damaged during testing. Fortunately, multimeters are available in many shapes, sizes, and colors to accommodate individual testing requirements.
Another useful tester has to do with the electrical field around something. Electric field is often measured in terms of polarizations - either positive or negative. This tester measures how strong the electric field actually is in order to detect faults that might not otherwise show up in a testing procedure. This can be particularly useful when testing electronics and other delicate materials that could be damaged by even the slightest electric field variations.
Mains testers and multimeters are not the only methods of testing circuits without direct metallic contact. There are some instruments that utilize a magnetic field to gauge the integrity of conductors and other components. These magnetic test lamps are sometimes called magnetic field testers. They work in a similar fashion to multimeters, but instead use a small magnetic circuit to gauge the resistance of conductors. This method can also detect short circuits that might not otherwise show up in an examination.
A third type of voltage tester uses light to reveal problematic areas of conductors and circuit conditions. These products are called test lights and they are often made to look like regular incandescent bulbs. They can be plugged into an existing outlet and will produce visible light as a measure of current. While these are not actually full-sized lights, the way they operate is still very similar. The way they determine the levels of voltage in a circuit is by shining a bright light directly onto the circuit.
If you happen to have a non-contact voltage tester around your home, you are in luck! The basic principle behind most multimeters and other testers for this purpose is the same. In a non-contact voltage tester, the probe of the meter senses either a positive or negative voltage, and then compares it against a reference voltage. If the reference voltage is not a constant, the multimeter subtracts one from the measured value. When a constant reference is present, the tester measures the difference between the two voltage levels.
Inductance testers use the concept of the capacitor. Like a capacitor, the amount of charge carried by a conductor decreases as the charge level on the wire increases. For this reason, the meter always reads a positive value when a load is attached. However, there are some inductance testers that have two reference levels, one for a lower value (zero) and one for a higher value (anything between - infinity).
Finally, there are the thermistors. When an electrical current is applied to a wire, it causes a change in the temperature of the wire. Because of this change in temperature, the current passes through a small opening, which is the terminal of the thermistor. When a current is applied, the thermistor absorbs energy, causing the terminal to become hot. Once the current is removed, the wire becomes cool, and the terminal no longer conducts electricity.