Electrical Resistance

Introduction

A multitester or multimeter is a device that can be used to gather data about electrical circuits. A basic multitester can measure resistance, voltage, and continuity; while more advanced versions may be able to provide additional data. This tool can be very useful to have around the house, and anyone who plans on doing electrical repairs should most definitely use a multitester for safety reasons. Multitesters can be used with the current off or on in most cases, although using the device with the current on can sometimes result in damage to the device. Theory Ammeters are employed for measuring current in a circuit and connected in series with the circuit. As ammeter is connected in series, the voltage drop across ammeter terminals should be as low as possible.

This requires that the resistance of the ammeter should be as low as possible. The current coil of ammeter has low current-carrying capacity whereas the current to be measured may be quite high. For this reason, low resistance is connected in parallel to the current coil. Voltmeters are employed to measure the potential difference across any two points of the circuit these are connected in the parallel to the circuit. The resistance of the voltmeter is kept very high by connecting a high resistance in series of the voltmeter with the current coil of the instrument. The actual voltage drop across the current coil of the voltmeter is only a fraction of the total voltage applied across the voltmeter which is to be measured. An ohmmeter is a measuring instrument used to measure the resistance placed between its leads. The resistance reading is indicated through a mechanical meter movement that operates on electric current. The ohmmeter must then have an internal source of voltage to create the necessary current to operate the movement, and also have appropriate ranging resistors to allow just the right amount of current through the movement at any given resistance.

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One major problem with this design is its reliance upon a stable battery voltage for accurate resistance reading. If the battery voltage decreases, the ohmmeter scale will lose accuracy. Conclusion Aside from using devices such as multitester, the resistance value of a resistor can be determined by its color-coding. There are small differences between the measured and color-coded values of the resistances. These differences may be caused by some factors such as the multitester used in the experiment and some mistakes made by the experimenters. It is much easier to read the resistance value of a resistor through a digital multitester than by using an analog multitester and by color-coding. In addition, in using an analog multitester, you have to first consider the range of the resistance and make the zero-ohm adjustment in each and every reading. In that case, that is the only time you can acquire the resistance value after a slightly inconvenient process.

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