Analog voltmeters are instruments that measure voltage or voltage drop in a circuit. They display values on a dial, usually with a needle or moving pointer. Analog voltmeters (analog volt meters) are used to locate excessive resistance that may indicate an open circuit or ground. They are also used to identify low voltage or voltage drops that may indicate a poor connection. Analog voltmeters are connected in parallel (and never in series) with the circuit being tested so that the meter can tap a small amount of current. The positive lead is connected to the circuits positive side and the negative lead is connected to the circuits ground. The analog voltmeters internal resistance is the impedance, which is usually expressed in ohms per volt. This amount is relatively high in order to prevent the analog voltmeter from drawing significant current and disturbing the operation of the circuit being tested. The sensitivity of the current meter and the value of the series resistance determine the range of voltages that analog voltmeters can measure.
With the advent of digital technology, analog voltmeters are used less frequently; however, some applications still require them. For example, analog voltmeters are suitable for troubleshooting small, intermittent changes in voltage or current that digital voltmeters smooth out by displaying only stable values. Analog voltmeters also foster greater accuracy by requiring users to establish a range of possible values before attaching probes to the circuit. Depending on the device, analog voltmeters can measure levels of alternating current (AC), direct current (DC), or both AC and DC. Different types of devices have different ranges and scales. For example, some analog voltmeters have voltage ranges of 4.0 V, 20 V and 40 V and scales of 4.0 V and 20 V. In order to use the 40 V range, users need to multiply the needle reading on the 4.0 V scale by 10.
Analog voltmeters are available with a variety of features. Battery powered devices can be operated without plug-in power. Temperature compensated devices provide programming or electrical components designed to counteract known errors caused by temperature changes. Analog voltmeters with a mirrored scale improve readability by enabling users to avoid parallax errors. Devices with a range switch allow users to select the range of units to measure. Analog voltmeters with overload protection and diode testing are also available. Some devices are handheld and portable, while others are designed for benchtop or shop floor use.
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