AC Voltmeter using Rectifiers: AC Voltmeter using Rectifiers – Rectifier type instruments generally use a PMMC movement along with a rectifier arrangement. Silicon diodes are preferred because of their low reverse current and high forward current ratings. Figure 4.16 (a) gives an ac voltmeter circuit consisting of a multiplier, a bridge rectifier and a PMMC […]
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DC Standard Differential Voltmeter: A basic DC Standard Differential Voltmeter can be operated in different modes. The three basic modes of operation are as a dc voltage standard, as a dc differential voltmeter, and as a dc voltmeter (conventional). 1. DC Voltage Standard: A + 1 V dc stable supply is obtained from a temperature
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Differential Voltmeter: The Differential Voltmeter technique, is one of the most common and accurate methods of measuring unknown voltages. In this technique, the voltmeter is used to indicate the difference between known and unknown voltages, i.e., an unknown voltage is compared to a known voltage. Figure 4.14 (a) shows a basic circuit of a differential
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Solid State Voltmeter: Solid State Voltmeter – Figure 4.13 shows the circuit of an electronic voltmeter using an IC OpAmp 741C. This is a directly coupled very high gain amplifier. The gain of the OpAmp can be adjusted to any suitable lower value by providing appropriate resistance between its output terminal, Pin No. 6, and
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Chopper type DC Amplifier Voltmeter (Microvoltmeter): Chopper type DC Amplifier Voltmeter the dc input voltage is converted into an ac voltage, amplified by an ac amplifier and then converted back into a dc voltage proportional to the original input signal. The balanced bridge voltmeter has limitations caused by drift problems in dc amplifier. Any fluctuations
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Transistor Voltmeter (TVM): Transistor Voltmeter – Direct coupled amplifiers are economical and hence used widely in general purpose low priced VTVM’ s. Figure 4.9 gives a simplified schematic diagram of a dc coupled amplifier with an indicating meter. The dc input is applied to a range attenuator to provide input voltage levels which can be
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DC Meter: The most commonly used dc meter is based on the fundamental principle of the motor. The motor action is produced by the flow of a small amount of current through a moving coil which is positioned in a permanent magnetic field. This basic moving system, often called the D’Arsonval movement, is also referred
Measurements of very Large Currents by Thermocouples: Measurements of very Large Currents by Thermocouples – Thermocouples instruments with heaters large enough to carry very large currents may have an excessive skin effect. Ordinary shunts cannot be used because the shunting ratio will be affected by the relative inductance and resistance, resulting in a frequency effect.
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Various Factors of Frequency Effect on Calibration: The Various Factors of Frequency Effect on Calibration such as: Skin effect Non uniform distribution of current along the heater wires Spurious capacitive currents 1. Skin Effect: The skin effect causes a higher reading at higher frequencies, especially if the heater wire is small. A low current instrument
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Thermocouple Principle and Types of Thermocouple: Thermocouple Principle consists of a junction of two dissimilar wires, so chosen that a voltage is generated by heating the junction. The output of a thermocouple is delivered to a sensitive dc microammeter. (Calibration is made with dc or with a low frequency, such as 50 cycles, and applies
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