Rectifier type instruments

Rectifier Type Instrument

rectifier type instrument measures alternating electrical signal by means of D.C measuring instrument. As the name implies, this instrument first rectifies an A.C signal to D.C then measures. Although it measures the rectified A.C signal (D.C signal), but the scale of the instrument is calibrated for A.C. The sensitivity of D’ Arsonval instrument is quite high. But a D’Arsonval instrument can only measure to D.C. So, to utilize the sensitivity of D’Arsonval movement for A.C, we use a rectifier type instrument.

The sensitivity of the rectifying instruments is high as compared to the moving coil and the Electrodynamo meter instrument. Thereby, it uses for measuring the current and voltage. The circuit arrangement of the rectifier instrument shown in the figure below. The device uses the four diodes which act as a rectifying element.

Factors Affecting the Performance of Rectifier Type Instruments

The following are the factors that affect the performance of the instrument when it is used on AC.

  1. Effects of Waveform – The calibration of the rectifier instrument can be done regarding the RMS value of voltage and current. The form factor of the half wave and the full wave rectifier type instrument fixes on the calibrated scale. And if the waveform of the other form factors applies to the device,  the waveform error occurs in the reading.
  2. Effect of Temperature Change – The resistance of the rectifying element varies with the change in temperature. And this property of the rectifying component causes the error in the instruments.
  3. Effect of Rectifying Instrument – The rectifier instrument has the property of the imperfect capacitance. It allows the high-frequency current to pass through it.
  4. Decreases in Sensitivity – The sensitivity of the rectifier type instrument for AC operation is lower than that of the DC operation.

Advantages of Rectifier Type Instrument

  • This instrument can measure an electrical signal of very low frequency to radio frequency.
  • The instrument is also capable of measuring electrical signals up to several mega Hz.
  • The sensitivity of the instrument is much higher than that of any other type of A.C measuring instruments. Actually, for achieving very high sensitivity in A.C measurements, we use rectifier type instruments.

Applications of Rectifying Instrument

The following are the applications of the rectifying instrument.

  • The instrument uses for measuring the voltage whose range lies between 50 – 250 V.
  • It use as a milli-ammeter or micro-ammeter.
  • The rectifying instrument use in the communication circuit for measurement.

The sensitivity of the rectifying type voltmeter is less than that the sensitivity of the DC voltmeter. Thus, the loading effect of the ac rectifier voltmeter is higher than the dc voltmeter.

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