• Product
  • Suppliers
  • Manufacturers
  • Solutions
  • Free tools
  • Knowledges
  • Experts
  • Communities
Search


MENU

Rectifier Type Instrument

Edwiin
Field: Power switch
China
Definition
Instruments that utilize a rectifying element to measure voltage and current are known as rectifying instruments. The rectifying element converts alternating current (AC) into direct current (DC), which is then indicated by a DC-responsive meter. A Permanent Magnet Moving Coil (PMMC) instrument is commonly used as the indicating device.
Rectifying instruments exhibit higher sensitivity compared to moving coil and electrodynamometer instruments, making them suitable for current and voltage measurements. The circuit arrangement of a rectifier instrument is shown in the figure below, featuring four diodes that function as the rectifying element.
The multiplier resistance Rs is used to limit the current such that its value does not exceed the rating of the PMMC instrument.
Rectifying Element
A rectifying element converts alternating current (AC) to direct current (DC), ensuring unidirectional current flow through the PMMC instrument. Common materials for rectifying elements include copper oxide, selenium cells, germanium diodes, and silicon diodes.
The rectifying element exhibits zero resistance in the forward-biased state and infinite resistance in the reverse-biased state, a property critical for rectification.
Characteristic Curve of Rectifying Element
The characteristic curve of a rectifying circuit is shown in the figure below. Ideally, the rectifying element has no voltage drop in the forward direction and blocks all current in the reverse direction.
But practically, this is not possible. The real characteristic curve of the rectifying element shown in the figure below.
Half-Wave Rectifier Circuit
The figure below illustrates a half-wave rectifying circuit. The rectifying element is connected in series with the voltage source, resistance multiplier, and permanent magnet moving coil (PMMC) instrument. The forward resistance of the diode is assumed to be negligible.
When a DC voltage source is applied to the circuit, a current Im flows through it, with a magnitude equal to V/(Rm + RS). This current causes full-scale deflection in the instrument.
When an AC voltage is applied to the same circuit, the rectifying element converts the AC voltage into unidirectional DC voltage, yielding a rectified output through the instrument. The PMMC instrument deflects based on the average value of the current, which depends on the average voltage of the AC source.
Average Value of Voltage
The above calculation indicates that the sensitivity of the instrument for AC is 0.45 times the current sensitivity for DC.
Full-Wave Rectifier Instrument
The circuit of a full-wave rectifier is shown in the figure below.
The DC voltage applied to the circuit causes the full-scale deflection of the PMMC meter. The sinusoidal voltage applies to the meter express as
For the same voltage value, the average value of AC is 0.9 times that of DC. In other words, the sensitivity of the instrument with AC is 90% of that with DC.
The sensitivity of a full-wave rectifier instrument is double that of a half-wave rectifier instrument.
Sensitivity of Rectifier Instrument
The sensitivity of an instrument reflects how the measured quantity varies from input to output, such as the DC sensitivity of a rectifier instrument.
The sensitivity of an AC rectifier-type instrument depends on the type of rectifying element used in the circuit.
Factors Affecting the Performance of Rectifier-Type Instruments
The following factors impact the instrument’s performance when used with AC:
Effects of Waveform
Rectifier instruments are calibrated based on the RMS (root-mean-square) value of voltage and current. The form factor of half-wave and full-wave rectifier instruments is fixed for the calibrated scale. If a waveform with a different form factor is applied, reading errors due to waveform mismatch will occur.
Effect of Temperature Change
The resistance of the rectifying element varies with temperature, introducing errors into the instrument’s measurements.
Effect of High-Frequency Currents
Rectifier instruments have imperfect capacitance characteristics, allowing high-frequency currents to pass through and affect readings.、
Decrease in Sensitivity
The sensitivity of rectifier-type instruments for AC operation is lower than that for DC operation.
Advantages of Rectifying Instruments
  • Expanded Frequency Range: Operates from 20 Hz to high-frequency ranges.
  • Low Current Consumption: For voltmeters, the current operating range is much lower than other AC instruments.
  • Uniform Scales: Provides uniform scales across a wide measurement range.
  • Moderate Accuracy: Achieves ±5% accuracy under normal operating conditions.

Applications of Rectifying Instruments

  • Measures voltage in the range of 50–250 V.
  • Used as milliammeters or microammeters.
  • Applied in communication circuits for signal measurement.
  • Note: The sensitivity of an AC rectifier voltmeter is lower than that of a DC voltmeter, resulting in a higher loading effect for AC measurements.
Give a tip and encourage the author!
About experts
Edwiin
China
Expertise area
Power switch
Professional article
348
Recommended
More
Why Regular Transformer Maintenance Matters: 5 Serious Consequences of Neglecting It
I. Allowable TemperatureWhen a transformer is in operation, its windings and iron core generate copper loss and iron loss. These losses are converted into heat energy, causing the temperature of the transformer's iron core and windings to rise. If the temperature exceeds the allowable value for a long time, the insulation will gradually lose its mechanical elasticity and age.The temperature of each part of the transformer during operation is different: the winding temperature is the highest, fol
Rockwell
09/12/2025
How to Implement Condition-Based Maintenance for Power Transformers? A Complete 4-Step Process Analysis
1. Definition of Condition-Based MaintenanceCondition-based maintenance refers to a maintenance method where decisions on whether and how to perform maintenance are determined based on the real-time operating status and health condition of equipment. It has no fixed maintenance methods or schedules. The prerequisite for condition-based maintenance is the establishment of equipment parameters and the comprehensive analysis of various operational information of the equipment, so as to make reasona
Noah
09/12/2025
Can't choose a dry-type transformer? Get expert advice – free.
Traction Rectifier TransformersRated capacity: 800 to 4400 kVA; Voltage class: 10 kV and 35 kV; Rectifier pulse number: 12-pulse and 24-pulse. Compared with 12-pulse rectifier circuits, 24-pulse rectifier circuits can reduce the harmonic pollution of the power grid by 50%, and no filtering equipment is needed at this location. It is suitable for power supply systems of urban subways and rail transit.Excitation Rectifier TransformersRated capacity: 315 to 3000 × 3 kVA; Voltage class: 10 kV, 13.8
Vziman
09/12/2025
High harmonics? Your transformer may be overheating and aging fast.
This report is based on the analysis of one-day power quality monitoring data of your company's distribution system. The data shows that there is significant three-phase current harmonic distortion in the system (with a high total harmonic distortion of current, THDi). In accordance with international standards (IEC/IEEE), harmonic currents at this level have posed substantial risks to the safe, reliable, and economical operation of the power supply transformer, mainly manifested in additional h
Leon
09/12/2025
About experts
Edwiin
China
Expertise area
Power switch
Professional article
348
Source professional electrical partners, experts, and explore smart grid & energy solutions.
Seed Inquiry
Download
Get the IEE Business Application
Use the IEE-Business app to find equipment, obtain solutions, connect with experts, and participate in industry collaboration anytime, anywhere—fully supporting the development of your power projects and business.
App Store App Store App Store App Store App Store App Store App Store App Store
App Store