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ELECTRICAL MULTI-FUNCTION METERS

What are the other types of electric meters which uses multi-function?

A multi-function meter is a combination device that performs the functions of instruments, transducers, and meters. It is flexible, allowing the user to monitor many quantities simultaneously. It contains a central processing unit (CPU) for the calculation and digital display of desired quantities. Most multifunction meters can be user configured to normally display a few quantities simultaneously while all quantities can be read using push buttons on the front of the device or via remote monitoring.

Many multi-function meters also have digital memory for storing measured quantities recorded over a defined period. Stored quantities can be downloaded to a laptop computer or other digital device. Input Quantities Multi-function meters require three voltage and three current inputs to monitor three-phase power circuits. Because the multi-function meter is a microprocessor-based device, it can be set to calculate primary voltage and primary current values based on inputs from potential and current transformers with a wide range of primary-to-secondary ratios.

The instrument transformer ratios are set at the factory but may be changed in the field. Once the instrument transformer ratios are set, the meter will calculate and display primary values with correct units. No scale factors are required to accurately read the meter display.

Measured and Calculated Values
Multi-function meters can measure and calculate many electrical quantities including instantaneous volts, amps, watts, VARs, volt-amperes, power factor, and hertz. The meter may also record the instantaneous maximum and minimum for each of these values over a pre-defined period.

Accumulating quantities that can be calculated include watt-hours and VAR-hours. The latest versions of multifunction meters are incorporating programmable alarm levels and various power quality measurements. The meter can also initiate communications to a remote master or PC when certain events or levels are measured.

Communications
Multi-function meters may communicate with remote terminal units (RTUs), programmable logic controllers (PLCs), human–machine interfaces (HMIs), and other digital devices via local communications network, common telephone lines, radio, or carrier signals coupled to power circuits. Local network hardware typically conforms with either RS-232 or RS-485 standards.

 Additional hardware and software requirements are defined by the communications protocol specified for the local communications network. Telephone lines, radio, and carrier signals are often used by utilities for remote meter reading. (See CRN’s Guide to Automatic Meter Reading: A Tutorial, Project 98-06.)
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