What are the different types of electric meters indicating and recording devices?
Types of Meter Indicating and Recording Devices
Each meter has a device that records the measured quantity. An electric meter usually has a register, which registers the integrating load. The demand meter has an indicating, graphic (recording), printing, or digital device. Digital device meters may also have communications circuitry to permit remote monitoring of the measured quantities.
Each meter has a device that records the measured quantity. An electric meter usually has a register, which registers the integrating load. The demand meter has an indicating, graphic (recording), printing, or digital device. Digital device meters may also have communications circuitry to permit remote monitoring of the measured quantities.
Electric Meter Registers and Register Constants:
The registers are the prime concern of the operators since the registers furnish the magnitude of electrical energy consumed by the load.
The registers are the prime concern of the operators since the registers furnish the magnitude of electrical energy consumed by the load.
Register:
The meter register may be dial (pointer) type or cyclometric (digital) type. In the dial-type register, four or five dials are used to show the quantity measured. The register reads from left to right with the highest reading on the four-dial register 9999 and on the five-dial register 99999. The cyclometric register usually consists of four numbered rotating discs with the applicable number on each disc visible through a slot on a plate in front of the register.
The meter register may be dial (pointer) type or cyclometric (digital) type. In the dial-type register, four or five dials are used to show the quantity measured. The register reads from left to right with the highest reading on the four-dial register 9999 and on the five-dial register 99999. The cyclometric register usually consists of four numbered rotating discs with the applicable number on each disc visible through a slot on a plate in front of the register.
Register Constant: The register or dial constant of a meter is the multiplier used to convert the register reading to the actual measured value. Its value may be 1, 10, or any multiple of 10. Another constant, used with watt-hour meters, is the watt-hour constant, which is the registration of one revolution of the meter disc expressed in watt-hours. This constant is used only when calibrating watt-hour meters, but can be used to calculate the register constant. The register constant is usually marked on the meter register, and the watt-hour constant is shown on the meter nameplate.
Electronic Register:
Many modern electric meters have electronic registers. The electronic register displays the quantity measured on a liquid crystal display (LCD) or other electronic screen. Typically the units of the measured quantity are also displayed. No multiplier is required to convert the displayed value to the actual measured value.
Many modern electric meters have electronic registers. The electronic register displays the quantity measured on a liquid crystal display (LCD) or other electronic screen. Typically the units of the measured quantity are also displayed. No multiplier is required to convert the displayed value to the actual measured value.
Indicating Demand Meter:
This meter has a sweep hand to indicate the maximum demand for any given period. This period might be 15, 30, or 60 minutes. The maximum demand indicating hand is generally reset every month when the watt-hour meter reading is obtained.
This meter has a sweep hand to indicate the maximum demand for any given period. This period might be 15, 30, or 60 minutes. The maximum demand indicating hand is generally reset every month when the watt-hour meter reading is obtained.
Recording Demand Meter:
This meter may be found in existing installations but is generally not specified for new construction. The recording meter records the demand for each given demands period on either a round or strip chart. This chart, therefore, indicates all the demands over a given period. The maximum demand is determined by inspection of the meter chart.
This meter may be found in existing installations but is generally not specified for new construction. The recording meter records the demand for each given demands period on either a round or strip chart. This chart, therefore, indicates all the demands over a given period. The maximum demand is determined by inspection of the meter chart.
Contact Device:
This was originally a pair of contacts on a cam geared to the rotating disc shaft of the watt-hour meter to produce a series of pulses. The pulse rate was directly proportional to the speed at which the meter disc rotated. On more recent analog types, a second slotted disc geared to the meter shaft passes between a photocell and a light source. The resultant voltage pulse train produced is amplified and applied to a reed relay to produce a contact pulse output.
This was originally a pair of contacts on a cam geared to the rotating disc shaft of the watt-hour meter to produce a series of pulses. The pulse rate was directly proportional to the speed at which the meter disc rotated. On more recent analog types, a second slotted disc geared to the meter shaft passes between a photocell and a light source. The resultant voltage pulse train produced is amplified and applied to a reed relay to produce a contact pulse output.
Totalizer:
This solid-state device receives pulse trains from several watt-hour meters and produces a single output pulse train proportional to the sum of the inputs. Inputs may be additive or subtractive.
This solid-state device receives pulse trains from several watt-hour meters and produces a single output pulse train proportional to the sum of the inputs. Inputs may be additive or subtractive.
Demand Meter Constant:
The constant of a demand meter is the multiplier used to convert the indicated or recorded demand reading on the meter to actual measured values. This constant may be 1, 10, or a multiple of 10. The demand meter constant and the register constant on the watt-hour meter do not necessarily have the same value.
The constant of a demand meter is the multiplier used to convert the indicated or recorded demand reading on the meter to actual measured values. This constant may be 1, 10, or a multiple of 10. The demand meter constant and the register constant on the watt-hour meter do not necessarily have the same value.
Digital Memory:
Electronic meters typically have digital memory that will retain measured values for a defined period. The values may be stored in random access memory (RAM) or on a magnetic medium such as a tape drive, hard drive, or floppy disk. The values stored in digital memory can be read by a computer connected to the digital memory device via local connection or through a communications link.
Electronic meters typically have digital memory that will retain measured values for a defined period. The values may be stored in random access memory (RAM) or on a magnetic medium such as a tape drive, hard drive, or floppy disk. The values stored in digital memory can be read by a computer connected to the digital memory device via local connection or through a communications link.
Connection of Watt-Hour and VAR-Hour Meters
Watt-hour and VAR-hour meters have to have both current and potential connections to measure the
active and reactive energy. Watt-hour and VAR-hour meters are classified with respect to circuit connections and the type of load being measured.
Watt-hour and VAR-hour meters have to have both current and potential connections to measure the
active and reactive energy. Watt-hour and VAR-hour meters are classified with respect to circuit connections and the type of load being measured.
Self-Contained Watt-Hour and VAR-Hour Meters:
The current and potential coils of self-contained meters are connected directly to the circuit. These meters are normally used where the circuit voltage does not exceed 240 volts and the continuous load does not exceed 30 amperes. Self-contained watt-hour meters for 200- and even 400-ampere continuous load currents and 480 volts circuit voltage are available but are usually only used in special cases.
The current and potential coils of self-contained meters are connected directly to the circuit. These meters are normally used where the circuit voltage does not exceed 240 volts and the continuous load does not exceed 30 amperes. Self-contained watt-hour meters for 200- and even 400-ampere continuous load currents and 480 volts circuit voltage are available but are usually only used in special cases.
Transformer-Type Meters:
The current and potential coils of transformer-type meters are connected to the circuit by means of current and potential transformers. These meters are normally used when the circuit voltage exceeds 240 volts and/or the current is above 200 amperes. Current transformers are used to reduce the current to the meter to 5 amperes at rated load. Potential transformers are used to reduce the voltage to the meter to 120 volts.
The current and potential coils of transformer-type meters are connected to the circuit by means of current and potential transformers. These meters are normally used when the circuit voltage exceeds 240 volts and/or the current is above 200 amperes. Current transformers are used to reduce the current to the meter to 5 amperes at rated load. Potential transformers are used to reduce the voltage to the meter to 120 volts.
Single-Phase Watt-Hour Meter: Both self-contained and transformer-type meters may be used for single-phase systems. These meters have only one current and one potential coil. The transformer-type meter is usually equipped with a small indicating lamp to show when the potential coil is energized. This is important where the secondary of the potential transformer is fused.
Three-Phase, Two-Element Watt-Hour Meter:
These meters have two current and two potential coils and are used on three-phase, three-wire systems. Transformer-type meters require two current transformers and two potential transformers. The meters often have two small indicating lamps to show when the two potential coils of the watt-hour meter are energized.
Three-Phase, Two and a Half-Element Watt-Hour Meter:
These meters have three current coils and two potential coils and are used on three-phase, four-wire systems where the error due to voltage unbalances on the three-phase system can be neglected. Transformer-type meters require three current transformers and two potential transformers. There are two potential indicating lamps to show when the two potential coils are energized.
These meters have three current coils and two potential coils and are used on three-phase, four-wire systems where the error due to voltage unbalances on the three-phase system can be neglected. Transformer-type meters require three current transformers and two potential transformers. There are two potential indicating lamps to show when the two potential coils are energized.
Three-Phase, Three-Element Watt-Hour Meter:
These meters have three current coils and three potential coils and are used on three-phase, four-wire systems where both current and voltage unbalances can be expected. Transformer-type meters require three potential transformers and three current transformers. There are three potential indicating lamps to show when the three potential coils are energized.
These meters have three current coils and three potential coils and are used on three-phase, four-wire systems where both current and voltage unbalances can be expected. Transformer-type meters require three potential transformers and three current transformers. There are three potential indicating lamps to show when the three potential coils are energized.
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