Process Instrumentation · Panel Meters

Digital AC Panel Meter

Panel meter showing AC voltage and current together on two rows of digits, self-powered from the measured circuit and supplied with a split-core current transformer.

AC-10A (3 models) ·

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Key specifications

Voltage range
AC 60 to 500 V, for 220 V single-phase and 380 V three-phase circuits
Current ranges
10 A, 50 A and 100 A versions, the 10 A version resolving to 0.01 A
Supply
No separate supply; the measured voltage powers the instrument
Display
Two rows of digits, voltage in red and current in blue, with AC symbols on the right
Accuracy
Stated as about plus or minus 1 percent
Refresh
About 0.4 seconds per update
Current transformer
Split core, 12 mm bore on the 10 A and 50 A versions and a larger bore on the 100 A version
Mounting
Panel mounting through a 45.5 x 27 mm cut-out
Body
48 x 29 x 22 mm, with the current transformer supplied on a lead
Operating temperature
Minus 20 to 65 degrees Celsius

A panel meter earns its place by answering a question without anybody having to fetch an instrument to ask it. The question here is the one an operator asks of any live circuit: what is it doing right now, in volts and in amps. Showing both on one instrument at the point of use is the whole purpose, and it is why this meter takes its supply from the circuit it measures rather than from a separate pair of wires.

The trade that comes with that is a fixed function. It displays voltage and current and nothing else, and it does so on a scale chosen when it is ordered rather than when it is used.

Product overview

The instrument is one meter offered in three versions, distinguished only by the current range: 10 A, 50 A and 100 A. The voltage input is common to all three at AC 60 to 500 V, which covers a 220 V single-phase supply and a 380 V three-phase supply on the same part.

A split-core current transformer is supplied with the meter and is also available on its own. It is the current that sets the choice of version, and the choice matters more than the headline range suggests, because the three versions differ in resolution as well as in scale.

How the measurement is made

Voltage and current reach the two displays by different routes. The circuit voltage is taken across the red terminals, scaled, rectified and used both to drive the voltage row of digits and to power the instrument, which is what removes the need for a separate supply. The current is not measured in the meter at all: a conductor is passed through the bore of the split-core transformer, and the signal the transformer develops is brought to the white terminals and converted to a reading.

The two rows are distinguished by colour, voltage in red and current in blue, with an AC symbol beside each. Two trimmers on the back of the body allow the voltage and current indications to be adjusted.

How to select the right panel meter

Begin with the current the circuit normally carries, not the current it could carry under fault. The three versions differ in resolution as much as in scale: the 10 A version resolves to 0.01 A, while the 50 A and 100 A versions resolve to 0.1 A and state their lower end at 0.3 A. A panel fitted with a 100 A meter to watch a circuit that idles at a few tenths of an amp will show that current poorly or not at all.

Then match the transformer bore to the conductor, since the transformer has to close around a cable that is already installed. Finally confirm that the supply is a sinusoid. The material excludes thyristor controllers, non-sinusoidal inverters and high-frequency equipment, and a drive output is none of those things to a meter built for a sinusoidal supply.

Measurement limitations and selection considerations

The reading is a single-phase voltage and the current in one conductor. On a three-phase circuit that is one line current rather than a measure of the load as a whole, which is adequate for watching a branch but not for balancing phases; for that, three meters or a different instrument are needed.

Two practical limits come with the design. The meter is dark when the circuit is dead, because the circuit is its supply, so it cannot indicate that a circuit is off rather than failed. And the current reading depends entirely on the transformer: a conductor that does not pass centrally through the bore, or two conductors passed through together, will produce a figure that does not correspond to the current in either. The material also leaves the voltage display resolution and the frequency band unstated, and the page records that rather than implying a precision the material does not give.

Features

  • Voltage and current shown together on one instrument, so a circuit can be watched for both at once rather than read on two meters
  • Self-powered from the measured circuit, which removes a separate supply and an extra pair of wires behind the panel
  • A split-core current transformer, so a conductor does not have to be broken to fit it
  • A red and a blue row of digits, which distinguishes the two quantities without reference to a label
  • Panel mounting through a standard 45.5 by 27 mm cut-out, in a body 22 mm deep
  • A range of current versions so that a circuit can be measured on the scale that suits it, down to 0.01 A resolution on the 10 A version

Technical specifications

Every value below is taken from source documentation. Where a parameter is not stated in the available material it is marked as information required rather than estimated.

Measurement
Voltage rangeAC 60 to 500 V, common to 220 V single-phase and 380 V three-phase suppliesStandard
Current ranges10 A on the AC-10A version with a resolution of 0.01 A; 50 A on the AC-50A with 0.1 A; 100 A on the AC-100A with 0.1 AStandard
Lower end of the current rangeGiven as 0 A on the AC-10A version and as 0.3 A on the 50 A and 100 A versionsStandard
AccuracyAbout plus or minus 1 percentStandard
DisplayTwo rows of digits with voltage in red and current in blue, each with an AC symbolStandard
Refresh rateAbout 0.4 secondsStandard
SupplyNo separate supply; the measured voltage is used as the supply, over the same range as the measurementStandard
Resolution of the voltage displayNot stated in the materialInformation required
RepeatabilityNot stated in the materialInformation required
Behaviour outside the stated frequency rangeNot stated; the material excludes non-sinusoidal supplies without giving a frequency bandInformation required
Construction and installation
Body48 x 29 x 22 mm, described in the dimension table as a surface height of 29 mm, a surface length of 47.5 mm and a body thickness of 22 mmStandard
Panel cut-out45.5 x 27 mm, panel mountingStandard
TerminalsRed terminals for the circuit, which are connected to any two lines without regard to line and neutral; white terminals for the current transformerStandard
AdjustmentVoltage and current trimmers on the back of the bodyStandard
Current transformerA separate split-core transformer, 12 mm bore on the 10 A and 50 A versions and given as 15 mm bore on the 100 A version; the material also quotes 14.5 mm for the same part elsewhereStandard
Lead length20 cmStandard
Enclosure material and protection ratingNot stated in the materialInformation required
Dielectric strength and impulse ratingNot stated in the materialInformation required
Environment and use
Operating temperatureMinus 20 to 65 degrees CelsiusStandard
Supplies the meter may not be used onExcluded by the material: circuits with a thyristor voltage controller, a non-sinusoidal inverter, or high-frequency equipmentStandard
Current transformer matchingThe 10 A and 50 A versions take the 12 mm bore transformer; the 100 A version takes the larger oneStandard
Small-current dutyThe material advises the 10 A version where small currents have to be resolved, since it is the only one stating 0.01 AStandard
Altitude and humidity limitsNot stated in the materialInformation required

Available models

Selection table
Model Configuration Key ranges Availability
AC-10A Panel meter with an AC voltage display and an AC current display rated 10 A, supplied with the 12 mm bore current transformer Current 10 A with a resolution of 0.01 A; voltage AC 60 to 500 V; body 48 x 29 x 22 mm The version for small currents, and the only one whose stated resolution reaches 0.01 A
AC-50A The same meter rated 50 A, supplied with the 12 mm bore current transformer Current 50 A with a resolution of 0.1 A and a stated lower end of 0.3 A; voltage AC 60 to 500 V The general-purpose version for a branch circuit on a 220 V or 380 V supply
AC-100A The same meter rated 100 A, supplied with the larger bore current transformer Current 100 A with a resolution of 0.1 A and a stated lower end of 0.3 A; voltage AC 60 to 500 V The version for a main circuit, where the conductor is larger and the bore has to pass it
Current transformer The split-core transformer alone, without the meter 12 mm bore for the 10 A and 50 A versions; a larger bore, given as both 15 mm and 14.5 mm in the material, for the 100 A version A separate line item for replacement or for a spare transformer

Customization

  • The current range, in 10 A, 50 A and 100 A versions, which must be matched to the transformer that comes with it
  • The current transformer, available separately and matched by bore to the conductor
  • The displayed quantities, which are fixed as voltage and current rather than configurable
  • The scale of the display legends, which is not offered as a variable in the material

Certification and compliance

Certification documents not yet supplied

Certifications are only published once a certificate copy can be produced, so this section is deliberately empty rather than populated with assumed approvals. Tell us which approvals your application requires and we will confirm what is available for this instrument.

Parameters still to be confirmed

The following are required for a complete specification but are not stated in the documentation supplied to us. They are listed rather than estimated:

  • The official model numbers, where the codes in the material are the only designations given
  • The resolution of the voltage display, which is not stated
  • Repeatability, as distinct from the stated accuracy
  • The frequency band over which the accuracy is quoted, since the material excludes non-sinusoidal supplies without giving a range
  • The enclosure material and the protection rating, which are not stated
  • Dielectric strength and impulse withstand, which are not stated for a panel instrument on a mains circuit
  • Altitude and humidity limits for the mounting position
  • The bore of the current transformer for the 100 A version, which the material gives as both 15 mm and 14.5 mm
  • The overall length of the body, given as 47.5 mm in one table and 48 mm in another
  • Whether an English-language datasheet and a declaration of conformity are available

Frequently asked questions

Does the meter need a separate power supply?

No. It takes its supply from the voltage it is measuring, over the same range as the measurement, so the only connections behind the panel are the two circuit terminals and the lead from the current transformer. That is worth having on a small panel, where a separate supply would mean an extra pair of wires and an extra place for a fault. The consequence is that the meter is dark when the circuit is dead, which for a local indication of a live circuit is usually the intended behaviour rather than a limitation.

Why does the meter come with a current transformer?

Because a panel meter cannot carry the current directly on the larger versions. The transformer is split so that it can be opened and closed around a conductor that is already installed, without breaking the circuit. The conductor passes through the bore and the transformer produces a signal proportional to the current in it; any one line can be passed through, since the direction of the reading is what the bore and the lead orientation determine rather than line and neutral. Matching the transformer bore to the conductor is what decides whether the 10 A, 50 A or 100 A version can be fitted at all.

Can it be used on a variable-frequency drive output?

No, and the material excludes it explicitly, along with thyristor voltage controllers, non-sinusoidal inverters and high-frequency equipment. The meter is built to measure a sinusoidal supply, and the waveform at the output of a drive is not one: it is switched, and its harmonic content is high. A meter of this type reading that waveform produces a number that does not mean what an RMS value means. Where a drive output has to be measured, the instrument has to be one specified for it.

Which version should be chosen for a small current?

The 10 A version, and the reason is resolution rather than range. It is the only version whose stated resolution reaches 0.01 A; the 50 A and 100 A versions resolve to 0.1 A and their stated lower end is 0.3 A, so a current of a few tenths of an amp would be read on the coarsest part of their scale, if at all. Selecting by the largest current the circuit can carry and not by the current it normally does is the way a panel ends up insensitive where the process actually runs.

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