Electro-Numerics, Inc.
42213 Sarah Way, Temecula, CA 92590, USA


Tel: 800-854-8530 (USA)
Tel: 951-699-2437 
Fax: 951-695-7246


    Micro Series True AC RMS
Voltage & Current Panel Meters

0.2 V - 660 V and 2 mA - 5 A full-scale ranges


  • Available in three digit heights: 0.56" for panel mounting, 1.0" (Mighty-1) or 5.0" (Mighty-5) for long-distance viewing.
  • 0.2, 2, 20, 200 & 660 V ranges.
  • 2, 20, 200 mA & 5 A ranges.
  • 4 1/2 digit resolution.
  • 99.9% accuracy of full scale.
  • AC coupled input.
  • Crest factor of 2.4 at full scale.
  • Priced competitively with less capable averaging AC meters.
  • Scalable for direct readout of external current shunts or current transformers.
  • Peak value display.
  • 95-240 Vac 10% and 95-370 Vdc power standard.
  • Green or red display.
  • Choice of isolated plug-in options for control and computer interface:
    dual relays, 4-20 mA & 0-10 V analog output, RS232/485 serial I/O, low voltage AC & DC power.
  • 1/8 DIN case environmentally sealed to NEMA-4X from front panel.
  • 1/8 DIN version certified to UL 3101-1, CAN/CSA-C22.2, EN 61010-1 (CE Mark).


Micro Series True RMS meters offer a high accuracy 4-1/2 digit display for five voltage ranges and four current ranges. It is suited for AC applications where there is considerable distortion of current waveforms from nonlinear loading. The input is AC coupled to read only the AC component, such as ripple on a power supply.

Signal conditioner board for Laureate™ True AC RMS Voltage & Current digital panel meterThe True RMS meter uses precision circuitry to compute the root-mean-square of complex waveforms from 10 Hz to 10 kHz. Spikes up to 2.4 times the maximum of each range are accurately measured. This provides a crest factor (Vp / Vrms) of 240 for a signal amplitude of 1% of full scale, decreasing to 2.4 at 100% of full scale.

Use with Current Transformers

High common mode rejection allows stable readings with current shunts located on the high side of the line. Five amp input capability allows the output of 5 A current transformers to be applied directly to the meter, with no need for a stepdown transformer. The current reading can easily be scaled to display the input to the current transformer. Digital scaling and calibration eliminate zero and span drift associated with potentiometers in non-microcomputer based meters.

High Accuracy

Frequency and amplitude operating range of Laureate True AC RMS Digital Voltmeters and Ammeters

Maximum error as a function of frequency
and signal amplitude

The typical accuracy is 99.9% of full scale, decreasing to 99.8% for low frequency at high amplitude, or high frequency at low amplitude. The above graph shows that maximum error is 0.1% of full scale over all frequency ranges of interest to AC power measurement. Error increases to 0.2%, represented by the two shaded areas, at low frequency and high amplitude, or high frequency and low amplitude.

Crest factor increases in inverse proportion to signal amplitude. As shown on the same graph, the maximum crest factor (Vp / Vrms) is 2.4x at full-scale amplitude, increasing to 240 at 1% of full-scale amplitude.

The Micro RMS meter utilizes the same high-speed analog-to-digital conversion method as all other Micro Series panel meters. However, the meter settling time and control response to a step change in AC amplitude are limited by the RMS converter circuit to approximately 1 second.

Built-in Flexibility

Plug-in isolated analog output, dual setpoint controller, and RS232/485 serial communications boards can upgrade Micro and Mighty Series meters from a simple monitor to system interface and control.

Micro Series meters can be powered from 95-240 Vac 10% and 95-370 Vdc, or optionally from 12-34 Vac and 10-48 Vdc. Any setup functions and front panel keys may be locked out for simplified usage and security. The popular 1/8 DIN version with 0.56" high digits is environmentally sealed to NEMA-4X (IP65) from the front when panel mounted, and is available with red or green LEDs.


AC Voltage (1% to 100% of full scale)

AC Voltage Range Resolution Input
Typ Error
at 25C
200.00 mV
2.000 V
20.000 V
200.00 V
660.0 V
10 V
100 V
1 mV
10 mV
100 mV
22 M
22 M
1 M
1 M
1 M
0.1% FS
10 Hz to 10 kHz

AC Current (1% to 100% of full scale)

AC Current Range Resolution Input
Typ Error
at 25C
2.0000 mA
20.000 mA
200.00 mA
5.000 A
0.1 A
1.0 A
10 A
1.0 mA
0.1% FS
10 Hz to 10 kHz

AC Voltage & Current

Digit Height
5 digits, 7-segment
Available with 0.56", 1.0", 4.0" or 5.0" digits.
High brightness red. Green available with 0.56" digits.
-99999 to +99999
-99990 to +99990 (selectable count by 10 with rounding)
2 red LED lamps
Span Tempco
Zero Tempco
Crest Factor
0.005% of reading/C
0.1 counts/C
2.4x at 100% of full scale
Response Time
A-to-D rate
Output Update
Display Update
1 s conversion settling time
60/s at 60 Hz, 50/s at 50 Hz
56/s at 60 Hz, 47/s at 50 Hz
3.5/s at 60 Hz, 3/s at 50 Hz
Maximum Signal
Max applied
660 Vac for 20, 200 and 600 V ranges, 125 Vac for other
25x for 2 mA, 8x for 20 mA, 2.5x for 200 mA, 1x for 5 A
Voltage, std.
Voltage, opt.
Power isolation
95-240 Vac 10% and 95-370 Vdc
12-34 Vac and 10-48 Vdc
DC or 49-440 Hz
Safety-rated to 250 Vac, meter ground to earth ground,
DC to 60 Hz, 4.2 kVp per High Voltage Test
Excitation Output
5 Vdc
10 Vdc
24 Vdc
Output isolation
5 Vdc 5%, 100 mA max
10 Vdc 5%, 120 mA max
24 Vdc 5%, 50 mA max
50 Vdc to meter ground
Connector Pin Assignments
conrmsnobox.gif (904 bytes)
Operating Temperature
Storage Temp.
Relative Humidity
0C to 60C
-40C to 85C
95% at 40C, non-condensing
NEMA-4X (IP-65) when panel mounted

AC line monitorint using a Laureate AC RMS Voltmeter, AC RMS Ammeters, and AC Line Frequency Meter

Using Micro Series Meters and Counters to Instrument an AC Line

Why Measure AC Power?

Many AC loads, such as electrical motors, will only operate reliably if the AC line voltage and frequency are within specified tolerances. Otherwise permanent damage to expensive plant equipment may occur. Motor generators and UPS systems will only operate reliably with the load for which they are rated. Drops in line voltage or frequency may indicate an excessive load and the possibility of equipment damage.

Micro Series meters and counters are low-cost means to instrument AC power lines with great accuracy:

  • AC RMS Voltmeter. Full-scale ranges of interest are 200.00 V with 10 mV resolution and 660.0 V with 100 mV resolution. True RMS capability allows the display of RMS voltage for non-sinusoidal waveshapes, such as square waves from a UPS.

  • AC RMS Ammeter. A built-in 5 A range can be used to display currents up to 5.000 A with 10 mA resolution, or to accept the output of 5 A current transformers. The 200.00 mV range can be used with external current shunts. With either transformers or shunts, scaling to the input current is easily accomplished via the meter's front panel pushbutton switches.

  • Frequency Meter. Inverse period is used to determine AC line frequency to six-figure accuracy (60.0000 or 50.0000) in a few line cycles plus 30 ms.

  • Phase Angle Meter. Two signals with identical periods are applied to Channels A and B of the Micro phase angle meter. A display from -180 to +180 is obtained by timing the rising edge of one channel and the falling edge of the other channel. A resolution of 1, 0.1 or 0.01 is selectable. Accuracy is .01% up to 100 Hz, .1% at 1 kHz, and 1% at 10 kHz.

Using Laureate digital AC panel meters, a frequency meter and phase meter to synchronize two motor generators

Using Micro Series Meters to Synchronize Motor Generators

Successful synchronization of two motor generators requires that the voltage outputs of the generators be close to each other, that the two frequencies be identical, and that the voltage waveshapes be in phase.

  • The two voltages can be measured by two Micro AC RMS Voltmeters, which offer 200.00 V and 660.0 V ranges. Or a single meter can be multiplexed by using an external toggle switch.

  • The two frequencies can be measured to six-figure accuracy by a single Micro Dual Channel Frequency Meter, where each channel monitors a generator. The two AC neutrals must be tied to meter ground. Pressing a front-panel key toggles the reading between the channels.

  • Phase angle can be measured using the Micro Phase Meter.

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Electro-Numerics, Inc., 42213 Sarah Way, Temecula, CA 92590, USA
Tel: 800-854-8530 (USA), 951-699-2437;  Fax: 951-695-7246;  sales@electronumerics.com