True RMS AC Voltage & Current Meter, 1 Cycle Update at 50/60 Hz.

200 mV - 600 V and 2 mA - 5 A full-scale ranges



  • 0.2, 2, 20, 200 & 600V AC or AC+DC voltage ranges
  • 2, 20, 200 mA & 5A AC or AC+DC current ranges
  • True AC RMS measurement with crest factor of 3.0 at full scale
  • Fast response: reading in 0-16.7 ms after each signal cycle to full accuracy
  • Accurate to 0.03% of full scale, 0.1% to 100% of FS, 10 Hz to 15 kHz
  • Universal 85-264 Vac / 90-300 Vdc or 10-48 Vdc / 12-32 Vac power
  • Wide choice of options:
    - 2 or 4 relays, mechanical or solid state (isolated)
    - Analog output, 4-20 mA, 0-10V, or -10V to +10V (isolated)
    - Serial data I/O: Ethernet, USB, RS485, RS232 (isolated)
    - Custom curve linearization, rate from consecutive readings
True RMS digital panel meter by TD Micronic

The True RMS meter is a 60,000 count digital panel meter with exceptional performance at half the price of a bench top meter. It can measure true RMS voltage or current of AC signals where there is considerable distortion of the waveform, such as rectifier outputs or waveforms chopped by an SCR, TRIAC or transistor circuit, as illustrated.

  • True RMS readings in 0-16 ms after completion of one input signal cycle allow anomalies to be detected and alarmed before they become expensive problems. Fast on/off control and alarm can be achieved with optional dual or quad relays, either contact or solid state. The meter can also capture peak and valley readings that occur at the nominal rate of 50/60 Hz.
  • Accuracy to 0.1% of full scale for signals from DC to 10 kHz and signal amplitudes down to 0.1% of full scale. The crest factor (Vp / Vrms) is 3.0 at full-scale Vrms of 20,000 counts and a Vp of 60,000 counts. The meter starts to flash overrange at 132% of full scale Vrms , at which point the available crest factor is 60,000 / 26,400 = 2.27. Meaningful readings with rated resolution continue to be obtained up to 212% of full scale Vrms (42,433 counts) for sinusoidal signals, at which point the available crest factor is 1.414. For safety reasons, the maximum RMS input signal should never exceed 600V or 5A. ETL certification is for a maximum voltage of 300 Vrms.

Power AC or DC coupling is jumper selectable on the signal conditioner board. AC coupling accommodates signals from 10 Hz to 10 kHz and is suitable for applications such as measuring AC ripple on a DC power supply. DC coupling accommodates signals from 0 to 10 kHz. Multiple integral cycles are averaged for signals above 50/60 Hz. A single cycle is captured for signals from 3 Hz to 50/60 Hz. Below 3 Hz and at DC, the capture rate is 3/sec.

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 5A current transformers to be applied directly to the meter, with no need for a stepdown transformer. The meter reading can easily be scaled for the current transformer ratio. Digital filtering is selectable for noisy signals.

Designed for system use. Optional plug-in boards for communications and control include Ethernet and other serial communication boards, dual or quad relay boards, and an isolated analog output board. s may be powered from 85-264 Vac or optionally from 12-32 Vac or 10-48 Vdc. The display is available with red or green LEDs. The 1/8 DIN case meets NEMA 4X (IP65) specifications from the front when panel mounted. Any setup functions and front panel keys can be locked out for simplified usage and security. All power and signal connections are via UL / VDE / CSA rated screw clamp plugs.


AC Voltage

AC Voltage
FS Range
AC Voltage to
Overrange Flash
Resolution Input Resistance Error at 25°C **
200.00 mV 264.00 mV 10 µV 22 MΩ ± 0.03% of FS ± 2 cts, 0-100% of FS
2.0000 V 2.640 V 100 µV 1 MΩ
20.000 V 26.400 V 1 mV 1 MΩ
200.00 V 264.00 V 10 mV 1 MΩ
600.0 V* 650 V 0.1 V 1 MΩ ± 0.48V
300.0 V 650 V 0.1 V 1 MΩ ± 0.8 V

AC Current

DC Current Range AC Current to
Overrange Flash
Resolution Input Resistance Error at 25°C **
2.0000 mA 2.6400 mA 0.1 µA 100 Ω ± 0.03% of FS ± 2 cts, 0-100% of FS
20.000 mA 26.400 mA 1.0 µA 10 Ω
200.00 mA 264.00 mA 10 µA 1 Ω
5.000 A 5.4 A 1 mA 0.01Ω ± 20 mA
*   Range not ETL certified. For purposes of accuracy calculation, the 600V range is 2000V (20,000 counts), and the 5A range is 20A (20,000 counts).
**  10 Hz to 15 kHz (AC coupling) or DC to 15 kHz (DC coupling)

Both AC Voltage & Current

Readout 5 LED digits, 7-segment, 14.2 mm (.56"), red or green
Range -99999 to 99999 or -99990 to 99990 (count by 10)
Display Update Rate 3.75/s at 60 Hz power, 3.1/s at 50 Hz power
Indicators 1 LED lamp per relay setpoint
Crest factor Vp / Vrms 3.00 at full scale range
Output Update Rate
A-to-D rate 60/s at 60 Hz power, 50/s at 50 Hz power
Signals > 50/60 Hz 60/s at 60 Hz power, 50/s at 50 Hz power
Signals 3 to 50/60 Hz Signal frequency
Signals DC to 3 Hz 3 per second
Maximum Signal
Max applied voltage 600 Vac for 2, 20, 200, 600V ranges, 50 Vac for 0.2V range
Current protection 25x for 2 mA, 8x for 20 mA, 2.5x for 200 mA, 1x for 5A
Voltage, standard 85-264 Vac or 90-300 Vdc
Voltage, optional 12-32 Vac or 10-48 Vdc
Frequency DC or 47-63 Hz
Power consumption (typical, base meter) 1.2W @ 120 Vac, 1.5W @ 240 Vac, 1.3W @ 10 Vdc, 1.4W @ 20 Vdc, 1.55W @ 30 Vdc, 1.8W @ 40 Vdc, 2.15W @ 48 Vdc
Power Isolation 250V rms working, 2.3 kV rms per 1 min test
Analog Output (optional)
Output levels 4-20 mA, 0-20 mA, 0-10V, -10 to +10V (jumper selectable)
Current compliance 2 mA at 10V ( > 5 kΩ load)
Voltage compliance 12V at 20 mA (< 60Ω load)
Scaling Zero and full scale adjustable from -99999 to +99999
Resolution 16 bits (0.0015% of full scale)
Isolation 250V rms working, 2.3 kV rms per 1 min test
Relay types 2 Form C contact relays or 4 Form A contact relays (NO) 2 or 4 Form A, AC/DC solid state relays (NO)
Current tatings 8A at 250 Vac or 24 Vdc for contact relays 120 mA at 140 Vac or 180 Vdc for solid state relays
Output common Isolated commons for dual relays or each pair of quad relays
Isolation 250V rms working, 2.3 kV rms per 1 min tes
Serial Data I/O (optional)
Board selections RS232, RS485 (dual RJ11 or RJ45 connectors), USB, Ethernet, USB-to-RS485 converter, Ethernet-to-RS485 converter
Protocols Modbus RTU, Modbus ASCII, Modbus TCP (Ethernet), TDM ASCII
Data rates 300 to 19200 baud
Digital addresses 247 (Modbus), 31 (TDM ASCII),
Isolation 250V rms working, 2.3 kV rms per 1 min test
Signal Connections
Operating temperature 0°C to 55°C
Storage temperature. -40°C to 85°C
Relative humidity 95% at 40°C, non-condensing
Protection NEMA-4X (IP-65) when panel mounted
Using Meters to Synchronize Two 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 AC RMS Voltmeters, which offer 200.00 V and 600.0 V ranges. Or a single meter can be multiplexed by using an external toggle switch.
  • Two frequencies A & B can be measured to six-figure accuracy by a single Dual Channel Counter, 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. The meter can also display frequency A - frequency B, or frequency A / frequency B without toggling.
  • Phase angle can be measured using the Phase Meter.
Using 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. Drops in line voltage or frequency may indicate an excessive load and the possibility of equipment damage. meters and counters are low-cost means to instrument and alarm AC power lines with great accuracy:

  • AC RMS Voltmeter and Ammeter, as documented in this page. True RMS capability allows the display of RMS voltage for non-sinusoidal waveshapes, such as square waves from a UPS. A built-in 5 A range can be used to display currents up to 5.000 A with 1 mA resolution or 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 of 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 & Power Factor Meter. Two signals with identical periods are applied to Channels A and B. A phase angle 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.

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