TECHNICAL NOTES

IMPORTANT! To ensure safe and reliable operation, DMR20-1-ACV

AC voltage monitors must be installed and serviced by qualified

technical personnel. Contact Murata Power Solutions if there is

any doubt regarding installation or operation.

1. Measurement Type: DMR20-1-ACV series AC voltmeters employ a

precision true-rms signal conditioning IC, a 13-bit analog-to-digital

converter, and a stable voltage reference to measure and display 85 to

264Vac 50/60Hz AC supplies. DMR20-1-ACV voltmeters can be pow-

ered from—and accurately measure—AC supplies with sine, triangle,

square, and quasi-sine waveforms. High-frequency harmonic compo-

nents up to 65kHz will be measured with minimal additional error.

2. Calibration: DMR20-1-ACV voltmeters are factory calibrated; there are

no provisions for calibrating these meters in the field.

3. Operating Range: As the AC input voltage is lowered to 95.0Vac (50 or

60Hz) or below, the DMR20-1-ACV’s display will begin to dim slightly,

but it will remain accurate down to its 85Vac rating. Input voltages

above 265Vac will cause the display to flash on and off at approxi-

mately one-second intervals.

4. Panel Installation: All electrical connections to DMR20-1-ACV must

be made after the voltmeter is securely attached to the panel, and with

the input AC supply de-energized (off). In high-vibration environments,

adequate strain reliefs must be used on all supply wiring. See Figure 1

for typical panel mounting details.

Tightening Torque:

The recommended tightening torque for the M30 x 1.5 plastic hex nut

is 10 to 17 in-lbs (1.3 to 1.9 N-m). If a torque wrench is not available,

this recommended range can be approximated by hand tightening the

hex nut SLOWLY until it just bottoms out against the panel’s rear sur-

face. From this bottomed-out reference position, using a suitable tool,

tightening the hex nut ¼ turn clockwise will produce approximately 10

in-lbs (1.3 N-m) of torque; tightening it 3/8 turn clockwise will produce

approximately 17 in-lbs (1.9 N-m).

Check to make sure the housing’s anti-rotation key is aligned with the

notches on both the panel and the gasket before tightening the hex

nut. Over tightening the hex nut will distort the rubber gasket and may

damage the threads on both the nut and the housing, thereby compro-

mising the installation’s mechanical integrity and its ability to protect

against environmental effects.

Panel Thickness:

When using both the factory supplied EPDM gasket and hex nut (the

recommended standard installation method), the DMR20-1-ACV can be

mounted in panels ranging from 0.032" to 0.250" (0.8 to 6.4mm) thick.

When the gasket is not used, the panel thickness range is 0.075" to

0.325" (1.9 to 8.3mm). However, using the factory supplied hardware

and tightening torque recommendations results in optimal resistance to

vibration, dust, and moisture ingress.

!

Panel Materials:

Acceptable panel materials include aluminum, mild steels, plastics,

FR-4 pc-board (fiberglass), and many other materials with a flat matte

surface on both sides of the cutout. The DMR-20-x-KP tools can be

used with most panel materials except for stainless steel or other

hardened metals.

DMR20-1-ACV has passed vibration testing combined with temperature

cycling while mounted to the materials noted above, using the speci-

fied tightening torques. If the voltmeter will be mounted to extremely

smooth, slippery surfaces, the user is advised to test the completed

assembly under the environmental conditions encountered in the end

application.

5. AC Input Fusing and Wiring: DMR20-1-ACV voltmeters contain an

internal, self-resettable fuse. However, the supply wires connected to

input terminals TB1-A and TB1-B must be fused with an external, user

supplied, 0.25A/300V time delay/time lag fuse, in accordance with

applicable regulatory codes.

All supply wiring must be rated for the voltages and currents they will

conduct and comply with any code or application-mandated require-

ments pertaining to the user’s specific installation. 300V, UL-rated

hook-up wire suitable for the intended application is required. TB1 is to

be used only for powering the meter’s internal circuitry; it must not be

used to supply power to external loads.

The recommended TB1 supply wire size is 18AWG to 22AWG (0.83mm2

to 0.33mm2) solid or stranded copper wire. The supply wires must be

properly stripped and attached to TB1 such that their insulation is not

pinched by the screw terminal. Recommended insulation strip length is

0.25" (6.4mm). When using stranded wire, verify that there are no loose

or stray strands that could potentially cause a short circuit across the

AC supply input.

6. AC Input Polarity and Grounding: The AC supply inputs TB1-A and

TB1-B terminals are not polarity sensitive, that is, neither terminal is

designated as “AC LO” or “AC HI.” DMR20-1-ACV voltmeters do not

include, nor require, a connection to earth/chassis ground.

Figure 1. Panel Installation

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DMR20-1-ACV

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