TECHNICAL NOTES

IMPORTANT! To ensure safe and reliable operation, DMR20-10-DCM

DC 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. Operating Input Range: The unit is shipped with auto-range jumper

JP1 in the open position. With JP1 open, auto-range operation is

disabled and the unit will display input voltages between +6 to +75Vdc

with a fixed 0.1V resolution. Changes to JP1’s configuration must only

be made when the unit is off (de-energized). The unit will not recognize

JP1 configuration changes made with power applied to TB1.

Closing jumper JP1 (see Figure 1) places the unit in the auto-range

mode of operation. With auto-range enabled and Vin between +6V to

+51V, the displayed resolution is 0.01V (i.e., the unit is in LO Range).

When the unit is in LO Range and Vin is increased to +51V, it will auto-

range to the HI range and display 0.1V resolution. When the unit is in

HI range and Vin drops below +49V, it will auto-range back to the LO

Range and display 0.01V resolution.

Operation below +6Vdc will produce a noticeably dimmer display and

accuracy is not guaranteed. Continuous operation between +75 and

+80Vdc, while not recommended, will not adversely affect the unit. See the

“Performance/Functional Specifications” section for more information.

2. Calibration: DMR20-10-DCM voltmeters are factory calibrated; there

are no provisions for calibrating these meters in the field.

3. Panel Installation: All electrical connections to DMR20-10-DCM must

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

the input DC input supply source de-energized (off). In high-vibration

environments, adequate strain reliefs must be used on all supply

wiring. See Figure 2 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 DMR20-10-DCM 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, and 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.

DMR20-10-DCM has passed vibration testing combined with tem-

perature cycling while mounted to the materials noted above, using

the specified tightening torques. If the voltmeter will be mounted to

extremely smooth or slippery surfaces, the user is advised to test the

completed assembly under the environmental conditions expected in

the end application.

4. Input Fusing and Wiring: DMR20-10-DCM voltmeters contain an

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

input terminals TB1’s “+” and “–” terminals must be fused with an

external, user supplied, 0.25A/300V time delay/time lag fuse, in accor-

dance 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.

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

DC supply input.

5. Input Polarity: The input terminal block TB1 is polarity sensitive, and

connections to it must be made as shown in the Mechanical Specifica-

tions section of this data sheet. However, intermittent or continuous

application of reverse-polarity voltages up to –100V will not damage

the meter.

Figure 1.

JP1 configured for auto-range operation

www.murata-ps.com/support

DMR20-10-DCM

2-Wire, Self-Powered,

Auto-Ranging DC Voltage Monitor

MPM_DMR20-10-DCM.A01 Page 2 of 4

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