TECHNICAL NOTES
IMPORTANT! To ensure safe and reliable operation, DMR20-10-DCM
DC voltage monitors must be installed and serviced by qualifi ed
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 fi xed 0.1V resolution. Changes to JP1’s confi guration must only
be made when the unit is off (de-energized). The unit will not recognize
JP1 confi guration 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 Specifi cations” section for more information.
2. Calibration: DMR20-10-DCM voltmeters are factory calibrated; there
are no provisions for calibrating these meters in the fi eld.
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 (fi berglass), and many other materials with a fl at 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 specifi ed 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 specifi c 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 (0.83mm
2
to 0.33mm
2
) 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
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 Specifi ca-
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 confi gured 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.B01 Page 2 of 4
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