DMS-20RM Series
True-rms ac Voltmeters with Isolated Inputs
www.murata-ps.com/dpm
email: sales@murata-ps.com
15 Mar 2011 MPM_DMS-20RM.A05 Page 2 of 4
IMPORTANT! To ensure safe and reliable operation, DMS-20RM ac
voltmeters must be installed and serviced by qualifi ed technical personnel.
Contact Murata Power Solutions if there is any doubt regarding installation
and/or operation.
TECHNICAL NOTES
1. Measurement Type: DMS-20RM series ac voltmeters employ a preci-
sion rms-to-dc converter and a high-precision voltage reference to
measure and display the rms value of complex ac waveforms. Please
note, the rear-mounted potential transformer is used to isolate the
input signal being measured (TB2) from the ammeter’s operating power
source connected to TB1. Do not pass any conductors through this
transformer’s center hole as this will introduce signifi cant measure-
ment errors.
2. Wiring: All power supply and input signal wiring must be rated for the
voltages and currents they will carry and must comply with any code
or application-mandated requirements pertaining to the user’s specifi c
installation.
3. Power Supply Polarity, Fusing, and Grounding: As shown in Figures
1A, 1B, and 2, the two power supply inputs, TB1-A and TB1-B, on
ac-powered DMS-20RM voltmeters (“-AC1” suffi x) are not polarity
sensitive, that is, they have no “AC LO” or “AC HI” designations. Also,
ac-powered models do not include or require a connection to earth/
chassis ground. DC-powered models (“-DC2” suffi x) are reverse-polarity
protected, and must be connected as shown in Figure 2 for proper
operation.
DMS-20RM voltmeters are not internally fused. Terminal block TB1 is to
be used only for powering the power meter’s internal circuitry; it must
not be used to supply power to external loads. The supply wires feeding
these power meters must be fused with a 0.25A/250V time delay/time
lag fuse, in accordance with applicable regulatory codes.
Wire insulation must be stripped to within ±10% of the stated dimen-
sions, and wires should be inserted into TB1 such that their insulation
is not pinched by the screw terminal. See the Functional Specifi cations
section of this data sheet for wire sizes and tightening torque for TB1’s
screw terminals.
4. Calibration: Periodic recalibration of DMS-20RM voltmeters is not
required under normal, indoor operating environments. If calibration is
necessary, it should only be performed by qualifi ed technical personnel.
Calibration is performed with potentially lethal voltages applied to the
DMS-20RM and its associated wiring. A plastic, fully-insulated adjust-
ing tool must be used to access the recessed calibration potentiometer
located on the back of the unit (see Mechanical Specifi cations). Contact
Murata Power Solutions if additional information is required regarding
calibration, setup, or any other technical issue pertaining to DMS-20RM
ac voltmeters.
ORDERING INFORMATION
DMS-20RM-1-AC1-R-C 0 to 19.99Vac, AC Powered
DMS-20RM-2-AC1-R-C 0 to 199.9Vac, AC Powered
DMS-20RM-3-AC1-R-C 0 to 300Vac, AC Powered
DMS-20RM-1-DC2-R-C 0 to 19.99Vac, DC Powered
DMS-20RM-2-DC2-R-C 0 to 199.9Vac, DC Powered
DMS-20RM-3-DC2-R-C 0 to 300Vac, DC Powered
A DMS-BZL4-C bezel assembly with sealing gasket is supplied with each meter.
Performance/Functional Specifi cations
Typical at TA=+ 25ºC with 60Hz sine-wave input, unless otherwise noted
Full-Scale Input Voltage (TB2) Min. Typ. Max. Units
DMS-20RM-1
DMS-20RM-2
DMS-20RM-3
0
0
0
—
—
—
19.99
199.9
300
Vac
Vac
Vac
Frequency Range 47 60 1000 Hz
Performance
Sampling Rate 2.5 reading per second
Accuracy ➀
±0.4%FS ±2 counts
with 60Hz sine wave input
Measurement Type rms responding, Crest Factors of 1-5
Temperature Drift (0 to 60ºC) ±0.2 ±0.4 Counts/ºC
Zero-Volt Reading (within 30 sec.) -001 000 001 Counts
Breakdown Voltage, TB1 to TB2 2000 — — Vdc
Input Impedance
DMS-20RM-1
DMS-20RM-2
DMS-20RM-3
—
—
—
20
200
266
—
—
—
kΩ
kΩ
kΩ
Power Supply Voltage (TB1)
DMS-20RM-X-AC1 85 — 264 Vac/47-63Hz
DMS-20RM-X-DC2 +10.0 — +40.0 Vdc
Power Supply Current (TB1, ➁)
DMS-20RM-X-AC1 — 30 50 mA/47-63Hz
DMS-20RM-X-DC2 — 10 15 mAdc
Terminal Block Wiring (TB1 and TB2)
Wire Size 16-22AWG, Solid or stranded
Insulation Strip Length 0.250 inches
Screw Tightening Torque 3.6 pound-inches (0.4Nm)
Rated Voltage 300Vac
Display
Display Type and Size 3½ Digit LED, 0.37”/9.4mm high
Overrange Indication “1___”
Decimal Point Fixed, model dependent (see full-scale input
voltage above)
Physical/Environmental
Operating Temperature -25 — +60 ºC
Storage Temperature -40 — +75 ºC
Humidity (non-condensing) 0 — 85 %
Dimensions Model dependent; see product datasheet.
Weight: 1.3 Ounces (36 grams) nominal
➀ Specifi ed accuracy applies to inputs with crest factors (CF) up to 2.0, where CF = Vpeak/Vrms.
Crest factors of 2 to 5 introduce an additional error of ±3% of full scale. Voltmeters are calibrated
with a near full-scale, 60Hz sine-wave input.
➁ Specifi ed maximum power supply currents are steady state; larger surge currents can occur at
initial application of power.
