Figure 1. DMS-EB-RMS Schematic Diagram

PRODUCT OVERVIEW

Description: The DMS-EB-RMS board allows the true rms value of ac signals to be displayed on

5V-powered DMS-30PC/LCD digital voltmeters. The meter/board combination has an input range of

0-750Vac with ±2V meters (1Vac resolution) or 0-199.9Vac with ±200mV meters (0.1Vac resolution).

A built-in screw-terminal block reliably interfaces signal and power connections. The DMS-EB-RMS

now accommodates user-installed modifications such as input-scaling resistors and isolated +5V dc/dc

converters.

Power and Safety Precautions: The DMS-EB-RMS’s AC HI and AC LOW inputs are not electri-

cally isolated from its 5V supply (AC LOW is connected directly to 5V RETURN). When measuring any

input signal which is derived from ac power mains, a dedicated (i.e., it only powers the DMS-EB-RMS),

transformer-isolated +5V supply, with a minimum 1kV breakdown rating, must be used to power the

DMS-EB-RMS board/meter combination. When measuring ac power mains inputs, never connect the

DMS-EB-RMS’s 5V RETURN to chassis/earth ground anywhere in the system. Failing to follow these

instructions could defeat any safety grounding and will place the system +5V power supply, and all its

associated circuitry, at dangerously elevated ac-line potentials. In many applications, the MS-EB-RMS

installation is required to meet electrical code requirements. To ensure safe operation, the DMS-EB-

RMS board should only be installed and serviced by technically qualified personnel. See DMS

Application Note 11 for more details.

FEATURES

Displays true rms values of ac inputs

±0.5% accuracy for DMS-30PC-0 or DMS-

30LCD-0-5

±2% accuracy for DMS-30PC-1 or DMS-

30LCD-1-5

Also works with DMS-40PC/LCD meters (see Ap

Note 11)

(–) INPUT LO

(+) INPUT HI

REF. OUT

REF. IN

1

56

3

+5V

5V Return

TB1

CAV

OUT

COM

CF

CC

LV

OSC

V+

CAP–

GND

CAP+

BOOST

SG1

SG2

SG3

5V RETURN

DP3

DP2

DP1

+5V SUPPLY

C5

2.2μF

+

+

R1

988k

R2

988k

R3

1.98k

+

C2

10μF

C1 100μF

+

1

2

3

4

5

6

7

8

5

6

7

8

1

2

3

4

U1

U2

AC HI

3

4

5

6

1

2

SG4

J1

12

11

8

7

10

9

JP1

J6

GND 2

1

3

U3

PS1

1

2

3

4

C4

2.2μF

J4

J5

AC LOW

Note: Components are user-supplied

and not part of the standard product.

DC/DC

–V

+V

DMS-EB-RMS

AC-to-RMS Converter Application Board for DMS-30PC/LCD Meters

For full details go to

www.murata-ps.com/rohs

www.murata-ps.com

MPM_DMS-EB-RMS.B01 Page 1 of 2