Figure 3. Differential Input Configuration

R2

R1 + R2

x VIN = Reading

50k

Ω < R1 + R2 < 10MΩ

Figure 6. Floating Input Measurements

(Alternate Configuration)

Figure 5. Floating Input Measurements

Figure 4. Input Attenuation Circuit

RShunt = R1 = VFsr /IFsr

Where:

VFsr = Full scale reading (in Volts)

IFsr = Relative full scale current (in Amps)

5. Process Control (4-to-20mA) Measurements: In many common pro-

cess-control applications, a 4-to-20mA current loop is used to transmit

information. Because DMS-30DR meters have such high input imped-

ance, a simple shunt resistor across the meter's input can be used to

convert the loop current to a voltage. See Figure 7. The value of the

shunt resistor is a function of the scaling requirements of the particular

application and can be calculated using the following equation:

2. Differential Input Configurations: Differential measurements can be

made with all DMS-30DR meters. Figure 3, though not a practical real-

world application, uses a voltage divider to demonstrate the concept

of a differential input signal. Be careful not to exceed the ±2V common

mode voltage limitation for 5V-powered meters.

3. Engineering Scaling: For measuring voltages greater than the full

scale input range of a given meter, the input signal must be attenuated.

A simple voltage divider (similar to that shown in Figure 4) will scale

the input to within the range of the selected meter. R1 and R2 should

be precision, ±1%, metal-film resistors with absolute TCR's less than

50ppm/°C. See Ap Note 4 for more information on engineering scaling.

4. Floating Signal Source Measurements: Floating signals can be

measured using the circuits shown in Figures 5 and 6. Connecting pin

10 (ANALOG COMMON) or pin 3 (5V RETURN) to (–) INPUT LO (pin

12) provides the reference point for the meter's input.

A "floating" input is a signal that has no galvanic connection to the

meter's power supply. In the figures below, the 1.5V battery illustrates a

true floating input.

1

12

3

+5V SUP

(–) IN LO

5V RET

11

(+) IN HI

6

AC to DC Converter

R2

R1

R3

1k

1k

1k

8

7

REF IN

DP1

REF OUT

DMS-30DR-1

85-264Vac

R2

11

12

(+) IN HI

(–) IN LO

VIN

R1

–

1

3

+5V SUP

5V RET

8

7

REF OUT

REF IN

DMS-30DR-1

85-264Vac

1

3

+5V SUP

5V RET

6

DP1

AC to DC Converter

DMS-30DR-1

12

(–) IN LO

11

(+) IN HI

1.5V

CELL

–

8

REF OUT

REF IN

7

85-264Vac

1

3

5V RET

6

DP1

12

(–) IN LO

10

ANA COMM

11

(+) IN HI

1.5V

CELL

–

8

7

REF OUT

REF IN

DMS-30DR-1

+5V SUP

AC to DC Converter

85-264Vac

www.murata-ps.com/support

DMS-30DR Series

Sunlight Readable, 3½ Digit Panel Meters

with Auto-Dimming LED Displays

MPM_DMS-30DR.C0

3 Page 4 of 6

APPLICATIONS