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

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.

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

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

transmit information. Because DMS-30PC meters have such high

input impedance, 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-30PC meters. Figure 3, though not a practi-

cal 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 attenu-

ated. 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 engineer-

ing scaling.

4. Floating Signal Source Measurements: Floating signals can be

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

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-30PC-1

85-264Vac

R2

11

12

(+) IN HI

(–) IN LO

VIN

R1

–

1

3

+5V SUP

5V RET

AC to DC Converter

8

7

REF OUT

REF IN

DMS-30PC-1

85-264Vac

1

3

+5V SUP

5V RET

6

DP1

AC to DC Converter

DMS-30PC-1

12

(–) IN LO

11

(+) IN HI

1.5V

CELL

–

8

REF OUT

REF IN

7

85-264Vac

13

5V RET

6

DP1

12

(–) IN LO

10

ANA COMM

11

(+) IN HI

1.5V

CELL

–

8

7

REF OUT

REF IN

DMS-30PC-1

+5V SUP

AC to DC Converter

85-264Vac

DMS-30PC Series

3½ Digit, LED Display Low-Power,

Miniature Digital Panel Voltmeters

MPM_DMS_30PC.G01 Page 4 of 6

www.murata-ps.com/support

APPLICATIONS