4

DMS-30PC

3 ½

DIGIT , LED

DISPLA Y

DIGIT AL

P ANEL V O L TMETERS

Figure 3. Differential Input Configuration

R2

R1 + R2

50k

Ω < R1 + R2 < 10MΩ

Figure 6. Floating Input Measurements

(Alternate Configuration)

Figure 5. Floating Input Measurements

Figure 4. Input Attenuation Circuit

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.

Where:

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:

Applications

2. Differential Input Configurations: Differential measurements

can be made with all DMS-30PC 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.

1

12

3

+5V SUP

(–) IN LO

5V RET

DATEL

UPA-5/500

120 VAC

11

(+) IN HI

6

AC to DC Converter

R2

R1

R3

1k

1k

1k

8

7

REF IN

DP1

REF OUT

DMS-30PC-1

R2

11

12

(+) IN HI

(–) IN LO

R1

–

1

3

+5V SUP

5V RET

DATEL

UPA-5/500

120 VAC

AC to DC Converter

8

7

REF OUT

REF IN

DMS-30PC-1

1

3

+5V SUP

5V RET

DATEL

UPA-5/500

120 VAC

6

DP1

AC to DC Converter

DMS-30PC-1

12

(–) IN LO

11

(+) IN HI

1.5V

CELL

–

8

REF OUT

REF IN

12

7

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

DATEL

UPA-5/500

120 VAC

AC to DC Converter