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DMS-30LCD Series

3½ Digit, LCD Display Digital Panel Voltmeters

MPM_DMS30LCD.E01 Page 5 of 6

APPLICATIONS

R2

(R1 + R2 + R3)

= 0.1

Figure 7. 4-to-20mA Current Loop Operation

(5V-Powered Models)

Figure 9. External Gain Adjustment

Figure 8. Power Supply Monitor

(9V-Powered Models)

6. Power Supply Monitoring: A popular application for Murata Power

Solutions’ low-power LCD meters is monitoring the supply voltage in

battery-operated portable equipment. Figure 8 demonstrates how a

9V-powered DMS-30LCD can be used to monitor its own supply. The

meter used is the DMS-30LCD-1-9. A three-resistor voltage divider is

used to attenuate the battery voltage and also to satisfy the require-

ment that the input voltages applied to pins 12 and 11 be at least 1.5

Volts above and below the battery voltage applied to pins 1 (+BAT-

TERY) and 3 (–BATTERY). The divider should be designed so that

1/10th the battery voltage falls across the inputs to the meter:

To calibrate the circuit of Figure 7, perform the following:

1. With 4mA applied, adjust the 50kΩ potentiometer (R2) to

display a reading of "000" (assuming that is the desired

reading).

2. With 20mA applied, adjust the gain-adjust potentiometer on

the back of the meter to display a reading of "1999". For different full

scale readings, alter the RShunt value accordingly.

RShunt = R1 = VFsr /IFsr

Where:

VFsr = Full scale reading (in Volts)

IFsr = Relative full scale current (in Amps)

Example: For a meter with a 2V full scale input (1.999 full

scale reading) and a desired full scale display reading of

1000 (with an input of 20mA), VFsr = 1.000 Volts

RShunt = 1.000V/(0.020 – 0.004)A

RShunt = 1.000V/0.016A = 62.5 Ohms

7. External Gain Adjustment: Connect REFERENCE OUT

(pin 8) to REFERENCE IN (pin 7) for normal, factory calibrated, opera-

tion. Use the +1.23V REFERENCE OUT (pin 9) for applications need-

ing external gain adjustment. Figure 9 shows the wiring configuration

for each model. Calibration is performed with a precise, near-full-scale,

input voltage.

Therefore, the 9V battery voltage appears to the meter inputs as 0.9V.

With the decimal point moved to its DP2 position

(pin 5 tied to pin 3), the meter reads 9.00 Volts.

The circuit can be calibrated by first measuring the actual battery volt-

age with another meter and then adjusting the gain-adjust potentiom-

eter on the back of the DMS-30LCD until a similar reading is obtained.

If possible, the resistors in the divider should be ±1% metal-film types

with TCR’s less than 50ppm/°C.

1

12

3

+BAT

(–) IN LO

11

–BAT

5

DP2

(+) IN HI

R2

R1

R3

45.3k

10.1k

9V

45.3k

BATTERY

–

8

7

REF OUT

REF IN

DMS-30LCD-1-9

9

(+) IN HI

(–) IN LO

10

ANA COMM

1.23V REF

1k

8

REF IN

11

10 to 20 Turns

1k

10 to 20 Turns

8.45k, 1%

5V RET

8.45k, 1%

7

NC

12

3

For 5V models tie

(–) IN LO to pin 3

For 9V models tie

12

(–) IN LO to pin 10

VOLTAGE

OUT

COM

CALIBRATOR

Connections

for ±2V and

±20V models

Connections

for ±200mV

models

DMS-30LCD

3

1

+5V SUP

5V RET

120 VAC

AC to DC Converter

(–) IN LO

ANA COMM

(+) IN HI

R1

–

4-20mA

50k

R2

8

7

REF OUT

REF IN

DMS-30LCD-1-5