Figure 10. External Gain Adjustment

Figure 8. 4.5 -18V Power Supply Monitor

Figure 9. Basic DC Ammeter Circuit

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

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 "1000". For

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

scale reading) and a desired display reading of

6. Power Supply Monitoring: One of the most common digital panel

meter applications involves monitoring the output voltage of the

system power supply — often this supply also powers the meter

itself. The low-power, red LED DMS-30PC-2-RL can be configured

to allow power supply monitoring over the range of 4.5-18Vdc. The

circuit in Figure 8 uses a low-drop-out, three-terminal regulator (LM-

2931Z-5, available from National Semiconductor) to provide regulated

5V power to the meter. The LM-2931 was chosen because it has the

following on-chip protection features: reverse polarity, short circuit

and thermal run-away. When using other, higher-power, DMS-30PC

models with three-terminal regulators, be sure to consult the regula-

tor manufacturer's data sheet to ensure the regulator is being utilized

safely and correctly.

7. Digital Ammeter: Digital ammeters are finding ever-increasing

usage because analog-style ammeters (moving-vane types) now cost

roughly the same as their digital counterparts. Additionally, analog

ammeters are not nearly as rugged as modern digital panel voltme-

ters. Figure 9 illustrates a typical ammeter application. The circuit

uses a ±200mV input meter

— the preferred range for most ammeters — to measure the voltage

developed across a 0.1Ω current shunt. The circuit shown represents

a basic ammeter connection diagram. A detailed application note

describing digital dc ammeters is included in DATEL's new Digital

Panel Meter Databook.

8. External Gain Adjustment: Connect REFERENCE OUT

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

operation. Use the +1.23V REFERENCE OUT (pin 9) for applica-

tions needing external gain adjustment. Figure 10 shows the wiring

configuration for each model. Calibration is performed with a precise,

near-full-scale, input voltage.

13

5V RET

AC to DC Converter

DMS-30PC-1

12

(–) IN LO

10

ANA COMM

11

(+) IN HI

R1

–

4-20mA

50k

R2

8

7

REF OUT

REF IN

9

1.23V

REF

5V SUP

DATEL

DMS-PS1-CM

85-264Vac

DMS-30PC-2-RL

5

712

+

–

11

1

4.5 - 18Vdc

LM2931Z-5

GND

IN

OUT

+5V SUP

3

5V RET

DP2

REF

IN

(+) IN HI

8

REF

OUT

(–) IN LO

22μF

10V

+

DMS-30PC-0

6

3

+

–

1

1.5 Amp (Load Current)

5Vdc

7

8

+5V SUP

5V RET

DP1

REF OUT

REF IN

11

0.150V

(+) IN HI

0.1

Load

(3.3 )

12

(–) IN LO

W

W

9

(+) IN HI

(–) IN LO

ANA COMM

10

1.23V REF

1k

10 to 20 Turns

8

REF IN

11

1k

10 to 20 Turns

8.45k, 1%

8.45k, 1%

5V RET

Connections

for ±2V, ±20V

and ±200V models

Connections

for ±200mV

models

7

NC

12

3

DMS-30PC

VOLTAGE

CALIBRATOR

OUT

COM

DMS-30PC Series

3½ Digit, LED Display Low-Power,

Miniature Digital Panel Voltmeters

MPM_DMS_30PC.F03 Page 5 of 6

www.murata-ps.com

APPLICATIONS