5

3 ½

DIGIT , LED

DISPLA Y

DIGIT AL

P ANEL V O L TMETERS

DMS-30PC

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 50k

Ω 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 regulator

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 voltmeters. 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 0.1

Ω 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

applications needing external gain adjustment. Figure 10 shows

the wiring configuration for each model. Calibration is performed

with a precise, near-full-scale, input voltage.

Applications

1

3

5V RET

DATEL

UPA-5/500

120 VAC

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

DMS-30PC-2-RL

5

7

12

+

–

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-YS

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

Ω

Load

(3.3 )

12

(–) IN LO

Ω

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

12

VOLTAGE

CALIBRATOR

OUT

COM