Figure 9. External Gain Adjustment

Figure 8. 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

different full scale readings, alter the value of RShunt accordingly.

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

scale reading) and a desired 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

6. 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 available at www.cd4power.com.

7. External Gain Adjustment: Connect REFERENCE OUT

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

operation. Use the +1.225V 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.

1

3

5V RET

AC to DC Converter

DMS-30DR-1

12

(–) IN LO

10

ANA COMM

11

(+) IN HI

R1

–

4-20mA

50k

R2

8

7

REF OUT

REF IN

9

1.225V

REF

5V SUP

85-264Vac

www.murata-ps.com/support

DMS-30DR Series

Sunlight Readable, 3½ Digit Panel Meters

with Auto-Dimming LED Displays

MPM_DMS-30DR.C0

3 Page 5 of 6

APPLICATIONS