DMS-20LCD Series

3½ Digit, LCD Display Digital Panel Voltmeters

www.murata-ps.com

MPM_DMS20lcd.B03 Page 3 of 6

APPLICATIONS

point location pins should be left open. For 5V-powered models, the

decimal location pins are TTL compatible and may be hard wired as

described above or driven with 5V TTL logic gates.

DMS-20LCD meters are available in either 5V-powered or 9V-powered

models. 9V devices operate directly from 7.5V to 14V supplies (usually

batteries) without the need for external voltage regulators. 9V devices,

however, can not be used to measure voltages referenced to the negative

battery terminal (pin 3) because the minus input to the meter (pin 12, (–)

INPUT LO) must always be at least 1.5V above pin 3. 9V-powered meters

can only be used to make differential and not single-ended measurements.

5V-powered devices operate from any well-regulated +5V supply and will

accurately measure voltages both above and below pin 3 (5V RETURN) in

either single-ended or differential configurations.

1. Single-Ended Input Configurations: True single-ended measure-

ments can only be made with 5V-powered meters. The circuit of Figure

2 avoids problems normally associated with ground-loop currents.

Separate ground runs should be used for 5V RETURN (pin 3) and (–)

INPUT LO (pin 12).

8. Suggested Mating Connectors:

Panel mounted:

Connector housing

DATEL P/N 4320-01069-0

Terminal type

DATEL P/N 4400-01032-0

Crimping tool

DATEL P/N 39-2099000

Wire size

22 to 26 AWG

Insulation diameter

0.062” (1.57mm) maximum

Stripping length

0.100 to 0.125” (2.54 to 3.17mm)

Board mounted:

Socket

DATEL P/N 4320-01074-0

Figure 2. Single-Ended Input Configuration

(5V-Powered Models)

Ohms

+12.6 – 9.2V

0.035

Example: If +BATTERY (pin 1 with respect to pin 3) is +12.6V,

+BATTERY – 9.2V

0.035

Ohms

5. Low Battery Annunciator: The “B” annunciator in the upper left-hand

corner of the display turns on when the supply voltage for 5V-powered

models falls below approximately +3.7V, or when the supply voltage for

9V-powered models falls below approximately 7.2V. However, the low-

battery annunciator’s turn-on threshold can vary significantly from unit-

to-unit: as low as 2.7V for 5V-powered meters, and as low as 5.4V for

9V-powered models. Applications that use the LOW BAT annunciator

must be fully tested by the user, using a combination of low supply volt-

ages and the input signal’s minimum and maximum levels, to ensure

that all display readings are valid as long as the LOW BAT annunciator

remains off.

6. Gain Adjust: There is a gain-adjust potentiometer on the back of each

meter. It has approximately ±50 counts (±2.5%) range of adjustment.

Since these devices essentially have no zero/offset errors, a gain

adjustment is effectively an overall accuracy adjustment. Though they

may be performed at any point (except zero), accuracy adjustments

are most effective when performed with higher level input signals. The

circuit shown in Figure 9 provides ±10% range of adjustment.

7. Soldering Methods: All models in the DMS-20LCD Series easily

withstand most common wave soldering operations. We recom-

mend, however, that you evaluate the effects your particular soldering

techniques may have on the meter’s plastic case and high-precision

electrical performance. We recommend the use of no-clean solders.

4. BACKLIGHT (Pin 9) Function: Grounding pin 9 (i.e. connecting it to

pin 3) turns on the backlighting LED’s. For non-backlit models, pin 9

has no internal connection. All backlit models include internal current-

limiting resistors. With nominal +5V or 9V supplies, backlit devices

typically draw 35mA of supply current. The current drawn by the back-

light (and therefore the current drawn by the meter) can be reduced by

installing a 1/4 Watt resistor between pins 3 and 9. The brightness of

the meter will be reduced proportionately.

9V-powered backlit models function with supply voltages up to +14V,

however, activating the backlight with voltages greater than 9.2V can

damage the meter. Therefore, a 1/4 Watt series resistor must be

installed between pins 3 and 9 in these situations. The value of the

series resistor is determined using the following formula:

1

12

3

+5V SUP

(–) IN LO

5V RET

DATEL

UPA-5/500

120 VAC

11

(+) IN HI

6

DP1

+

–

AC to DC Converter

DMS-20LCD-1-5

7

REF OUT

REF IN

8