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

ments can be made with any DMS-30PC meter. 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). This will ensure that large LED currents will not

flow in the wiring that connects VIN to (–) INPUT LO (pin 12). Ground-

loop currents can cause unstable readings.

Figure 2. Single-Ended Input Configuration

DMS-30PC meters are highly versatile devices that can be used in

hundreds of applications. The application circuits chosen for this sec-

tion have historically received many inquiries. Every attempt has been

made to ensure technical accuracy, and all of the following circuits

have been prototyped and tested to ensure functionality. Please keep

in mind, however, that real-world applications are seldom as straight-

forward as the approaches presented here. Most applications have

many more components — and many more connections — than the

illustrations show.

The simplified schematic shown in Figure 1 can be very useful when

debugging a malfunctioning panel meter circuit, particularly if the

user has some knowledge of operational amplifiers (op amps). The

meter's high-impedance input consists of an op amp powered from a

±5Vdc power supply (the –5V is internally generated). Knowing this,

one can easily see why input signals applied to (–) INPUT LO and (+)

INPUT HI have to be kept within the power supply rails of ±5V. Also

note that only pin 11 has a current-limiting 909kΩ series resis-

tor. High input voltages that have a common ground with pin 3 (5V

RETURN) should only be applied to pin 11 ((+) INPUT HI) and never to

pin 12. In these high-voltage cases, pin 12 should always be tied to

pin 3 (5V RETURN).

One of the simplified schematic's noteworthy features is that it

shows internal voltage values. It also shows that pin 3 is the meter's

zero-volt reference point — regardless of the type of power or signal

source used. This is an important point to keep in mind when a digital

or analog multimeter is used to make system measurements. The

multimeter's negative lead (usually the black one) must be connected

to pin 3 (5V RETURN).

4. DISPLAY TEST (Pin 2): Connecting pin 2 to +5V SUPPLY (pin 1) will

activate all LED segments, except the decimal points, and the display

will read "1888" regardless of the actual applied input. If a negative

input is applied, DISPLAY TEST will also activate the minus sign. To

protect the LED's, the display should not be left in the "test" mode for

more than 10 seconds.

5. Decimal Point Placement: The location of the decimal point is user-

selectable, and the decimal point control pins (DP1-DP3) are active

low functions. Select the desired decimal point by tying the appropri-

ate pin (pin 4, 5 or 6) to pin 3 (5V RETURN). Unused decimal point

location pins should be left open.

Hard wiring is preferable, however, you can use logic gates to

exercise dynamic control over the location of the decimal point if the

following drive conditions are met:

Model

Applied "0" Voltage

Load Current*

DMS-30PC-X-RL

+0.05V max.

0.7mA max.

All Others

+0.4V max.

6mA max.

*The driving gates must be able to sink this much current

(IOL) with a logic "0" output.

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

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

range. 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 10 provides ±10% range of

adjustment.

7. Soldering Methods: All models in the DMS-30PC Series easily

withstand most common wave soldering operations. We recommend,

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.

8. Suggested Mating Connectors:

Panel mounted:

Connector housing

Murata Power Solutions P/N 4320-01069-0

Terminal type

Murata Power Solutions P/N 4400-01032-0

Crimping tool

Murata Power Solutions 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

Murata Power Solutions P/N 4320-01074-0

1

12

3

+5V SUP

(–) IN LO

5V RET

11

(+) IN HI

6

DP1

+

–

AC to DC Converter

VIN

DMS-30PC-1

8

7

REF OUT

REF IN

85-264Vac

DMS-30PC Series

3½ Digit, LED Display Low-Power,

Miniature Digital Panel Voltmeters

MPM_DMS_30PC.G01 Page 3 of 6

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