3
3 ½ D I G I T , L E D D I S P L A Y D I G I T A L P A N E L V O L T M E T E R S
DMS-30PC
Applications
1. Single-Ended Input Configurations: True single-ended
measurements 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
V
IN
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
section 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 straightforward 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 909k
Ω
series
resistor. 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 appropriate 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.
DMS-30PC-X-BS
+0.3V max.
18mA max.
All Others
+0.4V max.
6mA max.
* The driving gates must be able to sink this much current
(I
OL
) 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 water-soluble solders and thorough cleaning
procedures.
8. Suggested Mating Connectors:
Panel mounted:
Connector housing
DATEL P/N 39-2079400
Terminal type
DATEL P/N 39-2099090
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 39-2359625
1
12
3
+5V SUP
(–) IN LO
5V RET
DATEL
UPA-5/500
120 VAC
11
(+) IN HI
6
DP1
+
–
AC to DC Converter
V
IN
DMS-30PC-1
8
7
REF OUT
REF IN