3
3 ½
DIGIT ,
LCD
DISPLA Y DIGIT A L P ANEL
VOL TMETERS
DMS-20LCD
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
measurements 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 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
Applications
Figure 2. Single-Ended Input Configuration
(5V-Powered Models)
RSeries =
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
RSeries =
Ohms
RSeries = 97 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 +3.75V or
when the supply voltage for 9V-powered models falls below
approximately 7.2V. This function can not be disabled.
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
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.
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 backlight (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
1 2
3
+ 5 V S U P
( ) I N L O
5 V R E T
D A T E L
D M S - P S 1 - C M
8 5 - 2 6 4 V a c
1 1
( + ) I N H I
6
D P 1
+
A C t o D C C o n v e r t e r
V I N
D M S - 2 0 L C D - 1 - 5
7
R E F O U T
R E F I N
8
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