DMS-20LCD Series
3�½ Digit, LCD Display Digital Panel Voltmeters
APPLICATIONS
2. Differential Input Configurations:
Differential measurements can be
made with either 5V-powered or 9V-powered meters. Figure 3, though
not a practical real-world application, uses a voltage divider to demon-
strate the concept of a differential input signal. Be careful not to exceed
the ±2V common mode voltage limitation for 5V powered meters.
R1
1k
4. Floating Signal Source Measurements:
Floating signals can be
measured using the circuits shown in Figures 5 and 6. Figure 5 uses
a 5V-powered meter. Figure 6 uses a 9V-powered meter. Connecting
pin 10 (ANALOG COMMON) to (–) INPUT LO (pin 12) provides the
reference point for the meter’s input.
A “floating” input is a signal that has no galvanic connection to the
meter’s power supply. In the figures below, the 1.5V battery illustrates a
true floating input.
11
(+) IN HI
DMS-20LCD-1-5
REF OUT
8
11
(+) IN HI
REF IN
7
DP1
6
12
(–) IN LO
R2
1k
DMS-20LCD-1-5
8
REF OUT
1
+5V SUP
3
5V RET
R3
1k
1.5V
CELL
+
–
12
(–) IN LO
120 VAC
DATEL
UPA-5/500
7
REF IN
1
3
5V RET
6
DP1
+5V SUP
AC to DC Converter
Figure 3. Differential Input Configuration
(5V-Powered Models)
120 VAC
DATEL
UPA-5/500
AC to DC Converter
3. Engineering Scaling:
For measuring voltages greater than the full
scale input range of a given meter, the input signal must be attenuated.
A simple voltage divider (similar to that shown in Figure 4) will scale
the input to within the range of the selected meter. R1 and R2 should
be precision, ±1%, metal-film resistors with absolute TCR’s less than
50ppm/°C. See Ap Note 4 for more information on engineering scaling.
50k < R1 + R2 < 10M
R2
R1 + R2
+
1.5V
CELL
+
Figure 5. Floating Input Measurements
(5V-Powered Models)
11
(+) IN HI
10
ANA COMM
12
(–) IN LO
1
+ BAT
DMS-20LCD-1-5
8
REF OUT
–
7
REF IN
3
–BAT
+
x V
IN
= Reading
6
DP1
9V
BATTERY
R1
V
IN
R2
11
(+) IN HI
DMS-20LCD-1-5
DMS-20LCD-1-9
–
8
REF OUT
–
12
(–) IN LO
7
REF IN
1
+5V SUP
3
5V RET
Figure 6. Floating Input Measurements
(9V-Powered Models)
120 VAC
DATEL
UPA-5/500
AC to DC Converter
Figure 4. Input Attenuation Circuit
5. Process Control (4-to-20mA) Measurements:
In many common
process-control applications, a 4-to-20mA current loop is used to
transmit information. Because DMS-20LCD meters have such high
input impedance, a simple shunt resistor across the meter’s input can
be used to convert the loop current to a voltage. See Figure 7. The
value of the shunt resistor is a function of the scaling requirements of
the particular application and can be calculated using the following
equation:
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Technical enquiries
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+1 508 339 3000
MPM_DMS20lcd.B03
Page 4 of 6
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