4
DMS-20LCD
3 ½
DIGIT ,
LCD
DISPLA Y DIGIT A L P ANEL
VOL TMETERS
R2
R1 + R2
x VIN = Reading
50k
Ω < R1 + R2 < 10MΩ
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.
Figure 3. Differential Input Configuration
(5V-Powered Models)
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
Figure 6. Floating Input Measurements
(9V-Powered Models)
Figure 5. Floating Input Measurements
(5V-Powered Models)
Figure 4. Input Attenuation Circuit
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 demonstrate the concept of a differential input
signal. Be careful not to exceed the ±2V common mode voltage
limitation for 5V powered meters.
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.
1
1 2
3
+ 5 V S U P
( ) I N L O
5 V R E T
1 1
( + ) I N H I
6
A C t o D C C o n v e r t e r
R 2
R 1
R 3
1 k
1 k
1 k
8
7
R E F I N
D P 1
R E F O U T
D M S - 2 0 L C D - 1 - 5
D A T E L
D M S - P S 1 - C M
8 5 - 2 6 4 V a c
R 2
1 1
1 2
( + ) I N H I
( ) I N L O
V I N
R 1
1
3
+ 5 V S U P
5 V R E T
A C t o D C C o n v e r t e r
8
7
R E F O U T
R E F I N
D M S - 2 0 L C D - 1 - 5
D A T E L
D M S - P S 1 - C M
8 5 - 2 6 4 V a c
1
3
+ 5 V S U P
5 V R E T
6
D P 1
A C t o D C C o n v e r t e r
1 2
( ) I N L O
1 1
( + ) I N H I
1 . 5 V
C E L L
8
7
R E F O U T
R E F I N
D M S - 2 0 L C D - 1 - 5
D A T E L
D M S - P S 1 - C M
8 5 - 2 6 4 V a c
1
3
+ B A T
B A T
9 V
B A T T E R Y
6
D P 1
1 2
( ) I N L O
1 0
A N A C O M M
1 1
( + ) I N H I
1 . 5 V
C E L L
8
7
R E F O U T
R E F I N
D M S - 2 0 L C D - 1 - 9
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