DMS-20PC Datasheet, PDF (4/6 Pages) List of Unclassifed Manufacturers – 3½ Digit, LED Display Low-Cost, Subminiature Digital Panel Voltmeters

APPLICATIONS
2. Differential Input Configurations: Differential measurements
can be made with all DMS-20PC meters. Figure 3, though not
a practical real-world application, uses a voltage divider to
demonstrate the concept of a differential input signal. Be care-
ful not to exceed the ±2V common mode voltage limitation for
5V-powered meters.
REF OUT 8
DMS-20PC-1
R1
11
1k
(+) IN HI
REF IN 7
DP1 6
R2
12
1k
(–) IN LO
1
2
3
R3
1k
+5V SUP
DISPLAY _{5V RET}
ENABLE
DATEL
85-264Vac _DMS-PS1-CM
AC to DC Converter
Figure 3. Differential Input Configuration
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.
50k7 < R1 + R2 < 10M7
R2
x VIN = Reading
R1 + R2
R1
VIN
11
(+) IN HI
DMS-20PC-1
8
REF OUT
R2
12
(–) IN LO
–
1
+5V SUP
2
DISPLAY
ENABLE
7
REF IN
3
5V RET
DATEL
85-264Vac _DMS-PS1-CM
AC to DC Converter
Figure 4. Input Attenuation Circuit
DMS-20PC Series
3½ Digit, LED Display, Low-Cost, Subminiature
Digital Panel Voltmeters
4. Floating Signal Source Measurements: Floating signals can be
measured using the circuits shown in Figures 5 and 6. Connecting
pin 10 (ANALOG COMMON) or pin 3 (5V RETURN) 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.
1.5V
CELL
–
11
(+) IN HI
12
(–) IN LO
1
+5V SUP
DATEL
85-264Vac _DMS-PS1-CM
DMS-20PC-1
8
REF OUT
2
DISPLAY
ENABLE
3
5V
RET
7
REF IN
6
DP1
AC to DC Converter
Figure 5. Floating Input Measurements
1.5V
CELL
–
11
(+) IN HI
10
ANA COMM
12
(–) IN LO
1
+5V SUP
DATEL
85-264Vac _DMS-PS1-CM
DMS-20PC-1
8
REF OUT
2
DISPLAY
ENABLE
3
5V
RET
7
REF IN
6
DP1
AC to DC Converter
Figure 6. Floating Input Measurements
(Alternate Configuration)
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-20PC 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 require-
ments of the particular application and can be calculated using
the following equation:
RShunt = R1 = VFsr / IFsr
Where: VFsr = Full scale reading (in Volts)
IFsr = Relative full scale current (in Amps)
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MPM_DMS_20PC.D02 Page 4 of 6