DMS-20PC Series
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.
R1
1k
3�½ 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.
11
(+) IN HI
+
DMS-20PC-1
REF OUT
8
11
(+) IN HI
DMS-20PC-1
8
REF OUT
REF IN
7
DP1
6
2
DISPLAY
ENABLE
12
(–) IN LO
R2
1k
1.5V
CELL
–
12
(–) IN LO
7
REF IN
1
+5V SUP
2
DISPLAY
ENABLE
3
5V
RET
6
DP1
1
+5V SUP
3
5V RET
R3
1k
85-264Vac
DATEL
DMS-PS1-CM
85-264Vac
DATEL
DMS-PS1-CM
AC to DC Converter
AC to DC Converter
Figure 3.
Differential Input Configuration
Figure 5.
Floating Input Measurements
DMS-20PC-1
8
REF OUT
1.5V
CELL
50k < R1 + R2 < 10M
R2
x V
IN
= Reading
R1 + R2
+
85-264Vac
R1
V
IN
R2
11
(+) IN HI
DMS-20PC-1
8
REF OUT
–
12
(–) IN LO
7
REF IN
1
+5V SUP
2
DISPLAY
ENABLE
3
5V RET
85-264Vac
DATEL
DMS-PS1-CM
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:
R
Shunt
= R1 = V
Fsr
/ I
Fsr
Where:
V
Fsr
= Full scale reading (in Volts)
I
Fsr
= Relative full scale current (in Amps)
AC to DC Converter
Figure 4.
Input Attenuation Circuit
www.murata-ps.com
Technical enquiries
email: sales@murata-ps.com, tel:
+1 508 339 3000
+
–
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.
11
(+) IN HI
10
ANA COMM
12
(–) IN LO
1
+5V SUP
7
REF IN
2
DISPLAY
ENABLE
3
5V
RET
6
DP1
DATEL
DMS-PS1-CM
AC to DC Converter
Figure 6.
Floating Input Measurements
(Alternate Configuration)
MPM_DMS_20PC.D02
Page 4 of 6
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