Datasheet

Figure 3. Differential Input Confi guration
R2
R1 + R2
x VIN = Reading
50kΩ < R1 + R2 < 10MΩ
Figure 6. Floating Input Measurements
(Alternate Confi guration)
Figure 5. Floating Input Measurements
Figure 4. Input Attenuation Circuit
RShunt = R1 = VFsr /IFsr
Where: VFsr = Full scale reading (in Volts)
I
Fsr = Relative full scale current (in Amps)
2. Differential Input Confi gurations: 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.
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-fi lm resistors with absolute TCR's less than 50ppm/°C.
See Ap Note 4 for more information on engineering scaling.
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 "fl oating" input is a signal that has no galvanic connection to
the meter's power supply. In the fi gures below, the 1.5V battery
illustrates a true fl oating input.
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:
1
12
3
+5V SUP
(–) IN LO
5V RET
11
(+) IN HI
6
AC to DC Converter
DMS-20PC-1
R2
R1
R3
1k
1k
1k
8
7
REF IN
DP1
REF OUT
2
DISPLAY
ENABLE
85-264Vac
DMS-20PC-1
R2
11
12
(+) IN HI
(–) IN LO
VIN
R1
+
–
13
+5V SUP 5V RET
AC to DC Converter
8
7
REF OUT
REF IN
2
DISPLAY
ENABLE
85-264Vac
13
+5V SUP
6
DP1
AC to DC Converter
DMS-20PC-1
12
(–) IN LO
11
(+) IN HI
1.5V
CELL
+
–
8
7
REF OUT
REF IN
2
DISPLAY
ENABLE
5V
RET
85-264Vac
DMS-20PC-1
12
(–) IN LO
10
ANA COMM
11
(+) IN HI
1.5V
CELL
+
–
8
7
REF OUT
REF IN
13
+5V SUP
6
DP1
AC to DC Converter
2
DISPLAY
ENABLE
5V
RET
85-264Vac
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DMS-20PC Series
3½ Digit, LED Display, Low-Cost, Subminiature
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MPM_DMS_20PC.D07 Page 4 of 6
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