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
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.
RShunt = R1 = VFsr /IFsr
Where: VFsr = Full scale reading (in Volts)
I
Fsr = Relative full scale current (in Amps)
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-30PC 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:
2. Differential Input Confi gurations: Differential measurements can
be made with all DMS-30PC 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 attenu-
ated. 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 engineer-
ing scaling.
4. Floating Signal Source Measurements: Floating signals can be
measured using the circuits shown in Figures 5 and 6. Connecting
1
12
3
+5V SUP
(–) IN LO
5V RET
11
(+) IN HI
6
AC to DC Converter
R2
R1
R3
1k
1k
1k
8
7REF IN
DP1
REF OUT
DMS-30PC-1
85-264Vac
R2
11
12
(+) IN HI
(–) IN LO
V
IN
R1
+
–
1
3
+5V SUP 5V RET
AC to DC Converter
8
7
REF OUT
REF IN
DMS-30PC-1
85-264Vac
1
3
+5V SUP
5V RET
6
DP1
AC to DC Converter
DMS-30PC-1
12
(–) IN LO
11
(+) IN HI
1.5V
CELL
+
–
8
REF OUT
REF IN
7
85-264Vac
13
5V RET
6
DP1
12
(–) IN LO
10
ANA COMM
11
(+) IN HI
1.5V
CELL
+
–
8
7
REF OUT
REF IN
DMS-30PC-1
+5V SUP
AC to DC Converter
85-264Vac
DMS-30PC Series
3½ Digit, LED Display Low-Power,
Miniature Digital Panel Voltmeters
MPM_DMS_30PC.F05 Page 4 of 6
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