4
DMS-30PC
3 ½ D I G I T , L E D D I S P L A Y D I G I T A L P A N E L V O L T M E T E R S
Figure 3. Differential Input Configuration
R2
R1 + R2
x V
IN
= Reading
50k
Ω
< R1 + R2 < 10M
Ω
Figure 6. Floating Input Measurements
(Alternate Configuration)
Figure 5. Floating Input Measurements
Figure 4. Input Attenuation Circuit
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.
R
Shunt
= R1 = V
Fsr
/ I
Fsr
Where:
V
Fsr
= 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:
Applications
2. Differential Input Configurations: 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
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.
4. Floating Signal Source Measurements: Floating signals can
be measured using the circuits shown in Figures 5 and 6.
1
12
3
+5V SUP
(–) IN LO
5V RET
DATEL
UPA-5/500
120 VAC
11
(+) IN HI
6
AC to DC Converter
R2
R1
R3
1k
1k
1k
8
7
REF IN
DP1
REF OUT
DMS-30PC-1
R2
11
12
(+) IN HI
(–) IN LO
V
IN
R1
+
–
1
3
+5V SUP
5V RET
DATEL
UPA-5/500
120 VAC
AC to DC Converter
8
7
REF OUT
REF IN
DMS-30PC-1
1
3
+5V SUP
5V RET
DATEL
UPA-5/500
120 VAC
6
DP1
AC to DC Converter
DMS-30PC-1
12
(–) IN LO
11
(+) IN HI
1.5V
CELL
+
–
8
REF OUT
REF IN
12
7
1
3
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
DATEL
UPA-5/500
120 VAC
AC to DC Converter