Datasheet DMS-20PC (Murata) - 4

DMS-20PC Series
3½ Digit, LED Display, Low-Cost, Subminiature Digital Panel Voltmeters
APPLICATIONS 2. Differential Input Confi gurations
: Differential measurements
4. Floating Signal Source Measurements
: Floating signals can be can be made with all DMS-20PC meters. Figure 3, though not measured using the circuits shown in Figures 5 and 6. Connecting a practical real-world application, uses a voltage divider to pin 10 (ANALOG COMMON) or pin 3 (5V RETURN) to (–) INPUT LO demonstrate the concept of a differential input signal. Be care- (pin 12) provides the reference point for the meter’s input. ful not to exceed the ±2V common mode voltage limitation for A "fl oating" input is a signal that has no galvanic connection to 5V-powered meters. the meter's power supply. In the fi gures below, the 1.5V battery illustrates a true fl oating input. R1
DMS-20PC-1 11
1k
11 DMS-20PC-1
REF OUT
8
(+) IN HI
8
(+) IN HI REF OUT + R2 REF IN
12 7
1k 1.5V CELL (–) IN LO
12
DP1
6
– (–) IN LO
7
R3 REF IN
1 2 3
1k
1 2 3 6
+5V SUP DISPLAY 5V RET ENABLE +5V SUP DISPLAY 5V DP1 ENABLE RET 85-264Vac 85-264Vac AC to DC Converter AC to DC Converter
Figure 3.
Differential Input Confi guration
Figure 5.
Floating Input Measurements
3. Engineering Scaling
: For measuring voltages greater than
DMS-20PC-1
the full scale input range of a given meter, the input signal
11 8
(+) IN HI must be attenuated. A simple voltage divider (similar to that REF OUT +
10
shown in Figure 4) will scale the input to within the range of 1.5V ANA COMM CELL the selected meter. R1 and R2 should be precision, ±1%, –
12
metal-fi lm resistors with absolute TCR's less than 50ppm/°C.
7
(–) IN LO REF IN See Ap Note 4 for more information on engineering scaling.
1 2 3 6
+5V SUP DISPLAY 5V DP1 ENABLE RET 50kΩ < R1 + R2 < 10MΩ 85-264Vac R2 x VIN = Reading R1 + R2 AC to DC Converter +
Figure 6.
Floating Input Measurements (Alternate Confi guration) R1
DMS-20PC-1 11
(+) IN HI
8
VIN REF OUT
5. Process Control (4-to-20mA) Measurements
: In many common R2 process-control applications, a 4-to-20mA current loop is used to
12
(–) IN LO transmit information. Because DMS-20PC meters have such high –
7
REF IN input impedance, a simple shunt resistor across the meter's input
1 2 3
can be used to convert the loop current to a voltage. See Figure 7. +5V SUP DISPLAY 5V RET ENABLE The value of the shunt resistor is a function of the scaling require- ments of the particular application and can be calculated using 85-264Vac the following equation: AC to DC Converter RShunt = R1 = VFsr / IFsr
Figure 4.
Input Attenuation Circuit Where: VFsr = Full scale reading (in Volts) IFsr = Relative full scale current (in Amps)
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