http://www.murata-ps.com/data/meters/dms-an6.pdf
Figure 10. External Gain Adjustment
Figure 8. 4.5-18V Power Supply Monitor
Figure 9. Basic DC Ammeter Circuit
Figure 7. 4-to-20mA Current Loop Operation
To calibrate the circuit of Figure 7, perform the following:
1. With 4mA applied, adjust the 50kΩ potentiometer (R2) to
display a reading of "000" (assuming that is the desired
reading).
2. With 20mA applied, adjust the gain-adjust potentiometer
on the back of the meter to display a reading of "1000".
For different full scale readings, alter the value of R
Shunt
accordingly.
The LM-2931 was chosen because it has the following on-chip
protection features: reverse polarity, short circuit and thermal
runaway. When using other, higher-power, DMS-20PC models
with three-terminal regulators, be sure to consult the regula-
tor manufacturer's data sheet to ensure the regulator is being
utilized safely and correctly.
7. Digital Ammeter: Digital ammeters are fi nding ever-increasing
usage because analog-style ammeters (moving-vane types)
now cost roughly the same as their digital counterparts. Addi-
tionally, analog ammeters are not nearly as rugged as modern
digital panel voltmeters. Figure 9 illustrates a typical ammeter
application. The circuit uses a ±200mV input meter — the
preferred range for most ammeters — to measure the voltage
developed across a 0.1Ω current shunt. The circuit shown
represents a basic ammeter connection diagram. Click
here to
view a detailed application note describing digital dc ammeters.
8. External Gain Adjustment: Connect REFERENCE OUT
(pin 8) to REFERENCE IN (pin 7) for normal, factory calibrated,
operation. Use the circuit shown in Figure 10 for applications
needing external gain adjustment. Calibration is performed
with a precise, near-full-scale, input voltage.
6. Power Supply Monitoring: One of the most common digital
panel meter applications involves monitoring the output voltage
of the system power supply — often this supply also powers the
meter itself. The low-power, red LED DMS-20PC-2-RL can be
confi gured to allow power supply monitoring over the range of
4.5-18Vdc. The circuit in Figure 8 uses a low-drop-out, three-ter-
minal regulator (LM-2931Z-5, available from National Semicon-
ductor) to provide regulated 5V-power to the meter.
Example: For a meter with a 2V full scale input (1.999 full scale
reading) and a desired display reading of "1000" (with an
input of 20mA), V
Fsr = 1.000 Volts
R
Shunt = 1.000V/(0.020 – 0.004)A
R
Shunt
= 1.000V/0.016A = 62.5 Ohms
13
+5V SUP 5V RET
AC to DC Converter
DMS-20PC-1
12
(–) IN LO
10
ANA COMM
11
(+) IN HI
R1
+
–
4-20mA
50k
R2
8
7
REF OUT
REF IN
2
DISPLAY
ENABLE
85-264Vac
5
78
+
–
DMS-20PC-2-RL
12
11
1
4.5 - 18Vdc
LM2931Z-5
GND
IN
OUT
+5V SUP
3
DP2
REF
IN
REF
OUT
(–) IN LO
5V RET
2
DISP EN
(+) IN HI
22μF
10V
+
6
3
+
–
DMS-20PC-0
11
0.150V
1
1.5 Amp (Load Current)
5Vdc
7
8
+5V SUP
5V RET
DP1
(+) IN HI
REF OUT
REF IN
2
DISP EN
0.1W
R
Shunt
Load
(3.3 )
12
(–) IN LO
W
12
VOLTAGE
CALIBRATOR
OUT
10
(+) IN HI
(–) IN LO
ANA
COMM
= 10 to 20 Turns
7
REF
IN
11
732, 1%
8.06k, 1%
5V RET
Connections
for ±2V, ±20V
and ±200V models
Connections
for ±200mV
models
COM
17.4k, 1%
2k
24.3k, 1%
3
12
DMS-20PC-1
8
NC
200
+5V IN
1
1
1
1
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DMS-20PC Series
3½ Digit, LED Display, Low-Cost, Subminiature
Digital Panel Voltmeters
MPM_DMS_20PC.D07 Page 5 of 6
APPLICATIONS
