Datel DMS-30PC Series Посібник - Сторінка 5

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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
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
R
= 1.000V/(0.020 – 0.004)A
Shunt
R
= 1.000V/0.016A = 62.5 Ohms
Shunt
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
11
(+) IN HI
10
ANA COMM
12
4-20mA
R1
(–) IN LO
9
1.23V
R2
REF
–
50k
DATEL
120 VAC
UPA-5/500
AC to DC Converter
Figure 7. 4-to-20mA Current Loop Operation
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-30PC-2-RL can be
configured to allow power supply monitoring over the range of
4.5-18Vdc. The circuit in Figure 8 uses a low-drop-out, three-
terminal regulator (LM-2931Z-5, available from National
Semiconductor) to provide regulated 5V power to the meter. The
LM-2931 was chosen because it has the following on-chip
(+) IN HI
LM2931Z-5
1
+5V SUP
IN
OUT
3
+
+
GND
5V RET
4.5 - 18Vdc
22µF
–
10V
5
DP2
Figure 8. 4.5-18V Power Supply Monitor
Applications
= 1.000 Volts
Fsr
accordingly.
Shunt
DMS-30PC-1
8
REF OUT
7
REF IN
1
3
5V SUP
5V RET
DMS-30PC-2-RL
11
7
8
12
REF
(–) IN LO
REF
IN
OUT
protection features: reverse polarity, short circuit and thermal run-
away. When using other, higher-power, DMS-30PC models with
three-terminal regulators, be sure to consult the regulator
manufacturer's data sheet to ensure the regulator is being
utilized safely and correctly.
7. Digital Ammeter: Digital ammeters are finding ever-increasing
usage because analog-style ammeters (moving-vane types) now
cost roughly the same as their digital counterparts. Additionally,
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. A
detailed application note describing digital dc ammeters is
included in DATEL's new Digital Panel Meter Databook.
1
+5V SUP
+
5Vdc
3
–
5V RET
6
DP1
1.5 Amp (Load Current)
Figure 9. Basic DC Ammeter Circuit
8. External Gain Adjustment: Connect REFERENCE OUT
(pin 8) to REFERENCE IN (pin 7) for normal, factory calibrated,
operation. Use the +1.23V REFERENCE OUT (pin 9) for
applications needing external gain adjustment. Figure 10 shows
the wiring configuration for each model. Calibration is performed
with a precise, near-full-scale, input voltage.
11
(+) IN HI
OUT
3
VOLTAGE
12
5V RET
CALIBRATOR
12
COM
(–) IN LO
ANA COMM
Figure 10. External Gain Adjustment
5
DMS-30PC
DMS-30PC-0-YS
8
REF OUT
7
REF IN
12
11
(–) IN LO
(+) IN HI
0.150V
0.1Ω
Load
Ω
R
(3.3 )
Shunt
DMS-30PC
10
8
7
9
NC
REF IN
1.23V REF
8.45k, 1%
Connections
for ±2V, ±20V
1k
and ±200V models
10 to 20 Turns
Connections
1k
8.45k, 1%
for ±200mV
10 to 20 Turns
models