DMS-40PC ETC-unknow, DMS-40PC Datasheet - Page 4

• Manufacturer Part Number: DMS-40PC
• Description: 4 1/2digit, Led Display Precision, Miniature Digital Panel Voltmeters
• Manufacturer: ETC-unknow

DMS-40PC
2. Differential Input Configurations: Differential inputs can also
3. Power Supply Monitoring: One of the most widely used digital
8 5 - 2 6 4 V a c
be measured with DMS-40PC meters as shown in the circuit of
Figure 3. Differential inputs must also originate from power
supplies that have a common ground with the meter's 5V
RETURN (pin 3). However, differential inputs usually have both
terminals above and/or below 5V RETURN. Figure 3, though not
necessarily a typical real-world application, does serve the
purpose of illustrating the concept of a differential signal.
The voltages developed across R1, R2 and R3 are equal to each
other and measure approximately +1.6666Vdc or 1/3 of the +5V
power source. More importantly, while the signal across R3 is
single-ended, both ends of R1 and R2 are well above ground
and are described here as being differential. Please note that
while the DMS-40PC can measure the voltages across either R2
or R3, it cannot measure the +1.6666 volts across R1! The
voltage at the lower end of R1 is approximately 3.333V and this
exceeds the common mode voltage limit of ±2V.
panel voltmeter applications is monitoring the output voltage of a
system power supply — often the same supply that also powers
the meter. The low-power, red LED DMS-40PC-2-RL, with its
excellent 0.001Vdc resolution, can be configured to monitor
power supplies with outputs in the range of 4.5-18Vdc. The
circuit in Figure 4 uses a low-drop-out, three-terminal regulator
(LM-2931T-5, in a T0-220 package, available from National
Semiconductor) to provide regulated 5V power to the meter.
The LM-2931 was chosen because it has the following on-chip
protection features: reverse polarity, short circuit and thermal
runaway. The DMS-40PC-3-RL can monitor voltages up to
±200Vdc, provided a separate +5V power source is used since
many three-terminal regulators cannot operate with supply
voltages greater than 24V. Red, low-power LED models, with
their very low self-heating, are recommended for applications in
A C t o D C C o n v e r t e r
D M S - P S 1 - C M
D A T E L
D P 1
Figure 3. Differential Input Configuration
+ 5 V S U P
1
D M S - 4 0 P C - 1 - G S
4 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
3
5 V R E T
1 1
( + ) I N H I
1 2
( – ) I N L O
Applications
R 1
R 2
1 k
1 k
R 3
1 k
4
4. Floating Signal Source Measurements: A floating input is a
+
–
which low calibration drift is desirable. When using other, higher-
power, DMS-40PC models in combination with three-terminal
regulators, be sure to consult the regulator manufacturer's data
sheet to ensure the device is being utilized safely and correctly.
signal that, before it is applied to the DMS-40PC's inputs, has no
galvanic connection (direct current path) to the meter or the
meter's power supply. The circuit shown in Figure 5 illustrates
the necessary connections for measuring floating inputs. The
1.5V battery represents a true floating input signal since it
initially has no connection whatsoever in common with the
meter. Real-world floating inputs typically originate from power
supplies which are transformer isolated from the DMS-40PC’s
+5V supply.
The connection of pin 12 ((–) INPUT LO) to pin 10 (ANALOG
COMMON) is required in order to provide a bias return for the
meter’s input amplifier. This is because neither pin 11 nor pin 12
are tied to any reference voltage inside the DMS-40PC (see
Figure 1). These connections are not made internally in order to
give the meter the ability to make differential measurements as
described in a previous section.
4.5 - 18Vdc
C E L L
1 . 5 V
8 5 - 2 6 4 V a c
–
LM2931T-5
IN
Figure 4. 4.5-18V Power Supply Monitor
A C t o D C C o n v e r t e r
Figure 5. Floating Input Measurements
GND
D M S - P S 1 - C M
OUT
A N A C O M M
D A T E L
22µF
10V
( – ) I N L O
( + ) I N H I
+
1 1
1 0
1 2
+ 5 V S U P
+5V SUP
5V RET
DP2
1
1
3
5
(+) IN HI
D M S - 4 0 P C - 1 - G S
11
5 V R E T
(–) IN LO
12
3
DMS-40PC-2-RL
D P 1
6