DMS-30LCD Series
3½ Digit, LCD Display Digital Panel Voltmeters
www.murata-ps.com/dpm
email: sales@murata-ps.com
06 Jan 2011 MPM_DMS30LCD.D02 Page 5 of 6
APPLICATIONS
R2
(R1 + R2 + R3)
= 0.1
Figure 7. 4-to-20mA Current Loop Operation
(5V-Powered Models)
Figure 9. External Gain Adjustment
Figure 8. Power Supply Monitor
(9V-Powered Models)
6. Power Supply Monitoring: A popular application for DATEL’s low-
power LCD meters is monitoring the supply voltage in battery-oper-
ated portable equipment. Figure 8 demonstrates how a 9V-powered
DMS-30LCD can be used to monitor its own supply. The meter used
is the DMS-30LCD-1-9. A three-resistor voltage divider is used to
attenuate the battery voltage and also to satisfy the requirement that
the input voltages applied to pins 12 and 11 be at least 1.5 Volts above
and below the battery voltage applied to pins 1 (+BATTERY) and 3
(–BATTERY). The divider should be designed so that 1/10th the bat-
tery voltage falls across the inputs to the meter:
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 "1999". For different full
scale readings, alter the R
Shunt value accordingly.
R
Shunt = R1 = VFsr /IFsr
Where: VFsr
= Full scale reading (in Volts)
I
Fsr = Relative full scale current (in Amps)
Example: For a meter with a 2V full scale input (1.999 full
scale reading) and a desired full scale display reading of
1000 (with an input of 20mA), VFsr = 1.000 Volts
R
Shunt = 1.000V/(0.020 – 0.004)A
R
Shunt
= 1.000V/0.016A = 62.5 Ohms
7. External Gain Adjustment: Connect REFERENCE OUT
(pin 8) to REFERENCE IN (pin 7) for normal, factory calibrated, opera-
tion. Use the +1.23V REFERENCE OUT (pin 9) for applications need-
ing external gain adjustment. Figure 9 shows the wiring confi guration
for each model. Calibration is performed with a precise, near-full-scale,
input voltage.
Therefore, the 9V battery voltage appears to the meter inputs as 0.9V.
With the decimal point moved to its DP2 position
(pin 5 tied to pin 3), the meter reads 9.00 Volts.
The circuit can be calibrated by fi rst measuring the actual battery volt-
age with another meter and then adjusting the gain-adjust potentiom-
eter on the back of the DMS-30LCD until a similar reading is obtained.
If possible, the resistors in the divider should be ±1% metal-fi lm types
with TCR’s less than 50ppm/°C.
1
12
3
+BAT
(–) IN LO
–BAT
11
(+) IN HI
5
DP2
R2
R1
R3
45.3k
10.1k
45.3k
9V
BATTERY
+
–
8
7
REF OUT
REF IN
DMS-30LCD-1-9
9
(+) IN HI
(–) IN LO
ANA COMM
10
1.23V REF
1k
10 to 20 Turns
8
REF IN
11
1k
10 to 20 Turns
8.45k, 1%
8.45k, 1%
5V RET
7
NC
12
3
For 5V models tie
(–) IN LO to pin 3
For 9V models tie
(–) IN LO to pin 10
12
VOLTAGE
CALIBRATOR
OUT
COM
Connections
for ±2V and
±20V models
Connections
for ±200mV
models
DMS-30LCD
31
+5V SUP
5V RET
120 VAC
AC to DC Converter
(–) IN LO
ANA COMM
(+) IN HI
R1
+
–
4-20mA
50k
R2
8
7
REF OUT
REF IN
DMS-30LCD-1-5
