DMS-20LCD Series
3½ Digit, LCD Display Digital Panel Voltmeters
www.murata-ps.com/dpm
email: sales@murata-ps.com
05 Apr 2011 MPM_DMS20LCD.B08 Page 5 of 6
APPLICATIONS
To calibrate the circuit of Figure 7, perform the following:
1. With 4mA applied, adjust the 50k: 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 value of R
Shunt 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
Figure 7. 4-to-20mA Current Loop Operation
(5V-Powered Models)
R2
(R1 + R2 + R3)
= 0.1
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-20LCD can be used to monitor its own supply. The meter used
is the DMS-20LCD-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:
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-20LCD 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.
7. External Gain Adjustment: Connect REFERENCE OUT
(pin 8) to REFERENCE IN (pin 7) for normal, factory calibrated,
operation. Use the circuit shown in Figure 9 for applications needing
external gain adjustment. Calibration is performed with a precise,
near-full-scale, input voltage.
Figure 9. External Gain Adjustment
Figure 8. Power Supply Monitor
(9V-Powered Models)
1
12
3
+BAT
(–) IN LO
–BAT
11
(+) IN HI
5
DP2
DMS-20LCD-1-9
R2
R1
R3
45.3k
10.1k
45.3k
9V
BATTERY
+
–
8
7
REF OUT
REF IN
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/
–BAT IN
Connections
for ±2V, ±20V
and ±200V models
Connections
for ±200mV
models
COM
1
+5V IN/
+BAT IN
17.4k, 1%
2k
24.3k, 1%
3
12
DMS-20LCD
For +5V models, tie (–) IN LO to pin 3.
For +9V models, tie (–) IN LO to pin 10
8
NC
200
c
c
c
13
+5V SUP
5V RET
120 VAC
AC to DC Converter
12
(–) IN LO
10
ANA COMM
11
(+) IN HI
R1
+
–
4-20mA
50k
R2
8
7
REF OUT
REF IN
DMS-20LCD-1-5
