4. DISPLAY TEST/HOLD (Pin 9) Function: Pin 9 is a dual-function
pin. On all standard models (without "-H" suffi x), tying pin 9 to pin 1
(+5V SUPPLY) activates the meter's DISPLAY TEST feature. All display
segments, except the decimal points, will be illuminated. The display
will show "1888" ("–1888" if a negative input signal is present). Do
not leave the meter in the test mode for more than 10 seconds as
this will cause the meter's operating temperature to rise and possibly
affect its performance. Pin 9 must be left open when the test function
is not being used.
On models with the "-H" suffi x (DMS-20PC-1-RS-H for example), pin
9 serves as a DISPLAY HOLD control pin. Tying pin 9 to +5V SUPPLY
(pin 1) on these models will hold or "freeze" the current display read-
ing indefi nitely. Pin 9 must also be left open when the hold function is
not being used. After disabling DISPLAY HOLD, allow the meter a full
10 seconds to resume normal calibrated operation before holding a
new reading.
The DISPLAY TEST or DISPLAY HOLD pin should normally be con-
nected, via a selector switch, to pin 1 (+5V SUPPLY). If automatic,
logic-controlled operation is desired, only PNP or MOSFET transis-
tors should be used. The base or gate of these transistors should be
driven suffi ciently hard to bring pin 9 within 0.05V of +5V SUPPLY.
5. DISPLAY ENABLE (Pin 2) Function: On all models, tying pin 2 to
pin 1 (+5V SUPPLY) applies full power to the LED display. This is the
normal mode of operating the meter. Leaving DISPLAY ENABLE open
(no connection), only turns off the LED display. The meter's analog-
to-digital converter continues to sample the input signal. Total current
consumption with the display off is approximately 400μA (0.4mA).
This is a very useful feature if the meter is used in battery-powered
equipment.
With the exception of the low-power red LED models (DMS-20PC-X-
RL), a regulated voltage lower than +5V SUPPLY can be used to dim
the display intensity. Display intensity control is best performed with
the high brightness, red LED, DMS-20PC-X-RH model. All low-power
red LED models must have DISPLAY ENABLE tied directly to pin 1
(+5V SUPPLY). Voltages applied to DISPLAY ENABLE must never be
greater than +5V SUPPLY.
6. Gain Adjust: There is a gain-adjust potentiometer on the back of
each meter. It has approximately ±50 counts (±2.5%) range of
adjustment. Since these devices essentially have no zero/offset
errors, a gain adjustment is effectively an overall accuracy adjust-
ment. Though they may be performed at any point (except zero),
accuracy adjustments are most effective when performed with
higher level input signals. The circuit shown in Figure 10 provides
±10% range of adjustment.
7. Soldering Methods: All models in the DMS-20PC Series easily with-
stand most common wave soldering operations. We recommend,
however, that you evaluate the effects your particular soldering
techniques may have on the meter’s plastic case and high-precision
electrical performance. We recommend the use of no-clean solders.
8. Suggested Mating Connectors:
Panel mounted:
Connector housing DATEL P/N 4320-01069-0
Terminal type DATEL P/N 4400-01032-0
Crimping tool DATEL P/N 39-2099000
Wire size 22 to 26 AWG
Insulation diameter 0.062" (1.57mm) maximum
Stripping length 0.100 to 0.125" (2.54 to 3.17mm)
Board mounted:
Socket DATEL P/N 4320-01074-0
Figure 2. Single-Ended Input Confi guration
DMS-20PC meters are highly versatile devices that can be used in
hundreds of applications. The application circuits chosen for this section
are ones that have historically received many inquiries.
The schematic in Figure 1 shows that the meter's high-impedance input
consists of an op amp powered from a ±5Vdc power supply (the –5V is
internally generated). One can easily see why input signals applied to (–)
INPUT LO and (+) INPUT HI have to be kept within the power supply rails
of ±5V. Also note that only pin 11 has a current-limiting 909kΩ series
resistor. High input voltages that have a common ground with pin 3 (5V
RETURN) should only be applied to pin 11 ((+) INPUT HI) and never to pin
12. In these high-voltage cases, pin 12 should always be tied to pin 3
(5V RETURN).
The schematic also shows that pin 3 is the meter's zero-volt reference
point — regardless of the type of power or signal source used. This is
an important point to keep in mind when a digital or analog multimeter
is used to make system measurements. The multimeter's negative lead
(usually the black one) must be connected to pin 3 (5V RETURN).
1. Single-Ended Input Confi gurations: True single-ended measure-
ments can be made with any DMS-20PC meter. The circuit of Figure
2 avoids problems normally associated with ground-loop currents.
Separate ground runs should be used for 5V RETURN (pin 3) and (–)
INPUT LO (pin 12).
1
12
3
+5V SUP
(–) IN LO
5V RET
85-264Vac
11
(+) IN HI
6
DP1
+
–
AC to DC Converter
V
IN
DMS-20PC-1
7
REF OUT
REF IN
8
2
DISPLAY
ENABLE
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DMS-20PC Series
3½ Digit, LED Display, Low-Cost, Subminiature
Digital Panel Voltmeters
MPM_DMS_20PC.D07 Page 3 of 6
APPLICATIONS
