DMS-EB-AC/DC
Potentiometer R5 applies a stable, positive dc-offset voltage to the
meter’s IN LO terminal. This offset voltage has a range of 0 to +1.2Vdc,
measured with respect to TB1 terminal 2 (LO). It can be used to null (or
cancel) the effects of an input whose zero level is not exactly zero volts.
For example, adjusting R5 allows the display to read “000” with an input
whose lowest level is slightly above zero volts. Please note, R5 can not
compensate for inputs whose zero level is negative (i.e., if TB1 HI is
more negative than TB1 LO).
3. Measuring Input Voltages Greater than 1.999Vdc (Use DMS-30-0 or
DMS-30-1 Only): If possible, the resistors used for R1 and R2 should be
±1% metal-film types with TCR’s less than or equal to 100ppm/°C. More
information on selecting 1% resistors can be found in Application Note 14
of the DATEL Panel Meter Catalog.
CAUTION: Do not apply inputs greater than +/-250Vdc.
1. Open SG10. For applications in which input voltages exceed ±100Vdc,
also cut the 2 adjoining traces.
2. Configure the DMS-EB-AC/DC for span adjust using the procedure
previously outlined.
3. Calculate values for R1 and R2 as follows:
A typical value for R1 is 1M
?
. The sum of R1 + R2 should be between
50k
?
and 10M
?
.
R2 = (FSI x R1) / ( |Vin| - FSI)
Where:
FSI = The attenuated voltage between the meter’s (–) IN LO and (+) IN
HI pins (pins 12 and 11, respectively) needed to achieve the desired
display readings
Vin = Input signal at TB1 terminals 1 and 2, disregarding polarity
Example
Using a DMS-30-1 meter (+/-2V range), Vin is 0-5Vdc and the display
reading must be “000” to “1500”
1. Assume R1 = 1.0M
?
.
2. R2 = (FSI x R1) / ( |Vin| - FSI)
R2 = (1.500 x 1,000,000) / (5.0 - 1.500)
R2 = 428,571
?
or 432k
?
3. Calibrate the meter using a known voltage source. Adjust R4 to
compensate for tolerances in R1 and R2.
Applications
1. Decimal Point Placement: DATEL ships the DMS-EB-AC/DC with all
decimal point solder gaps (SG1, SG2, SG3 and SG4) open. To enable a
specific decimal point, close its respective solder gap with solder. When
reassigning decimal places for subsequent applications, remember to
open any previously closed solder gaps.
Close SG1 for 1.999 (DP1)
Close SG2 for 19.99 (DP2)
Close SG3 for 199.9 (DP3)
Close SG4 for 1999.9 (DP4 on DMS-40LCD)
2. Span (Gain) and Zero (Offset) Adjustments (See Figure 3): DATEL
offers a resistor accessory kit, part number RN-DMS, consisting of 20-
turn potentiometers R4 (2K Ohms) and R5 (50K Ohms) and leaded
resistor R3 (10.5K Ohms). However, the leaded resistor supplied with the
RN-DMS accessory kit is not needed with the DMS-EB-AC/DC since it
contains a factory-installed 10.5K Ohm chip resistor. Once installed,
these potentiometers permit the span and/or zero adjustments described
in the following sections. R4 provides span adjust, while R5 applies a
positive offset to the meter’s (–) IN LO input.
Using Potentiometer R4 for Span Adjustment (DMS-30PC and DMS-
30LCD Meters Only)
1. For DMS-30-1, -2, and -3 models (+/-2V, +/-20V, +/-200V ranges):
Configuring the DMS-EB-AC/DC for span adjustment is simply a matter
of installing potentiometer R4, opening SG13, and then closing SG8,
SG11, and SG12.
2. For DMS-30-0 models (+/-200mV ranges): Span adjustment requires that
you open SG8, SG11 (if closed) and SG13 and then close SG7, SG9
and SG12. Then install R4.
Adjust span as desired. DMS-30-1, -2, and -3 span adjustment range is
typ10% and –5%. The DMS-30-0 has a much wider span adjust,
however, it should be limited to ±10% for optimum accuracy and stability.
Using Potentiometer R5 to Apply a Positive Offset to Pin 12 (-) IN LO
1. Open SG14 and close SG6.
2. Install 50K potentiometer R5.
Figure 2. DMS-EB-AC/DC Board
3
1 0 0 - 2 6 4 V a c P O W E R S U P P L Y B O A R D F O R D M S - 3 0 M E T E R S
12
1
R3
SG3 (DP3)
SG2 (DP2)
SG1 (DP1)
SG9
SG11
SG6
SG10
SG14
SG7
SG8
SG13
SG4
SG12
TB1
TB2
HI(+)
LO(–)
AC LO
AC HI
1
2
1
2
DP4
