Vanguard DMOM-100 - Manual (Page 7)

Operating Procedures DMOM-100™
1
1.0 INTRODUCTION
1.1 Applicability
This manual applies to the Model DMOM-
100™, part number VIC-9000-100, which is
made by Vanguard Instruments Company.
1.2 Supersedure Notice
This manual is the basic issue for the Model
DMOM-100
 and does not supersede any
published document.
1.3 General Description
The DMOM-100™ is a Digital Micro-Ohm
Meter for precisely measuring non-inductive
resistances from 1 micro-ohm to 300 milli-
ohms. Applications include resistance
measurement of circuit-breaker contacts,
bushing joints, or any other low resistance.
It is field-portable, rugged, and easily
operated by first-time users having little
training (its microprocessor-driven, which
automates many functions). It has a 16-key
pushbutton pad for entering test parameters
and control functions, and a 4-line by 20-
character LCD readout for displaying
control-option menus, measured resistance
values, and related identifying data. The
DMOM-100
 has a built-in thermal printer,
which prints test data on 2.5-inch-wide
thermally sensitive paper.
Operation requires little more than
connecting the test leads to an unknown
resistance and selecting the test parameters;
It requires no calculation of lead-loss, hand-
written notes, or the memorizing of detailed
routines. Operators select the test current
(10 to 100 amperes) and test time (5 to 60
seconds). Measured resistance data is
displayed and can be printed on the thermal
printer. The measured resistance data can
also be stored (up to 63 records of 96
readings each) in FLASH EEPROM
memory; Operators can recall the stored
resistance-measurements and related data at
a later time for review and printing.
1.4 Functional Description
DMOM-100
 operation is based on the
electrical relationships described by Ohm’s
law: R=V/I, where I is a known test current
and V is the voltage across the unknown
resistance (e.g., breaker contacts). Since the
test current through the unknown resistance
is known and voltage across it is read by the
microprocessor, the resistance is calculated
using Ohm’s law.
The DMOM-100
 test voltage is supplied
by a filtered direct-current power supply. A
precisely regulated constant-current source
controls the current ramps up/down time and
the test current. The dc test current (10 to
100 amps) slowly ramps up/down, which
virtually eliminates magnetically induced
transients; thus, the risk of inductively
tripping a circuit-breaker’s bus differential
relay is virtually non-existent.
DMOM-100
 voltmeter test leads are run
separately from the current-bearing test
leads to the resistive load; thus, voltages are
measured at the terminals of the resistance
being measured, eliminating error from the
I•R voltage drop in the test current cables.
The DMOM-100
 makes precise micro-
ohm measurements possible without
calculating compensation for test-current-
lead resistance errors.
1.5 Furnished Test Accessories
The DMOM-100
 is supplied with a power
cord, a roll of 2.5-inch-wide printer paper,
and one 35-foot test cable set with quick-
disconnect plugs to the unit and heavy-duty
alligator clamps to the load. Heavy-duty
welding-type C-clamps (see Appendix B)
are also available as optional accessories (C-
clamps allow test- lead connection to a wide
variety of bushing sizes, bus bars, and many
other junctions that require low-contact
resistance).