Vanguard DMOM-100_200 s2 - Manual (Page 6)

DMOM-100/200 Series 2 Operating Procedures
6
Rev 2, 2009
1.0 INTRODUCTION
1.1 Applicability
This manual applies to the Model DMOM-100 S2™ and Model DMOM-200 S2™ (hereafter,
DMOM), made by Vanguard Instruments Company, Inc.
1.2 General Description
The DMOM-100/200 Series 2 are the third generation micro-ohmmeters made by Vanguard
Instruments Company. The DMOM-100/200 features microprocessor-controlled highly accurate
measuring of very low resistances, ranging from 1 micro-ohm to 300 milli-ohms. The DMOM is
field-portable, rugged, and easily operated by first-time users with a minimum of training. It
features a 16-key push button pad for entering test parameters and control functions and a 4-line
by 20-character LCD alphanumeric readout for displaying control-option menus, measured
resistance values, and related identifying data. The DMOM has a built-in thermal printer, which
prints test data on 2.5-inch-wide thermal sensitive paper. The operation requires little more than
connecting test leads to an unknown resistance and selecting the desired functions and options.
Operators select the test current (10 to 100 amperes for DMOM-100 or 10 to 200 amperes for
DMOM-200) and test time (5 seconds to 2 minutes). 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.
1.3 Functional Description
The DMOM’s operation is based on the electrical relationships described by Ohm’s law: R=V/I,
where I is a known current and V is the dc voltage measured across the unknown resistance
(typically, a circuit breaker’s contacts). Since the current (user selected) through the unknown
resistance is known and the voltage across the unknown resistance is read by a precision
voltmeter, the unknown resistance can be calculated using Ohm’s law.
The DMOM’s test voltage is supplied by a true 5Vdc power supply. The true DC test current is
selectable from 10 to 100 amperes for the DMOM-100 and from 10 to 200 amperes for the
DMOM-200. Test current is automatically ramped up and down slowly. This current ramp rate is
programmable from 5 seconds to 30 seconds.
Voltmeter test leads run separately from the current-bearing test leads to the resistive load to
eliminate any I•R voltage drop error in the current cables. These DMOM features make very
precise micro-ohm measurements possible without having to calculate compensations for
current-lead resistance errors.
1.4 Furnished Test Accessories
The DMOM is supplied with two 30-foot test cables with heavy-duty alligator clamps. Both the
current (#1 AWG) and sense leads are combined into one cable (Figure 1.0). A ground cable and
a power cord are also included with each DMOM.
Users can choose to have the current and sense leads separated as shown in Figure 2.0 and Figure
4.0. Optional hand spike sense leads are also available as shown in Figure 3.0.