Vanguard Auto-Ohm User Manual

OPERATING INSTRUCTIONS

for the

AUTO-OHM

LOW-RESISTANCE

OHMMETER

Series II

Part Number VIC-60000-S2

Vanguard Instrumentss Company

1710 Grevillea Court Ontario, California 91761

TEL: [phone]
FAX: [phone] Rev. 0

April 2001

Auto-Ohm Operating Procedures

SAFETY SUMMARY

The following safety precautions must be
observed during all phases of test set-up, test
hookups, testing, and test-lead disconnects.

Do Not Service or Test Alone

Do not perform test procedures or service
unless another person is also present who is
capable of rendering aid and resuscitation.

Avoid Contact with High Voltage

Because electrical utility station
environments contain high voltages and
currents, there is always the possibility of
personal contact with an unexpected lethal
voltage generated by magnetic induction
and/or electrostatic leakage from nearby live
circuitry. When test units are connected to
deenergized ("dead") power lines, regardless
of how short they are, always discharge the
lines before attaching any test lead. Because
of the possibly deadly consequences of
physical contact with such high-voltage
lines, engineers and technicians must always
treat electrical equipment and hookups as
though a lethal condition will eventually
occur. Therefore, no matter how unlikely it

may seem, never assume anything about the
safety of any test setup.

Ensure the safety of personal by checking
first-hand to eliminate all possible hazards!

Do Not Modify Test Equipment

Because of the added risk of introducing
additional or unknown hazards, do not install
substitute parts or perform any unauthorized
modification to the Auto-Ohm. To ensure
that designed safety features are maintained, it
is recommended that all Auto-Ohm repairs be
performed at Vanguard Instruments Co. or by
an authorized repair-service. Unauthorized
equipment modifications can create unknown
safety hazards and will void the Auto-Ohm
warranty.

Follow Exact Operating Procedures

Any deviation from the operating procedures
described in this manual may create one or
more safety hazards, damage the unit or cause
test result errors; Vanguard Instruments Co.
assumes no liability for unsafe or improper
use of the Auto-Ohm.

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Auto-Ohm Operating Procedures

Table of Contents

Safety Summary............................................................................................................................... i

Table of Contents............................................................................................................................ ii

1.0 Introduction...............................................................................................................................1

1.1 Applicability .............................................................................................................................1

1.2 Supersedure Notice ....................................................................................................................1

1.3 General Description ..................................................................................................................1

1.4 Functional Description..............................................................................................................1

1.5 Furnished Test Accessories.......................................................................................................1

2.0 Auto-Ohm Specifications .........................................................................................................2

3.0 Controls and Display ................................................................................................................3

4.0 Operating Voltages ...................................................................................................................5

5.0 Cable Connections ....................................................................................................................5

6.0 Operating the Auto-Ohm ..........................................................................................................7

6.1.0 Step-by Step Procedures ........................................................................................................7

6.1.1 Precautions.............................................................................................................................7

6.1.2 Preparations ...........................................................................................................................7

6.1.3 Run Test Procedure................................................................................................................7

6.1.4 Contrast Adjustment ..............................................................................................................9

6.1.5 100-Amp Cal Check ..............................................................................................................9

6.1.6 Display Previous Results Procedure ....................................................................................10

APPENDIX A: Auto-Ohm Troubleshooting Guide .....................................................................13

APPENDIX B: Illustration of Test Connectors............................................................................15

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Auto-Ohm Operating Procedures

1.0 INTRODUCTION

1.1 Applicability

This manual applies to Series II of the
Model Auto-Ohm™ (hereafter, Auto-Ohm),
identified by Part Number VIC-60000-S2
made by Vanguard Instruments Company.
A separate manual applies to Series I (the
first design configuration) of the Auto-Ohm.

1.2 Supersedure Notice

This Operator’s manual is the basic issue for
Series II Auto-Ohm and does not supersede
any previously published manual.

1.3 General Description

The Auto-Ohm micro-ohmmeter is made by
Vanguard Instruments Company and
features microprocessor-control for
measuring very low resistances ranging
from 1 micro-ohm to 300 milliohms with
high accuracy. The Auto-Ohm is field­portable, rugged, and is easily operated by
first-time users having little or no training; it
features a one-knob control and an LCD
alpha/numeric display of the resistance
measured. The one-knob control operation
is logical and simple: Turning the knob
scrolls through a menu of possible options
(which display in sequence) and pressing
the knob activates the selected function. As
its name implies, the Auto-Ohm operation is
automatic, requiring little more from the
user than connecting it to an unknown
resistance and selecting what it is to do and
how the test results are to be presented. The
Auto-Ohm stores the last 3 resistance
measurements, which can be displayed
during test.

1.4 Functional Description

The Auto-Ohm’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 circuit­breaker’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 resistance read-out is a direct function of
the voltage being measured. The voltage is
read directly as resistance (translated and
displayed on a digital readout). The dc test
current is selectable in 2-amp steps, from 10
to 100 amperes. Test current is gradually
ramped up and down (automatic function),
which virtually eliminates magnetically
induced transients through the circuit­breaker current transformers. The risk of

inductively tripping a circuit breaker (bus
differential relay) is virtually non-existent.

The Auto-Ohm performs all of these
functions in one simple process. Voltmeter
test leads run separately from the current­bearing test leads to the resistive load; thus,
voltages are measured at the terminals of the
resistance being tested, eliminating any I•R
voltage drop error in the current cables. The
Auto-Ohm test voltage is supplied by a DC
power supply. A precisely regulated
constant-current source ensures measured
voltage is a function of the resistance alone,
and not affected by current-cable resistance
losses. These Auto-Ohm features make very
precise micro-ohm measurements possible
without having to calculate compensations
for current lead resistances errors.

1.5 Furnished Test Accessories

The Auto-Ohm is supplied with one 35-foot
test cable with quick disconnect test plugs at
the unit end and heavy-duty alligator clamps
at the test-load end. Heavy-duty welding-

type C-clamps are available as optional
accessories (these C-clamps allow test lead

connections to a wide variety of bushing
sizes, bus bars, and conductors that require
low-resistance test-lead contacts).

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Auto-Ohm Operating Procedures

2.0 AUTO-OHM SPECIFICATIONS

Auto-Ohm specifications and leading
particulars are listed in Table 1
.

Table 1. Auto-Ohm Specifications and Leading Particulars

MODEL ...................... Auto-Ohm

PART NUMBER.......... VIC-60000-S2

TYPE ............................. Special-Purpose Test Equipment, Portable, Low Resistance-Ohmmeter

CONFIGURATION...... Second-generation (improved design, superseding original model)

SIZE (inches) .............. 16.8 Wide by 12.6 High by 10.6 Deep

WEIGHT........................ Less than 21 pounds

RESISTANCE

RANGE ......................... 1 micro-ohm to 300 milliohms

TEST CURRENT

RANGE ......................... 10 Amperes to 100 Amperes, Selectable with ±2 ampere increment

DISPLAY ...................... Backlit LCD, 2-lines high by 16 characters Wide

ACCURACY................. ± 1 % Reading, ± 1 Count

OPERATING

POWER ........................ 8 amps, 90-132 Vac or 200-230 Vac (selectable), 50/60 Hz,

With 10A built in circuit breaker

UNIT PROTECTION... thermal-overload sensor and cutoff

INTERFACE................. RS-232C Connector Port for PC Interface

ENVIRONMENT.......... Operating: 0°C to 55°C; Storage: -40°C to 65°C

FURNISHED ITEMS... One power cord, one 35-ft. test lead cable, one test-cable carrying bag

WARRANTY ................ One-Year Parts & Labor (Post-Warranty Service Contracts Available)

AUTO-OHM SPECIFICATIONS ARE SUBJECT TO UPGRADES AND TO BEING CHANGED WITHOUT PRIOR NOTICE.

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Auto-Ohm Operating Procedures

3.0 CONTROLS and DISPLAYS

(See Figure 1 and refer to Table 2.)
The Auto-Ohm controls and displays are
shown in the control-panel illustration,
Figure 1. Pointing leader lines reference
each item with an index number. Each index
number is cross-referenced to a functional
description in Table 2, which describes the

function and purpose of each item on the
control panel. Although the purpose of
these controls and the display may seem
obvious and intuitive, users should become
familiar with them before attempting to use
the Auto-Ohm. First-time users should also
review and become familiar with the Safety
Summary in the front page.

Figure 1. Auto-Ohm Control-Panel Controls and Display

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