iET LOM-4000, User And Service Manual

1

Introduction

LOM-4000 Series

Chapter 1

INTRODUCTION

1.3 Case Design

The case is ruggedly constructed from ABS plastic.
The front panel is a reverse-printed polycarbonate
overlay with clear and unambiguous text. The batter-
ies are housed in a removable cassette for quick and
easy replacement.

1.4 Available Accessories

Supplied:

1

Set of test leads

1

Set of alkaline batteries

1          Operation Manual

Optional Lead Sets:

HSO1-P

Duplex Handspikes with 2.5-meter

                        leads, for Kelvin measurements of
                        plates or buss bars

HSO2-P

Similar to HSO1-P but with 2.5-

                        meter and 15-meter leads

LSO3-P

Large Kelvin clips with 3-meter leads
– accept cables and bars up to 38
mm in  diameter

LSO4-P

Similar to LSO3 but with 3-meter
and 15-meter leads

Other Optional Accessories:

CO1

1 Meter Cable-Test Fixture – Wood Base

CO2

1 Meter Cable-Test Fixture – Metal Base

MTS2

  Calibration Standard

For most efficient operation, a spare battery

cassette (

BP-02

) is recommended.

1.1 General Description

The LOM-4000 and LOM-4001 are accurate bench/
portable handheld Digital Milli-ohmmeters for the mea-
surement of resistance in the range 10 µ

Ω 

to 4000 

Ω

.

They utilize the four-terminal (Kelvin) resistance-mea-
surement method to eliminate the effects of lead re-
sistance.  The measured values are displayed on a 4-
digit, 4000-count LED display; there is also an over-
flow indicator. The LOM-4001 allows temperature
compensation of readings and temperature measure-
ment if the user connects a 100-ohm platinum-resis-
tance thermometer (PRT).

Simple push-button or auto-range selection of the
range required makes the LOM-4000 Series easy to
use.  Error and status warnings are illuminated when
appropriate.  The unit will withstand accidental appli-
cation of line voltage to the measuring terminals.

1.2 Theory of Operation

The measurement is true 4-terminal, using the Kelvin
principle.  A stable current is produced across the
resistance to be measured via the current (I) termi-
nals, and the voltage drop across the unknown resis-
tance Rx is measured at the voltage (U) terminals.
This potential drop is then compared against the volt-
age drop across internal standards.  The ratio of these
is then converted to the resistance value of Rx and
displayed in ohms on the digital display. Use of  spe-
cially selected components assures high accuracy and
long-term stability .