Cropico DO7, Operating Instructions Manual

CROPICO LTD – DO7

Issue 7/2001

4

2. INTRODUCTION

The DO7 is an accurate bench/portable Digital Ohmmeter for the measurement of resistance in the
range 0.1µ

Ω

 to 60

Ω

.  It offers you the four terminal resistance measurement method to eliminate

the effect of lead resistance.  The measured values are displayed on a 4-digit LCD display; an
overflow of the selected range is also indicated.

Display range 6000

Simple push-button selection of the range required, ensures that the DO7 may be easily used by
unskilled personnel.  Error and status warnings are illuminated when appropriate.  The utmost care
has been taken to ensure that the ohmmeter will withstand an accidental mains voltage applied to
the measuring terminals, but it is not recommended that voltage should be applied.

3. MEASURING 

PRINCIPLE

The measurement is true 4 terminal, using the Kelvin principle.  A stable current is produced
across the resistance to be measured via the C terminals, and the voltage drop across the Rx is
measured at the P terminals.  This potential drop is then compared against the voltage 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.  High accuracy and long term stability is achieved by
using our own manufactured internal resistance standards.

4. CASE 

DESIGN

The case is ruggedly constructed from an ABS/polycarbonate alloy, coloured safety yellow.  A
strong internal sub-frame ensures that the DO7 will withstand the harshest of environments.  The
front panel is a reverse printed polycarbonate overlay with clear and unambiguous text.

5. MAINTENANCE

Normally no maintenance is required other than cleaning with a moist cloth.  Avoid aggressive
detergents or solvents.

CAUTION:

Before any maintenance, repair or exchange of parts or fuses, the instrument
must be disconnected from the mains supply and all power sources.  In the event
of a fault occurring, the instrument should be returned to our factory or Agent.  A
mains fuse is fitted to the mains inlet socket on the front panel, and should be
replaced if necessary.

CAUTION:

Disconnect mains lead and all connecting leads, before removing fuse holder.
Replace only with the correct fuse type, ie. according to the following chart.

Line

Voltage

Selection

Range

VAC

47-63Hz

Fuse (250V)

IEC 127

5 x 20 mm

100V
120V

87-110V

104-132V

2.5A (T)

220V
240V

191-242V
209-264V

1.25A (T)

Maximum Input Power : 80VA

The input circuits are protected by a 6 AMP fuse located in a holder on the main printed circuit
board.  Access is gained by removing the top cover.  Only replace with the correct fuse type as
below

.

10A Am  550V rms   HRC Ceramic Cartridge 10 x 38 mm

IEC 269-2-1  NFC63-210