Seaward DO7e - Manual (Page 7)

2. INTRODUCTION
The DO7e is an accurate bench/portable Digital Ohmmeter for the measurement of resistance
in the range 1µΩ to 600Ω. 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 LED
display; an overfl ow of the selected range is also indicated.
Display range 6000
Simple push-button or auto-range selection of the range required, ensures that the DO7e
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 Specially selected components.
4. CASE DESIGN
The case is ruggedly constructed from an ABS/polycarbonate alloy, coloured safety yellow. A
strong internal sub-frame ensures that the DO7e 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 fi tted 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.
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
Digital Microhmmeter Type DO7e Operating Instructions
4
Line
Voltage
Selection
120V
230V
Maximum Input Power : 18VA
Range
VAC
47-63Hz
104-132V
209-264V
Fuse (250V)
IEC 127
5 x 20 mm
250mA(T)
125mA(T)