Low Battery
The LOBAT LED will light when the battery has approx. 10% charge left, when this LED lights
the DO7e should be connected to a mains supply and the batteries automatically recharged.
Full measurement accuracy is maintained even when the LOBAT LED is lit.
12. Connections
When making good quality measurements, it is important to ensure that all measuring leads are
in good condition, and less than 0.2 ohms resistance.
It should also be noted that some spade tags and crocodile clips can produce high thermal
emfs when warmed, particularly nickel-plated brass types. This can cause problems when,
for example, connecting too hot motor windings. The solution is to use plain copper or brass
connections keeping them clean and oxide-free.
Measuring Terminals
The heavy duty measuring terminals are designed to accept 4mm banana plugs in the
top socket, Bare wires and spade tags may also be clamped in the side entry socket.
13. REMOTE
If a footswitch, test leads with start button or other similar external switch is plugged into the
REMOTE socket, it will behave as the MEAS key.
14. PROTECTION
Every effort has been made to protect the instrument against voltages being applied to the
terminals. A large 6 Amp fuse is fi tted internally to the C measuring line and a gas discharge
tube, GDT, is across the C terminals. If voltages above approximately 90V are applied to the
measuring terminals, the GDT will strike, effectively shorting the C terminals through the 6 Amp
protective fuse, which will interrupt the circuit.
The fuse fi tted will interrupt up to 40,000 Amps. The P terminals are not fused and will withstand
up to 460 Volts without damage to the instrument.
WARNING!
To replace the protection fuse, the top instrument panel should be removed, but only after the
mains supply and all input connections are removed. The protection fuse is located on the main
printed circuit board. Only replace with the correct fuse rating.
15. CALIBRATION
PROCESS
This procedure describes the standard calibration method for the DO7e Ohmmeter using
Cropico Calibration Standard Type MTS2. If discrete resistance standards are to be used
instead, refer to section 21 before proceeding.
CAUTION
The DO7e will be factory-calibrated to its full accuracy when delivered and any recalibration
by the user will invalidate this initial calibration. The user should therefore be certain that only
authorised and competent personnel are permitted access to the calibration facility, which is
code protected.
Digital Microhmmeter Type DO7e
Operating Instructions
12
