7
The motor can be infinitely adjusted via a friction wheel
drive unit but is operated in one position only. The power
output, rotational speed and torque of the motor are re-
garded as constant and are optimized for this operating
position. After the friction wheel drive the motor power
output is transmitted to the output shaft of the stirrer via
either the first or second stage of the subsequent manually
adjustable toothed gear train.
Neglecting all losses, the power at the output shaft during
power transmission (conversion) is always as great as the
power output of the motor.
Drive
• Unpacking:
- Please unpack the device carefully
- In the case of any damage a detailed report must be sent
immediately (post, rail or forwarder)
Unpacking
The speed can be infinitely adjusted between 60 and 1400
rpm 50 Hz; 72 and 1680 rpm 60 Hz. The machine can be
operated continuously and warms up during operation. The
generously proportioned cooling surfaces enable distribu-
tion and transference of heat to be as even as possible.
Useful information
• Delivery scope:
-
RW 28 digital
overhead stirrer
- user guide
- extension arm
- hexagonal socket screw
- hexagon socket offset screw key
- chuck key
- warranty card.
The two meters long mains lead makes it possible to work
on stands - even with high glass apparatus under vapor ex-
traction hoods - without extension leads.
The precision stirrer shaft is designed as a hollow shaft to
allow the stirrer shanks to be in serted.
The gear train merely provides rpm and torque conversion,
which can be described in purely theoretical terms by the
characteristic curve plotted in
Fig. 2
.
Friction wheel wear is kept low by a helical clutch matched
to the gear train. The down-pressure required at the fric-
tion wheel is adjusted by the helical clutch according to the
moment acting on the stirrer shaft. A low torque results in
a low down-pressure; a high torque results in a high down-
pressure.
The ball race capacitor motor (degree of protection IP 42)
is maintenance free. In its winding it carries a special over-
heating circuit breaker (self-locking temperature limiter)
which shuts down the motor permanently if the permissible
motor temperature is exceeded.
This special type of circuit breaker is used when the auto-
matic reactivation of the protected unit after overheating is
undesirable or impermissible. The principle of the tempera-
ture limiter is that of a switch that heats up and isolates the
motor from the power supply when the maximum permis-
sible temperature is reached.
Motor circuit breaker
When the self-locking temperature is exceeded,
Er 4
is
shown on the display (see section “
Error codes
“).
In this case the unit can only be switched back on after it
has been switched off for approx. 4-5 minutes by pressing
the rocker switch (A, see
Fig. 1
) on the front or by discon-
necting the mains plug.
After this short cooling, the contacts in the current circuit
are closed again and the unit is operational once more.
