© PSI (Photon Systems Instruments), spol. s r. o.
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5.6 MAGNETIC STIRRER
The magnetic stirrer module is designed for homogeneous mixing of the culture inside the cultivation vessel. The stirrer is
essential when the agitation by air or gas bubbles cannot be used, e.g. when the photosynthetic oxygen evolution or
respiratory oxygen uptake are measured or when growing the culture anaerobically without gas supply. It can be also used
to reduce cell sedimentation and clumping in addition to agitation by gas bubbling. The magnetic stirrer is highly
recommended when using the O
2
probe and CO
2
probe – very good stirring is essential for accurate measurements of these
probes.
The magnetic stirrer (Fig. 30) rotates – 35 mm long (Ø 6 mm) teflon-coated magnetic bar in a vertical plane of the front
glass panel inside the Photobioreactor. The speed of rotation is adjustable from 60 to 600 rpm (10 – 100 %) by the front
panel of the control unit (Setting > PWM mode) or by the PBR software. The current version of the magnetic stirrer has
own external control unit as shown in Fig. 30C whereas the older versions (Fig. 30A, B) were controlled by the PBR.
Fig. 30 Magnetic stirrer for A) FMT150.1 version (two different stirrer types: slow and high speed stirrer). B) FMT150.2 version (slow
and high speed stirrer). The production of A) + B) versions were stopped in May 2015. C) Current version of magnetic stirrer for PBR
FMT150.2 version with own control unit (speed of rotation 600 rpm).
The current version of magnetic stirrer implements a stepper motor powered by direct current (12 VDC/2 A) in contrast to
the older versions that comprised of a brushed electric motor driven by an alternating current. The main advantages of
this technology represent linear response of stirrer to applied voltage, better lifetime of motor, improved control and
accuracy that is not influenced by density or viscosity of mixed solution, lower susceptibility to failure, increased rotation
speed and range, improved guarantee of the rotation speed, etc. The motor is controlled by an additional external control
unit which allows precise adjustment of rotation speed either via front panel of the Photobioreactor or the PBR software.
The speed of rotation can reach up to 600 rpm and is fully and continuously adjustable in range of 60 – 600 rpm which
corresponds to 10 – 100 % setting of PWM_mode. Optimal gradual acceleration and deceleration of the stirrer is preset
by manufacturer and this parameter can't be changed by user. Moreover, PBR control software allows to set different
stirring modes: constant, linear, sinusoid or through scripts.
The older versions have slow-speed of rotation (labelled as 245) or high-speed of rotation (labelled as 770). The stirrer’s
type is stated on the label attached to the stirrer. For the relation between rpm and PWM value (%) of rotation speed
please refer to Fig. 31.
The front panel of the control unit houses connectors for all connecting cables (Fig. 35C). A metal button and USB port
intended for services purposes are located on the rear side of the power supply (Fig. 35F). DO NOT USE THE SERVICE
BUTTON WITHOUT PSI MANUFACTURER! LET THE SERVICE BUTTON IN HORIZONTAL POSITION (Fig. 35F).
Components for the magnetic stirrer: power source, communication cable, magnetic bars, service keys (Fig. 32).
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