Lauda LMTZ 831, Operating Instructions Manual

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PTT
8
Device description
YAME0020 / 30.06.11
3 Device description
3.1 Basic principles
3.2 Temperature display and control
The PTT Thermostating Unit facilitates the exact temperature stabilisation of small amounts of liquid up
to 60 ml from 5 °C to 80 °C.
The liquid can be stirred if required using an inserted magnetic stirring rod (included in the supplied
items).
For vibration-free measurement applications all electrical components (fans, magnetic stirrer, power
electronics for the thermostating unit) can be deactivated in the
standby
mode.
The PTT uses four Peltier elements spread uniformly around the circumference of the beaker. Heat is
supplied or extracted depending on the tempering situation. Ambient air enters the device through the
intake areas (ribbed regions at the front left and rear right), it circulates around the heat exchanger with-
in the device and leaves the device through the side exit areas.
In order to ensure perfect air circulation neither the ventilation openings nor the exit areas should be re-
stricted or covered.
The PTT is equipped with a protection system which safeguards the power electronics and Peltier ele-
ments from thermal overload.
A bimetallic switch fitted internally in the beaker receptacle provides additional protection from the con-
tainer overheating above 90 °C.
Measurements and setting values as well as operating statuses are displayed on the front of the PTT
using a 3-figure 7-segment display
888
. The entry of the set value and other settings occurs using the
button/rotary function of the control knob.
The Pt100 temperature sensor for the acquisition of the momentary sample temperature is connected
via the "Sensor" socket. A high resolving A/D converter processes the measurement. Further measure-
ment processing occurs via a special control algorithm which implements the control of the Peltier elec-
tronic tempering system.
To measure the temperature of the samples reliably the Pt100 sensor must be immersed by at least
three millimetres in the sample liquid. With thermostating processes extended over a longer period the
reduction in level due to evaporation must be taken into account as necessary.
The liquid should be kept in motion by an inserted stirring rod in order to facilitate improved heat
transport and to ensure a uniform temperature throughout the whole liquid volume.