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VDL (E3.1) 10/2020 Page 120/196
14. Temperature safety devices
14.1 Safety temperature limiter (TL) class 2
The safety temperature limiter (TL) serves to protect the vacuum drying oven, its environment and loading
material against exceeding the permitted temperature. It has a fixed switching threshold and prevents ex-
ceeding the maximum surface temperature of the inner chamber of 160 °C in the event of a fault. If this
temperature is exceeded, the heater turns off. The TL protects the VDL vacuum drying oven, its environ-
ment and the loading material against impermissible excess temperatures and prevents exceeding the
maximum drying temperature in case of a fault.
The safety temperature limiter (TL) provides temperature monitoring through a thermal switch (bimetal
switch). If the permissible temperature is exceeded, the heating is switched off and an additional self-hold-
ing circuit is activated, which is only reset when the power plug is removed and reconnected. This prevents
the heating from being automatically switched on again. When the TL is triggered, an alarm message is
displayed on the controller. An annual function check by the operator is recommended, for this a controller
test routine is provided (chap. 16.5).
The safety temperature limiter (TL) provides ignition source monitoring . For further information of its func-
tion as part of the manufacturer's safety plan, please refer to chap. 3.1.
14.2 Overtemperature safety controller class 2
The chambers are regularly equipped with an electronic overtemperature safety controller (temperature
safety device class 2 – temperature limiter) acc. to DIN 12880:2007). The safety controller protects the
chamber, its environment and the charging material against exceeding the maximum permissible temper-
ature. The safety device class 2 is electrically independent of the temperature controller and turns off the
chamber permanently.
In the event of a fault in the temperature controller, the safety controller turns off the vacuum drying oven
permanently, i.e. until manual alarm reset. This condition (state of alarm) is indicated visually and addition-
ally with an audible alert if the buzzer is enabled (chap. 16.4). You can turn off the buzzer with the OK
button / Confirm icon. The alarm persists until the chamber cools down below the configured safety con-
troller value.
Please observe the DGUV guidelines 213-850 on safe working in laboratories, issued by the employers’
liability insurance association (for Germany).
Check the setting regularly and adjust it following changes of the set-point or charge.
The temperature safety device only activates after the set-point has been reached once.
14.2.1 Safety controller mode
You can set the safety controller mode to “Limit” or “Offset”.
• Limit: Limit value, absolute maximum permitted temperature value
This setting offers high safety as a defined temperature limit will not be exceeded. It is important to adapt
the safety controller value after each modification of the temperature set-point. Otherwise, the limit could
be too high to ensure efficient protection, or, in the opposite case, it could prevent the controller from
reaching an entered set-point outside the limit range.
• Offset: Offset value, maximum overtemperature above any active temperature set point. The resulting
maximum temperature changes internally and automatically with every temperature set-point change.
This setting is recommended for program operation. It is important to check the safety controller set-
point and safety controller mode occasionally, as it does not offer a fix, independent limit temperature
value, which would never be exceeded.
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