Safety Systems - Oven; General Oven Information - Siemens Maxum II Manual

Safety Systems - Oven

3.1

General Oven Information

Chromatographic separations of samples are carried out inside the oven zone of the Maxum
II analyzer. For most separations to be performed, the oven must be kept at an elevated
temperature. This means that it must be heated from a hot source while simultaneously
ensuring that the source cannot ignite flammable vapors which might be present within the
oven. This is accomplished by the oven heater system.
A variety of oven configurations are available for the Maxum II. For isothermal (single set
temperature) analyses air bath, airless, and modular ovens are available. Since the Maxum II
is capable of performing analyses simultaneously on multiple trains (parallel chromatography),
the air bath oven is available as either a single oven or as a split oven configuration that offers
two independent temperature zones. The air bath oven heats by convection. The airless oven
heats by radiation and is available in the split configuration. For configurations requiring only
one airless oven, the second oven compartment is left unequipped. The modular oven
functions in a manner similar to the airless oven, heating by radiation. Either one or two
independent modular ovens may be equipped in a Maxum II Modular Oven analyzer.
It should be noted that there may be desired operating conditions which are mutually
incompatible. It is possible to desire to perform an application which requires a very hot oven
temperature (for example, the separation of very high molecular weight hydrocarbons or the
analysis of some heavy liquid chemicals). It is also possible that there may be flammable gases
and vapors present in the area of installation which can ignite at relatively low temperatures
(for example, some hydrocarbons). Because of these opposing constraints, it is possible to
desire an application which requires an oven temperature so high that the analysis zone itself
becomes capable of ignition. This situation is not permitted. It is the responsibility of the user
to ensure that the analyzer is never installed in an area that is not rated appropriately for the
oven temperatures required for the application.
Oven temperature is controlled by a resistance temperature device (RTD) sensor and other
circuitry. This circuitry maintains oven temperature at the software controlled set point. Within
the oven the highest temperature is found on the heater surface and this temperature is limited
in different ways depending on configuration.
In the airbath/airless oven configuration, the heater temperature is limited by two set point
resistors. These set point resistors are generally located on the Power Entry Control Module
(PECM). However, set point resistors for the oven heaters may also be located on a Detector
Personality Module (DPM). Instructions pertaining to this appear in other documentation.
However, for reference, a table of highest surface temperatures and area temperature ratings
is included at the beginning of this manual.
In a modular oven configuration, the heater temperature is limited by the Power Entry Control
Module - Direct Current (PECM-DC). Set point resistors are not needed with the modular oven
because, by design, oven temperature never exceeds the surface temperature limit for the T4
temperature rating as identified by the table at the beginning of this manual.
Thus, regardless of configuration, the oven heater system is designed to ensure that the
temperatures of the oven heaters are controlled in a safe manner and do not create a fire
hazard.
Explosion Protection Safety Standards
Manual, August 2017, A5E02220442001 Rev 8
3
35