Oven Types - Siemens Maxum II PD PA AP Service Manual

Oven Types

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 the oven zone must have a heat source, while simultaneously
preventing that heat source from being capable of igniting 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 analyses which
use a single set temperature, airbath, airless, and modular ovens are available. Since the
Maxum II is capable of performing analyses simultaneously on multiple trains (parallel
chromatography), the airbath oven is available as either a single oven or as a split oven
configuration that offers two independent temperature zones. The airbath oven heats by
convection. The airless oven heats by conduction and is available in the dual or single
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 conduction. 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 may be desirable to operate 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 that
this example application requires an oven temperature so high that the analysis zone itself
becomes a source 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. The temperature rating for the analyzer is
specified in the custom documentation package shipped with the analyzer.
Oven temperature is monitored by a resistance temperature device (RTD) sensor and
controlled by associated circuitry. This circuitry maintains oven temperature at the software
controlled set point along with monitoring actual surface temperatures. Within the oven the
highest temperature is found on or near 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 on a single set point board. These set point resistors are generally located on the
Power Entry Control Module (PECM) or 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 block temperatures are limited by the Power Entry
Control Module - Direct Current (PECM-DC). Fixed set point resistors are used on the PECM-
DC board. The 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.
Maxum II Valves and Oven Components
Service Manual, 10/2018, A5E42019844001
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