Modular Oven Heater System; Figure 1-10 Typical Modular Oven Configuration - Siemens Maxum II PD PA AP Service Manual

Oven Types

1.7 Modular Oven Heater System

1.7 Modular Oven Heater System
The Maxum II Modular Oven provides a stable isothermal oven temperature for certain lower
temperature applications. The hardware of the Maxum II Modular Oven analyzer configuration
is simplified and fully modular. Two independent ovens may be installed in the Maxum II
Modular Oven analyzer. Each of these may be a smaller or larger oven as shown below. The
ovens are designed such that pre-configured application modules may be easily installed and
removed. The image below shows a double application module in the right (large) oven and
no module installed in the left (small) oven. Visible in the left oven below is the manifold upon
which the application module mounts. The large oven has a double manifold and may
alternatively have two single sized application modules installed instead of the double size
module shown. In normal operation, the modular ovens are covered with face plates (not
shown) that are attached using thumb screws.
Figure 1-10
The oven heater system of the modular oven consists of two heated areas. The first is an
ambient control heater element mounted in a small manifold in the bottom rear of the oven.
This heater element maintains the temperature inside the oven near the desired temperature
for measurement, regardless of the ambient temperature outside the oven within the limits of
the analyzer specs. The second heated area is in the application-module manifold and the
mounted application module. The heater elements in the application-module manifold maintain
the temperature inside the application module at the desired temperature for measurement.
A small modular oven has one analytical heater element and a large oven has two analytical
heater elements (on for each side of the manifold).
Although they are mounted within manifolds inside of the modular oven, the heater elements
are installed in tubes that extend down from the electronics cabinet (EC) as shown in the figure
below. These tubes are separated from the oven by the aluminum walls of the manifolds. In
this way, the heaters are part of the purged space in the EC. As such, they are prevented from
being an ignition source.
Temperature for the modular oven heater system is detected and limited by RTD sensor probes
that are also embedded in tubes that extend down from the EC. These tubes run adjacent to
the tubes for the heater elements. These probes are connected to temperature control circuitry
on the Power Entry Control Module - Direct Current (PECM-DC).
The oven heater system of the Maxum II Modular Oven never exceeds the surface temperature
limit applicable to a T4 temperature rating.
Two relays control the power to the heater. One relay maintains the set point temperature of
the heater (oven temperature) in the software. The second relay is connected in series with
the first relay and is used for overtemperature shutdown. Because the overtemperature
shutdown sensor should not activate unless there is a mechanical failure of the set point
18
Typical Modular Oven Configuration
Maxum II Valves and Oven Components
Service Manual, 10/2018, A5E42019844001