Isothermal Air Bath Oven Heater System (Single And Split); Purging - Siemens Maxum II Manual

Safety Systems - Oven

3.2 Isothermal Air Bath Oven Heater System (Single and Split)

3.2 Isothermal Air Bath Oven Heater System (Single and Split)
The isothermal air bath oven is the most common oven used in the Maxum II. It is available in
single and split configurations to accommodate a wide range of chromatographic applications.
Because high temperatures are often necessary in order to carry out chromatographic
separations, the isothermal air bath oven heater system is equipped with various safety
features that are intended to prevent ignition.
3.2.1

Purging

The air bath oven heater is a purged system. This means that the hot element is located inside
an air purged tubular assembly. Clean instrument air continuously flows over the heating
element and into the oven. The flowing air ensures that the heater element cannot get too hot.
This air flow also works to distribute heat to the oven. The purge air flow is controlled by the
Purge Control Module (PCM). An air pressure sense switch on the PCM determines whether
air pressure exists in the tubing that supplies air to the heater. If pressure exists, then air is
flowing, and the switch is activated allowing the oven heater to be energized. If the switch does
not detect pressure, then it remains off, and power is not supplied to the oven heater. Refer
to figure 3-1. The air supply to the air bath oven heater system must be free of particulates,
clean of any hydrocarbon vapors or other flammable materials, and dry.
Figure 3-1
The air pressure switch is connected to the oven air flow using an extension that runs parallel
to the oven air flow line. This extension line is equipped with a coil. The coil is necessary in
order to create a short delay between the start of air flow and the activation of the pressure
switch. This forces the oven heater to purge for a short time before the oven is switched on
(much like the purge delay for the electronics enclosure which is described in section 2 of this
manual). Refer to figure 3-2.
36
Pressure Switch for Purge Control Module
Air Pressure
Sense Switch
for Oven Purge
Control
Explosion Protection Safety Standards
Manual, August 2017, A5E02220442001 Rev 8