Specifications

Maxum II Operation Overview, Continued
In most applications, there are multiple columns in use that are typically
switched by column valves located in between them. These column
valves are not shown in the illustration, but like the sample valves and
SSOs described above they are also controlled by the SVCM and
EMSNE software located in the electronics control section. The Siemens
Model 50 valve is used for any required column valves.
Column Valves
The carrier gas pressure that is used to push the sample through the
columns is controlled by an Electronic Pressure Control (EPC) Module(s)
(or optionally by mechanical regulators). All EPCs are mounted on a
manifold located on the EC right-side wall. The pneumatics for the EPC
is digitally controlled by the EMSNE software on the CIM (Control
Interface Module). Up to three EPCs can be mounted in an EC. Each
EPC contains two channels, and each channel can use a different gas at
a different pressure. Each EPC communicates the actual pressure back
to the EMSNE software.
Electronic Pressure
Control
Oven Heaters
For the columns and detectors to work correctly, they must usually be
operated at elevated temperatures. The Maxum II uses electrical heaters
to elevate the temperature. These heaters (not shown in block diagram)
are connected to relays in the Electronic Enclosure and, like the valves
and the EPCs, are controlled by the EMSNE software.
The sample eluted from the columns is transported to the associated
detector that senses the presence of the sample and converts it to an
electrical signal. The Maxum II Modular Oven is equipped with thermal
conductivity detectors. These detectors sense changes in heat flow
across detector beads relative to a reference as sample flows across the
beads. Depending upon the application, the Maxum II Modular Oven
may be equipped with up to 16 TCD channels (8 per oven, 2 of which
are reference).
Detector
The resulting electrical signal from the detector is then transmitted from
the beads (which are part of the Application Module) to the Detector
Personality Module located in the EC.
The Detector Personality Module (DPM) resides in the EC and amplifies
and then converts the analog signal from the detector beads into a digital
signal. The DPM in the Maxum II Modular Oven is the Intrinsically Safe
Thermal Conductivity Detector DPM (ISTCD-DPM). The intrinsically safe
designation indicates that the device has been designed such that it
cannot ignite flammable vapors or gases. This allows the DPM to control
the TCD beads in the oven without the need for explosion-proof or flame-
proof protection. Each ISTCD-DPM is capable of controlling up to 8
detector channels.
Detector Personality
Module
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