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Technical Description: Inlet
Rapid Multi-Stream Sampler
C-8
Prima PRO & Sentinel PRO Mass Spectrometers User Guide
via spare RMS ports (the latter may be more convenient if spare
ports are available).
The inlet assembly can be heated to 120°C to avoid condensation,
Heating
polymerization, etc. of sample gas mixtures. Two heaters are
required to heat the main body and peripheral parts of the inlet as
follows. Control of the heaters is discussed later in this chapter.
Main Body Heater
The bulk of the inlet body is maintained at the required
temperature by the use of one of two possible types of heater:
a. A ring heater clamped to the RMS stator on the enclosure
side. The heater has two windings with a common
connection, such that a three-wire connection is required.
b. Cartridge heaters (4-off) located in bores in the stator itself.
The four heaters are wired to mimic case (a), i.e. effectively a
twin element assembly, with a three-wire connection.
The three-wire connection allows for series or parallel connection
for 230 V or 115 V applications respectively, selected by a
switch on the inlet controller PCB. Insulation is provided to
minimize heat loss into the enclosure.
A K-type thermocouple is used to measure and thereby control
the temperature of the valve body via the control electronics. A
thermal switch assembly trips off the heater at a body
temperature of 140°C in the event of a runaway condition.
Sample Tube Heater
The sample tube body carries the selected gas stream flow and so
also requires heating.
A 30 W, 24 V cartridge heater heats the sample tube body, and a
PRT is provided for measurement and control. Typically, this
assembly is set to the same temperature as the main body.
Additional temperature limiting is not required as the heater
power is insufficient to take the assembly to a dangerous
temperature. The actual sample tube between the sample tube
body and the valve body is clad in copper, which greatly
improves the thermal conductivity and helps maintain a uniform
temperature along its length.
Gas Flow versus Temperature
The above heaters were specified assuming that the incoming
sample gases are heated to a temperature similar to that set for
the RMS. However, there may be situations where this is not the
Thermo Fisher Scientific
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