Technical Description: Inlet
Rapid Multi-Stream Sampler
Thermo Fisher Scientific
Prima PRO & Sentinel PRO Mass Spectrometers User Guide
C-9
case. For instance, all streams may be cold (a common situation
for Sentinel PRO applications), or there may be a combination of
hot and cold streams. Consideration must be given to the possible
general cooling of the RMS body or to localized cooling – for
example, the cooling effect of a cold gas flow on an adjacent port
or the cooling of the common flow regions (sample tube, etc.).
The latter could be important if a cold stream is sampled
immediately prior to sampling a temperature critical hot stream.
The following examples illustrate the limits of cold gas flows
(the cold gas streams are assumed to be air or nitrogen at a
temperature of 20°C).
a.
To maintain a body temperature of 80°C, the maximum cold
gas flow is 500 Nl/min.
b.
To maintain a body temperature of 120°C, the maximum cold
gas flow is 250 Nl/min.
c.
A cold gas flow of 10 Nl/min on a single port (the maximum
allowed) will cool an adjacent port by approximately 4°C.
d.
A cold gas flow of 10 Nl/min on a single port (the maximum
allowed) will cool the sample tube by approximately 10°C
(over a period of several minutes). Similarly, the temperature
takes several minutes to recover. This situation can be
avoided by reducing the cold gas flow rate or bypassing
approximately 80% of the cold stream to a spare (non-
sampled) RMS port.
Potential problems can be minimized by careful selection of
which ports hot and cold gas streams are connected to and the
sequence of sampling of these ports.
Details of the protection methods used for hazardous area operation,
both for the system as a whole and specifically for the RMS, are
given in
Appendix A: Hazardous Area Operation
An important point relating to hazardous area operation of the RMS
is that it must be possible to predict in a fault condition the maximum
leak rate of any sample into the enclosure. The sample pressure
therefore defines the flow rate through any leak, and the upper
pressure limit for the Prima PRO Ex of 0.2 bar(g) must be strictly
adhered to and forms part of the hazardous area certification for the
instrument. For the Sentinel PRO Ex, samples are maintained under
reduced pressure by virtue of the sample pump, which in turn
prevents any possible leakage into the enclosure.
Hazardous Area
Systems
