DETector Engineering &Technology, inc.
486North Wiget Lane
DET REPORT
Walnut Creek, CA94598-2408USA
No.53 JUNE
2011
Electrical Differences - DET Ceramic Ion Sources
VS.
aBios Glass Bead.
In aBios glass bead, the wire used to electrically heat
the glass must have a large enough diameter to also
provide support for the bead. In operation, the
electrical resistance of the Bios ion source is just 0.19
Ohms, which means that ion source heating power
heats lead wires and connectors in addition to the ion
source, and the temperature of the ion source is
extremelysensitive to the stabilityof the heatingpower
supply.
In DET ion sources, the heating wire is encased in a
supporting ceramic structure so that a higher
resistance 1.2 Ohm wire core is achieved. This
assures that ion source heating power is mainly
dissipated in the ion source rather than in the electrical
leads and connectors.
Figure 3 compares a DET ion source and the Bios
bead with regard to the magnitude of NPD baseline
changes associatedwith step function changes in the
heating power (l.e., Agilent Bead Voltage). A 1milliVolt
change in the Bios power produced almost the same
magnitudebaseline changeas a 10milliVolt change in .
the DETTID-2 power. Clearly, theBios bead demands
much better power supply stability.
Phone: 925-937-4203; FAX: 925-937-7581
e-mail:
6890 NPDSensitivity toChanges in
Bead Voltage and Hydrogen Flow
2pA full scale
Bios
Bead
Hydr. change
0.1 mUmin
DETTID-2
Hydr. change
0.1 mUmin·
BeadV
change
0.010V·
Figure 3. Baselinechangeswhen IonSourceHeating
(l.e., BeadVoltage) and Hydrogen flowwere changed by
incrementalamounts.Comparison of Biosglassbeadand
a
OETT10-2
(BlackCeramic) ionsource.
3.) SCIENCEOF THE NPD
Science of the NPDDetection Process.
For any GC detector, defining the science of the
detection process is an important part of designing
reliable and reproducible detection equipment. For an
NPD with a Bios glass bead, the
science
is
complicated by the fact that the glass bead is a non
rigid physical structure which appears to continually
evolve with operating time with respect to color
changes, internal bubble formation, particulatesurface
growths, and migration movement about the heating
wire core. Furthermore, both the glass and the
exposed metal support wire can contribute to the
detectable ionization, and there is likely also some
volatilization of glass material occurring due to its
semi-molten state. As a consequence, the science of
a Bios NPD cannot be easily defined.
The NPD detection process can be more easily
described when the ion source is a rigid ceramic
cylinder positioned on the axis of a collector electrode
such as illustrated in Figure 4. As depicted in this
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Figure 4. Schematic illustrationof anNPOconfiguration.
3
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