Abstrict
A sample vessel container in a sampling device for use in gas chromatography
includes a rotatable metal block having a circular array of axial
bores for accommodating a plurality of sample vessels. A heating
jacket operative as an electric heater is non-rotatably connected
to a housing, which jacket tightly surrounds in material contact
with, and is adapted to heat, the rotatable metal block.
Claims
What is claimed is:
1. A sampling device comprising: a rotatable sample vessel container
for accommodating a plurality of sample vessels, means for selectively
moving each of said sample vessels to a sample feeding position;
an electric heater for heating said container;
a housing, said container being positioned in said housing;
a heating jacket positioned between said container and said housing,
said jacket surrounding said container; said jacket including an
electric heating coil enclosed between two silicone mats;
means for maintaining said jacket in material contact with said
container whereby a thermal transfer relation is maintained therebetween
and;
means between said jacket and said housing for preventing rotation
of said jacket.
2. A sampling device comprising:
a rotatable sample vessel container for accommodating a plurality
of sample vessels, means for selectively moving each of said sample
vessels to a sample feeding position;
an electric heater for heating said container;
a housing, said container being positioned in said housing;
a heating jacket positioned between said container and said housing,
said jacket surrounding said container;
means for maintaining said jacket in material contact with said
container whereby thermal transfer relationship is maintained therebetween;
the radially inner surface of said jacket being coated with PTFE
whereby frictionally forces between said container and said heating
jacket are reduced; and
means, between said jacket.and said housing, for preventing rotation
of said jacket.
3. A sampling device comprising:
a rotatable sample vessel container for accommodating a plurality
of sample vessels, means for selectively moving each of said sample
vessels to a sample feeding position;
an electric heater for heating said container;
a housing, said container being positioned in said housing;
a heating jacket positioned between said container and said housing,
said jacket surrounding said container;
means for maintaining said jacket in material contact with said
container whereby a thermal transfer relationship is maintained
therebetween and;
means, between said jacket and said housing, for preventing rotation
of said jacket, said jacket including an electric heating coil enclosed
between two silicone mats, metal straps being affixed to said silicone
mat proximate said housing, which straps including brackets formed
at right angles and functioning to stretch said heating jacket about
said container by means of bow strings.
4. A sampling device as claimed in claim 3 wherein said jacket
rotation preventing means includes a metal protrusion affixed to
said silicone mat proximate said housing, and said housing having
a slot for accepting said metal protrusion.
Description BACKGROUND OF THE INVENTION
The present invention generally relates to an electric heater for
a rotating sample vessel container in a sampling device for gas
chromatography and, in particular, relates to an electric heater
which is stationary with respect to the rotating sample vessel container.
The sampling device is preferably of the type wherein a capillary
connecting conduit formed as a needle is connected to the inlet
of the separating column for the purpose of withdrawing samples
from sample vessels which are closed by self-sealing membranes.
A controllable valve is arranged in a carrier gas conduit leading
to the inlet of the separating column. The valve may be closed for
the purpose of sample feeding. The sampling device includes a table
mounted on an axle and thermally controlled means for accommodating
a plurality of sample vessels are provided such that each of the
sample vessels is positionable under the stationary needle. Together
the table and sample vessels are axially movable upwards in the
direction towards the needle, whereby the sample vessel is pushed
up on the needle such that the needle pierces the membrane.
One sampling device is known from German Auslegeschrift No. 1 297
904. In such sampling devices vapor from the head space above a
sample enclosed in a sample vessel by means of a self-sealing membrane
is supplied to the gas chromatograph. In the sample vessel closed
by the membrane a state of equilibrium exists such that, in the
head space above the sample, the different sample components are
present with partial pressures, which are representative of the
composition of the sample. A sample component, which is contained
in high concentration in the sample, has a high partial pressure
in the state of equilibrium in the head space. To obtain unambiguous
results, the sample has to be maintained at a well-defined, relatively
high temperature.
A sampling device for gas chromatographs is known from German Auslegeschrift
No. 1 297 904. Therein, a turntable accommodating the sampling devices
includes a thermostatized liquid bath. The sample vessels are inserted
into the liquid bath from above. The liquid of the liquid bath evaporates.
The turntable, which is rotatable relative to the liquid bath, is
supported on a sealing ledge provided at the edge of the liquid
bath. Furthermore, the liquid bath and the edge of the turntable
accommodating the sample vessels are provided with a covering which
is screwed on at the edge of the liquid bath. The covering is provided
with arcuate openings through which the sample vessels can be inserted
into the turntable. These openings are adapted to be closed by detachable
lids. This arrangement is complicated in construction and manipulation.
German Offenlegungsschrift No. 22 44 260 discloses a device for
preparing a series of sample preparations of physiological liquids
with a transporting disc. Therein the device intended for increasing
the temperature is provided in the area of the transporting disc.
Sample vessels are guided in a holding groove extending along the
circumference of the transporting disc. A heating liquid from a
container is pumped through a heating device into the holding groove
and exits via an overflow back into the container. Thus, the heating
liquid flows around the sample vessels. Temperature sensors are
arranged in the holding groove, by which the heating is controlled.
This is a sampling device for gas chromatographs with a turntable
arranged to be lifted against a needle. Also, a liquid bath is provided
as the thermostatizing means, only the liquid bath is heated and
regulated in circulation. This circulation heater is expensive.
Further, it is difficult to pass such a circulation through a rotatable
turntable arranged to be lifted axially, as it is required in a
sampling device of the above-mentioned type. In addition, when using
a liquid bath the temperature range is limited by the boiling temperature
of the liquid.
In German Offenlegungsschrift No. 28 18 251 an electrically heated
metal block is provided as a thermostatizing means for the sample
vessels. Therein, the metal block is rotatably mounted about a non-rotatable
axle and has a circular array of axial through-bores with the axle
as center. A base plate is non-rotatingly connected to the axle
and closes the axial through-bores towards the bottom.
A closable aperture, allows for the insertion of a sample vessel
into respective axial throughbores aligned with the aperture, is
provided in the base plates such that the sample vessels can be
inserted into the heated metal block by turning it. The axle with
the base plate and the metal block is arranged to be moved in axial
direction such that this axle is axially movable in the direction
towards the needle.
The thermally controlled means, in the form of an electrical heater,
includes an electric heating coil fixed to the metal block and is
thus arranged to rotate therewith. Thus, the heating power in the
form of electrical energy has to be transferred to the heating coil
through sliders, which transference is disadvantageous in operational
efficiency as well as being expensive to construct.
SUMMARY OF THE INVENTION
Accordingly, it is one object of the present invention to simplify,
with regard to the current supply, the electric heating of a rotatable
sampling device by a stationary heating coil.
This object is achieved, at least in part, by providing a heating
jacket operative as an electric heater which is non-rotatingly connected
to a housing but which tightly surrounds and is in material contact
with a rotatable metal block.
Other objects and advantages will become apparent to those skilled
in the art from the following detailed description read in conjunction
with the appended claims and the attached drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
An embodiment of the present invention is described hereinafter
in greater detail with reference to the accompanying drawing, not
drawn to scale, and in which:
FIG. 1 is a perspective view of a heating jacket embodying the
principles of the present invention;
FIG. 2 is a cross-sectional view of a sampling incorporating the
heating jacket shown in FIG. 1;
FIG. 3 is a sectional view taken along the line 3--3 of FIG. 2;
and
FIG. 4 is a partial sectional view of the sampling device shown
in FIG. 2 as viewed from the direction represented by the arrow
designated by X.
DETAILED DESCRIPTION OF THE INVENTION
A sample carrier, generally indicated at 10, in the drawing, includes
as a thermally controlled means, a metal block 12 adapted to be
heated by an electrical heater 14. The metal block 12 is rigid affixed
to a rotatable shaft 16 by, for example, two transverse pins, 62
and 72, and includes therein a circular array of axial throughbores
18. The shaft 16 is rotatably mounted in a sleeve 74 and serves
as the axis for the circular array of axial throughbores 18.
A housing 20 is affixed to a flange 75 of the sleeve 74 by, for
example, screws. The housing 20 includes two interconnected cup-shaped
housing parts, 21 and 23, one housing part 23 being positioned within
the other housing part 21. The housing 20 also includes a cover
25 and a disc 27, the disc 27 is provided with an annular ledge
26 which extends upwardly therefrom. In operation, the ledge 26
engages a radially annular slot 29 of the metal block 12 and supports
the sample vessels inserted into the axial throughbores 18 in position.
The throughbores 18 containing the sample vessels are charged through
an aperture 22 in the cup-shaped housing part 23, through which
aperture 22 a respective sample vessel can be inserted into an axial
throughbore 18 aligned with the aperture 22.
Upon rotating the shaft 16 the metal block 12 is rotated relative
to the housing 20 such that the sample vessels are lifted and brought
into position through inclined surfaces 28 provided on the annular
ledge 26. The cover 25 and the cup-shaped housing part 21 include
openings which are aligned to define an aperture 76 for the passage
of a needle.
The heater jacket 14 includes an electric heating coil 30 which
is sandwiched between two silicone mats 31. The jacket 14 cylindrically
surrounds the metal block 12 and is in thermal communication therewith
via the inner silicone mat 31. The inner side of the cylindric heating
coil 30 proximate the metal block 12 is preferably provided with
a layer 32 of material having minimal friction resistance, such
as, for example, polytetrofluroethelene (PTFE). The heater 14 tightly
engages, as is in material contact with the metal block 12. Hence
when the metal block 12 is rotated about the shaft 16 relative to
the heater 14 the PTFE layer 32 reduces the frictional forces therebetween
while nevertheless maintaining a thermal transfer relation between
the coil 30 and the metal block 12.
The silicone mats 31 with the heating coil 30 therebetween is placed
around the metal block 12. Preferably, this jacket 14 is secured
about the metal block 12 by a metal strap 3 which strap can be vulcanized
thereonto at their ends thereof to form a plurality of longitudinal
slots. Each of the metal straps 3 includes three sets of brackets
4 bent at a right angle with respect to the surface of the cylinder.
That is, the brackets 4 extend radially outwardly from the jacket
14. In the preferred embodiment bow springs 5 are provided to engage
recesses in the brackets 4 at two opposing brackets each and thereby
stretch the heating jacket 14 about the metal block 12. The jacket
is also provided with an elongated anti-rotating means 6 extending
outwardly at a right angle. The means 6 is preferably additionally
arranged on any one of the straps 3 and secures the heating jacket
14 against rotation relative to the housing 20 by engaging a longitudinal
groove 33 formed in the fixed cup-shaped part 23 of the housing
20.
The heating coil 30 is supplied with power through a current supply
7 which, preferably, includes a fire safety fuse 8. The heating
power is controlled and adjusted through a temperature regulator
9.
The present invention has been described herein by means of an
exemplary embodiment. Other arrangements and configurations may
be made by those skilled in the art which do not depart from the
spirit and scope of this invention. Hence, the present invention
is deemed limited only by the appended claims and the reasonable
interpretation thereof.
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