Sensor syringe

A sensor syringe or hollow needle arrangement for the automatic withdrawal of a liquid sample from a liquid contained within a vessel. A duct is enclosed in a sheath or jacket-like manner by a light conductor possessing an inlet for an optical source and an outlet leading to an optical detector. During sample withdrawal there is utilized the change in the reflection behavior of the lower end of the light conductor upon its immersion in the liquid in order to control sample withdrawal.

BACKGROUND OF THE INVENTION 
The present invention relates to a new and improved construction of a 
sensor syringe or hollow tubular needle arrangement for the automatic 
withdrawal of a sample from a liquid contained within a vessel or the like 
and which automatically adjusts its position with respect to the unknown 
liquid surface. 
If it is necessary to withdraw numerous liquid samples with consistent 
accuracy, or whenever access to the sample removal site is difficult, the 
withdrawal of the sample advantageously is carried out by an automatic 
mechanism. Also in those fields of application where manual sample removal 
would endanger the operating personnel due to radiation or chemical 
effects, it is absolutely necessary that the sample be withdrawn 
automatically. 
Apart from reliability in operation there is also imposed upon a sensor 
syringe the requirement that the liquid samples are not altered, for 
instance due to electrical effects, and that the syringe itself not be 
impaired as to its operational integrity by the liquid sample. 
With the aim of fulfilling these requirements there have been employed 
sensor syringes which detect the position of the surface of the liquid by 
virtue of changes in a measured physical parameter, and through the use of 
a suction device withdraw a quantity of sample at a certain immersion 
depth. 
Thus, in French Pat. No. 7,425,840 there has been disclosed a sensor 
syringe which indicates the liquid surface by virtue of pressure 
fluctuations or changes of a gas flow. A pipe or tube extends parallel to 
a sample duct or channel, the opening of the tube being arranged in spaced 
relationship with respect to the opening of the sample duct. The pressure 
of the gas flowing through the tube varies upon immersion of the tube 
opening into the liquid. This pressure fluctuation is detected by a 
measuring device and predicated upon the measurement result there is 
controlled sample removal. 
This sensor syringe and the required structural expenditure of equipment 
needed for the measurement, regulation and storage of the gas necessitates 
a rather voluminous piece of equipment which cannot be constructed to have 
an advantageous small dimensional design. A further drawback resides in 
the undesired expenditure in work needed for refilling or exchanging the 
gas container. 
Additionally, there are already known in this technology sensor syringes or 
duct arrangements wherein there are employed capacitances and inductances 
as well as changes thereof upon immersion into the liquid sample for the 
purpose of controlling sample removal. Also with these techniques the 
desired miniaturisation of the sensor syringe cannot be accomplished, and 
additionally there is demanded a disadvantageous coupling of the sensor 
electronic system with the sensor zone. 
SUMMARY OF THE INVENTION 
Therefore, with the foregoing in mind it is a primary object of the present 
invention to provide a new and improved construction of a sensor syringe 
or the like for the withdrawal of samples in a manner not associated with 
the aforementioned drawbacks and limitations of the prior art proposals. 
Another and more specific object of the present invention aims at providing 
a new and improved construction of sensor syringe of the previously 
mentioned type which can be constructed at increased economies and with a 
compact small design. 
A further significant object of the present invention aims at providing a 
new and improved construction of a sensor syringe arrangement which 
enables an automatic and reliable sample removal even when encountering 
inclined and difficultly accessible liquid surfaces, such as arise in 
centrifuges. 
Now in order to implement these and still further objects of the invention, 
which will become more readily apparent as the description proceeds, the 
sensor syringe arrangement of the present development is manifested by the 
features that there is provided a hollow, light-conducting rod which 
surrounds in a sheath or jacket-like fashion the channel or duct of the 
sensor syringe. The hollow light-conducting rod utilises the phenomenon 
that during each sample withdrawal or removal there results a change in 
the reflection behaviour at the lower rod end upon immersion into the 
liquid sample, in order to thereby control sample withdrawal. 
The sensor syringe of the present development has the further advantage 
that the sensor electronic system is decoupled from the sensor zone by 
virtue of the optical signal transmission which is employed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Describing now the drawings, in FIG. 1 there is shown in sectional view an 
exemplary embodiment of sensor syringe 10 and also schematically a light 
source 1, a regulator 2, a suction device 3, a drive 4, a light detector 5 
as well as a duct or channel 11 shown in side view. The light source 1 
transmits in conventional manner its emitted light to the branch 24 of a 
light-conducting rod 12. The branch 24 is formed by splitting the 
light-conducting rod 12 at its upper region of the showing of FIG. 1. 
Without any appreciable intensity losses and irrespective of the curvature 
of the rod 12 the light, generally indicated by the arrows 13, is 
conducted to the rod surface or end 17 where, depending upon the optical 
density or refractive index of the surrounding medium, it either departs 
out of the light-conducting rod 12 or is returned by reflection. By virtue 
of the mentioned splitting of the rod 12 there is formed, apart from the 
branch 24 a further rod branch 25 having a light exit location 25' 
operatively associated with a conventional light detector 5. This light 
detector 5 measures the intensity of the light which departs from the 
second branch 25 of the split rod 12. Detector 5 delivers the measured 
value in the form of an electrical signal by means of a line 26 to the 
regulator 2 which acts by means of a line or conductor 21 upon the drive 
or drive means 4 to move such selectively in either of both movement 
directions 28 and 29, and further, the detector 5 controls or regulates 
the suction device 3, for example a pump, by means of the line or 
conductor 23. 
The sensor syringe 10 is secured by means of a holder 32 or equivalent 
structure at the drive or drive means 4 which can be displaced in both 
directions 28 and 29 along a rail or guide 31. The liquid sample 9 having 
the liquid surface 7 is contained within the schematically illustrated 
vessel or container 33 which, for instance, can be a whole blood pipette 
or small tube or a container of a centrifuge. 
The end region or surface 17 of the light-conducting rod 12 is preferably 
conical in configuration and inclined at approximately 45.degree. with 
respect to the lengthwise axis of the duct or channel 11. Thus, the 
conical surface may be considered to possess, by way of example, a half 
aperture angle of about 45.degree.. However, the lower end of the light 
conductor, i.e. the light-conducting rod 12 can be spherical, prismatic or 
wedge-shape in configuration. The duct tip 19 protrudes past the rod 
surface 17 and is provided at its front end with a duct opening 20. 
FIG. 2 illustrates the conditions which prevail when the sensor syringe 10 
is not immersed in the liquid 9. The light beam 13 which is transmitted 
from the light source 1 (FIG. 1) to the light-conducting rod 12 is 
conducted in conventional manner up to the rod surface or end 17. Since 
the surrounding air has a smaller refractive index than the 
light-conducting rod 12 the light beam 13 is reflected at the surface 17 
and conducted back in the direction 14 towards the detector 5. 
On the other hand, FIG. 3 shows the conditions prevailing when the sensor 
syringe 10 is immersed in the liquid sample. Now the rod surface 17 is 
immersed in the liquid 9 and consequently surrounded by a medium having a 
refractive index similar to that of the light-conducting rod 12. The light 
beam 13 which impinges at the rod surface 17 and delivered by the light 
source 1 is refracted and escapes into the liquid 9, as shown in FIG. 3. 
Consequently, the detector 5 measures no or only very little light when 
the rod surface 17 is immersed in the liquid sample or liquid 9. 
While there are shown and described present preferred embodiments of the 
invention, it is to be distinctly understood that the invention is not 
limited thereto, but may be otherwise variously embodied and practiced 
within the scope of the following claims. ACCORDINGLY,