Apparatus for automated polyelectrolyte measurement

Apparatus for automated polyelectrolyte measurement of liquid process materials including a sample vessel which defines an electrically insulating, cylindrical cavity below a larger-diameter reservoir. Electrodes are located at the ends of the cylindrical cavity and an insulating piston is reciprocated with a predetermined, small clearance within the cavity. The charge displacement is measured between the electrodes. An outlet channel opening at the floor of the cylindrical cavity is connected to an outlet pipe. A rinsing duct with valve control for introducing a rinsing fluid into the reservoir. A controller is connected to an actuator for reciprocating the piston, to a valve in the outlet pipe and to the rinsing valve. After each polyelectrolyte measurement the substance under test is removed from the sample vessel through the outlet channel, rinsing fluid is introduced, and the rinsing fluid is removed through the outlet channel while the piston reciprocates. The reciprocation of the piston provides a pumping action which is used to expel the substance under test and enables effective rinsing and cleaning of the apparatus with no need for manual intervention.

FIELD OF THE INVENTION 
The present invention relates to an apparatus for automated polyelectrolyte 
measurement. 
DESCRIPTION OF THE PRIOR ART 
In the U.S. publication "12th Material ISA Analysis Instr. Symposium, 
Houston, Tex., 1966: Vol. 4, pp 181-198" apparatus of the same kind as 
that of the present invention is described. However, this apparatus has 
been designed not for automated polyelectrolyte measurement but rather as 
a device for purely manual operation. Hence, with the said device samples 
taken for measurement of the polyelectrolyte consumption in a process are 
introduced by hand into a sample vessel and a piston is moved so as to 
generate a streaming potential which is recorded and measured by 
electrodes, a titration operation being carried out at the same time. 
After the measurement has been taken in this way, which is a conventional 
procedure, the piston is withdrawn from the sample vessel and the sample 
is removed. The piston and the sample vessel are then cleaned so as to be 
ready for a subsequent measurement procedure. 
In many cases polyelectrolyte consumption must be monitored in the course 
of an industrial chemical process in order to regulate that process. 
Examples of such processes include the manufacture of paper, the disposal 
of aqueous waste and similar processes in which flocculents, for instance, 
are employed. These processes have always required the continual presence 
of a worker to carry out the necessary measurements, the results of which 
are needed for regulating the process. This sort of purely manual 
measurement has the disadvantages of, on the one hand, being 
labor-intensive and, on the other, of often not making the results of the 
measurement available soon enough to regulate or control the process 
correctly. 
SUMMARY OF THE INVENTION 
The object of the present invention is directed to provide an apparatus by 
means of which polyelectrolyte measurement can be carried out 
automatically in a simple and reproducible way. 
According to the present invention there is provided an apparatus for 
automated polyelectrolyte measurement of a substance comprising a sample 
vessel defining an electrically insulating cylindrical cavity and provided 
with a reservoir of larger diameter than said cylindrical cavity and 
located above and in communication with said cavity, electrodes located 
substantially at the ends of said cylindrical cavity respectively, an 
electrically insulating piston, which defines a predetermined clearance 
with walls defining said cylindrical cavity, an actuating means for 
reciprocating said piston within said cylindrical cavity and a means of 
measuring a charge displacement between said electrodes, and wherein the 
improvement comprises the provision of an outlet arrangement located at 
the bottom of said cylindrical cavity, a first valve for the control of 
fluid through said outlet arrangement, a rinsing duct for the introduction 
of a rinsing fluid into said reservoir, a second valve located in said 
rinsing duct to control the flow of said rinsing fluid through said 
rinsing duct, and a controller which is connected to and can control 
operation of said actuating means, said first valve and said second valve 
so that after a polyelectrolyte measurement has been carried out, the 
substance under test can be expelled from said cylindrical cavity through 
the outlet arrangement and said rinsing fluid can be introduced into said 
reservoir and thence expelled through the outlet arrangement as said 
piston is reciprocated. 
Thus the advantage of the invention is that the movement of the piston, 
which is necessary for the purpose of measurement, is combined with the 
operation of the valve in the outflow arrangement and the positioning of 
the outlet channel so that it opens at the floor of the cylindrical 
section, in such a way as to provide a pumping action which enables 
effective rinsing and cleaning of the apparatus with no need for manual 
intervention. This pumping action further serves to expel the process 
material being tested, which results in an independently controlled, 
automatically operating arrangement. 
It should be noted that the rinsing of an analysis vessel for measurement 
of the conductance of a medium by a piston/cylinder arrangement with 
moving piston is described in German patent Specification DE-AS 25 21 009. 
Here, however, the medium to be measured is itself used as the rinsing 
medium and furthermore it is not drained off through a separate outlet. 
Instead, the whole arrangement is dipped into the liquid to be tested in 
such a way that the liquid is both drawn in and expelled through an 
annular gap between piston and cylinder at the top of the apparatus. 
To achieve precise regulation it is an advantage for the drive mechanism to 
include a position sensor to monitor the position of the piston. Where the 
piston is reciprocated by a crank mechanism, a suitable instrument is an 
angle indicator that signals the crank rotation. 
In order to clean the apparatus it advantageous to couple an ultrasonic 
oscillator mechanically to the sample vessel, so that during the rinsing 
process the rinsing fluid can be set into oscillation by way of the sample 
vessel. In this way particles adhering to the surfaces of the vessel are 
removed primarily by a cavitation effect. 
Thus, it is advantageous for the floor of the sample vessel to consist of 
metal, which provides a zero-loss coupling of the ultrasonic oscillations 
to the liquid, as opposed to coupling by way of insulating surfaces made 
of plastic which would involve an excessive attenuation. 
Impedance-matching is preferably achieved by constructing the portion of 
the vessel defining the floor with a flared cross-section. 
The sample vessel preferably comprises an outer vessel made of metal which 
defines a substantially cylindrical interior cavity into which is 
shrink-fitted an insulating block. The insulating block, which preferably 
consists of polytetrafluoroethylene, defines an open bore with an upper 
section forming the reservoir, a graduated transition portion, and a lower 
cylindrical section defining said cavity. In the bottom surface of the 
insulating block a channel is cut which, when closed off by the flat floor 
of the outer vessel, forms a duct. This arrangement makes it possible to 
empty the sample vessel completely so that there is hardly any residual 
rinsing fluid can remain to contaminate a subsequent sample. 
It is particularly advantageous for the apparatus to incorporate a sampling 
device comprising a pumping means connected on its input side to a suction 
pipe, through which the process material to be tested can be sucked in. On 
its output side the pumping means communicates through a pressure pipe 
with a first input of a valve, by means of which a sampling container can 
be connected either with the pressure pipe or with a source of compressed 
gas. The other end of the sampling tube is connected by way of a further 
valve either to a source of the process substance to be tested or to the 
reservoir. In operation, the process substance is allowed to flow through 
the sampling tube so that the latter is constantly filled with a sample 
representative of the momentary situation. Whenever it is desired to 
withdraw a sample from the tube and subsequently determine its 
polyelectrolyte content, the valves are switched so that the compressed 
gas impinges on the contents of the sampling tube and pushes them into the 
reservoir section. This arrangement ensures that the amount of liquid in 
the sample is reproducible and simultaneously avoids the risk of 
contaminating the sample.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
In the embodiment of the invention shown in FIG. 1, a sample vessel 30 is 
provided, which comprises an inner insulating block 37 and an outer metal 
part consisting of an outer wall 38 and a floor 39. Preferably, the block 
37 is made from polytetrafluoroethylene and the vessel 30 is made from V2A 
grade stainless steel, as defined in the standard German "Stahl 
Schlussel". 
A bore formed substantially in the middle of the insulating block 37 
defines a cylindrical cavity 31, the upper end of which is continuous with 
a larger-diameter, also cylindrical reservoir 32. At the upper end of the 
cylindrical cavity 31 there is an annular indentation 36, within which is 
fixed an annular first electrode 34 made of a non-corroding metal. The 
floor 39 closes off the cylindrical cavity 31 at its lower end and forms a 
second electrode 35 at this site. 
The electrodes 34 and 35 are connected to the inputs of an amplifier 56, 
the output of which is connected to an input of a control mechanism 22. 
The floor 39 is integral with a flared section 40, to the end of which are 
attached two annular piezo oscillators 44,45 which are stacked one above 
the other and pressed against the floor by means of a screw bolt 48 and a 
washer 47. Between the piezo rings 44 and 45 is inserted an electrode 46. 
The arrangement is such that the outer annular surfaces of the piezo rings 
44, 45 are in electrical contact with one another by way of the bolt 48, 
so that the piezo rings 44, 45 are electrically in parallel and 
mechanically in series. They are controlled electrically by way of the 
electrode 46 and the metal parts 39/40, 47 and 48, by an ultrasound 
generator 54 the output of which is passed through a driver amplifier 55. 
The whole arrangement preferably includes feedback so that the oscillation 
frequency is automatically set to a value that is optimized on the basis 
of all the electrical and mechanical components. In addition, the flared 
cross-sectional shape of the section 40 assists in the prevention of 
excessive attenuation. 
In the bottom surface of the insulating block 37 is cut a radial channel 41 
to provide a duct with a part circular cross-section, resembling that of a 
highway tunnel, formed by the walls of the channel and the floor 39. Where 
the outer end of the channel 41 meets the outer wall 38 there is a hole in 
the latter adjoining a connection piece 42. To the connection piece 42 is 
attached a conduit leading to a solenoid valve 28, by way of which the 
connection piece 42 is connected to an outlet pipe 29. The solenoid valve 
28 is connected to the controller 22 by way of a control line. 
Inserted into the cylindrical cavity 31 is a piston 33, which is made of an 
electrically insulating material and is dimensioned so that there is a 
very narrow gap of the order of a few tenths of a millimeter between the 
outer surface of the piston 33 and the insulating block 37 defining the 
walls of the cavity 31. The piston 33 has a planar end surface and at its 
opposite end is joined by a shaft 49 to a crank 51 that can be rotated by 
an electrical motor 52. An angle indicator 53 is attached to the crank 51 
to monitor the angle of rotation of the crank 51, which is a measure of 
the vertical position of the piston 33, and to signal it to the controller 
22. The motor 52 can be adjusted by the controller 22 by way of a driver 
amplifier 57, so that the actuation 50 of the piston 33 can be precisely 
regulated. 
There are three inputs to the reservoir section 32. One is a rinsing duct 
26, which can be connected to a container filled with a rinsing fluid, 
such as distilled water, by way of a solenoid valve 27 controlled by the 
controller 22. A titration duct 24 also opens into the reservoir section 
32 and can be connected to a container in which the titration fluid is 
stored by way of a solenoid valve 25 which, again, is controlled by the 
controller 22. Finally, a sample of the liquid to be tested is introduced 
to the sample vessel by a duct 19 that opens into the reservoir section 
32. This introduction of a sample is also carried out under the control of 
the controller 22. 
The operation of the above apparatus will now be described. 
A predetermined amount of sample liquid is introduced into the reservoir 
section 32 by way of the duct 19. The piston 33 is reciprocated by the 
actuating means 50 and the streaming potential so produced is conducted to 
the controller 22 by way of the electrodes 34, 35 and the amplifier 56. 
The controller 22 processes the data and indicates or records the measured 
value by way of a measuring device 58 or makes the measured value 
available as a control signal to other parts of the system (not shown). At 
the same time, titration is performed by way of the duct 24. 
After the measurement has been completed, the valve 28 is opened during 
each down stroke of the piston 33 and closed during each up stroke. As a 
result, all the liquid contained in the vessel is pumped into the outlet 
pipe 29 and can be discarded. After the pumping has proceeded for a time 
sufficient to ensure that no appreciable quantity of sample remains in the 
vessel, the rinsing valve 27 is opened so that rinsing fluid can enter the 
reservoir section 32 by way of the duct 26. As it does so, the piston 33 
continues to reciprocate, the valve 28 opening and closing in synchrony 
with this motion as described above. At the same time the ultrasound 
generator 54 is turned on by the controller 22, so that ultrasonic 
oscillation is induced in the rinsing fluid. By the cavitation action of 
the ultrasonic oscillation of the fluid, in combination with the flow of 
the rinsing fluid through the chamber while the piston is moving, the 
parts that had been in contact with the sample are thoroughly cleaned. The 
channel 41 is also thoroughly cleaned, because part of its wall is formed 
by the floor 39, which is set into oscillation by the ultrasonically 
oscillating unit 43. 
When the rinsing process has continued for a sufficient time, the inflow of 
rinsing fluid is cut off by closing the valve 27, whereupon the rest of 
the rinsing fluid is pumped out by movement of the piston 33. A new sample 
can be now be introduced. 
In order to take the sample from a process conduit 20, (FIG. 2), or a 
process vessel it is advantageous to use the apparatus that will now be 
described with reference to FIG. 2. This apparatus comprises a suction 
pipe 11, which communicates at one end with the process conduit 20 or with 
a process vessel, and at the other end with the input side of a pump 10. 
On its pressure side, the pump 10 is connected by way of a pressure pipe 
12 to an input a of a first solenoid valve 13, the output b of which is 
attached to one end of a sampling tube 15. The other end of the sampling 
tube 15 is connected to an input b of a second solenoid valve 14, the 
output a of which communicates with the process conduit 20 or a process 
vessel by way of a return pipe 16. With the solenoid valves 13, 14 in the 
states illustrated in the indicated inner diagrams in FIG. 2, liquid is 
continuously drawn from the process conduit 20 and pumped through the 
sampling tube 15, so that the contents of the sampling tube 15 are the 
same as the momentary contents of the process conduit 20. Thus, FIG. 2 
illustrates the filling of the sampling tube 15 with fluid from the 
process conduit 20, when the solenoid valves 13, 14 are in the states 
illustrated in the indicated inner diagrams in FIG. 2. 
A second input c of the first valve 13 is connected to a source of 
compressed gas 18 by way of a compressed-gas pipe 17. A second output c of 
the second valve 14 is connected to the sampling pipe 19, which opens into 
the reservoir section 32. With the solenoid valves 13, 14 in the states 
indicated in the inner diagrams in FIG. 2, it can be seen that the source 
of compressed gas 18 is not connected to the sampling tube 15. 
When the solenoid valves 13, 14 are switched by the controller 22 to the 
states shown in the alternate outer diagrams in FIG. 2, the source of 
compressed gas 18 is connected to the sampling tube 15 so that the 
contents of the sampling tube 15 and residual contents of the valves 13 
and 14 (i.e., any droplet of fluid which may be trapped in the valves) are 
pushed by compressed gas, from the source 18, through the sampling pipe 19 
into the reservoir section 32. The gas is preferably allowed to flow until 
even the remaining droplets have been introduced into the reservoir 
section 32. With this method of sampling an unusually precise, 
reproducible dosage is achieved in the simplest way, with no change in the 
composition of the sample. Furthermore, the sampling device is 
invulnerable to liquids otherwise difficult to handle, containing 
potentially abrasive solids, because all parts are rinsed with an excess 
of process liquid on the one hand and compressed air on the other hand. 
This advantage, especially important in monitoring aqueous waste, is 
complemented by the particularly effective cleansing of the part of the 
apparatus shown in FIG. 1. 
The condition of the surfaces of electrodes 34 and 35 can be monitored by 
means of the initial potential developed, the fluid remaining 
substantially constant because the chemical properties of the fluid remain 
substantially constant such that, when filling the sample vessel 30 with a 
fresh sample, the same initial potential between the electrodes 34 and 35 
can be expected as with the original sample. In another embodiment of the 
invention, a constant standard fluid having known and constant chemical 
properties is introduced into the reservoir section 32 instead of a 
sample, so that the initial potential provides an exact criterion by which 
to evaluate the surface condition of electrodes 34 and 35. As soon as the 
initial potential falls below a critical level, the controller 22 actuates 
a warning system so that the electrodes can be serviced.