Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02349380 2007-05-25
Method and Device for detecting the quantity of a product dissolved in a
solution flow
The invention relates to a method for detecting of the quantity of a product,
preferably in
paste or powder form, dissolved in a solution flow of known flow rate and
unknown,
variable concentration. In addition, the invention relates to a device for
carrying out this
method.
Various meters, for example, impeller wheel meters, oval wheei meters and
turbine
meters, are known in practice for detecti.on of the throughflow quantity or
admetering
quantity of liquid products in a fixed and constant mixture ratio. The
detection of products,
for example of pasty or pulverulent consistency, dissolved in water is
possible by these
meters only if a fixed and constant mixture ratio is maintained. These known
meters are
not suitable for detection of the quantity of a product dissolved in a
solution flow of known
flow rate, but unknown, variable concentration, as the throughflow quantities
measured
by them do not allow any conclusions to be drawn about the concentration of
the
product in the solution flow.
For ascertaining the concentration of a product dissolved in a sotution flow
it is known in
practice to determine the product concentration in the solution flow by means
of
conductivity measurements. For example, there is known from EP 0 229 038 B1 a
method
of dispensing a predetermined quantity of a chemical in a solution of unknown
or variable
concentration, in which the determination of the product concentration in the
solution flow
is carried out by means of conductivity measurements and temperature
measurement.
The product quantity dissolved in the solution flow is subsequently computed
from the
measured conductivity and temperature values in a computer by reference to
known
conductivity characteristic curves for the respective product. The computed
dissolved
product quantities are summated and compared with the maximum product quantity
necessary for the method. As soon as the product quantity ascertained on the
basis of the
conductivity measurements corresponds with the product quantity which may, at
most, be
consumed in the method to be controlled, the solution flow is interrupted.
Thus, it is
possible with this known method to perform quantity detection and admetering
of a product
for a specific purpose of use. The admetering on the basis of comparison of
the
respectively ascertained product quantities with a predetermined maximum
product
quantity and the obligatory temperature measurement for compensation for
temperature-
induced fluctuations in conductivity is very complicated in practice for this
known method
and in each instance can be used only with a defined, integrated specific
control.
CA 02349380 2006-11-10
2
Having regard thereto the invention is based on the technical problem of
providing a
method for detection of the quantity of a product dissolved in a solution flow
of known flow
rate and unknown, variable concentration, which method processes and delivers
the
detected quantity in such a form that the method can be used in variable
manner and
applied to discrete, different control and evaluating units and is usable in
this way. In
addition, the invention has the object of providing a device for carrying out
this method.
The fulfilment of this object in terms of method is characterised by the
following steps:
a) cyclic measurement of the conductivity of the solution;
b) determination of the concentration of the solution by comparison of the
measured conductivity with conductivity/concentration characteristic curves
stored in a data store;
c) calculation of the product quantity from the ascertained product
concentration of the solution and the known flow rate; and
d) summation of the calculated product quantities and generation of a pulse
as soon as a presettable product quantity is reached.
Figure 1 schematically illustrates a method according to one embodiment of the
invention.
The method according to the invention is distinguished by the fact that no
comparison of
the ascertained product quantity with a predetermined product quantity or
product
concentration takes place, but instead thereof a pulse is generated by a pulse
transmitter
per calculated product quantity. The generated pulses are passed on as a pulse
train to
commercially available forms of control and output unit. The pulse train is
comparable with
the result in the case of product detection by means of a normal meter. The
product
quantity necessary to generate a pulse can be freely predetermined in the
computer for
each purpose of use. Through use of this simple pulse transmitter, which
issues the pulses
as a pulse train like a normal meter, the outlay on equipment for performance
of this
method is small.
The measurement and calculation results can be improved, in accordance with a
preferred
embodiment of the invention, if in step b) a temperature compensation is
additionally
included in the calculation, as the conductivity of a product is very strongly
dependent on
temperature and the stored conductivity/concentration characteristic curves
are filed in the
data store only for some selected temperatures. The including of the
temperature
compensation is advantageously carried out in accordance with the following
formula
known from conductometry:
JUN-21-2001 17: 35 ADAMS CASSICA 02349380 2001-04-30 1 613 828 0024 P.06i09
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3
Xg = X,, 1 + aZ5/100 ' (S - 25)]
wherein:
Xd, = conductance value at measured temperature,
X2, ~ conductance value at 25 C,
a25 = temperature coefficient of the product to be measured, and
S = measured temperature.
In an advantageous variant of the method the water throughflow is limited. The
magnitudes influencing the conductance value are thereby minimised. Since
merely the
conductance value, optionally with temperature compensation, is utilised for
determination
of the metered quantity, the accuracy of the determination is thereby
increased.
In order to be able to also ascertain with sufficient accuracy the quantities
of products
without conductivity/concentration charactetistic curves stored in the data
store, in
accordance with a further embodiment of the invention a correction factor for
determination
of the concentration of these products is included in the calculation in
method step b)_
The device for canying out the method according to the invention is
characteris,ed by a
pulse transmitter, which is connected with the computer, for generating count
pulses per
predetermined product quantity and by a pulse counter connected with the pulse
transmitter. Apart from the at least one conductivity measuring cell and the
computer with
permanent data store, in order to provide a device able to be connected to the
most
diverse fomis of control and evaluating unit it is simply necessary in the
case of this device
according to the invention to provide, as a further component, a pulse
transmitter which for
preference is similarly realised within the computer.
Further features and advantages of the invention are evident from the
following description
of the accompanying drawing, in which the sequence of the method according to
the
invention is schematically illustrated.
A solution L of unknown, variable concentration is prepared in metering
apparatus I
starting from a solvent LM, for example water, and a product P of preferably
pasty or
pulveruient consistency. For detection and detemiination of the quantity of
dissolved
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product P contained in the solution flow, which is of known flow rate, the
solution L flows
through a conductivity measuring cell 2 connected by way of a oonductor line 3
with a
computer 4. The computer includes a permanent data store.
Conductivity/concentration
characteristic curves 4a of different products are stored in this permanent
data store.
From the conductance value, which is ascertained by the conductivity measuring
cell 2, of
the product L to be investigated, the concentration of the product P in the
solution L is
determined by reference to the characteristic curve 4a belonging to the
product P
contained in the solution L. The quantity of the product P delivered from the
admetering
apparatus I is calculated from the ascertained concentration on the basis of
the known
flow rate of the solution L The calculated product quantities are summated in
the
computer 4 and communicated by way of a conductor line 5 to a pulse
transmitter 6
whenever a freely presettable product quantity is reached. The pulses 7
generated by the
pulse transmitter 6 per product quantity are counted by a pulse counter 8
connected with
the pulse transmitter 6.
For improvement in the measurement or calcula6on results it is in addition
possible to
supply a temperature T to the computer 4 as a further computation magnitude.
The
temperature compensation connected therewith serves the purpose of taking into
account
the different conductance values of the product at changing temperatures.
Moreover, it is
possible to supply a correction factor K to the computer 4 in order to be able
to ascertain
with sufficient accuracy even the quantities of products P without
characteristic curves
stored in the data store of the computer 4.
Altogether, the method described in the foregoing is thus distinguished by the
fact that it is
universally connectible to the most diverse forms of control and evaluating
unit.
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Reference Numeral Ust:
1 metering apparatus
2 conductivity measuring cell
3 conductor line
4 computer
4a characteristic curve
5 conductor line
6 pulse generator
7 pulse
8 pulse counter
LM solvent
P product
L solution
T temperature compensation
K correction factor
