Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
6~
This invention relates to apparatus for determining the
freezing points of liquids, particularly of liquids lying on
or taken from roadways, of the type having a chilling device
and a thermometer probe for measuring the temperature of the
liquid.
If, during the chilling of a liquid, its temperature is
continuously measured and plotted against the time, the tem-
perature curve (so-called solidification or freezing-point
curve) first slopes downward, then rises rapidly at a certain
pointr thereafter runs more or less horizontally for a time,
and finally drops off again. This phenomenon is described, for
example, in Der Chemikant, by Dr. Fritz Merten, Gebr. Janeke-
Verlag, Hanover, 1966, p. 77.
The chilling of the liquid to be examined and the plot-
lS ting of the temperature curve, e.g., with the aid of record-
ing apparatus, is no problem in the laboratory. It would nat
urally be possible to take samples of liquid found on a road-
way to a laboratory and determine the freezing point of the
samples there. However, until now there has been no simple
apparatus for convenient and reliable on-the-spot determina-
tion of the freezing point of liquids found on a roadway,
e.g., r~inwater or melted snow in which a thawing agent such
as salt is dissolved.
It is an object of this invention to provide improved
2S apparatus by means of which the freezing point of liquid ly-
ing on or taken from a roadway can be reliably, simply, and
quickly determined on the spot.
To this end, in the apparatus according to the present
invention, of the type initially mentioned, a plate which is
a good conductor of heat is heat-conductively connected to
the chilling device, there is a recess in the central area of
the plate, the thermometer probe is embedded in the recess by
means of a heat-insulating material, and the thermometer
probe is connected to an evaluating device for determining
and displaying the freezing point of the liquid as a func-
tion of the temperature gradient.
-- 2 --
The apparatus of the invention is suitable either for
monitoring the freezing point of liquid on the roadway at
one specific loca~ion or for mobile duty so that measure-
ments can be carried out at any desired location.
Preferred embodiments of the invention will now be
described in detail with reference to the accompanying draw-
ings, in which:
Figure 1 is a graph showing in terms of time the temper-
ature curve of a liquid chilled beyond its freezing or so-
lidification point,
Figure 2 is a diagrammatic representation of the meas-
uring arrangement in one embodiment of the invention by means
of which the temperature curve of Figure 1 was recorded,
Figure 3 is a top plan view of part of the chilling
arrangment in an embodiment of the invention,
Figure 4 is a section taken on the line IV-IV of
Figure 3,
Figure 5 is a block diagram of another embodiment of
the invention,
Figure 6 is a graph showing the sampling process of
the temperature curve,
~igure 7 is a simplified representation of the storage
locacions of three memories of the microprocessor in the
apparatus of Figure 5,
Figure 8 is a flow chart according to which the appa-
ratus of Figure S operates r and
Figure 9 is a further flow chart.
In the graph of Figure 11 the time in seconds is plot-
ted on the x-axis and the temperature in degrees Celsius on
the y-axis. Broken~line curve 1 shows the shape of the tem
perature curve of a pure liquid, e.g., water, during the
chilling process. As cooling increases, the temperature
drops until it reaches a point A, whereupon there is a
sudden rise in temperature to point B, following which the
temperature remains constant for a certain time, tnen drops
again. The marked drop in the temperature of the liquid be-
- 3
low the solidification temperature is called undercooling~
This is a lag in solidification attributable to delayed
crystallization when no seed crystals are present. The so-
lidification then remains totally constant for a short pe
S riod of time only when the chilled liquid is completely
pure. If the liquid is contaminated, the temperature curve
takes the shape shown by solid-line curve 2~
Figure 2 illustrates a basic measuring arrangement by
means of which the temperature of a liquid 3, which wets the
upper surface 4 of a chilling arrangement 5, can be visually
indicated. Chilling arrangement 5 comprises a metallic
cooling plate 6~ having in the central area thereof a recess
7 in which a quick-response thermometer probe 8 is embedded,
and two series-connected Peltier elements 9 and 10 which can
be connected to a voltage source 12 via a switch 11. Ele-
ments 9 and 10 are in heat-conductive contact with cooling
plate 6, and when switch 11 is closed, a current flows through
Peltier elements 9 and 10 in a direction such that plate 6
is chilled. Thermometer probe 8, preferably an NTC resistor
is embedded in a heat-insulating material 13 and is thus
heat~insulated relative to the refrigerating zone of cooling
plate 6 so that probe 8 really responds only to the temper-
ature of the liquid situated above probe 8 and not to the
temperature of the mentioned refrigerating zone.
Thermometer probe 8 is connectible across a resistor
14 and a further switch 15 to a second voltage source 16. The
~oltage drop occurring at probe 8 is dependent upon the tem-
perature of the liquid situated above probe 8 and is supplied
to the vertical deflector plates of a phosphorescent oscillo-
graph 17, indicated symbolically in the drawing, The hori~on-
tal deflector plates of oscillograph 17 are connected to a
sweep circuit ~not shown) which deflects the luminous spot
once from left to right during each chilling operation,
i.e., during a period of from 30 to 60 seconds, so that curve
2, for example, appears on the screen of oscillograph 17.
3~fi~
Figure 3 is a top plan view of the chilling arrangement
in an embodiment of the invention, while ~igure 4 is a sec-
tion taken on the line IV-IV of Figure 3. The chilling de-
vice proper comprises cooling plate 6, made of a metaI which
is a good conductor of heat, e.g., copper, and the two Peltier
elements 9 and 10. The faces of elements 9 and 10 which heat
up during their operation rest against a cooling block 18,
also of a metal which is a good conductor of heat, e.g.,
copper. Cooling block 18 absorbs the heat withdrawn from the
liquid and the dissipated heat of Peltier elements 9 and 10.
The faces of elements 9 and 10 which are cooled during their
operation rest against cooling plate 6.
In order to ensure good heat transmission between the
lower faces of Peltier elements 9 and 10 and cooling block
18, and between the upper faces of those elements and
cooling plate 6, elements 9 and 10 are clamped between plate
6 and block 18 by means of two screws 19 securing plate 6
to block 18. In order to prevent the formation of heat
bridges, screws 19 are made of plastic. Thermometer probe
8 is embedded in recess 7 by means of heat-insulating plas-
tic material 13 in such a way as to be protected from mois-
ture, and CO that the temperature-sensitive portion of probe
8 is situated close to the surface of the plastic material 13,
thereby ensuring that this portion responds as quickly as
possible to the temperature of the liquid above it~
As may be seen from Figure 3, Peltier elements 9 and 10
are connected in series, and both the other two connections
20 of the Peltier elements and the two connections 21 of
thermometer probe 8 exit laterally. The space between the
plane defined by the upper surface 4 of cooling plate 6 and
the upper surface of cooling block 18 is filled with a heat-
insulating plastic material 22 so that heat is withdrawn by
Peltier elements 9 and 10 only from cooling plate 6 insofar
as possible.
When the chilling arrangement illustrated in Figures 3
and 4 is intended for stationary use~ it will be countersunk
3~
~ s - :
in the roadway so that upper surface 4 of cooling plate 6
is flush with the road surface and as horizontal as possible.
The chilling arrangement is then connected by a four-wire
cable to an evaluating device, to be described below, by
S means of which the freezing point of the liquid on cooling
plate 6, hence on the roadway, can be determined. The heat
withdrawn from the liquid, and the dissipated heat of Peltier
elements 9 and 10, passes into the ground via cooling block 18.
When the chilling arrangement illustrated in Figures 3
and 4 is intended for mobile duty, it will be mounted on a
monitoring vehicle in such a way ~hat the upper surface 4 of
cooling plate 6 is as horizontal as possible and that cooling
block 18 is in close, heat-conductive contact with, for
instance, the chassis of the vehicle. In order to find out
the temperature at which a mixture of salt, mud, and liquid
on the road will freeze, a small amount of this mixture is
taken up with a pipette or a spoon and placed on cooling
plate 6 so that the heat-insulated zone, i.e., the plastic
material 13, in the central area of plate 6, and at least
the marginal region around central recess 7, are covered
by the mixture. Preferably, the mixture is taken up from
the roa~ay with a blotter, and t~e saturate~ b'otter is
then laid on cooling plate 6.
In both stationary and mobile use of the chilling
arrangement, the temperature variation during the chilling
process of the portion of test liquid situated on plastic
material 13 is ascertained by means of thermometer probe 8
and transmitted to the evaluating device now to be described
with reference to Figure 5.
Instead of the evaluating device shown in Figure 2,
utilizing a long-persistence oscillograph, the evaluating
device illustrated in Figure 5 comprises a constant-current
source 23, an impedance transformer 24, a measuring amplifier
25, an analog-to-digital converter 26, a commercially avail-
able microprocessor 27, e.g., of the 8748 type, and a digital
display 28. Current source 23 is connected in series to ther-
~3~
-- 6 --
mometer probe 8, which is an NTC resistor. The voltage drop
occurrin~ at probe 8, dependent upon the temperature meas-
ured, is supplied to the input of impedance transformer 24.
The latter controls amplifier 25, which amplifies the signal
proportional to the solidification curve to a desired volt-
age so that this voltage can be converted into a digital
signal by A-D converter 26. Via a control line 29, micro-
processor 27 periodically transmits orders to A-D converter
26 to sample the analog signal received from amplifier 25,
convert it to digital values, and introduce it via a data
bus 30 into microprocessor 27 for storage and processing of
such digital signals. The data introduced into micro-
processor 27 are processed there in a manner to be described
below, and the result is visually indicated by means of
diqital display 28, from which the freezing-point temper-
ature of the liquid on the cooling plate can be read off
directly in degrees Celsius. Via another control line 31, a
relay 32 having a make contact 11', corresponding to switch
11 of the measuring arrangement illustrated in Figure 2, is
periodically energized by microprocessor 27. Each time this
happens, a new chilling operation is initiated inasmuch as
contact 11' connects Peltier elements 9 and 1~ to voltage
source 12.
The mode of operation of the apparatus illustrated in
Figure 5 will now be described with reference to Figures 6
and 7. Figure 6 shows the variation in temperature of the
portion of liquid situated above thermometer probe 8 during
the chilling process. The voltage at the output of measuring
amplifier 25 varies identically. The size of the insulating
zone formed by plastic material 13 and the cooling capacity
of Peltier elements 9 and 10 are such that within 30 to 60
seconds, the amount of liquid in that 20ne is frozen solid.
Microprocessor 27 is so programmed that when a start
button 33 is pressed, the microprocessor energizes relay 32
via control line 31 and thereby initiates the chilling
operation. At the same time, via control line 29, it gives
3~
-- 7 --
A-D converter 26 the order to convert the first measured
value M1 to a digital measurement signal and to supply
this signal to microprocessor 27 itself via data bus 30.
This order is repeated at regular intervals r, e.g,, every
0.2 seconds, during the whole chilling cycle. In this way,
all the measured values (only M1 to M25 being shown in
Figure 6 for the sake of simplicity) are introduced into
microprocessor 27 in the form of digital measurement signals
during the course of a working cycle. After the last digital
measurement signal has been introduced into microprocessor 27,
relay 32 is de-energized and the chilling cycle terminated.
Measured values M1 to M25, represented by small
circles in Figure 6, belong to the solidification curve of
a contaminated liquid mixture such as is formed on the sur-
face of a road or street by water in which a thawing agent,
e.g., salt, is dissolved and which is mixed with impurities.
The measured values represented by small circles in paren-
theses are those obtained when substantially uncontaminated
rainwater is subjected to the chilling process.
Microprocessor 27 contains first, second, and third mem-
ories 34, 35 and 36, respectively. These memories are very
schemati~ally repre~ented in Figure 7. Instead of three mem-
ories, one large memory with three separate storage zones
may be used. First memory 34 comprises at least as many stor-
age locations as are needed to store all the digital measure-
ment signals, corresponding here to measured values M1 to
M25 . All the digital measurement signals supplied to micro-
processor 27 via data bus 30 during a chilling cycle are
stored in memory 34. For example, if a chilling cycle lasts
50 seconds and the sampling intervals are 0.2 seconds, a to
tal of 250 measured values are stored in memory 34. The rel-
atively short sampling intervals 7~ are necessary in order
to be sure that no jumps of temperature are missed.
Aft~r the second measured value has been fed into mem-
ory 34, the difference between the first and second rneasured
values is determined and compared with a predetermined tem-
~ - 8 -
perature difference x. The result of this comparison, i.e.,
whether the difference is greater ~han x or not, is stored
in the first storage location of second memory 35, which may
be called a marker memory, binary 1 meaning "yes" and binary
O meaning "nol', for example. In the same way, the difference
is determined between each further measured value fed into
memory 34 and the value introduced immediately before, this
difference is compared with the quantity x, and the result
is introduced into memory 35~ Upon completion of a chilling
cycle, all results o~ the comparisons, i.e., the answers to
whether the difference between a preceding measured value
Mn and a directly following measured value Mn~1 is greater
than the quantity x or not, are stored in second memory 35.
The answers shown in parentheses in memory 35 in Figure 7
apply to the solidification curve for which the measured
values are shown as (o) in Figure 6. The end of the chilling
cycle is fixed by a time-monitoring counter (not shown) which
counts the number of orders given to A-D converter 26 and
stops the chilling process by causiny relay 32 to be de-ener-
gized when a pre-settable count is reached--in the simplified
case described above, for example , 25.
At the end of the chilling operation, the actual eval-
uation of measured values M1 to M25 stored in first mem-
ory 34 is begun.
The flow chart in Figure 8 shows the mode of operation
o the apparatus of Figure 5 for reading in and storing the
measured values in first memory 34 and for marking certain
such values. After start button 33 has been pressed~ ini-
tialization takes place, i.e., A-D converter 26 receives the
first order to sample the first measured value M1 and to
convert the analog val~e into a digital value which is then
supplied to microprocessor 27 via data bus 30 and stored in
first memory 34, the time-monitoring counter (not shown) is
set to its starting position, the quantity x is set, relay 32
is energized for initiating the chilling process, and after
time r has elapsed a second order is given to A-D converter
-
- 9 -
26 to sample the second measured value ~2~
After initialization, the second measured value M2 on
the data bus is introduced into memory 34. The difference
between the first and second measured values is then ascer-
tained. At a decision point 37, it is decided whether thisdifference is greater than x or not. If it i5 not, the fact
is retained in second memory 35, which marks the storage
location of value M2. After marking of the respective
storage location, or if it is decided at the decision point
that the difference is greater than x, the time-monitoring
counter is indexed by one step/ and it is checked at a
further decision point 38 whether the counter has reached
its set point or not. If it has not, a new order is given
to A-D converter 26 after time ~r has elapsed, whereby the
third measured value M3 is put'on data bus 30. The same
procedure as described abov,e is then repeated over and over'
until the count of the time-monitoring counter has reached
its set point. When this happens, the chilling process is
terminated in that relay 32 is de-energized, and immediately
thereafter the evaluation of the measured values stored in
first memory 34 and marked by second memory 35 is initiated.
The evaluation operation may be seen from the flow chart
in Figure 9. At a decision point 39, it is checked whether
only "yes" responses are stored in memory 35. If so, this
means that the freezing point of the liquid tested is below
the temperature range examined. For instance, if the chilling
arrangement is designed to chill the liquid to -15C and if
a "yes" is stored at every storage location in memory 35, this
means that the freezing point of the liquid is below -15C.
This fact can be indicated by the flashing of one or more
symbols of display device 28. After such a display, both the
chilling operation and the evaluation of the measured data
are ended.
If it is ascertained at decision point 39 that not only
"yes" responses are stored in memory 35, a search for the
first measured value in the marked storage zone of memory 34 "
is thereby initiated. At a decision point 40, it is checked
- 10 -
whether still other storage locations in first mem-
ory 34 have been marked by second memory 35. If so, the
difference between the previo~s marked value and the sub-
sequent one is ascertained. At a further decision point 41,
it is decided whether this difference is greater than O. The
result of the comparison, "yes" or "no", is stored in third
memory 36. I, is then checked again at decision point 40
whether there are any further marked storage locations. This
procedure continues to be repeated until it is ascertained
at decision point 40 that there are no further marked stor-
age locations. It is thereupon checked at a decision point
42 whether any "no" responses are stored in third memory
36. If not, the display of the first measured value marked
by second memory 35 is initiated. In Figure 6, this first
marked value is the first one, M10, in the substantially
horizontal portion of the solid-line curve and simultane-
ously the freezing point of the liquid tested. Upon display
of the freezing point, both the chilling operation and the,
evaluation are ended.
If it is found at decision point 42 that there is a "no"
stored in third memory 36, it is checked at a further de-
cision point 43 whether still other "no" responses are stored
there. I.f not, the m~asured value marked by this "no" is read
out of first memory 34 and displayed. In the temperature
curve formed by the measured values (o) in Figure 6, the one
marked by the "no" in memory 36 is measured value M13,
which is displayed as the freezing point. This ends the
chilling process and the evaluation.
If it is found at decision point 43 that memory 36 con-
tains further "no" responses, the check continues until no
more such responses are found stored in that memory. Several
"no" responses may be stored in memory 36 if the temperature
does not rise abruptly but gradually after undercooling. The
measured value marked by the last "no" in memory 36 is read
out of memory 34 and displayed as the freezing point. The
chilling process and evaluation are thus endedO
Microprocessor 27 may be programmed to initiate a
.
6~
1 1
chilling operation and effect an evaluation approximately
every 10 minutes.
The flow chart described above with reference to Figure
9 is but one of several possibilites of evaluating the shape
of the solidification curve with the aid of microprocessor
27 and digitally indicating the freezing point.
.
