DE2456663C3 - Device for measuring and evaluating temperature gradients - Google Patents

Description

F =

1.8 T / "C-218

_——. (1)

T is the assumed constant temperature of the product at the critical point ("core temperature") during the period r and ζ is a numerical value assigned to the pH value of the product (1).

In practice, however, the core temperature of the product must not be assumed to be constant, if only because of the heating or cooling process. In this case, the actual sterilization value L of the sterilization process can be determined as the total sum of the partial sterilization values of many successive short heat effects with the duration Δ t and the associated core temperature:

L = Σ 10

1.8 T / 'C-218

(2)

The preservation of the tinned food is guaranteed if L = Fist has been achieved by applying appropriate heat, ie its actual sterilization value L must be monitored to control the sterilization process, ie the value of the sum in equation (2) must be determined. The solution to this task requires knowledge of the temperature Γ as a function of time. If certain simplifying assumptions can be made for this temperature curve, it may be possible to also simplify the calculation of the total value. Such simplifying assumptions are, for example: 7 "is constant; T is a linear function or a logarithmic function of time. In the general case that T is not a simple function of time, it is common to use the graphical method of B ige 1 ο w To do this, the experimental core temperature curve must first be determined. Subsequently, associated temperature values T are taken from the same successive time intervals and the associated partial sterilization values AL are calculated from them. The sterilization value L is obtained by adding the partial sterilization values

_At

The present invention relates to a device for measuring and evaluating temperature gradients during heating and / or cooling processes of goods, especially for determining the sterilization value of canned food.

or in that the partial sterilization values AL are plotted as ordinate values over the associated time abscissa values, the area under the curve then reproducing the sterilization value L.

The procedures with simplifying assumptions regarding the temperature profile are - there such Assumptions are always only approximate - generally subject to errors. All of the above procedures are in common that they are time-consuming and cumbersome to use in practice, and that with calculation errors can easily creep in to cumbersome invoices.

The invention is now based on the object of creating a device with which the measurement and Weighting of measured values and their evaluation can be carried out immediately, and with the in particular, a sterilization value is delivered directly and accurately.

This object is achieved according to the invention by the subject matter of claim 1.

The advantages consist in particular in that no temperature curves have to be absorbed, FER, ₀ ner that no tedious calculation is by a measurer is required so that, for example, the sterilization value is rapidly determined during a sterilization process a lot, and that the reliability of the experimental result substantially increased will. , <_;

Refinements of the invention are to be undertaken in the subclaims.

In an embodiment of the device according to the invention, the code converter can be used as a computer, in particular be designed as an incremental calculator. This calculator forms z. B. in a sterilization process assuming a certain z-value from the supplied 7 values are the powers of ten according to equation (2)

multiplies this by the time f and adds these products over the period f ₂ - ii. The formation of powers of ten from individual temperature values represents a weighting of these temperature values. Computers and incremental computers are known in data processing, so their mode of operation does not need to be explained in more detail. It should only be mentioned that in the present case a constant time unit At is selected, that is, the computer is operated with a

Clock frequency - ^ clocked, so that the factor At in front of the

Sum symbol can be drawn and therefore the computer only has to calculate and add the power of ten in clock terms, while the multiplication with At can then follow later when the sum is available.

For circuit reasons, for example if the electronic components are cheaper or a simpler one Allow assembly, it may be useful to use the code converter as a digital read-only memory to train. Such read-only memories are also known in data processing. At a Sterilization process are z. B. in the temperature range of interest for suitably graded temperatures the powers of ten

10

1.8 TfC-218

calculated and stored digitally in the read-only memory as a set of values. For this purpose, a certain one is used in each case z-value used. At specified time intervals

At, ie with a fixed clock frequency — 7 — is through

digital core temperature readings Γ the assigned power of ten

₁₀ 1.8TfC-2 18

retrieved and totaled in a counter. This retrieval of the stored associated powers of ten can can be referred to as the weighting of the core temperature measured value.

It may be desirable for the food technician as well, except after the completion of the The sterilization value reached also to know its temporal course on this For example, if the sterilization value is greater than the sterilization setpoint value, it can easily be recognized how the sterilization process would have to be appropriately controlled in order to reach the setpoint in the future not to exceed. The course over time can be displayed in that the measured value output device a digital-to-analog converter with a connected analog recorder z. B. a chart recorder is.

Since the use of galvanic lines makes one measurement procedure cumbersome and a number of brings further disadvantages with it, so form galvanic lines especially if they are not permanently laid a foreign body in technical equipment and possibly disrupt movement sequences and are themselves exposed to the risk of destruction. It can therefore be used to replace the galvanic Lines are advantageous if the input part of the measuring device consists of the analog-to-digital converter, the measured value memory connected to this, as well as those required for operation Auxiliary circuits and the associated power supply, separated from the rest of the measuring device in is installed in a heat-insulated and / or moisture-proof vessel. This is the inventive Measuring device divided into two assemblies and the measuring process divided into two periods of time. While the actual measuring time, the temperature sensor is connected to the first assembly, and that of Measured temperature values supplied to it are stored in binary coded form in the measured value memory. Are there Suitable as temperature sensors, temperature measuring resistors or thermocouples. Later to one any point in time after the end of the measuring time f, the first assembly and the second assembly electrically connected, and read out the content of the measured value memory of the first assembly.

In a sterilization process, the temperature value ζ depends on the pH value of the product. For example, the z- value for fruit is 7.5, while for common vegetables it is e.g. B. 3 is. The deviation of the z-value with different contents can therefore be considerable. It may therefore be necessary to use different z-values for the weighting when preserving different filling goods. For this purpose, the code converter can have different measurement value ranges, which can be set by switching or by inserting plug-in cards, for weighting the measurement values. In this way, for example, during a sterilization process, an optional change in the z-value can be carried out. If a computer, in particular an incremental computer, is used as the code converter, the z-value contained in the exponent must be able to be changed in the computer program for the formation of the power of ten. If a digital read-only memory is used as the code converter, the powers of ten must first be used in the temperature range of interest in a sterilization process for suitably graded temperatures

10

1.8 7 / ° C-218

can be calculated for different z-values. The choice of the z-value can then take place in that the

associated set of values is stored on each one plug-in card, and that this is then included in the circuit is used or by switching between the various sets of values using a switch.

The invention is illustrated by the exemplary embodiments shown in the drawings (FIGS. 1 and 2) explained in more detail.

During a time i | is the temperature in a can by means of a temperature sensor 1, the z. B. is a platinum measuring resistor, measured and converted in a compensation circuit into a digital electrical variable Fig. 1. A binary counter 2 controls a variable current source / _v from a reference value Ao for the comparison resistance Rv by connecting binary-weighted current sources and counts at the same time the control steps. In the event of a zero adjustment (Ud-O) , an amplifier 3 serving as a zero indicator switches off the binary counter 2. The counter reading now corresponds to the change in current Δ I _n, ie the temperature difference between the temperature of the measuring resistor Rn of the temperature sensor 1 and a reference temperature freely set at the beginning, eg 70 ° C. The counter reading is passed on to the measured value memory 4 after each adjustment process. The z. B. designed as a shift register measured value memory 4 has, for example, 64 memory locations with 6 bits each. Thus, 64 values can be stored in increments of 1 ° C, for example in a temperature measurement range between 70 ⁰ C and 133 ⁰ C. The maximum measuring time is given by the number of memory locations and the cycle, ie the time interval between two measurements. With a cycle time of one minute, the measurement time is about one hour. If other memories are used, the number of memory locations could be increased to 1000, for example, without any particular difficulty. The power supply of the device happens z. B. by an OV battery. With a readout cycle of one second, a measurement process lasting one hour is read out in one minute.

The binary-coded core temp> eralur measured values, which were measured at intervals of one minute, are called up by a clock generator 5 in the first Hz cycle from the measured value memory 4 and are sent to the read-only memory 6, FIG. 2. This contains a table showing the corresponding Δ L value for each core temperature

ίο assigns the binary coded to the set inputs of a binary settable down counter 7 is located.

The calculation of the L value for the entire measuring cycle of a maximum of 64 measured values by adding up the 4L values is carried out as follows: By pressing a start button 8, a totalizing counter 9 and a control counter 10 are set to zero and the flip-flop 11 is set. This opens the gate 12 for the 1 Hz clock pulses, which pass through a delay element 13 to compensate for the running time of the read-only memory 6 and to ensure that the coded Δ L value is at the set inputs of the down counter 7 before the set pulse arrives. The down counter 7 is set to the Δ L value by the set pulse, after a further delay 14 the set pulse sets the fiipfiop Ϊ5 and thus opens the gate 16 for the 20 kHz counting rate. The down counter 7 now counts from the 4L value to zero. When the count is Mull, the flip-flop 15 is reset by the negative edge of the gate 17 and the gate 16 is closed. All 64 measured values are processed in this way. At the 64th measured value, the control counter 10 tilts the flip-flop 11 back and blocks the gate 12 for the 1 Hz cycle. Dami has finished adding up. All zIL values have been added in totalizer 9. The sum can be read out via a decoder 18 and a display.

For this purpose 2 sheets of drawings

Claims (8)

Patent claims: 1. Device for measuring and evaluating temperature curves during heating and / or cooling processes of goods, in particular for determining the sterilization value of canned food, characterized in that characteristic process temperature values are first obtained digitally at regular time intervals, and that the measured values digitally obtained for a process sequence are initially obtained stored in a measured value memory (4) and read out at a later point in time from the measured value memory and fed to a code converter (read-only memory 6), which assigns weighting values (AL) to the measured values that reflect the effect on the process material at the respective process temperature in the time interval correspond, and that are added up in a summing element (counter 7, 9), and that the sum value (L) is output. 2. Apparatus according to claim 1, characterized in that the stored in the measured value memory (4) Measured values in addition to a digital display and / or a digital-to-analog converter with a connected Analog recorder are supplied. 3. Apparatus according to claim 1 to 2, characterized in that the code converter is a computer, in particular is an incremental calculator. 4. Apparatus according to claim 1 to 2, characterized in that the code converter is a digital one Read-only memory (6) is. 5. Device according to claims 1 to 4, characterized in that the summing element comprises an insertable downward counter (7) to which the weighting values (AL) are successively fed and to which, together with a summing counter ('?), Counting pulses until the count reaches zero are fed. 6. Device according to claims 1 to 5, characterized in that the sum values via a numeric display and / or a digital-to-analog converter with a connected analog recorder can be specified. 7. Device according to claims 1 to 6, characterized in that the input part of the measuring device consists of the analog-digital converter (2, 3), the measured value memory (4) connected to this, as well as the one for operation required auxiliary circuits and the associated power supply, separate from the rest of the part the measuring device is installed in a heat-insulating and / or moisture-proof vessel. 8. The device according to one or more of claims 1 to 7, characterized in that the code converter (6) has different assignments, which can be set by switching or inserting plug-in cards, for forming the weighting values (AL) . It is common in food preservation technology to have the sterilization effect of the action of heat to be marked on the product to be preserved by the so-called sterilization value. To a To ensure the desired reduction in the number of microorganisms, a sterilization setpoint value F can be achieved. This depends on the temperature, the duration of the temperature exposure and the pH value of the Depending on the product. The following applies: