Method for in-line measurement of product temperature moving on a conveyor during food processing operations

Abstract

1. A method for determining the temperature of a product being transported on a conveyor belt in a cold tunnel, comprising the steps of: - continuously measuring the surface temperature of the product moving on the conveyor belt; - measuring the thickness of the product at the point where the temperature measurement is taken; - performing the following evaluation: a. when the thickness of the product is within a certain range, the temperature measured for said product is considered to be a reliable value; b. when the thickness of the product is outside the range, the last temperature value measured for the product is considered to be a reliable value in accordance with paragraph a) above; and c. after a determined period of time during which the measured thickness is outside the range, it is concluded that there is no product on the conveyor belt and the temperature measurement is no longer taken into account.

Description

[Technical field]

[0001] The present invention relates to the field of the food industry, and more particularly to a method for measuring the temperature of products moving on a conveyor during food processing operations, in particular deep freezing operations. [Background technology]

[0002] In food production lines, it is often crucial to know the temperature of the product being processed. - in cooking operations it is therefore important to know the temperature reached by the product so that cooking can be stopped when the product is considered sufficiently cooked; Also in the case of cooling or freezing processes, it is important to know the temperature reached by the product in order to adjust the operating parameters, for example to avoid an insufficiently frozen product, and also to avoid obtaining an excessively cold product, which would result in unnecessarily high energy consumption.

[0003] It is common practice in the industry to take substantially random samples of product from the line and manually measure the temperature of the product.

[0004] While this practice works, of course, it is not a continuous measurement and requires cost because it assumes the allocation of a person to dedicate a portion of their time to this task.

[0005] Furthermore, it is known in the industry to use pyrometers to continuously measure the surface temperature of products moving on a conveyor. This method has provided useful and advantageous responses in this field. In fact, it has been observed that this measurement of surface temperature is very often an excellent indication of the average temperature of the product, which is the temperature we are primarily interested in. In addition to this, by performing the measurement continuously, the product line operator is always informed of the proper operation of his process and he can program alarms that will, in some cases, warn him about drifts in real time. On the other hand, it must be noted that empty parts of the conveyor that do not have products will give temperature measurements that can distort the overall evaluation. Therefore, a simple measurement of the surface temperature of products passing on a conveyor using a pyrometer is not sufficient. Too many erroneous measurements (conveyor temperature measurements) will cause this measurement to lose all value. Summary of the Invention [Problem to be solved by the invention]

[0006] It is therefore very apparent that it would be highly advantageous for the art to have a way to measure the temperature of the product being processed in-line and at low cost. This measurement must be performed continuously and must not be contaminated by the temperature of the conveyor or by any other interference. [Means for solving the problem]

[0007] As will be observed in more detail below, the invention proposes an in-line metrology method implementing the following characteristics: - a temperature measuring system, for example a pyrometer, fixed in space at a position near the conveyor (above or to the side of it), is implemented to carry out a continuous measurement of the surface temperature of the products moving therewith. In many applications, a non-contact temperature measuring system, such as a pyrometer or any other non-contact temperature measuring system, will be preferred. However, when contact with the products moving on the conveyor is possible, contact thermometers that scrape the top surface of the products can also be used. In this case, systems using Pt100, Pt1000 technology, other resistance probes, all types of thermocouples and optical fibers can be chosen. Thus, and without distinction, in the cases where a pyrometer is used, it provides a reading of the surface temperature of the conveyor belt and of the products present on this conveyor belt, the measurement being carried out at a fixed point opposite the pyrometer, - a laser distance measurement is also implemented (laser or another distance measurement system based on another principle such as ultrasound, visible light or possibly physical sensors), which measures the thickness of the product at the very place where the temperature measurement is performed by a pyrometer (or other system); The computer then: - when the thickness of the product is between the lower and upper limits, the system assumes that the temperature measured by the pyrometer is the correct temperature of the product; - When the thickness of the product is above the upper limit (passage of a foreign object in the measuring field) or, in some cases, below the lower limit (empty conveyor without any product), the system considers and stores in memory the last product temperature value measured by the pyrometer (and considered by the system as a reliable value according to the above paragraph), and this value is then conditionally considered as a good indication of the temperature of the product whose measured thickness is outside the limits. After a predefined period of time (usually a few seconds to a few minutes) during which the measured thickness is outside said range, the system concludes that there is no product present on the conveyor and no longer considers the temperature measurement provided by the pyrometer (or any other system), but the measurement value as a "default" value. This default value is determined by the user. This value does not lead to confusion with the actual measured temperature, and it is usually determined outside the expected measuring range. Thus, in the case of measuring the temperature of a frozen product, whose temperature normally varies from -15 to -25°C, this default value is determined, for example, at +100°C. When the system reports +100°C, it becomes clear to the user that the measured temperature is not +100°C, and this is the case of the absence of a product. It is also possible to advantageously add other calculations that allow further measurement improvements. Thus, it is possible to add a calculation that generates a sliding average of the presence of products on the conveyor. The following evaluation is being carried out.

[0008] This is, for example, an average calculated over 1-10 minutes. Values ​​considered are 0 and 1. Multiple 0's and 1's can generate an average.

[0009] For example, if 2 minutes were observed with the product (1) and 8 minutes were observed without the product (0), this would give a sliding average of 0.2.

[0010] The average can be calculated in several ways, so as an example, for an average over 10 minutes and at 1 calculation / second: - The measurements are taken once per second over 10 minutes and divided by 600. -The following calculations are performed once per second: New average = (600-1) / 600 * (previous average) + measured value / 600

[0011] Thus, as will be understood with reference to the above, when the thickness measurement is below the lower limit or above the upper limit, the value 0 is considered in the calculation of the average. When the thickness measurement is between the lower and upper limits, the value 1 is considered in the calculation of the average. A lower limit (Average Min) is defined for this average, where the average is calculated continuously. When the average is above the Average Min, the calculations described in the above sections remain unchanged. When the average is below the Average Min, the temperature reading by the pyrometer is not taken into account. As a result, the system considers and stores in memory the last product temperature value measured by the pyrometer, According to another embodiment of the invention, a temperature smoothing calculation can be added. The temperature smoothing is actually a sliding average that can be calculated in several ways. As an example, for smoothing over 3 minutes and at 2 calculations / second: - the measurements are taken 2 times per second over a 3 minute period and divided by 360; -The following calculations are performed 2 times per second: New average = (360-1) / 360 * (previous average) + measured value / 360

[0012] The smoothing factor can be relatively large or relatively small depending on the reactivity and measurement stability desired. The smoothing calculation will be interrupted when the measured value is equal to a predefined temperature and when the product thickness is less than a minimum thickness or greater than a maximum thickness. [Brief description of the drawings]

[0013] [Figure 1] The attached FIG. 1 allows a relatively good visualization of the installation allowing the implementation of the invention, in this case a product 2 moving on a conveyor 1 can be observed, with the presence of a pyrometer 3 and a laser 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Experiments carried out by the applicant under the conditions of the present invention show that: - the temperature measured by the present invention is more reliable than simple and conventional measurements performed by pyrometers alone; The invention also provides further information, the information relating to whether a product is present on the conveyor, - The systems used are certainly more expensive than simple pyrometers, but the quality and reliability of the obtained ("filtered") information is unmatched.

[0015] The present invention therefore relates to a method for determining the temperature of a product being conveyed on a conveyor belt of a cold tunnel, - a temperature measuring system, for example a pyrometer, fixed in space at a position near, above or to the side of the conveyor is implemented, which performs continuous measurements of the surface temperature of the products moving together on the opposite side to the temperature measuring system; a distance measurement system, such as a laser or ultrasonic system, is implemented to measure the thickness of the product whose temperature has been measured in a previous step; - a computer, - When the thickness of the product is between the lower and upper limits, the temperature measured by the temperature measuring system for this product is considered to be a definite value of the product's temperature; - when the thickness of the product is above the upper limit or well below the lower limit, the computer considers and stores in memory the last product temperature value measured by the system and considered by the computer as a reliable value according to the above paragraph, and this value is then considered as a good indication of the temperature of the product whose measured thickness is outside the limits; - after a predefined period of time during which the measured thickness is outside said range, the computer concludes that there is no product present on the conveyor and no longer takes into account the temperature measurements provided by the temperature measurement, but rather considers the measurements as "predefined" values; A computer is provided for performing the evaluation: It is characterized by the implementation of the following means.

Claims

1. A method for determining the temperature of a product (2) being conveyed on a conveyor belt (1) of a cold tunnel, comprising the steps of: a temperature measuring system (3) fixed in space at a position near, above or to the side of said conveyor belt is implemented to carry out continuous measurements of the surface temperature of products moving on said conveyor belt at a position opposite said temperature measuring system, a distance measurement system (4) is implemented to measure the thickness of the product whose temperature has been measured in a previous step; - a computer comprising: a) when the thickness of the product is between a lower limit and an upper limit, the temperature measured for the product by the temperature measurement system is considered to be a reliable value of the temperature of the product; b) when the thickness of the product is above the upper limit or well below the lower limit, the computer considers and stores in memory the last product temperature value measured by the temperature measuring system and considered by the computer as a definite value according to paragraph a) above, and this value is then considered as an indication of the temperature of the product whose measured thickness is outside the range between the upper and lower limits; c) after a determined period of time during which the measured thickness is outside the range, the computer concludes that there is no product present on the conveyor belt and no longer considers the temperature measurements provided by the temperature measurement system, but rather considers the measurements as "default" values; A computer is provided which then performs the evaluation: The method according to claim 1, characterized by implementing the following means:

2. a. a value of 0 is considered in calculating an average when the thickness measurement is below the lower limit or above the upper limit, and a value of 1 is considered in calculating an average when the thickness measurement is between the lower limit and the upper limit, the average being calculated continuously; b. a lower limit (Average Min) is defined for the average and when the average is below Average Min, the temperature reading by the temperature measuring system is not taken into account, and then the computer takes into account and stores in memory the last product temperature value measured by the temperature measuring system; 2. The method of claim 1 further comprising: performing a sliding average of the presence of the products on the conveyor belt.

Images