WO2021162644A1

WO2021162644A1 - Environmental control system suitable to operate at high temperatures for transient conditions with controled condensation effect

Info

Publication number: WO2021162644A1
Application number: PCT/SI2020/095001
Authority: WO
Inventors: Samo BEGUŠ; Janko DRNOVŠEK; Domen HUDOKLIN; Franci ŠTRAJHAR; Simon BREZOVNIK; Gaber BEGEŠ
Original assignee: Gorenje,D.O.O.; Hisense(Guangdong)Kitchen & Bath System Co.Ltd,
Priority date: 2020-02-12
Filing date: 2020-02-12
Publication date: 2021-08-19
Also published as: EP4078162A1; CN115803613A

Abstract

Environmental control system suitable to operate at high temperatures for transient conditions with controlled condensation effect in particular related to the method for evaluation of a humidity and temperature level in one or more temperature controlled environments part Z for cooking, baking or other environmental regulating procedures (e.g. built-in oven as a household appliance, etc.). The measurement cycle begins with thermocouple cooling in part (A) with applied current in positive direction. After more than 0.2 s, the cooling current is switched off and the measurement phase begins. Using the thermocouple sensitivity data, the depression temperature is calculated and with known temperature used to calculate absolute and relative humidity. After more than 0.5 s the measurement phase in part (B) is followed with the heating phase part (C) with current applied to the thermocouple in negative/opposite direction. During the cooling and heating the cooling and heating current is interrupted at constant intervals of 1 s, to be able to measure the thermocouple voltage. This thermocouple voltage is used in the heating phase to determine the state of the sensor system

Description

ENVIRONMENTAL CONTROL SYSTEM SUITABLE TO OPERATE AT HIGH TEMPERATURES FOR TRANSIENT CONDITIONS WITH CONTROLED

CONDENSATION EFFECT

FIELD OF INVENTION

The current application refers to the environmental control system suitable to operate at high temperatures for transient conditions with controlled condensation effect in particular related to the method for evaluation of a humidity and temperature level in one or more temperature controlled environments part Z for cooking, baking or other environmental regulating procedures (e.g. built-in oven as a household appliance, etc.). The method is comprised of established physical principles but implementing new methodology and configuration for fast response measuring static or quasi-static temperature and humidity within the temperature controlled environments part Z. The methodology implemented as an algorithm is supported by calculation over interchangeable multiplexing implementing of Peltier effect for cooling and heating, and Seebeck principle for measurements to achieve sensor dynamics, fast response and setting while using the inflection point as an actual measure for the humidity level at a particular temperature.

TECHNICAL PROBLEM

The technical problem that is solved by the proposed invention is how to realize a simple and low-cost sensor system and method for efficient/accurate measurement of air humidity in a heated compartment used for the treatment of materials/food, wherein the sensor is to be composed of commercially available components having a low price. Generally, it is known that the treatment of materials or cooking foodstuff can be obtained by different methods and under different conditions using known physical principles. Similar solutions for air humidity measurements may be adequately precise, but are comparatively expensive and do not resolve the problem of detection and elimination of condensed droplets on the sensor head. Therefore, it is an objective of the invention to provide a method with algorithm and sensor mentioned that, on one hand, maybe implemented comparatively to other solutions more simple and cost efficient, as well as comparatively more reliable and enables detection of missing properties during transient and high humidity or freezing conditions. Furthermore, under similar considerations, a method comprising humidity and temperature evaluations algorithm and algorithm correlating process control/cooking control in a regulated environmental compartment shall be provided.

DESCRIPTION OF RELATED ART

Humidity is an important factor in processes of a vast variety of industrial branches such as food industry and household appliances, pharmacy and medicine treatments, testing - safety and accelerated testing, etc. It is usually monitored during the treatment processes. Humidity is crucial in some instances, whereas it is a must to treat the material/food properly for example for food being healthier and materials being treated as in a natural environment. This is the reason why various ways of measuring humidity have been developed quite a long time ago. There exist measuring methods that are based on various physical principles such as capacitive measurement (US5844138), high frequency measurement (US6257049), impedance measurement (US5631418), lambda- principle (EP2848868A1) measurement. All these methods share at least one of the following disadvantages: imprecision, sophisticated production, demanding maintenance measurement of only relative humidity, slow response, complex and expensive equipment. A challenge that is not solved by known ideas is related to the dynamic conditions of high humidity and the problem of condensation of the sensor, that have not been resolved appropriately and they do not allow the detection and control of sensor freezing.

Physical principles are known and also published in different ways e.g. [D. C. SPANNER, 1951] dealing with Peltier effect in measurement, with depression points of up to 8,5 °C and usage limited to high RH, [J. L. MONTEITHB et.al., 1958] using thermocouples for measuring relative humidity in high ranges, [ERIC C. CAMPBELL, et.al., 1973] dealing with dew point hygrometers measurements.

The prior art is reflected in US3739629-1973 Apparatus and method for use in the measurement of the water or solvent potential of selected samples are described. It utilizes a psychrometer principle and a thermocouple is used for sensing and control of the sensing element temperature. As a single thermocouple is used a long term drift and environment influence and possible condensation are not taken into consideration thus making measurement in an environment where a rapid change in parameters is expected unreliable.), US3797312-1974 (A thermocouple hygrometer and method for determining the osmolality and water potential is presented. By maintaining a balance of energy into a wet thermocouple with the energy loss at the thermocouple to its surroundings, the temperature change, measured by the thermocouple voltage, is proportional to the actual osmolality or water potential of the sample. The system needs to be calibrated in a dry environment. As opposed to this invention, the proposed invention provides self-compensation long-term drift.) and US2128462- 1938 (This invention relates to temperature measuring devices, more particularly, a thermocouple hygrometer. Two thermocouples are used, a dry and a wet one. The system uses an external supply of water for thermocouple wetting. In the proposed invention no external wetting is needed.).

Other solutions, but with major disadvantage(s) are reflected in patent EP0949504 A1 (concentrating on condensation detection and heating and cooling of the sensor head - main difference is in algorithm with proper detection of the situation (measurement in consecutive time slot) and then implementation of a needed action (heating or cooling) and in generation of the reference signal. In the patent EP2469174A2 temperature sensors are used to measure the dew point temperature and the temperature of the oven. The cooling is performed by a Peltier element. A rather complicated duct system and an additional (to the fan in the cooking cavity) air moving fan is required to assure proper operation. Similar patent EP0567813 refers to humidity measurements in an oven by thermocouples and enables cooling from the outside environment, whereas our solution enables cooling by inverse current enforcement which in turn enables faster response time. Patent EP0949504 A1 is also similar in operating principle but has different implementations of the reference signal. The proposed invention eliminates drawbacks and limitations of the above cited humidity measurement devices by providing a set-up for the measurement of humidity.

SUMMARY OF THE INVENTION

Environmental control system suitable to operate at high temperatures for transient conditions with controlled condensation effect with one or more thermocouples of part A for evaluation of static or quasi-static relative or absolute humidity by using one or more known physical principles but implementing new configuration at wide temperature range (from 40 °C to 230 °C) comprising of an algorithm for successively and interchangeable multiplexing, supported by the algorithm to achieve dynamics and fast response and a configuration of at least three thermocouples mounted together as close as possible, manufactured in such a way, to be in good thermal contact but no physical contact is needed.

The described technical problem is solved by a sensor for measuring humidity in a heated compartment used for the treatment of different materials. The proposed invention provides method, algorithm and apparatus for making measurements of relative or absolute humidity in wider range and at high temperatures (Fig. 1), to be used for example in a cooking oven or other high temperature and wide relative or absolute humidity range appliances, industrial processes (chemical, pharmaceutical, electronics, food processing, etc.), environmental measurements, calibration measurements and similar. To achieve the required depression point, a different thermocouple material is used, in the current embodiment the P and N type Bismuth Telluride part A. The achieved depression point enables the measurement of the relative humidity below 50 % at the air temperature 98 °C. The basic structure of invention presents also electronic part B enabling heating and cooling of the sensors head, measurement system on microprocessor C and algorithm principle D that resolves challenges of condensations and freezing stages of competitive solutions. The system is suitable for the measurement of air humidity at temperatures of up to 230 °C. The sensor is based on an updated principle of evaporative cooling detection on a thermocouple while it is being heated. A derived wet-bulb temperature in conjunction with a pairing dry thermocouple enables the measurement of absolute and relative humidity. The temperature of the cooling (wet) thermocouple is alternatingly being measured also during the cooling cycle (Peltier effect) when the cooling current is being temporarily switched off. With the current reversal, the thermocouple is additionally able to eliminate potentially excessive water condensation.

BRIEF DESCRIPTION OF THE DRAWINGS The drawings are provided for purposes of illustration only and merely depict typical or example embodiments. These drawings are provided to facilitate the reader’s understanding and shall not be considered limiting of the breadth, scope, or applicability of various embodiments.

FIG. 1 shows a basic structure of invention which consists of one or more parts marked as A, B, C and D. Part Z presents any temperature adjustable environment described in this document or similar.

A sensor in part A is in the temperature environment and connected to the electronics in part B and part C with algorithm principle D.

FIG. 2 shows a basic algorithm principle used in the invented sensor system for humidity measurement. Part A presents a cooling algorithm of the sensor, part B includes measurement options and decision steps, including the final result for humidity, and Part C deals with the heating principle of the sensor.

FIG. 3 illustrates typical examples of sensors outputs. These outputs present inputs for the algorithm to proceed with the correct step to achieve a result for humidity measurement. A particular part of FIG.3 show different possible stages, for example: (a) Too low RH, no depression point could be observed. Hi time constant during the measurement cycle. Hi time constant during the heating cycle. No RH calculated. Under-range.

(b) Use the depression point to calculate dT and RH. Hi time constant during the measurement cycle. Hi time constant during the heating cycle. Turn over detected in measurement regime. Use turn over point to calculate RH.

(c) Depression during almost whole measurement time. At the end the TC T rises. Lo time constant during the measurement cycle. Hi time constant during the heating cycle. Use mid TC U to calculate RH.

(d) Depression during the whole measurement time. No turn over during heating. Lo time constant during the measurement cycle. Hi time constant during the heating cycle. Use end TC voltage to calculate RH.

(e) Hi time constant during the measurement cycle. Hi time constant during the heating cycle. Use end TC voltage to calculate RH.

(f) Too high temperature gradient and/or rapid temperature fluctuation.

(g) E.g.: The oven doors opened. No RH calculated.

(h) Measurement: Measurement data, exp. fit, lin. fit ‘middle’ (linearly fitted data used for UTC calculation) in the last part of measurements (linearly fitted data used for UTC calculation).

(i) Measurement: Turn - over point determination. Measurement data, exp. fit, turn over area (linearly fitted data used for UTC calculation), values to calculate over voltage (linearly fitted data used for UTC calculation).

(j) Heating: Measurement (linearly fitted data used for UTC calculation), exp. fit (linearly fitted data used for UTC calculation).

DETAILED DESCRIPTION OF THE INVENTION

Environmental control system suitable to operate at high temperatures for transient conditions with controlled condensation effect with known hardware is solving a basic challenge of condensation of the sensor in dynamic conditions. Four feedback loops presented in Fig. 2 enables evaluation of static or quasi static relative or absolute humidity. Sensor as an element does not need additional cooling elements, sensors are in the same position, very close together in the same environment with no additional hoses or air chambers. Activating or deactivating algorithm for steam generation (in the contorled environment) in dependence of pre-set algorithm for process control is implemented by managing input of precise steam generator using part (C). The measurement sequence begins with thermocouple cooling in part A with an applied current in a positive direction. After more than 0.2 s, the cooling current is switched off and the short term measurement check is performed. Until the sesnsor is sufficiently cooled or a predertemined time has elapsed, cooling and measurements are repeated. All this represents cooling cycle preferably 5 s long. Then the measurement cycle begins. The thermocouple voltage in this regime develops a ‘turn over’ point where the depression voltage is measured. Using the thermocouple sensitivity data, the depression temperature is calculated and with known temperature used to calculate absolute and relative humidity. After more than 0.5 s, the measurement phase in part B is followed with the heating phase part C with current applied to the thermocouple in - direction. Heating phase lasts preferably 5 s. With additional heating of the thermocouple, a persistent condensation is avoided. During the cooling and heating, the cooling and heating current is interrupted at constant intervals of 0,2 s, to be able to measure the thermocouple voltage. This thermocouple voltage is used in the heating phase to determine the state of the sensor system as presented in Fig. 3 ((a) to (e)) and described in chapter “Brief description of the drawings”.

Two thermocouples are used to compensate the sensor environment dependences, a “passive one”, which is not cooled and heated during the measurement cycle and an “active one”, which is cooled and heated during the measurement cycle. The passive thermocouple remains dry during the measurement cycle, thus serving as a reference. In case of too high temperature gradient and/or rapid temperature fluctuation the measurement of absolute and relative humidity is not performed, the sensor output signals the state. Examples are presented in Fig. 3 ((f) to (j)) and described in chapter “Brief description of the drawings”.

The measurement system includes an algorithm for successively and interchangeable multiplexing, supported by the algorithm to achieve dynamics and fast response of sensors. A configuration of at least three thermocouples mounted together as close as possible is manufactured to be in good thermal contact but no physical contact is needed. The third sensor is used for measurement of the reference environment temperature. Mass of the sensor elements of the part (A) is from 20 mg to 50 mg, preferably 30 mg enabling fast response with the steps of cooling, measuring and heating phase. A method according to the claims provides the user with a delighting experience in at least one cooking or processing result in an automated way. Enforced current in the sensor enables programmed condensation cycling in one measurement cycle, applying procedure with a measurement part in time intervals. Thermocouple principle and enforced current in the sensors are function of one or more parameters (kTst, ¾ ¾, t_H, kMiN-MAx p, kMEPs, kBF, UOTCI , UOTC2, UOTC3) that determines the correct measurement process. The method according to claims solves condensation problems and erroneous measurements are managed or prevented. Multimode operation is possible: slow - condensation cycling and fast - ‘always in the condensation point/regime’ with fast RH tracking. According to the measured data of relative humidity in the built-in oven, the process of precise steam generation is carried out depending on the type of e.g. food in the oven. The precise measured value of relative humidity is a key information in achieving the correct hardness, colour and firmness properties of the food.

Program flow

Initialization of the microcontroller (pC), Real-time clock (RTC), Data input- output lines, etc. Three ADCs are used (could be one multiplexed, if its sampling frequency >75 Hz and has ‘single cycle settling time including multiplexer’. If the thermocouple ‘gain calibration’ is not performed (as in current implementation) only 2 ADCs are necessary. ADC range should be at least ±20 mV with >10-bit effective resolution at ±20 mV range. Each ADC samples with constant sampling frequency 25 Hz. For the temperature measurements only every fifth measurement is stored (only when heating and/or cooling is not active). Acquired ADC data are collected to a buffer with sufficient length to store the whole measurement cycle (for 15 s that is 825 data words).

ADC1 . thermocouple 1 - active, heated and cooled) ADC2 . thermocouple 2 - for compensation purposes

ADC3 . thermocouple 3 - T type thermocouple for T measurements

The microcontroller should provide two digital outputs to activate the heating and cooling of the thermocouple by switching on a DC current to the thermocouple 1. The current source is not needed, a simple resistor connected to a regulated power supply is sufficient. Cooling is switched on and interrupted each 200 ms for measurement for the first 5 s. Heating is switched on for the last 5 s of the measurement sequence and also interrupted for 200 mswith short term measurement chechs. This way the thermocouple state could be checked during the cooling (currently not used) and heating cycle (currently used). After the measurement sequence (15 s) the acquired data is analysed as follows:

Lhc = U Utc2

Measurement cycle (from 5 s to 10 s is analysed for turn-over detection point and its voltage determined) - curve (a) in Fig. 3. If the turn-over detection point could not be detected, the time constant of the fitted curve is compared to the reference value and estimation is made considering the shape of the curve if the thermocouple condensation is taking place - curves (c) and (d) in Fig. 3. According to the different signals shown in the table, the sensor state is determined and the thermocouple voltage is calculated from the acquired measurements. Different states are presented in (b), (c), (d) and (e) in Fig. 3. Turn over point presence is determined by fitting the measured data with exponential function and checking the residuals of the fit to the reference value. If the residuals are higher, the turn over point is present. Details are presented in Fig. 3.

The wet-bulb temperature is calculated using a first order temperature compensation of the thermocouple sensitivity coefficient with the following equation (determined experimentally, dependent on the thermocouple material used and material production):

Arc / (mV/K) = -0,0035 ^* 7/ (°C) - 0,20 ; temperature in (°C) ~ ATC in (mV/K) dTI (°C) = Utc / (mV) / Arc / (mV/K) ; Utc in (mV), Arc in (mV/K) ~ dT in

(°C)

Using the wet-bulb temperature and environment temperature the relative (and absolute) air humidity is calculated. Sensor and/or wiring breakage detection is carried out by feeding current 0.25 mA and 4 mA through the thermocouples and observing the voltage value for proper software decisions about abnormal state of sensor system. Environmental control system and measurement system comprises configuration of electronic components and materials providing low cost sensor solution also due to absence of a separate condensation detection device, or sensor cooling device.

OBJECTIVE OF THE INVENTION

Environmental control system suitable to operate at high temperatures for transient conditions with controlled condensation effect may be used for different applications when measuring and controlling one or more heated compartments with adjustable and controllable humidity settings using one or more sensors. The rapid response to transient conditions and adaptation to instantaneous changes, such as opening of the compartment, cumulative effects of load, change of absolute and relative humidity and temperature and similar or combination of all mentioned cases. Dynamics of the one or more sensors results in correlation with the algorithm. No initial temperature of the environment shall be set in advance to start the algorithm and no sensor warm-up is needed. An automatic inflection point is detected by the algorithm process including one or more cooling phases, one or more measuring phases and one or more heating phases, or combination of said. A low-cost sensor with measuring system algorithm for measuring humidity in a heated compartment used for the treatment of different materials (e.g. household appliance oven for treatment of food, climatic ambient for treatment of test samples, etc.) with one or more algorithms connecting hardware system with one or more process controls is developed. The sensitivity of the sensor system is higher or at least comparable to known implementations by using two or more sensors made of highly sensitive materials in combination with heating, cooling and measuring. Condensation problems on sensor head are detected and resolved as an explicit difference and advantage to other solutions.

Claims

PATENT CLAIMS

1. Environmental control system suitable to operate at high temperatures for transient conditions with controlled condensation effect wherein the sensor system of thermocouples in a part (A) comprising:

• TC materials used in a current embodiment in the part (A) with sensitivity from 0.2 mV/K to 0.6 mV/K, preferably 0.4 mV/K, important for achieving depression point which enables a range of relative humidity measurement from 60 % to 100 %;

• mass of elements of the part (A) from 20 mg to 50 mg, preferably 30 mg enabling fast response with the steps of cooling, measuring and heating phase;

• algorithm principle (D) using four feedback loops for evaluation of static or quasi-static relative or absolute humidity;

• configuration of part (A) and algorithm principle (D) enabling temperature range from 40 °C to 230 °C, preferably 100 °C;

• of at least three thermocouples in part (A) mounted together as close as possible manufactured to be in good thermal contact but no physical contact is needed between them, and located in (Z), and wherein the method comprising the steps of

• cooling thermocouple in part (A) with applied current from 0.1 A to 2 A, preferably 1 A, in positive direction;

• switching off cooling current after 0.16 s and instant measurement with the thermocouple in part (A) according to algorithm principle (D) for 0.04 s. • reversing current by part (B), electronic (C) and algorithm principle (D) in preferably 5 s, to eliminate condensation or freezing of thermocouples in sensor system;

• dynamically adjusted heating time according to current humidity conditions in part (Z) by implementing algorithm principle (D) and considering environment condition;

• compensation of sensor for environmental dependences by separate thermocouple within part (A);

• additional heating of thermocouple to avoid a persistent condensation;

2. Environmental control system according to claim 1 , wherein a cooking oven or other high temperature and wide absolute and relative humidity range appliances / industrial processes (chemical, pharmaceutical, electronics, food processing,...) / environmental measurements / calibration laboratory use, are realised with the automatic dew point tracking measurement using the electronic control in part (B) with set parameters according to claim 4 obtained by experiments and calibrations in the climatic chamber, to obtain correct inflection point and error of the measurement system in the range of ± 5 %.

3. Environmental control system according to claim 1 , wherein measurement system (C) tracks the inflection point for determination of dew point and consequently the relative humidity in a randomly disturbed humidity environment, using mathematical fit analysis for determination of more than one different stage of sensors passage voltage.

4. Environmental control system according to claim 1 , wherein measurement system enables management of dew point, where cooling, heating and measuring processes on the same thermocouple sensors are possible in order to optimize humidity measurements in short cycles, wherein thermocouple principle and enforced current in the sensors are function of one or more parameters (kist, x_c, ¾, t_H, MIN-MAC,IR, kMEPs, kBF, UOTCI , UOTC2, U0TC3) that determines the correct measurement process.

5. Environmental control system according to claim 4, wherein the parameters kTc and kTcf are calibrated for each application.

6. Environmental control system according to claim 1 , where sensor and/or wiring breakage detection carried out by feeding current 0.25 mA and 4 mA through the thermocouples and observing the voltage value for proper software decisions about abnormal situations detection.

7. Environmental control system according to claim 1, wherein sensor as an element does not need additional cooling elements, sensors are in the same position, very close together in the same environment with no additional hoses, air chambers.

8. Environmental control system according to claim 1 , wherein double condensation detection during abrupt environment cooling or humidifying or during initial range testing - auto ranging for reliable measurements and enhanced depression point detection is carried out with observing depression point during heating cycle.

9. Measurement system with algorithm of operating a measurement process in an environmental compartment or cooking compartment (Z), comprising: a) interchangeable multiplexing procedure for achieving an actual value of the humidity level; and b) activating or deactivating algorithm for steam generation in dependence of pre-set algorithm for process control by managing input of precise steam generator using part (C).

10. Environmental control system according to claim 1 and measurement system according to claim 9 comprises configuration of electronic components and materials providing low cost sensor solution also due to absence of a separate condensation detection device, or sensor cooling device.

11. Environmental control system according to claim 1 using separate thermocouple within part (A) for compensation other TC measurements in non-stationary T (and RH) environments by subtracting the measured voltage.

12. Environmental control system according to claim 5, wherein one or more sensors, controlled over one or more algorithms (D), and operating by interchangeable multiplexing of peltier effect and seebeck principle within part (A) are supported by parts (B and C).

13. Environmental control system according to claim 5, wherein controlled condensation effect occurs due to changed environmental conditions in the part (Z) by rapid change of temperature examples observed as in (f), (g).