CN1074127C

CN1074127C - Water activity detecting method and instrument

Info

Publication number: CN1074127C
Application number: CN 95113366
Authority: CN
Inventors: 达式奎
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-12-14
Filing date: 1995-12-14
Publication date: 2001-10-31
Anticipated expiration: 2015-12-14
Also published as: CN1152127A

Abstract

The present invention relates to a method and an apparatus for measuring the water activity of materials, and mainly solves the problems of improving measurement precision, shortening measurement time and not damaging measured materials. The present invention is characterized in that measured materials are placed in airflow regulating humidity in air channels; the apparatus measures the temperature and the humidity difference of airflow entering the air channels; the apparatus regulates the humidity of the airflow in the air channels, and measures the temperature rise of the airflow before and after humidity regulation, and the temperature difference of the airflow and the surface of the materials; the water activity is calculated according to obtained data. The present invention can be used for measuring the water activity of materials, particularly the water activity of food.

Description

Water activity detecting method and instrument

The present invention relates to measure the method and the instrument of material moisture activity.

Measuring material moisture activity at present is material to be measured to be pulverized place dry airtight container, survey the character relevant of air in this airtight container when treating its water evaporates with humidity to balance, as electrical conductivity, electric medium constant, density etc., and the variation that causes other materials in this container owing to this water evaporates, weightening finish as drying agent, casing, the change of hairline elasticity coefficient etc., so as to conversion material moisture activity, as NOVASINA water activity instrument is exactly the electrical conductivity of measuring gas in the airtight container, also having various electrohydrometers to measure water activities also is to borrow the data that the record related properties water activity that converts, this method all is a static determination, its measurement is more time-consuming, need half an hour at the soonest, and the water activity of being surveyed is the maximal value that this material is pulverized water activity in the grain, also need simultaneously to stop the moisture infiltration of interfering material in addition with semi-permeable diaphragm when measuring, existing in addition surveying instrument monitoring error is bigger, and needs to proofread and correct with standard water activity value sample.

One of purpose of the present invention provides a kind of water activity detecting method of measuring rapidly, recording again higher precision, do not need comminuting matter simultaneously; In addition, provide a kind of instrument of realizing the water activity detecting method of aforementioned purpose.

The present invention is the damping air-flow that material to be measured is placed the air channel, it is dried wet poor at first to measure the gas flow temperature, the air-flow that enter the air channel, air-flow in the air channel is carried out humidity regulation thereupon and measure the air-flow temperature rise of damping front and back and the temperature difference on air-flow and material surface, utilize the above-mentioned data reduction that records to be water activity then.A socket can be set as the air channel according to said method, the thermometric hygrostat of measuring gas flow temperature and doing wet difference is set at the socket inlet end, the center section of socket is provided with the humidistat that air-flow is carried out humidity regulation, the outlet side of socket is provided with the thermocouple sensor of measuring air-flow and material surface temperature difference, and it is material upside to be measured that the thermocouple cold junction of measurement air-flow temperature rise places thermometric hygrostat, hot junction to place the outlet side of socket.

Because the present invention utilizes the damp and hot transfer rate of air-flow very fast, can reach mobile equilibrium in several minutes, therefore measured data only 3 minutes, more quick than static measurement method; Littler according to air-flow and material temperature difference, record the data precision high principle that heals, the present invention is provided with the temperature difference that temperature and humidity regulator is controlled air-flow and material surface, measure simultaneously directly the temperature difference and avoid measuring respectively the multiple measurement computing that gas flow temperature and temperature of charge are calculated the temperature difference again, can reduce the error of data-switching, and directly measure airflow humidity with doing wet difference method by what this method, therefore this method need not the standard model correction, and precision can be less than 0.01AW; This method is directly inserted thermopair in the material, does not need comminuting matter, does not destroy material properties, also can carry out point measurement, therefore also has the advantage of applied range.

Realize best way of the present invention below in conjunction with description of drawings:

Accompanying drawing 1 is a process flow diagram of realizing best way of the present invention, the expression air is sent into the air channel again among the figure through humidification after, shows in advance that for the most accurate relative humidity with air-flow increases to accurate that 96%-100% helps measuring with relative humidity Φ → 100% during from dried wet plate method hygrometric; Air-flow enters the air channel just can measure the dried wet difference E3 of gas flow temperature E1 and air-flow, subsequently the air-flow in the air channel is carried out humidity regulation, the adjusting airflow humidity can adopt the method for intensification dehumidification, also can adopt the method for sneaking into dry gas stream, but comparatively easy with the intensification dehumidification; Humidity regulation is 0 o'clock at the material surface temperature and the air-flow temperature difference, and relative humidity at that time equates with water activity, thus humidity regulation to material surface temperature and air-flow temperature difference E4=0 or → 0 be best, air-flow temperature difference E4 represents promptly that near 0 the temperature difference is less than 0.1 ℃; From process flow diagram as can be known the present invention the measurement of water activity is changed into the measurement of relevant temperature, therefore as long as record the water activity that gas flow temperature E1, air-flow humidity E3, air-flow temperature rise E2, air-flow and material surface temperature difference E4 can be scaled material by process flow diagram.

Accompanying drawing 2 is the instrumentation diagram that comprise water activity detecting method of the present invention, expression is that inlet end connects a wet gas current generator as the socket front end in air channel among the figure, the wet gas current generator is set can be avoided inserting the dependence of extraneous air-flow, the wet gas current generator can be made of blower fan 1, gauze 2, well heater 3, gauze is suspended on the place ahead of blower fan along the trend of air-flow, well heater is located at the below of gauze, and wet gas current generator body bottom is a tank; The wet gas current generator also can be made of blower fan and sprayer; In order to give wet gas current humidification, the refrigeratory 10 of between wet gas current generator and socket, packing into; The inlet end of socket is provided with measures the cold junction that air-flow is done the thermometer 5 of wet poor dried wet plate 4 of thermopair and measurement gas flow temperature and measured the thermopair 7 of air-flow temperature rise; The middle part of socket evenly is provided with heating wire 6 and makes the air-flow thermally equivalent, and the heating wire external transformer constitutes humidistat; The outlet side of socket is provided with the temperature difference that thermocouple sensor 8 is used for measuring air-flow and material surface, and thermocouple sensor can be needle-like or sheet; The hot junction of measuring the thermopair 7 of air-flow temperature rise is located near the upstream of material 9 to be measured.Have fast, accurately, do not destroy material structure and have the advantage of point measurement according to this method and Instrument measuring water activity, the error of this method and Instrument measuring material moisture activity is less than 0.01AW, and is automatically-monitored for food processing, instruct food processing, preservation, packing significant.

Claims

1, water activity detecting method, it is characterized in that material to be measured is placed the damping air-flow in air channel, air-flow relative humidity is 96% to 100%, it is dried wet poor at first to measure the gas flow temperature, the air-flow that enter the air channel, the air-flow in the air channel is carried out humidity regulation thereupon and measures the air-flow temperature rise of damping front and back and the temperature difference on air-flow and material surface.

2, water activity detecting method according to claim 1 is characterized in that the temperature difference that the gas flow temperature in the air channel is adjusted to material surface temperature and air-flow is equaled 0 or less than 0.1 ℃.

3, the instrument of water activity detecting method setting according to claim 1 comprises air channel, thermometric hygrostat, thermocouple sensor, it is characterized in that the air channel is the inlet end installing thermometric hygrostat of a socket, socket, the outlet side installing thermocouple sensor of socket, the thermocouple cold junction of measuring the air-flow temperature rise places the thermometric hygrostat, the hot junction places the outlet side of socket, and there is the electric heating humidistat at the socket middle part.

4, the instrument of water activity detecting method setting according to claim 3 is characterized in that the front end of socket connects a wet gas current generator.

5, the instrument of water activity detecting method setting according to claim 4 is characterized in that refrigeratory of installing between wet gas current generator and socket.