GB2164449A - Monitoring temperature induced deterioration of stored articles - Google Patents
Monitoring temperature induced deterioration of stored articles Download PDFInfo
- Publication number
- GB2164449A GB2164449A GB08521028A GB8521028A GB2164449A GB 2164449 A GB2164449 A GB 2164449A GB 08521028 A GB08521028 A GB 08521028A GB 8521028 A GB8521028 A GB 8521028A GB 2164449 A GB2164449 A GB 2164449A
- Authority
- GB
- United Kingdom
- Prior art keywords
- output
- input
- circuit
- instrument according
- thermistor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K3/00—Thermometers giving results other than momentary value of temperature
- G01K3/02—Thermometers giving results other than momentary value of temperature giving means values; giving integrated values
- G01K3/04—Thermometers giving results other than momentary value of temperature giving means values; giving integrated values in respect of time
Abstract
An instrument for monitoring the deterioration of articles held in storage in particular, food in cold storage, comprises an input circuit including a temperature sensor and arranged to produce an output proportional to the rate of change at the sensed temperature of a property of the article, the output of the circuit being connected to the input of a linear amplifier, the output of which is integrated by an integrating device. As shown, a Wheatstone bridge includes a thermistor and is arranged to produce an output which is a quadratic function of the temperature in degrees Celsius, and the integrating device is a mercury coulometer display. <IMAGE>
Description
SPECIFICATION
Monitoring instrument
The invention relates to a monitoring instrument for monitoring the deterioration of articles held in storage in particular, food in cold storage.
The present invention provides an instrument for monitoring changes in an article during storage, comprising an input circuit including a temperature sensor and arranged to produce an output proportional to the rate of change at the sensed temperature of a property of the article, the output of the circuit being connected to the input of a linear amplifier, the output of which is integrated by an integrating device.
The input circuit and amplifier are preferably powered by a battery.
In monitoring food spoilage, as will be shown below, a Wheatstone bridge circuit with a thermistor in one arm may be made to model with considerable accuracy the rate of spoilage of food stuffs in chilled storage, which, as has been shown, can be expressed as a quadratic function of temperature in degrees Celsius.
Preferably the amplifier is a CMOS-type operational amplifier which has a very low current drain, and is therefore suitable for long term operation from a battery. Further operational amplifiers of this type with negative feedback may be included in the circuit to provide a very high input impedence, so that the resistor network may itself be constructed with high resistance components and so require only a small current in operation.
The invention will now be further described by way of example with reference to the accompanying drawing, which is a circuit diagram of a food spoilage monitor according to the invention.
Referring to the drawing the circuit of the food spoilage monitor consists of four parts, indicated by the dotted outlines 1, 2, 3, and 4. Of these 1 is the temperature sensing circuit, comprising a thermistor connected in a Whealstone bridge network, 2 is an amplifier section, 3 is a range-setting network by means of which the range of the monitor can be set to correspond to the characteristics of the food being monitored, and 4 is an indicator showing how much of the shelf life of the stored food has expired.
It has been shown, in a paper by Ratkowsky and others in Journal of Bacteriology Jan.
1982 pp. 1-5, that the relative rate of food spoilage can be represented by an equation of the form: r=a (T,+T)2, where a and To are constants. For a wide range of chilled foods it is shown that this can be expressed in the form r=b (1+0.1T)2.
The constant b varies with the type of food.
The above equation can be modelled to a satisfactorily high accuracy by a thermistor placed in one arm of a Wheatstone bridge circuit. The thermistor is an RSR-T matched thermistor, stock number 151-243, and was selected both for its temperature resistance characteristic and for its high resistance, which enables relatively high resistor values to be used in the rest of the bridge circuit, and thereby minimises current drain from the battery supplying the circuit. The thermistor is placed in the arm AC of the bridge circuit and the arm BC contains a variable resistor which allows for variations in the resistance of the thermistor, as small deviations have disproportionately larger effects on the potential difference across the output terminal CD of the bridge.The arm BC of the bridge circuit may also contain a small adjustable resistor to null any input offset voltages of the operational amplifiers in the amplifier portion of the circuit which is about to be described.
The amplifier 2 comprises two operational amplifiers IC 1 IC2 connected respectively to the terminals D and C of the Wheatstone bridge, and provided with feedback so as each to have unity gain. These present a very high input impedence to the bridge network terminals, which renders insignificant the effects of current drawn from the bridge, and their outputs are connected to the differential inputs of a further operational amplifier IC3.
This amplifier is provided with a resistor network for generating negative feedback, and this network includes a small variable resistor for precise adjustment of the gain. The operational amplifiers IC1, IC2 and IC3, are all
CMOS amplifiers type RS 7611.
The output from the amplifier 2 is applied to a range-setting network 3. This consists simply of a set of series resistors arranged in five pairs with a switch provided for shorting out each resistor pair. The resistances of the pairs are in the ratios 1: 2: 4: 8: 16 so that all ratios between 1 and 31 can be obtained by a suitable selection of switches. This range setting network determines the contant b in the equation set out above.
The output from the range-setting network passes through a mercury coulometer and series resistor, the coulometer providing the output indication of the instrument. This is a
Curtis CP3 elapsed time meter, obtainable from Curtis Instruments (UK) Limited of Northampton and it has a full-scale deflection at 3.2 m. amp hours.
Many foods have shelf lives at 0 C in the range 5-36 days. With the components described above, and the resistor value shown in the drawing, the time to full-scale deflection with all the switches in the range-setting network closed is 5 days. If it is desired to monitor a food with a shelf life of 26 days at 0 C, then switches 1, 3 and 5 would be open.
These correspond to 1, 4 and 16 days respectively, which together with the preset 5 days make up the desired 26 days shelf life.
Claims (6)
1. An instrument for monitoring changes in an article during storage, comprising an input circuit including a temperature sensor and arranged to produce an output proportional to the rate of change at the sensed temperature of a property of the article, the output of the circuit being connected to the input of a linear amplifier, the output of which is integrated by an integrating device.
2. An instrument according to claim 1 for monitoring the spoilage of food in cold storage, in which the temperature sensor is a thermistor and the input circuit produces an output voltage which is a quadratic function of temperature expressed in degrees Celsius.
3. An instrument according to claim 2 in which the input circuit is a Wheatstone bridge circuit with the thermistor connected in one arm.
4. An instrument according to any preceding claim in which the integrating device is a mercury coulometer.
5. An instrument according to any preceding claim in which the linear amplifier has a voltage-follower input.
6. An instrument according to any preceding claims which is portable and battery-operated.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB848421452A GB8421452D0 (en) | 1984-08-23 | 1984-08-23 | Temperature sensitive elapsed time indicator |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB8521028D0 GB8521028D0 (en) | 1985-09-25 |
| GB2164449A true GB2164449A (en) | 1986-03-19 |
Family
ID=10565744
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB848421452A Pending GB8421452D0 (en) | 1984-08-23 | 1984-08-23 | Temperature sensitive elapsed time indicator |
| GB08521028A Withdrawn GB2164449A (en) | 1984-08-23 | 1985-08-22 | Monitoring temperature induced deterioration of stored articles |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB848421452A Pending GB8421452D0 (en) | 1984-08-23 | 1984-08-23 | Temperature sensitive elapsed time indicator |
Country Status (1)
| Country | Link |
|---|---|
| GB (2) | GB8421452D0 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2235780A (en) * | 1989-09-05 | 1991-03-13 | Barker George & Co Ltd | A Temperature monitoring apparatus |
Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1104141A (en) * | 1964-04-24 | 1968-02-21 | Smiths Industries Ltd | Improvements in or relating to electrical apparatus for providing a representation of engine-life |
| GB1104949A (en) * | 1966-03-24 | 1968-03-06 | Commissariat Energie Atomique | Heat-quantity measuring unit |
| US3638495A (en) * | 1968-08-07 | 1972-02-01 | Dynametric Inc | Method for detecting aging of articles |
| GB1427515A (en) * | 1972-03-07 | 1976-03-10 | Secretary Trade Ind Brit | Explosive gas detectors |
| US4277974A (en) * | 1979-07-12 | 1981-07-14 | Karr Lawrence J | Time-temperature indication |
| GB2077928A (en) * | 1980-06-17 | 1981-12-23 | Fiat Ricerche | Heat meter device |
| GB2102964A (en) * | 1981-07-30 | 1983-02-09 | Satchwell Controls Limited | Meters |
| GB2145526A (en) * | 1983-08-26 | 1985-03-27 | Shirley Inst | Measuring temperature functions |
-
1984
- 1984-08-23 GB GB848421452A patent/GB8421452D0/en active Pending
-
1985
- 1985-08-22 GB GB08521028A patent/GB2164449A/en not_active Withdrawn
Patent Citations (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1104141A (en) * | 1964-04-24 | 1968-02-21 | Smiths Industries Ltd | Improvements in or relating to electrical apparatus for providing a representation of engine-life |
| GB1104949A (en) * | 1966-03-24 | 1968-03-06 | Commissariat Energie Atomique | Heat-quantity measuring unit |
| US3638495A (en) * | 1968-08-07 | 1972-02-01 | Dynametric Inc | Method for detecting aging of articles |
| GB1427515A (en) * | 1972-03-07 | 1976-03-10 | Secretary Trade Ind Brit | Explosive gas detectors |
| US4277974A (en) * | 1979-07-12 | 1981-07-14 | Karr Lawrence J | Time-temperature indication |
| GB2077928A (en) * | 1980-06-17 | 1981-12-23 | Fiat Ricerche | Heat meter device |
| GB2102964A (en) * | 1981-07-30 | 1983-02-09 | Satchwell Controls Limited | Meters |
| GB2145526A (en) * | 1983-08-26 | 1985-03-27 | Shirley Inst | Measuring temperature functions |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2235780A (en) * | 1989-09-05 | 1991-03-13 | Barker George & Co Ltd | A Temperature monitoring apparatus |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8421452D0 (en) | 1984-09-26 |
| GB8521028D0 (en) | 1985-09-25 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |