Communications: electrical – Condition responsive indicating system – Specific condition
Patent
1980-12-10
1983-07-05
Brigance, Gerald L.
Communications: electrical
Condition responsive indicating system
Specific condition
324 65R, G08B 2100, G01N 2704
Patent
active
043921272
DESCRIPTION:
BRIEF SUMMARY
This invention relates to grain moisture testing apparatus.
In some industries and especially in wheat and barley growing industries it can be essential for the long term storage of grain to know the moisture content of this grain.
Farmers may not have their crop accepted at a silo unless it is below a given moisture level and it can be quite essential that prior to harvesting grain, the farmer knows within adequate limits the moisture content of the grain so that he can be assured that the product in the silo will not unduly promote mould growth.
Indeed, if the farmer is mistaken with moisture level of his grain he may be required to provide costly additional drying prior to the acceptance of this material in the silo.
It is known to measure moisture level or organic material by crushing the material and then measuring conductance across a specified thickness of the crushed material.
This conductance is then compared to known standard conductances of similar materials for known moisture contents and related to the temperature at which the test is taken and a reasonably accurate estimate of the moisture content can then be obtained.
In a most popular instrument at the present time, there are provided means by which the conductance of the material can be obtained by using the well known principles of the wheatstone bridge and by using conventional techniques of firstly zeroing the readings and then obtaining a null point reading the conductance of the material can be obtained which can then be compared by tables with comparable conductances of known samples in relation to temperature and an accurate estimate of the moisture content for a standard temperature can then be assessed.
A first problem with this arrangement is the cost of the equipment necessary to achieve firstly an accurate and secondly a reliable measure of conductance in the circumstances.
To explain this further, one of the big difficulties is that the conductance of the sample will vary considerably from some thousands of megohms down to a few kilohms and especially at the higher ohmic readings, difficulties are experienced firstly with providing accurate and temperature stable ohmic references and secondly, because of the small currents involved in obtaining an accurate null reading, the use of very sensitive field effect transistors while very useful does make the instrument very prone to electrostatic voltages interfering with an accurate reading.
Also perhaps most importantly, the instrument while very suitable for those who are fully trained in the use of the instrument is not clearly useful for the normal person most likely to require to use the machine such as a farmer and herein perhaps lies the biggest difficulty. One generally must understand the principles of zeroing and finding the null reading and understanding the terminology and therefore such complicated steps require firstly that the person have some understanding and training and they do promote the high possibility of errors in the use of the machine.
There is a further difficulty in that inherently the system requires manually variable resistors and as the machines are used in situations where atmospheric conditions can be poor, long term maintenance of such a machine becomes a difficulty and reliability of the readings becomes less sure after a period of usage.
A further problem recalling that for accurate measurement, very high quality and therefore inherently expensive machines have hitherto been required but even with such previous macines, because in measuring moisture content, very high variations in resistances are necessary and it is inherently necessary to use in such machines as have hitherto been made, potentiometers generally known as having logarithmic variation in resistance characteristics.
Unfortunately, in practice such resistors as are commonly offered for purchase and use in electronic equipment are only an approximation of a logarithmic variation in resistance values, for instance typically if a wire-wound potentiometer is used, the wire varies its res
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patent: 3961247 (1976-06-01), Toki
patent: 4122389 (1978-10-01), Haagen
patent: 4259633 (1981-03-01), Rosenau
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