Fluid handling – Processes – Involving pressure control
Patent
1983-10-18
1986-07-01
Cohan, Alan
Fluid handling
Processes
Involving pressure control
137 85, 1374875, G05D 1600
Patent
active
045974055
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a process for controlling a controllable magnitude using a control circuit, whose servo drive is designed as a fluidic pressure drive. especially for controlling the throughput of pourable or fluid material through a material feed line in a flour mill plant.
The invention moreover relates to an apparatus for controlling a controllable magnitude with a set-point adjuster, an instantaneous value sensor, a comparator/controller unit having a discriminator and a servo unit (servo drive and servo element), which is downstream from the above elements and whose servo drive is designed as a fluidic pressure drive.
UNDERLYING STATE OF THE ART
The aforementioned process, as well as the aforementioned apparatus are known from the German Auslegeschrift No. 2,223,476 of Jan. 2, 1976 (Sampson Apparatebau AG). In the known apparatus, the servo component, that is the servo drive and the servo element, which is driven by the automatic control output, has a pneumatically operated diaphragm chamber (servo drive) and a discharge valve (servo element), which is operated by the diaphragm chamber. The known control apparatus is designed as a three-point controller. Its comparator/controller unit therefore differentiates only between three states of deviations, that is, values of the difference between the instantaneous value and the set point: namely, (i) the deviation is greater than zero; (ii) the deviation is less than zero; and (iii) the deviation is equal to zero. Since the known controller/comparator unit is in a position to differentiate between the three aforementioned states of deviation, the unit, intended for this differentiation, could also be considered as a discriminator. As for the rest, the teachings, known from the aforementioned Auslegeschrift, are concerned with the problem of simplifying the feedback, which affects the switching interval of the controller. According to the known teachings, this problem is solved owing to the fact that the time behavior of the feedback is adjustable with the help of chokes. The teachings, known from the aforementioned German Auslegeschrift, are not concerned with the problem of providing as accurate a control as possible and especially not with the problem of providing accurate control of the throughput of pourable or fluid material through a material feed line in a flour mill. This problem, which is not treated in the aforementioned publication, is however a central problem of any control system. It is particularly important for metering streams of material which flow continuously, for example, water or grain in a flour mill, because control of the throughput of pourable and fluid materials in the flour mill continues to be one of the critical interfaces between the well-known mechanical parts of the plant and modern means of control.
DISLCOSURE OF THE INVENTION
The inventive teachings start out from the objective of developing further a process as well as apparatus of the aforementioned type, so that the controllable magnitude can be controlled as accurately as possible. In particular, the aforementioned process, as well as the aforementioned control apparatus are to be developed further for as accurate a control as possible of a continuous throughput of pourable or fluid materials.
This objective is accomplished for the process owing to the fact that the fluid in the pressure drive is acted upon in the range of small deviations by transient micropressures (rapid transient pressures or pressure fluctuations with small peak values), the reversal points of the transient micropressures being determined essentially by two (a first and a second) threshold values lying in the range of small deviations.
This objective is accomplished for the control apparatus owing to the fact that the discriminator is so designed, that it emits a first discrimination signal when the deviations, measured by the comparator section of the comparator/controller unit, lie between two (a first and a second) threshold values within a preset first range abou
REFERENCES:
patent: 3462115 (1969-08-01), Barker
patent: 4481768 (1984-11-01), Goshorn
Kummer Emanuel
Oetiker Hans
Cohan Alan
Gebruder Buhler AG
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