Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1994-10-18
1996-10-15
Le, Que T.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
73314, 340623, G01N 1506
Patent
active
055656870
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to signal generating apparatus, and in particular to position-responsive apparatus, for example for monitoring a liquid level, and to a method of deriving position-responsive signals, eg. in order to sense and display particular values and/or to control a variable determining those values.
1. Background of the Invention
There are many processes in which a directly contacting probe or the like cannot be employed to monitor changes of position, for example because of a hostile environment or the aggressive nature of the material being monitored. Non-contacting sensors must then be used, such as devices responsive to magnetic fields.
2. Description of the Prior Art
Non-contacting liquid level indicators have been described employing a vertical array of magnetic switches, as in the examples of GB 997861 and U.S. Pat. Nos. 4,627,283 and 4,589,282, in which a magnet carried by a float operates the switches without contacting them. Such switches have an on-off operation so that they provide stepped measurements, but that is not necessarily a disadvantage if the steps are sufficiently small. In the last-mentioned U.S. Pat. No. 4,589,282 in particular, there is proposed the use of Hall-effect switches, which provide relatively compact and convenient switching devices with a small power consumption.
These earlier proposals are limited in respect of range and/or accuracy of measurement, however. It will be understood, that the incremented signal change between successive steps must be sufficient to be unaffected by circuit noise so that it soon becomes inconvenient to cope with the increasing signal voltage range if it is required to have an indicator with a very large number of steps, whether for increased accuracy or for greater range of measurement. In the apparatus of U.S. Pat. No. 4,589,282 a vernier-like arrangement of switches and magnets is proposed to increase the accuracy of measurement but that requires complex circuitry which itself poses a practical limit to the maximum number of steps or graduations over the range of measurement.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, there is provided position-responsive apparatus comprising a series of detecting elements disposed in succession alongside a path of relative movement with a non-contacting actuating means adapted to act on respective detecting elements by its proximity thereto along said path, and resistance means connected to the detecting elements to produce an output signal which is progressively changed with relative movement between the actuating means and the series of detecting elements over the length of said path of relative movement, the series of detecting elements being arranged in a plurality of arrays disposed in series to extend over different portions of said path of relative movement and means operable with the passage of the actuating means between successive arrays in a direction away from one end of said path for transmitting a cumulative output signal which includes a component corresponding to the output signal from each preceding array from said one end of the path of relative movement
Such apparatus provides for the possibility of connecting a supply voltage to each said array of detecting elements independently of the other arrays, conveniently by connecting them in parallel to a common supply, so that the range of measurement can be extended indefinitely and/or the accuracy of measurement is limited only by the nature of the detecting elements themselves. Nevertheless, because the signal state for each lower array can be made dependent to the action of the actuating means on a succeeding array, cumulative signals can be generated from the arrays jointly. Thus, if a liquid-level indicating means comprises a vertically arranged series of said detecting elements, when the actuating means rises above a first or lowest array of said detecting elements, the output signal indicating it had risen the height of that first array is maintained and is added
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patent: 3906469 (1975-09-01), Kronk
patent: 4466284 (1984-08-01), Dumery
patent: 4589282 (1986-05-01), Dumery
patent: 4627283 (1986-12-01), Nishida
patent: 4796472 (1989-01-01), Lew
patent: 4976146 (1990-12-01), Senghaas et al.
patent: 5056049 (1991-10-01), O'Neill
Le Que T.
Rolls-Royce and Associates Limited
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