Fluid level sensor

Details Fluid level sensor Fluid level sensor

2001-06-06

2003-06-03

Williams, Hezron (Department: 2856)

Measuring and testing

Liquid level or depth gauge

Immersible electrode type

C073S30400R, C307S118000, C340S620000

Reexamination Certificate

active

06571625

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to fluid level sensors.
BACKGROUND OF THE INVENTION
As one can ascertain, the prior art is replete with many devices which operate to monitor a fluid level in a tank or other storage vessel. Many devices operate by means of an electromechanical switch which is activated by a float. The float rides or floats on the surface of the fluid. When the fluid reaches a given level, a switch coupled to the float is operated. These types of devices are undesirably subject to sticking in either the on or off position though.
There are other systems which utilize electrical or electronic devices to detect the level of fluid in a vessel or otherwise. For example, fluid level controls for containers such as boilers are known as shown by U.S. Pat. No. 3,834,357 issued Sep. 10, 1974 to L. Kaczmarek et al. Conductance probe controls detect a level of a conductive media, such as a fluid, by passing an electrical current through a probe, into the conductive media and then back to a controller. The probe is at least partially immersed in the fluid when the fluid is at certain levels and not in contact with the fluid when the fluid is at lower levels. The controller measures the received current level to determine whether the probe is in contact with the media, i.e. whether a fluid is at or above a certain level. Such devices conventionally utilize AC currents, as applying a constant DC current to a probe exposed to a conductive fluid can undesirably promote probe deterioration. However, a drawback of using AC is that it requires the inclusion of support circuitry when also using a conventional microcontroller. This increases the cost and complexity of such a device.
To promote safety, probe excitation should also be limited to safe levels. Level control circuits in which the electrical path through an electrode or probe is at a low AC level such as 24 VAC is shown by U.S. Pat. No. 4,019,067 issued Apr. 19, 1977 to R. Gladstone.
It is an object of the present invention to provide a cost efficient fluid level sensor which overcomes these limitations of the prior art and yet allows for a sufficiently low probe excitation potential so as not to create an unnecessary safety risk.
SUMMARY OF INVENTION
A device for sensing a level of a fluid, the device including: a microcontroller; a probe coupled to the microcontroller; and a plurality of instructions for use by the microcontroller to apply a given DC potential to the probe for a first period of time, measure a voltage associated with the level of the fluid to be sensed after the first period of time, and apply a reference DC potential to the probe for a second period of time.


REFERENCES:
patent: 3644885 (1972-02-01), Radin
patent: 3665209 (1972-05-01), Webb et al.
patent: 3834357 (1974-09-01), Kaczmarek et al.
patent: 3999148 (1976-12-01), Miesterfeld
patent: 4019067 (1977-04-01), Gladstone
patent: 4027172 (1977-05-01), Hameline
patent: 4259982 (1981-04-01), Bartels
patent: 4356406 (1982-10-01), Bartels
patent: 4385290 (1983-05-01), Fiala
patent: 4390793 (1983-06-01), John
patent: 4678403 (1987-07-01), Rudy et al.
patent: 5613398 (1997-03-01), Lawson

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