Fluid level sensor

Details Fluid level sensor Fluid level sensor

2000-04-04

2001-02-27

Wu, Daniel J. (Department: 2632)

Communications: electrical

Condition responsive indicating system

Specific condition

C340S612000, C137S397000, C073S305000, C073S308000, C116S228000

Reexamination Certificate

active

06195013

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to float sensors in general, and to float sensors employing a reed switch to detect the movement of a float in particular.
BACKGROUND OF THE INVENTION
Reed switches have long found use in float sensors where the inherent advantages of reed switches bring reliability and low cost to float sensor designs. The reed switch is a low-cost component and if properly designed can have a service life of millions of cycles. The reed switch, moreover, is hermetically sealed which is an advantage any time a switch is employed near liquids. A reed switch is actuated by a change in magnetic flux with respect to the reed switch. This means that the switch can be opened or closed by the movement of a magnet, which is some distance from the reed switch. The ability of the reed switch to respond to the movement of a magnet allows a float incorporating a magnet to actuate a switch in response to change in liquid levels, usually to close an electrical circuit.
To limit the current, which flows through a reed switch, a current limiting resistor will often be installed in series with the reed switch. By limiting the switch current, the life of the reed switch may be increased almost arbitrarily to more than one hundred million cycles.
Float sensors are typically employed to return a single digital bit upon a single condition. The condition often indicates a-fluid container is nearly full or nearly empty. In these days of broad band sensors, the continuing utility of a sensor that can reliably indicate a single condition has not decreased. In fact, reed switches are often employed with more sophisticated solid state sensors to provide greater reliability in detecting particular system conditions.
Float sensors employing reed switches are generally divided into two types: those where the float containing the activation magnet is mounted in a hinged manner and those where the float is constrained to movement along an axis by a central shaft, or by a surrounding tube.
DISCUSSION OF THE PRIOR ART
U.S. Pat. No. 5,239,285 shows a typical float sensor of the type where a float containing a ring-shaped magnet is constrained to move along a vertical axis by a central shaft. A reed switch contained within the shaft detects the movement of the magnet in the float as liquid causes the float to rise along the length of the central shaft. The shaft extends vertically downwardly from a bracket to which the central shaft is mounted. The shaft has a lower stop and an upper stop between which the float is moved by the rise and fall of fluid within a container. A reed switch is positioned within the shaft between the upper and lower stops so that motion of the float caused by a rise or fall of fluid level causes the reed switch to actuate.
Although reed switches have long been used by Original Equipment Manufacturer (OEM) suppliers to incorporate float sensors into their equipment, the new economy means that equipment suppliers want complete assemblies which provide the float sensor function which have a simple design interface. In this way the OEM supplier can decrease internal engineering while obtaining flexibility in outside design support, resulting in a faster, lower cost product cycle.
SUMMARY OF THE INVENTION
The float sensor of this invention provides a modular, adaptable float sensing module which can interface with a tank having a simple circular flange, wherein the upper and lower surfaces of the flange are parallel. The float has a mounting bracket which incorporates an O-ring seal and bayonet style resilient mounting fingers that lock the mounting bracket to the horizontal flange. The mounting bracket incorporates an electrical connector that forms the electrical interface. A tube of a selected length is bonded or ultrasonically welded to the mounting bracket and positions a reed switch housing a fixed distance downwardly into the tank from the horizontal flange. The reed switch housing is ultrasonic welded or bonded to the end of the tube opposite the mounting bracket to seal the lower end of the tube. The reed switch housing incorporates a stop positioned above a depending cone. The cone terminates in a plurality of radially outwardly extending fingers which lock a float to the reed switch housing, the float being free to float upwardly along the cone to engage the stop. The float is constructed of a ring shaped magnet, foamed in place within a low density plastic foam body that hangs beneath the stop when not supported by fluid within the tank. When fluid is present, the fluid buoys the float and the magnet contained therein upwardly until the float engages the stop. The magnet and reed switch are selected such that the reed switch is closed when the float engages the stop.
The present invention provides a modular float sensor that can be readily sized for a variety of different applications.
The present invention also provides a float sensor that can be rapidly assembled by hand or by machine.
The present invention further provides a float sensor that can be rapidly mounted to a standard interface without tools.
The present invention still further provides a float sensor that is cantilevered downwardly from a single support flange.
The present invention even further provides a float sensor that isolates the reed switch from the monitoring liquid.
Further features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.


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