Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2000-01-18
2001-06-12
Lieu, Julie (Department: 2736)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S686100, C324S207110, C324S207200, C137S554000
Reexamination Certificate
active
06246331
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an apparatus for sensing fluid flow through a conduit and controlling a load based upon the sensing of the fluid flow. More specifically, the present invention is directed toward a fluid flow sensor and a load control circuit employing a variable time delay to control activation of an alarm circuit in a fire protection system.
BACKGROUND OF THE INVENTION
Numerous control circuits have been designed to apply a voltage or current to an electrical load after a time delay. Examples of such circuits are disclosed in U.S. Pat. No. 3,745,382 to Hoge et al., U.S. Pat. No. 3,597,632 to Vandemore, and U.S. Pat. No. 3,764,832 to Stettner. However, these and other known control circuits are relatively complicated and have numerous components, thus increasing manufacturing difficulty and costs. Further, these and other known control circuits typically provide relatively lengthy time delays, on the order of five minutes, and are unreliable when needed to be reduced to a lesser amount of time.
Control circuits are used in a variety of applications including, for example, to activate an alarm circuit in a fire protection system. Conventional fire protection systems typically include a source of water or other fire-extinguishing fluid, a detector for detecting the flow of the fire extinguishing fluid through a pipe or conduit, and an alarm circuit or other load that is activated when a sufficient flow is detected.
In such systems, the alarm is preferably not activated immediately upon detection of fluid flow in the conduit, because flow may occur due to a “water hammer” or fluid backwash within the system. If the alarm were activated immediately upon detection of a water flow, a large number of false alarms would result.
In order to reduce or eliminate such false alarms, a control circuit can delay the activation of the alarm for a predetermined time following detection of an alarm condition. Early detection and control circuits included simple mechanical devices, such as dashpots in which air was forced into and out of a chamber. The alarm would not sound until the air was completely out of the chamber, at which time a switch would close to activate the alarm.
These and other conventional detection mechanisms were designed to provide a delay in the range of 30 seconds to 90 seconds. However, these devices were unreliable and inaccurate, and were thus unsuccessful in eliminating false alarms. Accordingly, solid state electrical load control circuits were developed for fire protection systems such as the time delay circuit known as ICM/HMKS-W1104. These electrical load control circuits delay activation of the alarm until an electrical sensor or switch is rendered conductive.
It would be desirable to provide a relatively simple, reliable, and easy-to-install sensor circuit with minimal current draw, in order to detect a condition (such as fluid flow) which requires activation of a load such as an alarm. While certain flow sensing devices are known, such as those described in U.S. Pat. No. 3,749,864 to Tice, U.S. Pat. No. 4,791,254 to Polverari and U.S. Pat. Nos. 5,086,273 and 5,140,263 to Leon, these and other similar devices include relatively complex arrangements of moving parts. In addition, it would also be desirable to provide an accurate load control circuit which delays activation of a load by using an integrated circuit.
SUMMARY OF THE INVENTION
The present invention solves the foregoing problems, and provides additional advantages, by providing an apparatus for sensing fluid flow through a fluid-carrying conduit. According to exemplary embodiments of the present invention, a valve such as a spring loaded check valve disposed within the conduit has a spring loaded check valve member which is provided with a magnetic shield. A magnet is located on one side of the magnetic shield while a sensor, associated with the valve is located on the opposite side of the magnetic shield. The spring loaded check valve member, and hence the magnetic shield, moves to permit fluid flow. When the magnetic shield is removed from between the magnet and sensor, the magnet activates the sensor. Thus the sensor, which can be a Hall effect sensor, generates a signal when the valve is opened to permit fluid flow.
According to one aspect of the present invention, the sensor and magnet can both be encased in a tube sealed with substantially watertight material and inserted into the conduit (e.g., by threading the encased sensor through a threaded pipe opening) near the valve.
In another exemplary embodiment of the present invention, a load control circuit includes a supply terminal for receiving a supply voltage and a detector which detects a condition requiring the operation of a load. The detector causes a threshold voltage to be generated from the supply voltage, and a time delay controller controls the time required to generate the threshold voltage. A DIAC or equivalent element conducts to generate a first trigger signal once the threshold voltage is achieved, and a silicon-controlled rectifier (SCR) generates a second trigger signal in response to the first trigger signal. The load control circuit includes an opto-TRIAC and a TRIAC or similar switches which are rendered conductive by the second trigger signal to cause a voltage to be provided to the load. According to another embodiment of the present invention, multiple electrically isolated loads can also be controlled.
If the supply voltage is an AC (alternating current) voltage, the load control circuit also includes a rectifying diode or equivalent element for converting the AC voltage to a DC (direct current) voltage. The time delay controller may include a potentiometer (variable resistor) to vary the delay time required to generate the threshold voltage. Additionally, the time delay controller can be implemented via a digital implementation. When digitally employed, a dip switch is used in combination with a digital control to vary the amount of time delay from zero to ninety seconds.
For implementation in a fire protection system in accordance with the present invention, the detector may be a magnet operated reed switch, or a Hall effect sensor, for detecting a threshold fluid flow in a conduit and the load is an alarm for indicating the threshold flow in the pipe.
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Doner Thomas O.
McHugh George J.
AGF Manufacturing, Inc.
Burns Doane , Swecker, Mathis LLP
Lieu Julie
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