Fluid flow sensor and low flow cut-off device

Abstract

The present disclosure provides a fluid flow sensor and low flow cut-off device and an associated method for its operation that is easily integrated into a fluid delivery and/or fluid control system for a variety of appliances, such as boilers and water heaters. The fluid flow sensor and low flow cut-off device can determine a fluid flow rate in or to an appliance and whether that fluid flow rate meets or exceeds a predetermined fluid flow rate threshold for the safe and/or efficient operation of the appliance and, if the threshold is not met, disable the appliance from operating or continuing to operate under such conditions.

What is claimed is: 
     
         1 . A fluid flow sensor and low flow cut-off device for an appliance comprising:
 a probe disposed at a fluid supply to the appliance;   a first control unit in electrical communication with the probe; and   a second control unit in electrical communication with the first control unit and the appliance;   wherein the probe generates an output signal indicative of a fluid flow rate to the appliance;   wherein the first control unit monitors the output signal and determines the fluid flow rate over time and compares the fluid flow rate to a predetermined threshold fluid flow rate at a first time, and generates a first safety signal output if the fluid flow rate is greater than or equal to the predetermined threshold fluid flow rate, and compares the fluid flow rate to the predetermined threshold fluid flow rate at a second time and generates a second safety signal output if the fluid flow rate is greater than or equal to the predetermined threshold fluid flow rate;   wherein the second control unit comprises a switch operable to enable operation of the appliance, the switch having a first switch interface and a second switch interface, wherein the first safety signal output is received at the first switch interface and the second safety signal is received at the second switch interface; and   wherein only when both the first and second safety signal outputs are received, respectively, at the first and second switch interfaces does the switch enable operation of the appliance.   
     
     
         2 . The fluid flow sensor and low flow cut-off device for an appliance of  claim 1  wherein at least one of the first and the second safety signal outputs is a pulsed signal; and
 wherein at least one of the first and second switch interfaces comprises a pulse detector circuit. 
 
     
     
         3 . The fluid flow sensor and low flow cut-off device for an appliance of  claim 2  wherein the at least one of the first and second switch interfaces that comprises a pulse detector circuit is a resistor-capacitor circuit. 
     
     
         4 . The fluid flow sensor and low flow cut-off device for an appliance of  claim 2  wherein the switch comprises a relay having a normally-opened condition; and
 wherein the first switch interface and the second switch interface are electrically in series with the relay. 
 
     
     
         5 . The fluid flow sensor and low flow cut-off device for an appliance of  claim 4  wherein the first switch interface comprises a high-side control for the relay, and the second switch interface comprises a low-side control for the relay. 
     
     
         6 . The fluid flow sensor and low flow cut-off device for an appliance of  claim 4  wherein the first switch interface and the second switch interface are electrically in series with one another and together comprise either a high-side control or a low-side control for the relay. 
     
     
         7 . The fluid flow sensor and low flow cut-off device for an appliance of  claim 1  wherein the appliance is a boiler or a water heater and the switch is operable to enable operation of a burner for the appliance. 
     
     
         8 . A method for controlling the operation of an appliance, the method comprising:
 determining a first fluid flow rate at the appliance at a first time;   comparing the first fluid flow rate to a threshold fluid flow rate;   generating a first safety signal if the first fluid flow rate is greater than or equal to the threshold fluid flow rate;   determining a second fluid flow rate at the appliance at a second time;   comparing the second fluid flow rate to the threshold fluid flow rate;   generating a second safety signal if the second fluid flow rate is greater than or equal to the threshold fluid flow rate;   communicating the first safety signal to a high-side of a switch for enabling operation of the appliance;   communicating the second safety signal to a low-side of the switch;   closing the switch only when both the first safety signal and the second safety signal are communicated to the switch; and   enabling operation of the appliance.   
     
     
         9 . A fluid flow sensor and low flow cut-off device for an appliance comprising:
 a probe disposed at a fluid supply to the appliance;   a first control unit in electrical communication with the probe; and   a second control unit in electrical communication with the first control unit and the appliance;   wherein the probe generates an output signal indicative of a fluid flow rate to the appliance;   wherein the first control unit monitors the output signal and determines a fluid flow rate over time and compares the fluid flow rate to a predetermined threshold fluid flow rate, and simultaneously generates both a first safety signal output and a second safety signal output if the fluid flow rate is greater than or equal to the predetermined threshold fluid flow rate;   wherein the second control unit comprises a switch operable to enable operation of the appliance, the switch having a first switch interface and a second switch interface, wherein the first safety signal output is received at the first switch interface and the second safety signal is received at the second switch interface; and   wherein only when both the first and second safety signal outputs are received, respectively, at the first and second switch interfaces does the switch enable operation of the appliance.   
     
     
         10 . The fluid flow sensor and low flow cut-off device for an appliance of  claim 9  wherein at least one of the first and the second safety signal outputs is a pulsed signal; and
 wherein at least one of the first and second switch interfaces comprises a pulse detector circuit. 
 
     
     
         11 . The fluid flow sensor and low flow cut-off device for an appliance of  claim 10  wherein the at least one of the first and second switch interfaces that comprises a pulse detector circuit is a resistor-capacitor circuit. 
     
     
         12 . The fluid flow sensor and low flow cut-off device for an appliance of  claim 10  wherein the switch comprises a relay having a normally-opened condition; and
 wherein the first switch interface and the second switch interface are electrically in series with the relay. 
 
     
     
         13 . The fluid flow sensor and low flow cut-off device for an appliance of  claim 12  wherein the first switch interface comprises a high-side control for the relay, and the second switch interface comprises a low-side control for the relay. 
     
     
         14 . The fluid flow sensor and low flow cut-off device for an appliance of  claim 12  wherein the first switch interface and the second switch interface are electrically in series with one another and together comprise either a high-side control or a low-side control for the relay. 
     
     
         15 . The fluid flow sensor and low flow cut-off device for an appliance of  claim 9  wherein the appliance is a boiler or a water heater and the switch is operable to enable operation of a burner for the appliance.