Abstract:
An automatic system is disclosed which monitors and replenishes hazardous liquids in their holding tanks, as such liquids are typically used in manufacturing processes. The inventive system and method obviate the need for manual surveillance and handling of the hazardous liquids during the detection and replenishment maintenance tasks. In prior practice, maintenance personnel were subjected to dangers from the hazardous liquids and their noxious gases, while the work area (e.g., clean room) in the vicinity of the liquid tanks was also subjected to contamination.

Description:
FIELD OF THE INVENTION 
     The disclosed invention comprises a processor circuit and method for automating the replenishment of hazardous liquids in tanks, such as are used in microelectronics manufacturing. 
     BACKGROUND OF THE INVENTION 
     Many manufacturing processes, such as those in the field of microelectronics, require the use of various acids and chemicals in liquid form. These liquids are extremely hazardous to human operators, and are also a potential contaminant to the work environment (such as a clean room) if not properly contained. 
     Typically, the liquids are held in large tanks, which supply their contents to the manufacturing process, on demand from a system controller. When the liquid level in a tank falls below a pre-determined &#34;low&#34; level, it must be replenished to maintain the production process. Traditionally, manual surveillance was used to detect the need for replenishment. Once this need was determined, the task of replenishing the liquid was accomplished manually by maintenance personnel. Due to the hazardous nature of the liquid, there was a constant danger to personnel, as well as to the integrity of the manufacturing environment. In addition, the production process would normally be shut down during the replenishment period. 
     It is an object of the present invention, therefore, to eliminate the aforementioned danger to manufacturing personnel by automating the replenishment task. The disclosed automated procedure precludes the need for human intervention in the maintenance of adequate liquid levels in the liquid containment tanks. 
     It is a further object of the present invention to protect the working environment area adjacent to the liquid tanks during the liquid replenishment process. 
     It is another object of the present invention to minimize downtime of the production process during the hazardous liquid replenishment process. 
     SUMMARY OF THE INVENTION 
     The disclosed invention is an automatic system for detecting the need for replenishment, and then accomplishing such replenishment, for tanks containing hazardous liquids, such as acids and chemicals. 
     The present invention comprises a liquid supply, a liquid tank, a system processor, and a liquid level control circuit. 
     The liquid supply is fed to the liquid tank by means of an ON-OFF valve, which is electronically operated by a signal from the liquid level control circuit. 
     The liquid tank contains a FULL level sensor and a LOW level sensor. When the tank liquid reaches a pre-set FULL level, the FULL sensor outputs a FULL signal to the system processor. Similarly, when the tank liquid falls below a pre-set LOW level, the LOW sensor outputs a LOW signal to the system processor. 
     When the tank is full, the system processor routes the FULL signal to the liquid level control circuit, which is placed in an &#34;off&#34; mode by the FULL signal. Thus, normal operation is maintained, and the ON-OFF supply valve remains in the OFF position. 
     When the liquid level falls below the FULL level, the FULL signal is no longer outputted to the system processor. Thus, no FULL signal is routed to the liquid level control circuit by the system processor, and the liquid level control circuit is placed in an &#34;enable&#34; mode. 
     When the tank liquid falls below the LOW level, a signal is outputted from the LOW level sensor to the system processor. When the system processor completes its operational cycle, it generates a RUN signal in response to the received LOW signal. The system processor then outputs both RUN and LOW signals to the liquid level control circuit. 
     The liquid level control circuit &#34;ands&#34; the LOW and RUN signals to produce an internal signal, which activates a switching relay and indicator light. The switching relay causes a DC voltage to be applied to the ON-OFF valve, which opens its flow gate between the liquid supply and the liquid tank. At the same time, the switching relay causes the same DC voltage to be applied to a pressure release valve, which is mounted in the liquid tank above the FULL liquid level. The pressure release valve vents the tank gases to expedite the liquid replenishment process. 
     When the tank liquid reaches the FULL level, the FULL sensor outputs a FULL signal. This FULL signal is routed through the system processor to the liquid level control circuit, which is again placed in an &#34;off&#34; mode. This de-activates the switching relay and the indicator light, and removes the DC voltage from both the ON-OFF valve and from the pressure release valve. Both valves close, and the replenishing process is terminated. 
     The presence of the FULL signal, combined with the absence of the LOW signal, causes the system processor to disable the RUN signal, and to begin a new operational cycle. 
     Thus, the present invention provides a completely automatic replenishment process, which safeguards personnel, equipment, and the environment. At the same time, production down time is minimized, due to the elimination of manual handling of the hazardous liquids. 
     For illustrative purposes, the preferred embodiment of the present invention is represented by an automatic acid tank supply system, utilizing a simple transistor logic control circuit. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a single automatic acid tank supply system. 
     FIG. 2 schematically illustrates an acid level control circuit. 
     FIG. 3 illustrates a multiple tank automatic supply system. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The illustrated embodiment of an acid tank automatic supply system is depicted in block diagram form in FIG. 1. 
     An acid supply 2 is connected through an electronically controlled ON-OFF valve 3 to an operational acid tank 4. A FULL level sensor 5 is installed in tank 4, so that when the acid level reaches a pre-determined FULL level, FULL level sensor 5 outputs a FULL signal. 
     A LOW level sensor 6 is installed in tank 4, so that when the acid level falls below a pre-determined LOW level, LOW level sensor 6 outputs a LOW signal. 
     An electronically controlled Pressure Release valve 7 is also installed in tank 4, so that it can vent acid gases during the acid replenishment process. 
     A system processor 1 receives the FULL and LOW output signals from sensors 5 and 6, and outputs corresponding FULL and LOW logic signals. System processor 1 also outputs a RUN logic signal, upon receiving a LOW signal and having completed an operational cycle. 
     An acid level control circuit 8 receives the FULL, LOW, and RUN logic signals directly from system processor 1. When acid level control circuit 8 receives a FULL signal, control circuit 8 is disabled, and there are no outputs to either ON-OFF valve 3 or to Pressure Release valve 7. When acid level control circuit 8 receives both LOW and RUN signals, in the absence of a FULL signal, a DC voltage is outputted to both ON-OFF valve 3 and Pressure Release valve 7, opening the valves and initiating the replenishment of acid. 
     This process continues until the acid level in tank 4 reaches the FULL level, whereupon FULL sensor 5 outputs a FULL signal to system processor 1. System processor 1 then outputs a FULL logic signal to acid level control circuit 8, disabling the control circuit, closing valve 3 and valve 7 and terminating the replenishment of acid. 
     The FULL output signal from FULL sensor 5, in combination with no LOW output signal from LOW sensor 6, causes system processor 1 to disable the RUN output signal, and to reset its internal circuitry for the next operational cycle. 
     Acid level control circuit 8 is shown in detail in FIG. 2, and functions in the following manner. 
     When a FULL signal (logic high) is present at the input to inverter 20, the resulting output into the base of transistor Q2 is a logic low, cutting off Q2. Thus, no current can flow in Q2, Q1, LED 40, or relay 30. The contact arm of relay 30 remains in the normally open position, separating the 24v DC supply from ON-OFF valve 3 and Pressure Release valve 7. With no power applied, valve 3 and valve 7 remain closed. In this mode, no acid flows from supply 2 to tank 4, and no acid gas pressure is vented by valve 7. 
     When a FULL signal is not present at the input to inverter 20, the resultant output into the base of transistor Q2 is a logic high, enabling Q2 to conduct. Then, when AND gate 10 receives both a LOW signal and a RUN signal (logic highs), AND gate 10 outputs a logic high to the base of transistor Q1, causing Q1 to conduct. 
     Now, the series circuit of Q2, Q1, LED 40, and relay 30 is completed between the 12 vDC power source and circuit ground. Under this condition, current flows through Q2, Q1, LED 40, and the coil of relay 30. LED 40 is illuminated, indicating that control circuit 8 is active. The energized coil of relay 30 pulls its contact arm to the closed position. The closed contact arm of relay 30 connects the 24 v power source to ON-OFF valve 3 and Pressure Release valve 7. Valve 3 is thereby caused to open, allowing acid supply 2 to replenish the acid level in acid tank 4. At the same time, valve 7 is caused to open, venting the acid gas pressure in tank 4, which expedites the replenishment process. 
     When the acid level in tank 4 exceeds the LOW liquid level, LOW level sensor 6 ceases to output a signal to system processor 1, but system processor 1 maintains its RUN and LOW output signals to control circuit 8 until system processor 1 also receives a FULL signal from tank 4. This FULL signal is outputted from FULL sensor 5 when the acid level in tank 4 reaches the FULL level. When system processor 1 receives this FULL signal, it outputs a logic high to inverter 20 in control circuit 8. Inverter 20 then outputs a logic low signal to the base of transistor Q2, cutting off Q2. Thus, current can no longer flow in the Q2, Q1, LED 40, and relay 30 series circuit, deenergizing both LED 40 and the relay coil of relay 30. The contact arm of relay 30 reverts to its normally open position, removing 24 v power from valve 3 and valve 7. Valve 3 closes, shutting off the acid flow from supply 2 to tank 4, while valve 7 closes the gas vent of tank 4. System processor 1, having received a FULL signal in the absence of a LOW signal, disables its RUN and LOW output signals, and resets its internal circuitry to resume normal operation. 
     While the above described embodiment of the present invention refers to a single tank replenishment system, many alternative embodiments are feasible. For example, a multiple tank supply system 100 is shown in FIG. 3, which can include any number of tank sub-systems, e.g., #1, #2, #3. 
     In such a multiple system, each sub-system is controlled by its own FULL and LOW signals, in conjunction with its corresponding supply 101, tank 102 and control circuit 104. The master system processor 108 outputs individual FULL and LOW signals to each sub-system control circuit 104, as in the above described single tank embodiment. However, the RUN signal output from the master system processor is common to all sub-systems, and is available only at the completion of an operational cycle. 
     Since many embodiments of the inventive automatic liquid replenishment system are possible, the scope of the present invention is limited only by the following claims.