Abstract:
An improved boiler water-level controller. According to one aspect of the present invention, a positive blowdown signal is presented to indicate to the operator that the alarm probe is in steam; performing blowdown until this indicator turns on helps ensure that the alarm probe is working properly. According to another aspect of the present invention, the controller uses a novel methodology of sensing water level using conductivity probes. An embodiment of this methodology uses the charging and discharging of a capacitor through a resistive value to sense the presence of water.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Patent Application No. 60/215,604 filed Jun. 30, 2000, the entire disclosure of which is hereby incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to the field of feed-water level control in boilers, and more specifically to an automatic boiler level controller having an improved water level sensing methodology and a positive blowdown circuit to ensure that the alarm probe is free of debris or buildup. 
     BACKGROUND OF THE INVENTION 
     Steam boilers are used in various applications, e.g., generation of electricity with steam turbine generators. In typical boilers a burner burns fuel from a fuel supply to create heat to generate steam from feed-water inside the boiler and the steam is piped to a generator or other system. Thus, typical boilers have both steam and feed-water inside them. It is known that the level of feed-water inside a boiler must be kept above a certain level. It is also known in the art to use a controller and one or more conductivity sensors to automatically control the level of feed-water in the boiler by controlling a boiler feed pump that provides additional feed-water to the boiler when the feed-water level falls to below a first level. It is also known to provide an alarm and/or turn off the fuel supply to the burner when the feed-water level falls to below a second, lower level. 
     It is known in the art of boiler level control to sense the water level inside the boiler using conductivity sensors located inside a column positioned outside the boiler but in fluid connection with the boiler. The lowest conductivity sensor is typically the alarm sensor. One known problem with this known configuration is that debris can build up around the alarm sensor causing false readings, e.g., the alarm conductivity sensor is in steam, but debris surrounding the alarm sensor provides a conductive path causing the controller to falsely determine that the alarm sensor is in water. A known solution to the debris problem is to use pressure from steam to “blow down” the debris away from the alarm sensor by opening a blow down valve. This blowdown procedure has the additional effect of lowering the water level in the column containing the conductivity probes, which can be problematic, because as the water is blown down from the various conductivity probes, the controller falsely determines that the level of water in the boiler is lowering and turns on the feed-water pump and/or triggers an alarm and/or shuts off the fuel to the burner. A typical way to overcome this problem is to add circuitry that bypasses the control signals from the controller during blowdown. This prevents false alarms during blowdown, but does not provide any indication as to whether the blowdown process is complete or effective. 
     Additionally, the circuits typically used to determine water level with conductivity probes are relatively complex with a relatively high parts count. 
     There is a need, therefore, for an improved boiler controller. 
     SUMMARY OF THE INVENTION 
     The present invention is directed toward an improved boiler controller. According to one aspect of the present invention, a positive blowdown signal is presented to indicate to the operator that the alarm probe is in steam; performing blowdown until this indicator turns on helps ensure that the alarm probe is working properly. According to another aspect of the present invention, the controller uses a novel methodology of sensing water level using conductivity probes. An embodiment of this methodology uses the charging and discharging of a capacitor through a resistive value to sense the presence of water. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings, which are incorporated in and constitute a part of this specification, embodiments of the invention are illustrated, which, together with a general description of the invention given above, and the detailed description given below, serve to example the principles of this invention, wherein: 
     FIG. 1 is a block diagram of a typical boiler level control installation; 
     FIG. 2 is an end view of a typical boiler showing the probe column in cross-section; 
     FIG. 3 is a top view of the probe column; 
     FIG. 4 is a cross-sectional view of the probe column taken along path A A in FIG. 3 with the conductivity probes rotated for clarity; 
     FIG. 5 is a front plan view of the front cover of the controller of the present invention showing various indicators; 
     FIG. 6 is a block diagram showing the back cover of the controller of the present invention indicating various connections to the controller; 
     FIG. 7 is a block diagram showing an example configuration of the controller of the present invention that provides pump control and fuel cutoff with alarm; 
     FIG. 8 is a schematic block diagram showing the sensing configuration of the controller of the present invention; 
     FIG. 9 is a flow chart showing the sensing process used by the controller of the present invention to determine whether the conductivity probes are in water or in steam; 
     FIG. 10 is a flow chart showing the procedure used during blowdown; and 
     FIG. 11 is a schematic block diagram showing another embodiment of the sensing configuration of the controller of the present invention; and 
    
    
     The Appendix is a copy of U.S. Provisional Patent Application No. 60/215,604 filed Jun. 30, 2000, the entire disclosure of which was incorporated by reference above. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The automatic boiler level controller 10 according to the present invention is a microprocessor-based controller with a built in watch dog timer. The controller  10  includes many self diagnostic and safety features. It has the ability to detect out of sequence probe indications and alert the operator of a problem with the controller&#39;s sensing circuit. Along with the out of sequence logic, the controller  10  includes a positive blowdown circuit. During the blowdown, the controller  10  signals the operator that the alarm sensor has sensed steam. This feature ensures that the alarm probe is free of debris or build up. The controller uses proven conductivity technology to sense water level and uses a very unique methodology of sensing the conductivity: the I/O (input/output) ports of the microprocessor and the charging and discharging of a capacitor through a resistive value senses the presence of water. 
     FIG. 1 shows a typical boiler level control installation. A pump control and low water cut-off circuit  20  is connected to a water column  22 . Water column  22  is connected to steam boiler  24  by a steam connection  26  located at the top of the boiler  24  and by a water connection  28  located near the middle of the boiler  24 . The circuit  20  controls a boiler feed pump  30 , controls the burner  32 , and controls an alarm  34 . The boiler feed pump pumps feed-water from a water source, e.g., condensate receiver  36  to the boiler  24 . FIG. 2 shows a probe column  22  having a plurality of conductivity probes  40  and further shows a blow down valve  42  in fluid communication with the probe column  22  and with the water connection  28  of boiler  24 . The probe column  22  is in circuit communication with controller according to the present invention as shown in FIGS. 7 and 8. FIG. 3 shows three conductivity probes  40   a ,  40   b , and  40   c  positioned inside probe column  22 . As shown in FIG. 4, these three probes  40   a ,  40   b , and  40   c  are of three different lengths that extend into the probe column  22  to three different depths. In the probe column shown in FIG. 4 the tip of upper probe  40   a  is 0.75″ higher than the tip of middle probe  40   b  and the tip of middle probe  40   b  is 0.75″ higher than the tip of lower probe  40   c . The controller  10  will maintain the water level in the boiler  24  between the high probe  40   a  and middle probe  40   b  of the probe column  22 . If the water level falls to the low level probe  40   c  in the column  22  the alarm and fuel cut-off circuit will be activated cutting off the fuel to the burner and sound an alarm. The vertical position of the probe column  22  on the boiler  24  is very important. Improper positioning of the probe column  22  could result in damage to the boiler  24  and possible injury to operating personnel. It is recommended that all installation be done in accordance with the original boiler manufacturer&#39;s recommendations. If no such recommendations exist, position the high level probe  40   a  so that it matches the position of the normal water level in the boiler drum. By setting the high probe  40   a  at the normal water level the controller  10  will maintain the water level between the high level probe  40   a  and the middle probe  40   b . The distance between the high probe  40   a  and the middle probe  40   b  is ¾ inch. The water level will be allowed to fall an additional ¾ inch to the low probe  40   c  before the alarm circuit will be activated. Thus, the total distance between the high probe  40   a  and the low probe  40   c  is 1½ inches. 
     As shown in FIG. 5, the controller  10  according to the present invention generates four indicators: power/error indicator  50 , an alarm relay indicator  52 , a pump relay (energized) indicator  54 , and a positive blowdown indicator  56 . The controller  10  illuminates the power/error indicator  50  steady on to indicate normal operation and causes the power/error indicator  50  to slowly blink to indicate specific alarm conditions. The controller  10  illuminates the alarm relay indicator  52  to indicate that alarm condition exists. When an alarm condition exists, the controller  10  causes the power/error indicator  50  to display a number of flashes corresponding to an error condition (see Tables 1 and 2), thus permitting an operator observing the error code on the power/error indicator  50  to diagnose the specific error condition. 
     The controller  10  is able to diagnose problems with the probes  40  and probe wires. These are diagnosed as out of sequence errors. When a problem occurs, the controller will put the ALARM RELAY into the alarm state and continuously flash an error code. The error code will show a number of sequential flashes, followed by a longer interval. The error code is repeated in this manner. When the error condition is resolved, the error state can be cleared by pushing a user installed reset switch. A reset switch will not clear the error state until the error condition is resolved. Table 1 shows the error probe out of sequence codes flashed by the power/error indicator  50  during an out of sequence error condition: 
     
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 PROBES 
                   
               
             
          
           
               
                 Slow Flashes 
                 High 
                 Middle 
                 Low 
               
               
                   
               
               
                 1 
                 Water 
                 Water 
                 Steam 
               
               
                 2 
                 Water 
                 Steam 
                 Water 
               
               
                 3 
                 Steam 
                 Water 
                 Steam 
               
               
                 4 
                 Water 
                 Steam 
                 Steam 
               
               
                   
               
             
          
         
       
     
     For example, if liquid level was above the middle probe  40   b  (and below the upper probe  40   a ), and the low probe  40   c  were to become disconnected, then the controller would sense steam for the high probe  40   a , water for the middle probe  40   b , and steam for the low probe  40   c . The controller  10  would then set the ALARM RELAY into the alarm state and repeatedly flash the error code of three slow flashes (followed by a longer interval). 
     The controller  10  illuminates the pump relay (energized) indicator (LED) to indicate that the pump relay (not shown) is energized and the normally open contact is connected to relay common (i.e., closed). The controller  10  lights the positive blowdown indicator  56  to indicate that the low probe  40   c  is in steam. As discussed further below, blowdown should proceed until this indicator turns on to ensure that the low level probe is working properly. 
     Along with the ability of the controller  10  to detect problems with the probes and probe wires, the controller  10  also has the ability to detect and display many other error conditions that may arise. The following is a description of the general errors that the controller will detect: (i) blow down time out: if the normally-open momentary contact switch  152  (FIG. 7) connected between the terminal blocks  90 , 92  labeled “Blow Down” (FIGS. 7-8) is held closed for more than two minutes then the controller  10  will enter to into an alarm state; (ii) system hardware errors I and II: the controller  10  has the ability to detect faults that may occur with in its own circuitry and if this were to occur, a system hardware fault will be displayed on the indicator; and (iii) low level alarm: this error will flash when under normal operation the low level probe senses steam. Table 2 shows the error probe out of sequence codes flashed by the power/error indicator  50  for the foregoing error conditions: 
     
       
         
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Slow Flashes 
                 Description 
               
               
                   
               
             
             
               
                 5 
                 Blow Down Time Out 
               
               
                 6 
                 System Hardware Error I 
               
               
                 7 
                 System Hardware Error II 
               
               
                 8 
                 Low Probe in Steam 
               
               
                   
               
             
          
         
       
     
     The electronics for the controller  10  are located on the backside of the controller&#39;s enclosure cover. As shown in FIG. 6, the electronics for the controller  10  are divided into two sides: a high voltage side  60  and a low voltage side  62 . The following identifies and describes the components on the board. On the high voltage side  60 , the controller has: (i) a controller power 120 VAC terminal block connections  70  for power to the controller electronics (the controller input voltage is factory set at 120 VAC); (ii) an alarm relay common terminal block connection  72  to (SPDT) alarm relay common; (iii) an alarm relay normally closed terminal block connection  74  to (SPDT) alarm relay normally closed contact (this contact makes connection to the relay common  72  when an alarm condition occurs); (iv) an alarm relay normally open terminal block connection  76  to (SPDT) alarm relay normally open contact (this contact makes connection to the relay common  72  when no alarm condition occurs); (v) a pump relay common terminal block connection  78  to (SPDT) pump relay common; (vi) a pump relay normally open terminal block connection  80  to (SPDT) pump relay normally open contact (this contact makes connection to the relay common  78  when liquid level falls below the middle probe  40   b  level); (vii) a pump relay normally closed terminal block connection  82  to (SPDT) pump relay normally closed contact (this contact makes connection to the relay common  78  when liquid level reaches the high probe  40   a  level). Use copper conductors only to connect to the high voltage side  60 . 
     On the low voltage side  62 , the controller  10  has: (i) blow down  1   90  &amp; blow down  2   92  terminal block connections, (ii) reset  1   94  &amp; reset  2   96  terminal block connections, and (iii) probe terminal block connections: high probe terminal block connection  100 , middle probe terminal block connection  102 , low probe terminal block connection  104 , and probe ground terminal block connection  106 . The blow down  1  terminal block connection  90  and blow down  2  terminal block connection  92  can be connected to a momentary, normally open switch  152  (FIG.  7 ). When blow down  1   90  is connected to blow down  2   92 , the controller  10  will stop controlling the relays (the alarm relay and the pump relay). This switch contact is designed to allow the operator to blow down the probe column  22  without tripping the fuel cut out and alarm circuit. The controller  10  will return to normal operation once the connection between blow down  1   90  and blow down  2   92  is broken or after a period of two minutes, which ever comes first. 
     The reset  1  terminal connection  94  and reset  2  terminal connection can be used to implement system reset in two ways: automatic reset (m 1 ) and manual reset (m 2 ). For automatic reset (m 1 ), a jumper wire in placed across reset  1  and reset  2  terminal block connections  94 ,  96 . If an error is detected, once the level is back above the low level probe, the alarm will automatically reset. After the error condition has been corrected the alarm normally closed relay connection will once again be closed, and the normally open relay connection will be opened. For manual reset (m 2 ), reset  1  and reset  2  terminal block connections  94 ,  96  are connected to a momentary, normally open switch  150  (FIG.  7 ). After any error has been detected and corrected, connect reset  1   94  to reset  2  to reset the alarm relay, e.g., with switch  150 . After reset  1   94  is connected to reset  2   96  and the error condition has been corrected, the alarm normally closed relay connection will once again be closed, and the normally open relay connection will be opened. 
     As to the probe connections, the high probe terminal block connection  100  is connected to the high probe  40   a , the middle probe terminal block connection  102  is connected to the middle probe  40   b , the low probe terminal block connection  104  is connected to the low probe  40   c , and the probe ground terminal block connection  106  is connected to the ground screw (not shown) located on the controller&#39;s probe column  22 . All low voltage wiring to the controller  10  is required to be wired using NEC Class 1 wiring. 
     FIG. 7 shows an example configuration for the controller  10  that includes pump control and fuel cutoff, with alarm. In this example, the controller  10  controls power to the pump to keep the water level between the high level probe  40   a  and the middle level probe  40   b . If the water level falls below the low probe  40   c , or if a failure to sense water is detected, the controller  10  cuts power to the fuel control valve and sounds an alarm. As to power connections, with the power off, connect 120 VAC service wires to the two terminal block positions  70  labeled “POWER 120 VAC.” The power input terminal block  70  has three positions. Only two of the three positions are used. The center position is not to be used and is not connected to any circuits of the controller board. As to pump connections, connect the high voltage service wire  110  to the terminal block position  78  labeled PUMP COM (PUMP RELAY COMMON), connect the terminal block connection  80  labeled PUMP NO (PUMP NORMALLY OPEN) to the hot side  112  of the pump motor  114  or pump motor controller, and connect the neutral side  116  of the pump motor  114  to the neutral service wire  120 . The controller  10  PUMP RELAY can directly control a motor rated for 16 full load Amps at 120 VAC or 12 full load Amps at 240 VAC. If the pump motor has a higher current rating, do not connect the pump directly to the controller  10 . As to fuel cutoff connections, connect the high voltage service wire  110  to the terminal block  72  labeled ALARM COM (ALARM RELAY COMMON), connect the terminal block position labeled ALARM NC (ALARM NORMALLY CLOSED) to the hot side  130  of the fuel valve solenoid  132 , and connect the neutral wire  134  from the fuel valve solenoid  132  to the neutral service wire  120 . If an alarm is desired, connect the terminal block position labeled ALARM NO (ALARM NORMALLY OPEN) to the hot side  140  of alarm  142  (make sure that the alarm is rated for the same high voltage as the solenoid) and connect the neutral wire  144  from the alarm  142  to the neutral service wire  120 . The controller  10  ALARM RELAY can directly control  20  full load resistive Amps at 120 VAC or 240 VAC. If the alarm  142  or the fuel valve solenoid  132  has a higher current rating, do not connect these directly to the controller  10 . As to the probe connections, connect the terminal block position  106  labeled PROBE GND to the grounding screw on the probe column  22 , connect the terminal block position  104  labeled PROBE LOW to the lowest probe  40   c  of the three probes on the probe column  22 , connect the terminal block position  102  labeled PROBE MID to the middle probe  40   b  on the probe column  22 , and connect the terminal block position  100  labeled PROBE HI to the highest probe  40   a  on the probe column  22 . As to reset connections, for an Automatic reset alarm, connect the two terminal block positions  94 ,  96  labeled RESET with a jumper wire and for a Manual reset alarm, connect the two terminal block positions  94 ,  96  labeled RESET to a normally open momentary switch  150 . As to blow down connections, connect the two terminal block positions  90 ,  92 , labeled BLOW DOWN to a second normally open momentary switch  152 . Do not run wires from the low voltage probes, probe ground, reset and blow down switches in the same conduit as high voltage service wires. 
     FIG. 8 is a schematic block diagram showing the processor  200  of controller  10  and some of the components connected thereto. In this block diagram, the switches  150 ,  152  are connected to (not necessarily directly connected to) processor  200 , as are the alarm relay  202  and the pump relay  204 . Additionally, there are certain capacitive circuits connected to the processor  200 , one for each probe  40 . These capacitive circuits allow the controller  10  to sense the water level using conductivity probes  40 . More specifically, in FIG. 8, there are three capacitive circuits, C 1 , C 2 , and C 3 , connected to the processor  200 . The three capacitive circuits C 1 , C 2 , and C 3  are connected to the processor  200  by a driving pin DP and three sensing pins SP 1 , SP 2 , and SP 3 . The driving pin DP and the sensing pins SP 1 , SP 2 , and SP 3  are under control of the microprocessor  200 , making them either an input (high impedance) or an output (low impedance). Driving pin DP is connected through SP 1 , SP 2 , SP 3  through a small value capacitor. Sensing pins SP 1 , SP 2 , and SP 3  are connected to (not necessarily directly connected to) probes  40   a ,  40   b , and  40   c . As discussed above, controller  10  uses proven conductivity technology to sense water level and uses a very unique methodology of sensing the conductivity: the I/O (input/output) ports of the microprocessor  200  and the charging and discharging of a capacitor through a resistive value sense the presence of water. 
     The process by which processor  200  uses capacitive circuits C 1 , C 2 , and C 3  to sense water level is shown in FIG.  9 . The software routine starts at  252 . First the processor  200  makes sensing pins SP 1 , SP 2 , SP 3  outputs and sets them HIGH, at  254 , and at  256 , the processor makes driving pin DP an output and sets it HIGH. Then the software waits long enough for capacitors C 1 , C 2 , C 3  to go to steady state through a 100K ohm resistor, at  258 . Next, at  260 , the processor  200  makes sensing pins SP 1 , SP 2 , SP 3  all inputs, and drives the driving pin DP to zero volts (LOW), at  262 . Next, the processor reads sensing pins SP 1 , SP 2 , SP 3 , at  264 . Then, at  266 , if a pin is HIGH voltage, the corresponding probe is in water (voltage does not go through the 100 K resistor), at  268 , and if the pin is LOW voltage, the probe is in steam (voltage goes through the 100 K resistor), at  270 , and the routine ends at  272 . 
     As discussed above, the controller  10  has a positive blowdown circuit to ensure that the alarm probe is free of debris or buildup. The probe column  22  must be blown down once a day. FIG. 10 shows the blowdown procedure  300 . The procedure starts at  302 . To perform the blow down, the operator first depresses and holds the blowdown bypass button  152 , at  304 . Next, the blowdown valve  42  is slowly opened, at  306 . When the controller determines that low level probe  40   c  is in steam, the positive blow down indicator  56  located on the front of the controller  10  will illuminate indicating that the low level probe  40   c  is free of debris and is operating properly. Once the positive blow down indicator has been illuminated, at  308 , the blowdown should be continued for an additional twenty to thirty seconds, at  310 . Next, the blowdown valve is closed, at  312 , and the water level is allowed to rise to the point where the positive blowdown indicator  56  turns off, at  320 . Then, at  322 , the operator releases the blowdown bypass button  152  and allows the controller  10  to go back into normal operation. If the blow down bypass button  152  is depressed for more than two (2) minutes, the controller  10  will automatically reset itself and go back into normal operation. 
     While the present invention has been illustrated by the description of embodiments thereof, and while the embodiments have been described in some detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative apparatus and methods, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of the applicant&#39;s general inventive concept.