Abstract:
A low noise solenoid valve system includes a solenoid valve; and a controller configured to perform a power actuation sequence in which power to the solenoid valve undergoes a plurality of cycles that switch from an actuation level power to a hold level power, wherein the actuation level power is increased at each subsequent cycle, and wherein the actuation power level of one of the plurality of cycles is sufficient to fully actuate the solenoid valve.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application that claims priority to and the benefit of U.S. application Ser. No. 12/479,373, filed Jun. 5, 2009, the entire disclosure of which is hereby incorporated by reference herein. 
    
    
     BACKGROUND 
     The present disclosure relates generally to medical fluid delivery and more particularly to dialysis fluid delivery. 
     Certain dialysis machines use electrically actuated solenoid valves to open and close fluid flow through associated tubing. Peritoneal dialysis (“PD”) is often performed at night while the patient is sleeping. It is accordingly desirable to minimize the acoustical noise that the dialysis machine generates, so as not to disturb the patient while sleeping. Moreover, it is generally desirable to produce equipment that is not noisy. 
     In many cases, the electrically actuated solenoid valves are of a normally closed type, in which the valves are spring or mechanically actuated closed (to occlude flow) and electrically actuated open (to allow flow). Such configuration provides a “fail safe” valve, which closes the tube, occluding fluid flow upon a loss of power. The spring pushes a plunger of the solenoid valve against the tube to occlude the tube, preventing flow. The spring closing of the valves does not cause significant noise because the valve plunger upon a release of electrical power is pushed against pliable tubing, which cushions the impact of the plunger, preventing significant noise. 
     Actuation or energizing of the valves, however, results in rapid acceleration of the plunger and a high velocity impact against a magnetic metal body of the solenoid. The impact generates a fairly significant amount of noise, which can wake the patient and be a nuisance generally. While solenoids can be configured to eliminate metal-to-metal contact, the elimination results in a significant increase in the power needed to hold the solenoid in the actuated position. Some solenoids are equipped with a permanent magnet that reduces the hold power to zero. These solenoids however require power to overcome the permanent magnet to close the plunger and tubing and therefore fail to meet the fail safe or power-fail-closed requirement. 
     A need therefore exists for a solenoid operated pinch valve for medical applications, which reduces actuation noise, without increasing the required hold power, and which operates in a fail safe or fail closed manner. 
     SUMMARY 
     The solenoid actuated pinch valve of the present disclosure produces minimal noise when actuated, allowing for overall quiet operation of a medical device, such as a peritoneal dialysis (“PD”) machine, which is desirable for PD patients generally and especially those patients who wish to sleep during treatment. In one application, the machine is required to run on battery backup power for a relatively long period of time, such as six hours. It is desirable that the holding power of the solenoid pinch valves is kept to a minimum, so that the battery backup requirement can be met. The metal plunger of the solenoid valve is accordingly allowed to make contact with the metal solenoid body, providing efficient use of the holding power and reducing the overall operational power drain of solenoid pinch valve. The valve also operates a fail safe, spring closed and actuated open manner. 
     A characteristic of electrically actuated solenoid valves is that the power needed to fully actuate the valve varies based on environmental and other factors, such as temperature, tubing variation, valve unit to unit variation, power supply voltage, and spring wear. It is common practice therefore to apply a power level sufficient to fully actuate the solenoid under a worst case scenario, which is typically more power than is actually needed, causing the high acceleration and high velocity noise producing impact of the valve plunger against the valve body. 
     The solenoid valve is actuated via a controller. The controller is programmed to initially supply an actuation power that is very likely to be insufficient to fully actuate the plunger even under the best case scenario of environmental and other factors listed above. The initial actuation power moves the plunger some but likely not enough to fully actuate the plunger. Next, the actuation power is reduced to the hold power, which can for example be one-third or less than the actuation power. If the plunger had been fully actuated, the hold power would hold the plunger in the actuated position. But when the plunger is not fully actuated, the hold power will not hold the plunger, and the valve spring forces the plunger back to the closed or occluding position. 
     The controller applies the hold power momentarily to allow the plunger to be held if fully actuated and then increases the actuation power slightly. Assuming the previous actuation power was insufficient, the increased actuation power moves the solenoid plunger slightly farther in the valve open position than the previous application of actuation power. The power is again reduced to the hold power momentarily to see if the second, slightly increased actuation power is sufficient to fully actuate the plunger. 
     The above process is repeated until an actuation power is applied that actuates the plunger fully under a worse case scenario of the factors discussed above. In one embodiment, the control algorithm is open loop, that is, the controller does not know which incrementally increased application of actuation power caused the plunger to be fully actuated. What is known is that whichever application of power caused the full actuation was only slightly larger than the previous application of power, which did not cause full actuation. Thus, it can be assumed that the velocity at which the solenoid body fully actuated was very close to zero. The resulting noise produced is accordingly very minimal. 
     The controller in one embodiment uses pulse-width-modulation (“PWM”) to control the incremental increases in power. As described in detail below, the control circuitry in one embodiment includes a microprocessor that provides the PWM signal, which drives the gate of a solenoid driver transistor. 
     Power is applied at full strength in one embodiment for a certain percentage of the time. The percentage is increased in small increments over a range of percentages that are known to span best case to worst case scenario full actuation percentages. For example, assume it is known that seventy-five percent PWM will not fully actuate the plunger even under a best case scenario of environmental and other factors, and that one hundred percent PWM will fully actuate the plunger even under the worse case scenario of factors. The controller can then be programmed to vary the PWM percentage from fifty to one-hundred percent in one percent increments, totaling twenty-five. The percentage range in one embodiment is great enough to account for variables, such as wear, temperature, and unit to unit variation. It is contemplated to perform the entire sequence in a span of five seconds or less. For example if the solenoid requires 0.2 seconds to cycle through one attempt, and twenty-five attempts are made, twenty-five attempts times 0.2 seconds per attempt equals five seconds for the sequence to complete itself 
     The controller in another embodiment uses PWM but varies pulse magnitude instead of pulse width. Here, the PWM percentage is set, e.g., at fifty percent duty cycle. But instead of setting each pulse at full power, the first pulse is set at a power level that, at fifty percent duty cycle, will not fully actuate the plunger even under a best case scenario of factors. The power level is then increased incrementally to a level that, at fifty percent duty cycle, will fully actuate the plunger at some power level within this range. 
     It should be appreciated that when the solenoid plunger becomes fully actuated within the guard-banded range, the further increasing of actuation power does not cause noise because the plunger remains fully actuated through the remainder of the control sequence even though the current will at certain times during this remainder period be reduced to the hold current. In one embodiment, the dialysis machine ensures that a tube is loaded before employing the above actuation power control algorithm because without a tube in place the algorithm will cause a loud chattering as the spring repetitiously slams the plunger closed against a wall of the tubeless tube holder. 
     The repeated partial tube openings allow some flow of fresh or spent fluid prior to full actuation of the solenoid plunger. This small flow of fluid is not problematic for at least two reasons. First, the valve actuation and resulting tube opening takes place once at the initiation of a patient fill or a patient drain sequence only (assuming normal therapy with no alarms, etc.). The small amount of fluid flow due to the actuation power control algorithm is accordingly inconsequential to the overall fill or drain volume. Second, the amount of fluid delivered to or removed from the patient is accounted for gravimetrically in one embodiment, such that the small amount of fluid is weighed and taken into account. 
     It is accordingly an advantage of the present disclosure to provide a solenoid actuation valve that produces little acoustical noise upon actuation. 
     It is another advantage of the present disclosure to provide a low noise producing solenoid that has a low holding power requirement. 
     It is a further advantage of the present disclosure to provide a low noise producing solenoid that fails safe upon power. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a schematic, sectional elevation view illustrating the sequential movement of a solenoid plunger according to the systems and methods of the present disclosure. 
         FIG. 2  is a logic flow diagram illustrating one solenoid pinch valve actuation system and method of the present disclosure, which varies pulse-width-modulation (“PWM”) percentage. 
         FIG. 3  is a graph depicting varying PWM percentages and corresponding solenoid plunger openings. 
         FIG. 4  is a logic flow diagram illustrating another solenoid pinch valve actuation system and method of the present disclosure, which varies percentages of maximum current inputted to the solenoid. 
         FIG. 5  is a graph depicting varying percentages of maximum current and corresponding solenoid plunger openings. 
         FIG. 6  is a schematic view of one suitable circuitry for the systems and methods of the present disclosure. 
         FIG. 7  is a schematic view of another suitable circuitry for the systems and methods of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the drawings and in particular to  FIG. 1 , one embodiment of the reduced noise solenoid actuation system of the present disclosure is illustrated by system  10 . System  10  includes control circuitry  50 , which operates one or more solenoid pinch valve  20 . Solenoid pinch valve  20  and circuitry  50  in one embodiment are placed inside of a medical fluid delivery machine, such as a peritoneal dialysis, hemodialysis or other type of renal blood therapy machine. It should be appreciated however that system  10  and the various methods disclosed herein for operating system  10  can be used in other medical fluid delivery machines, such as drug infusion pumps or in any application in which it is desirable to reduce noise caused by a solenoid pinch valve. For example, in many peritoneal dialysis (“PD”), the patient undergoes PD treatment at night while sleeping. It is important here to reduce audible noise, so that the machine does not wake or otherwise disturb the patient or partner. With the reduction of noise comes the reduction of wear due to abrupt decelerations caused by the slamming shut of the solenoid plunger against the solenoid housing. 
       FIG. 1  illustrates a wall or fixture  12  of the application device, such as a dialysis machine wall or fixture. Tube  14  carries fluid, such as dialysate, to and/or from the patient in the case of PD or to or from a dialyzer or blood line in the case of hemodialysis, hemofiltration and hemodiafiltration. Wall  12  is shown generally and can in other embodiments have different shapes, for example, to hold tubing  14  in place. Sensor  16 , such as a capacitive or inductive proximity sensor, is fitted to fixture  12  in the illustrated embodiment to sense the presence of tube  14 . Sensor  16  sends a signal to control circuitry  50 , which can be programmed not to attempt to actuate solenoid valve  20  unless sensor  16  indicates that tube  14  is present. 
     Solenoid valve  20  in the illustrated embodiment is a spring-closed, actuated-open solenoid pinch valve. That is, when control circuitry  50  does not apply current or power to a coil  22  of solenoid valve  20 , spring  24  pushes a plunger  26  of solenoid valve  20  towards wall  12  to close or occlude tubing  14 . When control circuitry  50  does apply current or power to coil  22 , coil  22  creates a magnetic field around plunger  26  causing plunger  26  to move, in this case to the right, compressing spring  24  and allowing tube  14  to open and dialysate, drug or other medical liquid. 
     Solenoid valve  20  includes a housing  28 , shown here in cross-section for convenience. When valve  20  becomes fully actuated, a plate or end  30  of plunger  26  is pressed up against a portion  32  of housing  28 . As discussed above, in known solenoid valves it is common to apply a power level sufficient to fully actuate plunger  26  under a worst case scenario, taking into consideration factors such as temperature, tubing variation, valve unit variation, power supply and spring ware. The applied current or power in many instances is more than is needed to fully actuate plunger  26  under the actual operating conditions. The result is that endplate  30  is slammed against portion  32  of housing  28 , causing a relatively significant amount of audible noise. Control circuitry  50  and the methodology discussed here solve this problem. 
       FIG. 1  is helpful because it illustrates visually the impact of control circuitry  50 , and the methodology discussed herein, on plunger  26  as system  10  carries out the methodology. Plunger  26  is shown again figuratively in sequence below solenoid valve  20  to illustrate the end of travel of endplate  30  of plunger  26  at the end of a pulse of current or power provided via control circuitry  50 . In particular, at time t 1 , control circuitry  50  has supplied an initial input of power to coil  22 . This initial input of power is in one embodiment set to be lower than an expected amount of power needed to fully actuate plunger  26  under a best case scenario of the factors described herein. That is, the power inputted to coil  22  at time t 1  is expected not to fully actuate plunger  26 . At the end of time t 1 , control circuitry  50  then applies a hold current to coil  22 . As is known in the art, when plunger  26  becomes fully actuated, the amount of current necessary to maintain plunger  26  in the fully actuated position is significantly less (e.g., 20 percent of) the actuation current. But because plunger  26  is not fully actuated after time t 1 , when control circuitry  50  applies the hold current, spring  24  pushes plunger  26  back to the occluded position shown in  FIG. 1 . 
     Plunger returns  26  to the completely occluded position in a situation in which solenoid valve  20  requires a much higher actuating current than holding current, making the valve highly non-linear in this respect. At the point of complete actuation, end  30  of plunger  26  makes metal-to-metal contact with portion  32  of housing  28 , which closes the magnetic circuit and allows for a much reduced holding current due to highly increased magnetic efficiency. Spring  24  is preloaded so that plunger  26  does not begin to move until enough starting current is flowing to overcome the spring. As movement begins, the magnetic efficiency increases, so that plunger  26  continues to move to full actuation once the starting current level is reached. 
     Next, control circuitry  50  increments the current inputted to coil  22  by a small amount, e.g., ten mA. The following figures and associated disclosure illustrate in detail different methods for increasing the input. In any case, at time t 2  plunger  26  is shown in its furthest actuated position for this second application of power, here showing end  30  coming closer to housing portion  32  than did end  30  at time t 1 . However, the amount of power inputted to coil  22  in this second attempt still does not actuate plunger  26  fully. Accordingly, when the lower hold current is applied again, spring  24  pushes plunger  26  back to the occluded position shown in  FIG. 1 . Control circuitry  50  repeats this process as shown at times t 3  to t 10 , each time end  50  of plunger  26  comes increasingly closer to the fully actuated position, at which point end  30  is butted against housing portion  32 . 
     As illustrated, at the end of the power pulse of time t 9 , end  30  of plunger  26  comes very close to being fully actuated. Then at time t 10 , which is the end of the next power pulse, plunger  26  becomes fully actuated, such that when the hold current is thereafter applied, plunger  26  remains fully actuated, allowing flow through tubing  14 . The slight incremental power increase between times t 9  and t 10  ensures that the power applied just barely enables plunger  26  to become fully actuated, and ensures that end  30  of plunger  26  is at close to a zero velocity when it impacts portion  32  of housing  28 . There is accordingly a significant reduction in the amount of audible noise due to the opening of valve  20 . 
     As seen in  FIG. 1 , the system and method of the present disclosure continues to attempt to actuate the plunger  26  at times t 11  to t 15 , increasing power each time, until a final attempt is made at t 15  using a power that is expected to fully actuate plunger  26  under any set of conditions discussed above. This power level could be the power level applied in known solenoid systems, which is in most cases more than needed under the actual conditions. With plunger  26  fully actuated, the hold current in between will maintain the plunger in the fully actuated state, such that plunger  26  does not chatter against wall portion  32 . The differences in time between time segments t 1  and t 2 , and so on, is on the order of milliseconds, such that the entire sequence from t 1  to t 15  is a relatively short period of time. 
     The tubing  14  is made of a soft, compliant material, such that the repeated closing of tubing  14  does not produce audible noise. Also, the medical device employing system  10  in one embodiment employs weigh scales to measure how much fluid is delivered to or removed from a patient or dialyzer, such that the medical machine accounts for the small amount of fluid that flows through tubing  14  as plunger  26  chatters back and forth from time t 1  to time t 10 . Further, in systems such as peritoneal dialysis systems, the sequence shown in  FIG. 1  is only performed once per patient fill or patient drain, such that the very small amount of fluid as compared to the overall fill or drain volume is insignificant. 
     Referring now to  FIG. 2 , logic flow diagram  100  illustrates one method or algorithm for incrementally increasing the current or power to solenoid coil  22  to achieve the sequence of solenoid actuations to achieve reduced noise for plunger  26  opening as discussed above in connection with  FIG. 1 . Methodology  100  starts at oval  102  and sets a power-on level of current at block  104 . This can be a percentage of full current. In one embodiment, the power-on level of current for methodology  100  is one hundred. 
     At block  106 , system  10  employing methodology  100  receives a command to actuate solenoid valve  20 , for example, to open tube  14  to allow fluid flow. It is expected that the circuitry  50  of system  10  is provided on a subcontroller or printed circuit board, which interacts with one or more supervisory controller. The command to actuate solenoid valve  20  can come from such supervisory controller and be sent to a microprocessor of the subcontroller or circuitry  50  of system  10 . The setting of the power-on level at block  104  and the setting of the PWM level discussed next in connection with block  108  can be preset, such that the order of blocks  104  to  108  is unimportant. 
     At block  108 , system  10  employing methodology  100  sets the power level to an initial pulse-width-modulation (“PWM”) percentage. Again, the initial PWM percentage is one in which it is expected that plunger  26  is not fully actuated even under a best case scenario of the above-listed conditions. PWM is known in the art and generally involves the varying of time in which a stepped power input is on verses off.  FIG. 3  illustrates this variation of time graphically. 
     At block  110 , system  10  employing methodology  100  applies the power-on level of current set at block  104 , at the initial PWM percentage set at block  108 , to solenoid coil  22 . The input power causes plunger  26  to move as shown in  FIG. 1 . At diamond  112 , methodology  100  determines if solenoid plunger  26  has or has not actuated fully under the power input applied at step  110 . One important advantage of system  10  is that the system does not actually need to know whether plunger  26  has been fully actuated. That is, it is possible to incorporate a sensor with valve  20 , which detects whether the valve has been fully actuated. However, such sensors and additional circuitry at cost. Thus while the present disclosure does contemplate using a sensor, in one preferred embodiment such sensor is not provided. So, the steps shown at boxes  114  and  116  may not actually be steps carried out by system  10 , rather, blocks  114  and  116  show two possible outcomes of the application of the input power applied at block  110 . Dashed line  124  illustrates that methodology  100  in one preferred embodiment moves from block  110  to block  118 , in which case the increases in PWM percentage are made automatically and regardless of whether plunger  26  is actuated fully. 
     Block  114  illustrates the scenario in which the applied input power at block  110  is not sufficient to fully actuate plunger  26 , in which case spring  24  forces plunger  26  to close to occluded position when hold power is applied. Block  116  illustrates the alternative condition in which the power input supplied at block  110  is sufficient to fully actuate plunger  26 , such that the plunger remains actuated when hold current is applied. 
     If a sensor is provided to detect when the plunger  26  is fully actuated, methodology  100  can end when the fully actuated condition at block  116  is reached. Here, the incremental increase in PWM percentage at block  118  is performed only when the non-fully actuated condition occurs at block  114 . Methodology  100  in  FIG. 2  however illustrates one preferred embodiment, in which the PWM percentage is increased regardless of whether the condition of block  114  or block  116  is met. Referring again to  FIG. 1 , assuming system  10  has not reached one hundred percent PWM at the time t 10 , using methodology  100 , system  10  continues to increase the PWM percentage to a maximum, e.g., one hundred percent. It should be appreciated though that the maximum PWM may not be one hundred percent and can be any desirable PWM percentage. For example, a range of PWM percentages can range from fifty to sixty percent. 
     Importantly, when plunger  26  has become fully actuated, a continued application of actuation power and increasingly higher PWM percentages produces no physical effect on plunger  26 . Plunger  26  merely remains actuated, as it would if only the hold current had been applied. Eventually, methodology  100  runs through the entire sequence as shown in connection with diamond  120 , at which point sequence  100  ends, as shown at oval  122 . However, as shown in  FIG. 2 , until PWM percentage reaches its maximum, an increased PWM percentage power input is applied to solenoid coil at block  110  regardless of whether the plunger  26  is not fully actuated as seen in connection with block  114  or is fully actuated as seen connection with block  116 . 
     Referring now to  FIG. 3 , the outcome of methodology  100  is shown graphically. Here, the distance that the plunger  26  moves d is graphed in relation to time t, which marks the end of a modulated pulse of power. For illustrated purposes, PWM percentage is increased by 10 percent in each cycle of the sequence. It is expected that the increase may be much smaller, such as one or two percent. Further, the total expected range of increases may be, for example, seventy-five to one-hundred percent. 
       FIG. 3  also illustrates the power-on current to be the maximum allowable power-on current. It should be appreciated however that the power-on current may be at a level less than maximum current. In  FIG. 3 , however, it should noted that the power-on current is the same for each sequential increased percentage. It is contemplated, if desired, to also vary power-on current in combination with varying PWM percentage. 
     As seen in  FIG. 3 , at the end of time t 1  at PWM percentage of ten, solenoid plunger  26  moves very little as seen by d 1 . At time t 2  corresponding to twenty percent PWM, a slightly increased d 2  is reached as plunger  26  moves in a parabolic manner upwardly towards full actuation and then drops dramatically when power is reduced and resonates in a sinusoidal manner about zero distance moved. It is expected that due to the compliance of tubing  14 , the movement of plunger  26  will dampen to a stop as illustrated in  FIG. 3 . At the time t 3  corresponding to a thirty percent PWM, plunger  26  moves parabolically even closer to full actuation and then dampens out quickly when power is reduced to hold level. At time t 4 , plunger  26  moves to full actuation as seen by d full , and remains at d full  when power is reduced to hold level after time t 4 . 
       FIG. 3  illustrates one preferred implementation of methodology  100 , in which system  10  continues to increase PWM as shown by the increase in percentage to fifty percent ending at time t 5 , and so on. As discussed, such additional increases have no effect on the movement of solenoid plunger  26 , which reached d full  at time t 4 , and remained at d full  at time t 5  and so on. Eventually, methodology  100  reaches maximum PWM, at which time current is steadied at the hold current level until a controller, e.g., supervisory controller in communication with a subcontroller, for system  10  removes the hold current and allows plunger  26  to occlude tubing  14 . 
     Referring now to  FIG. 4 , logic flow diagram  200  illustrates another method or algorithm for incrementally increasing the current or power to solenoid coil  22  to achieve the sequence of solenoid actuations to achieve reduced noise for plunger  26  opening as discussed above in connection with  FIG. 1 . Methodology  200  starts at oval  202  and sets a power-on level of current at block  204 . The power-on level of current at block  204  is a percentage of full current, which is less than one hundred percent, e.g., fifty percent or less. 
     At block  206 , system  10  employing methodology  200 , e.g., running on a subcontroller, receives a command to actuate solenoid valve  20 , e.g., from a supervisory controller, to open tube  14  to allow fluid flow. The setting of the power-on level at block  204  and the setting of the PWM level discussed next in connection with block  208  can be preset, such that the order of blocks  204  to  208  is unimportant. 
     At block  208 , system  10  employing methodology  200  sets the power level to a constant pulse-width-modulation (“PWM”) percentage, e.g., fifty percent. Again, the initial power-on level running at the constant PWM percentage is one in which it is expected that plunger  26  is not fully actuated even under a best case scenario of the above-listed conditions. 
     At block  210 , system  10  employing methodology  100  applies the initial power-on level of current set at block  204 , at the constant PWM percentage set at block  208 , to solenoid coil  22 . The input power causes plunger  26  to move as shown in  FIG. 1 . At diamond  212 , methodology  100  determines if solenoid plunger  26  has or has not actuated fully under the power input applied at step  210 . Again, an important advantage of system  10  is that the system does not actually need to know whether plunger  26  has been actuated fully, and thus does not require (although it can use) position detection. So again, the steps shown at boxes  214  and  216  may not actually be steps carried out by system  10 , rather, blocks  214  and  216  show two possible outcomes of the application of the input power applied at block  210 . Dashed line  224  illustrates that methodology  200  in one preferred embodiment moves from block  210  to block  218 , in which case the increases in power level percentage are made automatically and regardless of whether plunger  26  is actuated fully. 
     Block  214  illustrates the scenario in which the applied input power at block  210  is not sufficient to fully actuate plunger  26 , in which case spring  24  forces plunger  26  to close to occluded position when hold power is applied. Block  216  illustrates the alternative condition in which the power input supplied at block  210  is sufficient to fully actuate plunger  26 , such that the plunger remains actuated when hold current is applied. 
     If a sensor is provided to detect when the plunger  26  is fully actuated, methodology  200  can end when the fully actuated condition at block  216  is reached and hold power is applied. Here, the incremental increase in power level percentage at block  218  is performed if only when the non-fully actuated condition occurs at block  214 . Methodology  200  in  FIG. 4  however illustrates one preferred embodiment, in which the power level percentage is increased regardless of whether the condition of block  214  or block  216  is met. Referring again to  FIG. 1 , assuming system  10  has not reached one hundred percent power level at the time t 10 , using methodology  200 , system  10  continues to increase the power level percentage to a maximum, e.g., one hundred percent. It should be appreciated though that the maximum power level may not be one hundred percent and can be any desirable power level percentage. For example, a range of power level percentages can range from 50 to 60 percent. 
     Importantly, like above with PWM modification of method  100 , when plunger  26  has become fully actuated, a continued application of actuation power and increasingly higher power level percentages produces no physical effect on plunger  26 . Plunger  26  merely remains actuated, as it would if only the hold current had been applied. Eventually, methodology  200  runs through the entire sequence as shown in connection with diamond  220 , at which point sequence  200  ends, as shown at oval  222 . However, as shown in  FIG. 4 , until power level percentage reaches its maximum, an increased power level percentage is applied to solenoid coil at block  210  regardless of whether the plunger  26  is not fully actuated as seen in connection with block  214  or is fully actuated as seen connection with block  216 . 
     Referring now to  FIG. 5 , the outcome of methodology  200  is shown graphically. Here, the distance that the plunger  26  moves d is graphed in relation to time t, which marks the end of a modulated pulse of power. For illustrated purposes, hold current is set to thirty percent power level is set initially at seventy percent and is increased by 7.5 percent in each cycle of the sequence. It is expected that the increase may be much smaller, such as one percent. Further, the total expected range of increases may be, for example, twenty-five percent. Still further alternatively, the increases in power level may be done in units of power or current instead of percentages. 
       FIG. 5  also illustrates that the PWM percentage is set at a constant fifty percent. It should noted that the PWM is the same for each sequential increased percentage. As discussed above, if desired PWM can be varied, e.g., increased, in combination with varying PWM percentage. 
     As seen in  FIG. 5 , at the end of time t 1  at power level percentage of seventy, solenoid plunger  26  moves very little as seen by d 1 . At time t 2  corresponding to 77.5 percent power level, increased d 2  is reached as plunger  26  moves in a parabolic manner towards full actuation and then drops dramatically and resonates sinusoidally about zero distance moved when power is reduced to hold level. It is expected that due to the compliance of tubing  14 , the movement of plunger  26  will dampen to a stop as illustrated in  FIG. 5 . At the time t 3  corresponding to a thirty percent power level, plunger  26  moves in a parabolic manner even closer to full actuation and then dampens out quickly when power is reduced. At time t 4 , plunger  26  moves in a parabolic manner to full actuation as seen by d full , and remains at d full  when power is reduced to the hold current after time t 4 . 
       FIG. 5  illustrates one preferred implementation of methodology  200 , in which system  10  continues to increase power level as shown by the increase in percentage to one hundred percent ending at time t 5 . As discussed, such additional increases have no effect on the movement of solenoid plunger  26 , which reached d full  at time t 4 , and remained at d full  at time t 5 . Methodology  200  reaches maximum power level at t 5 , after which current is steadied at the hold current level until a controller, e.g., supervisory controller in communication with a subcontroller, for system  10  removes the hold current and allows plunger  26  to occlude tubing  14 . 
     Referring now to  FIG. 6 , circuitry  50  illustrates one suitable circuit for system  10 . Circuitry  50  includes a first DC power supply  52   a,  e.g., twelve VDC, which supplies current to solenoid coil  22 , and a second DC power supply  52   b,  e.g., five VDC, which supplies the hold current to solenoid coil  22 . Analog to digital converter (“ADC”)  54  digitizes the actual voltage of power supply  52   a,  so that the voltage can be measured to allow PWM compensation for supply voltage variation. Diode  56   a  is a blocking diode that prevents current flow from power supply  52   a  to power supply  52   b  whenever FET switch  55  is closed. FET switch  55  has a PWM signal driving gate. Diode  56   b  is provided to allow current to continue to flow through the solenoid coil  22  during the portion of the PWM cycle when the FET switch  55  is open and before the current from supply  52   b  to solenoid coil  22  drops to a hold level. Line  58  carries the solenoid current. Resister  66  is a current sense resistor to measure current  58  flowing through solenoid coil  22 . Amplifier  62  amplifies the voltage across current sense resistor  66  to a level that a second ADC (not shown) can digitize so as to be measured. Ground  64  is the return path for all currents that supplies  52   a  and  52   b  pass through coil  22  and current sense resistor  66 . When solenoid valve  20  is to be released after actuation, power supply  52   b  is turned off or disconnected. 
     Referring now to  FIG. 7 , circuitry  60  illustrates another suitable circuit for system  10 . Here too, FET  55  includes a gate driven by a PWM signal. Circuitry  60  includes a DC power supply  52 , e.g., twelve VDC, which supplies current to power solenoid coil  22 . ADC  54   a  operates the same as ADC  54  of circuitry  50  of  FIG. 6 . Diode  56  allows current to continue to flow through solenoid coil  22  during the portion of the PWM cycle when the FET switch  55  is off. Current sense resistor  66   a  supplies to amplifier  62  a voltage proportional to current passing through coil  22 . Current sense resistor  66   b  provides an alternative means of measuring solenoid current during the portion of the PWM cycle when the FET switch  55  is closed. ADC  54   b  reads the voltage across the current sense resistor  66   b,  has the advantage of not requiring a differential input amplifier, but has the disadvantage of only being able to measure coil  22  current during periods when FET switch  55  is on. ADC  54   b  has the further advantage of being able to detect a high current associated with a shorted diode  56 . Ground  64  is the return path for all currents supplied by power supply  52 . 
     It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims.