Solenoid pinch valve apparatus and method for medical fluid applications having reduced noise production

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.

Claims

1. A medical fluid delivery machine comprising: 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 power level to a hold power level, wherein the actuation power level is increased at each subsequent cycle, and wherein the actuation power level of at least one of the plurality of cycles is sufficient to fully actuate the solenoid valve.

2. The medical fluid delivery machine of claim 1, wherein the medical fluid delivery machine is configured to perform at least one of dialysis, hemofiltration, hemodiafiltration, or peritoneal dialysis, and wherein the solenoid valve is operable with a tube carrying blood or a treatment fluid.

3. The medical fluid delivery machine of claim 1, wherein the plurality of cycles includes a predetermined number of cycles.

4. The medical fluid delivery machine of claim 1, wherein the actuation power level of each of the cycles after the cycle that fully actuates the solenoid valve is greater than needed to fully actuate the solenoid valve, the subsequent cycles non-noise producing because the solenoid valve has already been fully actuated.

5. The medical fluid delivery machine of claim 1, wherein the solenoid valve includes a valve plunger, the valve plunger at each of the cycles prior to the cycle that fully actuates the solenoid valve returning to a valve closed position.

6. The medical fluid delivery machine of claim 5, wherein the solenoid valve is positioned adjacent to a tube, the tube cushioning the valve plunger each time the plunger returns to the valve closed position.

7. The medical fluid delivery machine of claim 5, wherein the valve plunger becomes fully actuated at a velocity close to zero.

8. The medical fluid delivery machine of claim 1, wherein the hold power level is the same for each cycle.

9. The medical fluid delivery machine of claim 1, wherein at least one of: (i) the actuation power level of the first cycle of the plurality of cycles is insufficient to fully actuate the solenoid valve under a best case scenario of actuation factors, or (ii) the actuation power level of the last cycle of the plurality of cycles is sufficient to fully actuate the solenoid valve under a worst case scenario of actuation factors.

10. The medical fluid delivery machine of claim 9, wherein the actuation factors include at least one of temperature, tubing vibration, solenoid valve to solenoid valve variation, power supply fluctuation or solenoid valve wear.

11. The medical fluid delivery machine of claim 1, wherein the controller includes a microprocessor in communication with a solenoid driver.

12. The medical fluid delivery machine of claim 1, wherein switching from the actuation power level to the hold power level includes switching from an actuation power pulse width to a hold power pulse width, wherein the actuation power pulse width is increased at each subsequent cycle, and wherein the actuation power pulse width of the at least one of the plurality of cycles is sufficient to fully actuate the solenoid valve.

13. The medical fluid delivery machine of claim 12, wherein an amplitude of at least one of: (i) the actuation power pulse width or (ii) the hold power pulse width is constant.

14. The medical fluid delivery machine of claim 1, wherein switching from the actuation power level to the hold power level includes switching from an actuation power pulse magnitude to a hold power pulse magnitude, wherein the actuation power pulse magnitude is increased at each subsequent cycle, and wherein the actuation power pulse magnitude of the at least one of the plurality of cycles is sufficient to fully actuate the solenoid valve.

15. The medical fluid delivery machine of claim 1, wherein the controller is configured to perform the power actuation sequence by pulsing power to the solenoid valve a plurality of times from a first power level that is selected so as not to fully actuate the solenoid valve, increasing each time towards a second power level that is selected so as to ensure full actuation of the solenoid valve, wherein each pulse of power includes a reduction to a power level below the first power level.

16. The medical fluid delivery machine of claim 1, wherein the solenoid valve includes a plunger opposed by a biasing device, and wherein the controller is configured to perform the power actuation sequence by (i) actuating the plunger against the biasing device a plurality of times at increasing levels of acceleration and (ii) reducing the level of acceleration between the increasing levels of acceleration until one of the levels of acceleration is sufficient to push the plunger against the biasing device to a fully actuated position.

17. The medical fluid delivery machine of claim 16, wherein the controller is configured to increase the level of plunger acceleration from a first level that is selected so as to not fully actuate the plunger to a second level that is selected so as to fully actuate the plunger, the level of acceleration sufficient to push the plunger to the fully actuated position occurring between the first and second acceleration levels.

18. The medical fluid delivery machine of claim 15, wherein the first and second power levels are selected such that full actuation will occur at a power level between the first and second power levels.

19. The medical fluid delivery machine of claim 15, wherein each pulse of power after full activation includes a reduction to a hold power level that maintains the solenoid valve in a fully actuated state.

20. The medical fluid delivery machine of claim 17, wherein the biasing device, at each acceleration level prior to the level of acceleration sufficient to push the plunger to the fully actuated position, pushes the plunger back to an initial position.

21. The medical fluid delivery machine of claim 1, further comprising: a sensor positioned and arranged to detect that the solenoid valve is in a fully actuated position, wherein the controller is configured to stop the power actuation sequence and apply the hold power level when the sensor detects that the solenoid valve is in the fully actuated position.

22. A method for medical fluid delivery comprising: providing power to a solenoid valve over a plurality of cycles, including (i) providing power at an actuation power level, (ii) switching from the actuation power level to a hold power level, (iii) repeating (i) and (ii) and increasing, in each subsequent cycle, the actuation power level, and (iv) fully actuating the solenoid valve when the actuation power level of at least one of the plurality of cycles is sufficient to fully actuate the solenoid valve; and delivering medical fluid when the solenoid valve is fully actuated.

23. The method of claim 22, which includes determining, after at least one cycle of the plurality of cycles, whether the solenoid valve has fully actuated.

24. The method of claim 22, which includes determining, after at least one cycle of the plurality of cycles, whether the actuation power level is at a maximum level.

25. The method of claim 24, wherein, after the actuation power level reaches the maximum level, the power actuation sequence is completed without determining whether the solenoid valve has fully actuated.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) 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.

(2) 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.

(3) FIG. 3 is a graph depicting varying PWM percentages and corresponding solenoid plunger openings.

(4) 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.

(5) FIG. 5 is a graph depicting varying percentages of maximum current and corresponding solenoid plunger openings.

(6) FIG. 6 is a schematic view of one suitable circuitry for the systems and methods of the present disclosure.

(7) FIG. 7 is a schematic view of another suitable circuitry for the systems and methods of the present disclosure.

DETAILED DESCRIPTION

(8) 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.

(9) 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.

(10) 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.

(11) 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.

(12) 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.sub.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.sub.1 is expected not to fully actuate plunger 26. At the end of time t.sub.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.sub.1, when control circuitry 50 applies the hold current, spring 24 pushes plunger 26 back to the occluded position shown in FIG. 1.

(13) 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.

(14) 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.sub.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.sub.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.sub.3 to t.sub.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.

(15) As illustrated, at the end of the power pulse of time t.sub.9, end 30 of plunger 26 comes very close to being fully actuated. Then at time t.sub.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.sub.9 and t.sub.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.

(16) As seen in FIG. 1, the system and method of the present disclosure continues to attempt to actuate the plunger 26 at times t.sub.11 to t.sub.15, increasing power each time, until a final attempt is made at t.sub.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.sub.1 and t.sub.2, and so on, is on the order of milliseconds, such that the entire sequence from t.sub.1 to t.sub.15 is a relatively short period of time.

(17) 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.sub.1 to time t.sub.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.

(18) 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.

(19) 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.

(20) 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.

(21) 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.

(22) 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.

(23) 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.sub.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.

(24) 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.

(25) 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.

(26) 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.

(27) As seen in FIG. 3, at the end of time t.sub.1 at PWM percentage of ten, solenoid plunger 26 moves very little as seen by d.sub.1. At time t.sub.2 corresponding to twenty percent PWM, a slightly increased d2 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.sub.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.sub.4, plunger 26 moves to full actuation as seen by d.sub.full, and remains at d.sub.full when power is reduced to hold level after time t.sub.4.

(28) 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.sub.5, and so on. As discussed, such additional increases have no effect on the movement of solenoid plunger 26, which reached d.sub.full at time t.sub.4, and remained at d.sub.full at time t.sub.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.

(29) 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.

(30) 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.

(31) 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.

(32) 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.

(33) 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.

(34) 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.sub.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.

(35) 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.

(36) 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.

(37) 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.

(38) As seen in FIG. 5, at the end of time t.sub.1 at power level percentage of seventy, solenoid plunger 26 moves very little as seen by d.sub.1. At time t.sub.2 corresponding to 77.5 percent power level, increased d2 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.sub.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.sub.4, plunger 26 moves in a parabolic manner to full actuation as seen by d.sub.full, and remains at d.sub.full when power is reduced to the hold current after time t.sub.4.

(39) 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.sub.5. As discussed, such additional increases have no effect on the movement of solenoid plunger 26, which reached d.sub.full at time t.sub.4, and remained at d.sub.full at time t.sub.5. Methodology 200 reaches maximum power level at t.sub.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.

(40) Referring now to FIG. 6, circuitry 50 illustrates one suitable circuit for system 10. Circuitry 50 includes a first DC power supply 52a, e.g., twelve VDC, which supplies current to solenoid coil 22, and a second DC power supply 52b, 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 52a, so that the voltage can be measured to allow PWM compensation for supply voltage variation. Diode 56a is a blocking diode that prevents current flow from power supply 52a to power supply 52b whenever FET switch 55 is closed. FET switch 55 has a PWM signal driving gate. Diode 56b 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 52b 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 52a and 52b pass through coil 22 and current sense resistor 66. When solenoid valve 20 is to be released after actuation, power supply 52b is turned off or disconnected.

(41) 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 54a 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 66a supplies to amplifier 62 a voltage proportional to current passing through coil 22. Current sense resistor 66b provides an alternative means of measuring solenoid current during the portion of the PWM cycle when the FET switch 55 is closed. ADC 54b reads the voltage across the current sense resistor 66b, 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 54b 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.

(42) 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.