Patent Publication Number: US-2022236328-A1

Title: Solenoid system with position and temperature detection

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This claims priority benefit to all common subject matter of U.S. Provisional Patent Application No. 63/142,653 filed Jan. 28, 2021 and U.S. Provisional Patent Application No. 63/142,721 filed Jan. 28, 2021. The content of these applications is incorporated herein by reference in their entirety. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to electric solenoids, more particularly to electric solenoids implementing position and temperature detection. 
     BACKGROUND 
     Massive trends toward automation are underway in many industries, including manufacturing, health care, and automotive. This automation relies heavily on the electric solenoid, which provides a binary, unidirectional movement, with limited reach. 
     Illustratively, electronic solenoids play an important role in the medical field where precise and accurate motion is required, such as during the operation of dialysis and dosing machines. Industrial manufacturing can require the precise actuation of tens or hundreds of electric solenoids, for example in textile manufacturing systems. 
     When used in industrial manufacturing, the malfunctioning of one electric solenoid can impact the quality of a product, can stop a production line, and can even present a risk to an operator. When used in the medical or security industries, the malfunctioning of an electric solenoid can result in loss of life. 
     Furthermore, as an extension of the electronics industry, electronic solenoids have come under ever-increasing commercial competitive pressures demanding miniaturized, feature rich, low cost, and low power solenoids. Current technical problems constraining electric solenoids include determining solenoid temperature and position without costly external sensors coupled to the solenoid. 
     The temperature of the solenoid is an important indicator of solenoid health, with temperature aberrations indicating a solenoid that might fail to provide repeatable motion and should be changed. Determining the accurate position of the solenoid is critical to controlling the precise actuation of the solenoid. 
     Ensuring precise repeatable solenoid movement is at the core of insertion strategies outlined in road maps for development of next generation products. Many of these products depend at least in part, on precision machining and miniaturization; both of which, demand control systems for electric solenoids in the sub-millimeter range. One previous attempt utilizes back-electromotive-forces (BEMF) generated by the movement of a solenoid plunger to determine motion. However, the BEMF alone, does not provide a technical solution because the BEMF only provides an indication of solenoid movement, not position or temperature. 
     Other previous attempts use external sensors mounted to the solenoid for detecting attributes of the solenoid. These external sensors increase the control hardware footprint, increase costs for each solenoid monitored, increase power consumption, and many times require application specific engineering to ensure proper integration of the solenoid and sensors. 
     Furthermore, in many sterile or harsh environments, externally coupled sensors present a technical problem and cannot be used, as the external sensors would be exposed to the environment. Yet even further, external sensors and circuitry generally have large signal to noise ratios, and in some cases, detection might require enough power to affect the motion of the solenoid during measurement, which can create motion artifacts in an otherwise smooth solenoid motion. 
     These previous attempts to precisely control and monitor the electric solenoid have failed to provide a full solution for lower power, low cost, and integrated internal position and temperature measurements that the industry demands. In view of the ever-increasing commercial competitive pressures, along with growing consumer expectations and the diminishing opportunities for meaningful product differentiation in the marketplace, it is critical that answers be found for these problems. 
     Thus, a need remains for electronic solenoid with internal position and temperature measurements. Solutions to these problems have been long sought but prior developments have not taught or suggested any complete solution and, thus, solutions to these problems have long eluded those skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The solenoid system is illustrated in the figures of the accompanying drawings which are meant to be exemplary and not limiting, in which like reference numerals are intended to refer to like components, and in which: 
         FIG. 1  is a block diagram of the solenoid system in a position and temperature detection embodiment. 
         FIG. 2  is a block diagram of the AC carrier module of  FIG. 1 . 
         FIG. 3  is a block diagram of an equivalent circuit for the solenoid system of  FIG. 1 . 
         FIG. 4  is a first timing diagram for the solenoid system of  FIG. 1 . 
         FIG. 5  is a second timing diagram for the solenoid system of  FIG. 1 . 
         FIG. 6  is a third timing diagram for the solenoid system of  FIG. 1 . 
         FIG. 7  is a fourth timing diagram for the solenoid system of  FIG. 1 . 
         FIG. 8  is a fifth timing diagram for the solenoid system of  FIG. 1 . 
         FIG. 9  is a sixth timing diagram for the solenoid system of  FIG. 1 . 
         FIG. 10  is a seventh timing diagram for the solenoid system of  FIG. 1 . 
         FIG. 11  is an eighth timing diagram for the solenoid system of  FIG. 1 . 
         FIG. 12  is a control flow for the solenoid system. 
         FIG. 13  is a block diagram of the solenoid system in a low power embodiment. 
         FIG. 14  is a block diagram for an equivalent circuit of the solenoid system of  FIG. 13 . 
         FIG. 15  is a first timing diagram for the solenoid system of  FIG. 13 . 
         FIG. 16  is a second timing diagram for the solenoid system of  FIG. 13 . 
         FIG. 17  is a control flow for the solenoid system. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration, embodiments in which the solenoid system may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the solenoid system. 
     When features, aspects, or embodiments of the solenoid system are described in terms of steps of a process, an operation, a control flow, or a flow chart, it is to be understood that the steps can be combined, performed in a different order, deleted, or include additional steps without departing from the solenoid system as described herein. 
     The solenoid system is described in sufficient detail to enable those skilled in the art to make and use the solenoid system and provide numerous specific details to give a thorough understanding of the solenoid system; however, it will be apparent that the solenoid system may be practiced without these specific details. 
     In order to avoid obscuring the solenoid system, some well-known system configurations and descriptions are not disclosed in detail. Likewise, the drawings showing embodiments of the system are semi-diagrammatic and not to scale and, particularly, some of the dimensions are for the clarity of presentation and are shown greatly exaggerated in the drawing FIGS. Generally, the solenoid system can be operated in any orientation. As used herein, the term couple, as in “coupled” or “coupling” is defined as an electrical connection between coupled elements. 
     Referring now to  FIG. 1 , therein is shown a block diagram of the solenoid system  100  in a position and temperature detection embodiment. The solenoid system  100  is depicted having a solenoid  102  coupled to an integrated solenoid driver  104 . 
     The solenoid  102  can be an electromechanical component comprising a coil  106  with an armature  108  that moves or otherwise imparts mechanical force in response to a magnetic field generated by passing current through the coil  106 . One skilled in the art will appreciate that other words may be used to describe the armature  108  including but not limited to a piston, an actuator, a movable core, a movable slug, and a plunger. For descriptive clarity, hereinafter the armature  108  will be referred to as plunger  108 . 
     When the coil  106  is actuated by applying a voltage to the coil  106  of the solenoid  102 , the plunger  108  is either extended out of the coil  106  or retracted into the coil  106  depending on current direction and system assembly. 
     The position the plunger  108  takes when current is passed through the coil  106  is actuated is the actuated position. The solenoid  102  is shown having a first connection  110  and a second connection  111 . The first connection  110  can be coupled to VM, which can be a motor drive voltage larger than supply voltage Vdd  112 , while the second connection  111  can be coupled to a half bridge  113  contained within the integrated solenoid driver  104 . 
     Although the first connection  110  of the solenoid  102  is described as connected to VM, it is contemplated that the first connection  110  could alternatively be connected to ground when other half bridge configurations are used. Still further, it is contemplated that the first connection  110  could alternatively be connected to a second half bridge to form a full H-bridge for the coil  106 . 
     The solenoid  102  can further include a spring  114  for providing mechanical resistance against the motion of the plunger  108  and to limit the retraction or extension of the plunger  108  within the solenoid  102  during actuation. Both extension and retraction types of solenoids are contemplated and can be adapted. These types of solenoids differ in the location of the spring  114  and design of the plunger  108 . Rotary solenoids are yet a further contemplated implementation, again differing in the location and design of the spring  114  and also in the type of movement produced. 
     The integrated solenoid driver  104  can include a switch controller  116  coupled to the solenoid  102  through the half bridge  113 . The switch controller  116  is to be understood herein as a physical structural component at least having structural low power inputs and higher power outputs. Isolation for protecting delicate control circuitry is also a common structural component of switch controllers  116 . The switch controller  116  is typically referred to as a gate driver and for ease of description, the switch controller  116  will be referred to hereinafter as gate driver  116 . 
     Illustratively for example, the gate driver  116  is depicted as a high-side low-side PWM driver. The gate driver  116  can control the half bridge  113  with a pulse-width-modulated (PWM) signal in order to provide voltages to the solenoid  102 . The gate driver  116  can be implemented as dedicated IC s, discrete transistors, or transformers. The gate driver  116  can also be integrated within a larger IC or IC package. 
     The half bridge  113  is depicted having a high side N-Channel Depletion MOSFET and a low side N-Channel Depletion MOSFET. It is alternatively contemplated that the half bridge  113  could also be implemented using insulated-gate bipolar transistors (IGBTs) or one low side N-Channel Depletion MOSFET and one high side P-Channel Depletion MOSFET, for example. The solenoid  102  can be coupled to the source of the high side MOSFET and coupled to the drain of the low side MOSFET. 
     The N-Channel Depletion MOSFET is a depletion-mode MOSFET device which can be doped so that a channel exists with zero volts between the gate and source. To control the channel, a negative voltage is applied to the gate, which functions as a normally closed switch. The half bridge  113  and the solenoid  102  can further be coupled to an open load  118 . 
     The gate driver  116  can provide the PWM signal to the half bridge  113 . The PWM signal can provide a duty cycle proportional to an energizing voltage  410 , a hold voltage  412 , and a disable voltage  414 , all of  FIG. 4 , below. The gate driver  116  can also provide an adjustable ramp  416  of  FIG. 4  from the disable voltage  414  to the energizing voltage  410  by varying the PWM signal. The drain of the high side N-Channel Depletion MOSFET can be coupled to VM in order to drive the high side N-Channel Depletion MOSFET positive with respect to the supply voltage Vdd  112 . A charge pump  120  can optionally drive the high side of the half bridge  113 . 
     The gate driver  116  can include a PWM ramping module  122 . The PWM ramping module  122  generates the PWM duty cycle for the half bridge  113 . An AC carrier signal  424  of  FIG. 4  is added to the PWM duty cycle through superimposition. Illustratively for example, the frequency of PWM signal can be around 25 kHz, while the AC carrier signal  424  can be around 1 Hz to 1 kHz. It is contemplated that the frequency of the AC carrier signal  424  is programmable in the 1 Hz to 1 kHz range in order to cover a wide range of inductances from various different coils  106  in different solenoids  102 , which could range from 1 mH to 1 H. 
     It has been discovered that the AC carrier signal  424  signal being an order of magnitude lower than the PWM signal allows for very low amplitude of the AC carrier signal  424 . This has been found to provide a great signal to noise ratio by enabling many readings to be averaged across a digital voltage signal  422  of  FIG. 4  and also enables a very low power consumption with no residual oscillations felt on the solenoid  102 . It has been further discovered that the AC carrier signal  424  with a 1 Hz to 1 kHz frequency can be used as a dithering signal to overcome breakaway torques due to static friction within the solenoid  102 . This use of the AC carrier signal  424  as a dithering signal can be useful for valves, but also for DC motors with brushes for smooth starting at low speeds. 
     The combined signal can be an input voltage  406  of  FIG. 4 , and is a combination of the digital voltage signal  422  and the AC carrier signal  424 . The input voltage  406  is fed into a PWM modulator  124  within the gate driver  116 . The PWM modulator  124  generates the switching signal for high side and low side of the half bridge  113 . 
     The integrated solenoid driver  104  can further include a current sensor  126  coupled to the solenoid  102 . The current sensor  126  can detect current through the coil  106  of the solenoid  102  as an analog current signal. 
     The current sensor  126  is to be understood herein as a physical structural component at least having structural input and output connections. However, many forms of the current sensor  126  are contemplated including Hall effect linear sensors, galvanically isolated sensors, or GMR-based sensors. Yet other forms are contemplated including fluxgate sensors, shunt resistors, and even fiber optic interferometer based sensors. 
     The integrated solenoid driver  104  can further include an analog to digital converter  128  for converting the analog current signal to a digital current signal  408 , of  FIG. 4 , prior to distributing the digital current signal  408  to control logic  130 . The control logic  130  can be a digital computational block for performing Voltage Divider Rule (VDR) and Current Divider Rule (CDR) based calculations. 
     The half bridge  113 , the gate driver  116 , the open load  118 , the PWM ramping module  122 , the PWM modulator  124 , the current sensor  126 , and the analog to digital converter  128  can be reproduced for multiple solenoids  102 . As shown, the half bridge  113 , the gate driver  116 , the open load  118 , the PWM ramping module  122 , the PWM modulator  124 , the current sensor  126 , and the analog to digital converter  128  are reproduced for coupling to four solenoids  102 . 
     The control logic  130  is to be understood herein as a physical structural component at least having transistor logic gates for providing computation and control. Furthermore, the control logic  130  includes structural inputs and outputs typically operating between zero and five volts. It is contemplated that the control logic  130  can be a TTL or CMOS based architecture but could also include other logic families including RTL, DTL, and ECL, for example. 
     The control logic  130  can be coupled to the current sensor  126  through the analog to digital converter  128  and detect the digital current signal  408 . The control logic  130  can compare the digital current signal  408  with a reference current  132  to provide a highly accurate current reading. 
     The control logic  130  can provide the AC carrier signal  424  to the gate driver  116  to be superimposed onto the energizing voltage  410 , the hold voltage  412 , and the disable voltage  414 . 
     The control logic  130  can further include an AC carrier module  134 . The AC carrier module  134  can be implemented as discrete components as depicted in  FIG. 2  or by using distributed resources within the control logic  130 . Furthermore, the AC carrier module  134  can be implemented utilizing instructions running on the control logic  130 , which controls the technical process or the internal functioning of the control logic  130 . 
     The AC carrier module  134  can both create the AC carrier signal  424  as well as determine an AC current amplitude  428  of  FIG. 4  and a DC offset current amplitude  426  of  FIG. 4 . The AC carrier signal  424  is added to the PWM duty cycle through superimposition as shown between the PWM ramping module  122  and the PWM modulator  124 . Both the AC current amplitude  428  and the DC offset current amplitude  426  are combined and contained within the digital current signal  408  from the analog to digital converter  128  and the current sensor  126 . The solenoid  102  responds to the AC carrier signal  424  with a sinusoidal response signal, which is detected by the AC carrier module  134  as the AC current amplitude  428 . 
     The AC carrier module  134  can synchronously demodulate the digital current signal  408  by utilizing the same frequency as the AC carrier signal  424  for providing a clean sample and an extremely accurate reading. The synchronous demodulation occurs over exactly one period of the AC carrier signal  424  or can occur over an integer multiple of the AC carrier signal  424 . As such, the AC carrier module  134  can provide the AC current amplitude  428  reading every period of the AC carrier signal  424 . And, as the AC carrier signal  424  will have many periods during the digital voltage signal  422 , the AC carrier module  134  can utilize a series of samples during the digital voltage signal  422  to determine an average value, greatly increasing the signal to noise ratio. 
     It has been unexpectedly discovered that both the synchronous demodulation and the averaged samples unexpectedly and greatly increase signal to noises ratio. Due to this signal to noise ratio, these processes enable the use of very low amplitudes for the AC carrier signal  424 . Low amplitudes can prevent a shaking solenoid and is possible because the signal to noise ratio is good enough that only a low AC amplitude is needed. 
     The amplitude and frequency of the AC carrier signal  424  can be easily parameterized to match solenoid characteristics and provide an even better signal to noise ratio. Specifically, a sweep over frequency and amplitude in both an extended position and a retracted position of the plunger  108  is made. During this sweep, the AC current amplitude  428  is measured and recorded. The combination with highest signal to noise ratio should be chosen. 
     Once the AC carrier module  134  has sampled the digital current signal  408  and synchronously demodulated the digital current signal  408 , the AC current amplitude  428  is determined together with the DC offset current amplitude  426 . The AC current amplitude  428  represents the inductance response of the solenoid  102  while the DC offset current amplitude  426  can be proportional to the resistance of the coil  106 . 
     If the AC current amplitude  428  is high, the inductance is low and when the AC current amplitude  428  is low, the inductance is high. That is, the AC carrier module  134  can determine the AC current amplitude  428  is a low AC current amplitude based on the plunger  108  being in a retracted position and determine the AC current amplitude  428  is a high AC current amplitude based on the plunger  108  being in an extended position. 
     Based on this determination of high or low values for the AC current amplitude  428 , a binary signal indicating proper plunger  108  position can be determined. Illustratively for example, when the solenoid  102  is a retraction type solenoid, designed to retract when actuated, the control logic  130  can identify proper position of the plunger  108  when the low AC current amplitude is detected during an actuation duration  404  of  FIG. 4 . Alternatively, with the retraction type solenoid, the control logic  130  can identify improper position of the plunger  108  when the high AC current amplitude is detected during the actuation duration  404 . 
     Furthermore, when the solenoid  102  is an extension type solenoid, designed to extend when actuated, the control logic  130  can identify proper position of the plunger  108  when the high AC current amplitude is detected during the actuation duration  404 . Alternatively, with the extension type solenoid, the control logic  130  can identify improper position of the plunger  108  when the low AC current amplitude is detected during the actuation duration  404 . 
     The high AC and low AC current amplitude can be determined by an AC amplitude threshold  430  of  FIG. 4  or by comparing the AC current amplitude  428  to a previous value. The AC amplitude threshold  430  can be programmable trigger levels used to determine extended or retracted position of the plunger  108 . 
     In one contemplated embodiment, the control logic  130  can instruct the gate driver  116  to modify the PWM signal to provide the hold voltage  412  or for dropping from the energizing voltage  410  to the hold voltage  412  based on the position of the plunger  108  being detected in the proper position during the actuation duration  404  as determined by the AC current amplitude  428 . 
     That is, when the solenoid  102  is a retraction type solenoid, the control logic  130  can instruct the gate driver  116  to provide the PWM signal for driving the hold voltage  412  to the solenoid  102  based on the AC carrier module  134  detecting the low AC current amplitude during the actuation duration  404 , which indicates the plunger  108  is properly in the retracted position. Furthermore, when the solenoid  102  is an extension type solenoid, the control logic  130  can instruct the gate driver  116  to provide the PWM signal for driving the hold voltage  412  to the solenoid  102  based on the AC carrier module  134  detecting the high AC current amplitude during the actuation duration  404 , which indicates the plunger  108  is properly in the extended position. 
     As another result of the synchronous demodulation, the AC carrier module  134  determines the DC offset current amplitude  426 , which is calculated as the mean value of the DC offset current amplitude  426  over one AC scan period. The resistance of the coil  106  can be calculated from the digital voltage signal  422  and the DC offset current amplitude  426 . The resistance of the coil  106  should not change much from cycle to cycle unless there is a problem. 
     The resistance of the coil  106  is proportional to a heat of the coil  106  and therefore can be used to determine the temperature of the coil  106 . More particularly, the resistance of the coil  106  can follow Equation 1, as follows: 
       R=R0+R T ( T )   Equation 1
 
     where “R” is the resistance of the coil  106 , “R0” is a fixed resistance of the coil  106 , and “RT(T)” is a temperature induced resistance. A DC offset current amplitude threshold  432  of  FIG. 4  is used to determine a temperature fault based on the DC offset current amplitude  426  falling below the DC offset current amplitude threshold  432 . 
     It has been unexpectedly discovered that determining the temperature fault, as described, provides the ability to replace solenoids  102  prior to failure based only on operating parameters alone, and is accomplished without costly and complicated circuitry while simultaneously requiring no more power than originally is provided to the solenoid  102 . This provides a technical advantage to solenoid systems employing the presently disclosed technical solutions by ensuring solenoids function properly and efficiently, at very low power requirements. 
     The control logic  130  can be coupled to and control the gate driver  116  with a control signal indicating a voltage level. The AC carrier module  134  can synchronously demodulate the AC current amplitude  428  utilizing the AC carrier signal  424 , which can be based on the reference of an oscillator  136 . 
     Thus, the solenoid system  100  including control logic  130  coupled to the gate driver  116  and coupled to the current sensor  126  provides the AC carrier signal  424  superimposed onto the energizing voltage  410 , the hold voltage  412 , and the digital voltage signal  422 . It is contemplated that the AC carrier signal  424  could be superimposed onto one or any combination of the described voltages. And this AC carrier signal  424  can be used to sense the current through the coil  106  of the solenoid  102  including the AC current amplitude  428  and the DC offset current amplitude  426  which provides systems and methods of precise control and monitoring of the solenoid  102  that provides a full solution for lower power, low cost, and highly integrated internal position and temperature measurements, a solution not previously available in the electronic solenoid industry. 
     This solution is provided at least by enabling the determination of low AC current amplitude based on the plunger  108  being in a retracted position or the determination of high AC current amplitude based on the plunger  108  being in an extended position. This simple and cost effective solution unexpectedly provides a very low power solution by synchronously demodulating the sense input  202  of  FIG. 2  signals for the data signal of the digital current signal  408 , the digital current signal  408  including the DC offset current amplitude  426  and the AC current amplitude  428 . Furthermore, the DC offset current amplitude  426  and the AC current amplitude  428  can be calculated using multiple readings and averaging the results which provides an unexpectedly large signal to noise ratio allowing even smaller AC carrier signal  424  amplitudes to be used and greatly reducing power consumption. 
     Thus, the solenoid system  100  provides systems and methods of precise control and monitoring of the solenoid  102  that provides a full solution for lower power, low cost, and integrated internal position measurements. The solenoid system  100  further provides systems and methods of precise control and monitoring of the solenoid  102  temperature measurements in that the DC offset current amplitude  426  can be precisely calculated and used to divide the input voltage  406  in determining the resistance of the coil  106  and thereby the temperature of the coil  106 . 
     The information of plunger  108  position can be displayed to a user as the temperature of the solenoid  102 . The integrated solenoid driver  104  is shown including input output modules for providing this position and temperature information. 
     Illustratively, the input output modules can include a control interface  138  having multiple control pins. The input output modules can also include a serial peripheral interface  140  for providing movement and duration information. 
     Another example of the input output modules can include a voltage input and output  142  having a linear voltage regulator and coupled to the control logic  130  with an enable control line. The control logic  130  can also be coupled to and monitor the supply voltage Vdd  112  through an analog-to-digital converter  144 . 
     The control logic  130  can detect faults in the supply voltage Vdd  112  including under voltage lockout faults and over voltage threshold faults. The control logic  130  can also detect over current faults as well as faults based on the DC offset current amplitude  426  falling below the DC offset current amplitude threshold  432 . 
     These faults can be output with a fault interface  146  coupled to the control logic  126 . As yet another example of the input output modules, the control logic could be coupled to a multiplexed interface  148  having multiplexed input and output pins. 
     Referring now to  FIG. 2 , therein is shown a block diagram of the AC carrier module  134  of  FIG. 1 . The AC carrier module  134  is shown having a sense input  202 . The sense input  202  can be a data signal of the digital current signal  408  of  FIG. 4  including both the DC offset current amplitude  426  and the AC current amplitude  428 , both of  FIG. 4 . 
     The digital current signal  408  can be centered around the frequency of the AC carrier signal  424  of  FIG. 4 . The sense input  202  can be coupled to the current sensor  126  through the analog to digital converter  128 , both of  FIG. 1 . 
     The AC carrier module  134  is further shown having an AC carrier signal output that can communicate the AC carrier signal  424  from the AC carrier module  134  to the gate driver  116  of  FIG. 1  for superimposition onto the PWM signal controlling the solenoid  102  of  FIG. 1 . 
     The AC carrier signal  424  can be generated by direct digital synthesizer  206 . The direct digital synthesizer  206  can utilize a numerically controlled oscillator and a digital-to-analog converter to generate both a quadrature or sine component  208  of the AC carrier signal  424  as well as an in-phase or cosine component  210  of the AC carrier signal  424 . The cosine component  210  is shown to be the AC carrier signal  424 . The numerically-controlled oscillator component of the direct digital synthesizer  206  can have an AC frequency and voltage selection  211  as an input for providing an exact and predetermined AC carrier signal  424 . 
     The cosine component  210  generated by the direct digital synthesizer  206  can be input into a first multiplier  212  together with the digital current signal  408  from the sense input  202 . The sine component  208  generated by the direct digital synthesizer  206  also can be input into a second multiplier  214  together with the digital current signal  408  from the sense input  202 . 
     The output signal from the first multiplier  212  and the second multiplier  214  includes sum frequency and difference frequency components. 
     The digital current signal  408  can have a frequency substantially similar to the frequency of the AC carrier signal  424  and therefore, the difference frequency result of the first multiplier  212  is a substantially DC X signal  216  and similarly, the difference frequency result of the second multiplier  214  is a substantially DC Y signal  218 . The X signal  216  can be averaged in a first averaging block  224 , which can sum the X signal  216  and divide by a number of samples. The first averaging block  224  can calculate an average of the X signal  216  by integrating the X signal  216  over exactly one period of the AC carrier signal  424 . This has multiple advantages including the exclusion of frequencies other than the frequency of the AC carrier signal  424  which means filters are not needed. Furthermore, the result is available with a delay of one only one period of the AC carrier signal  424  in contrast to the phase delay of a filter which can be many periods and exhibit steep filter characteristics. 
     To facilitate the averaging of the X signal  216 , the direct digital synthesizer  206  can output a sample and save signal  226  which controls the integration of samples within the first averaging block  224 . More particularly, the sample and save signal  226  can be a single digit control signal, and for example, when “0”, the sample and save signal  226  directs the first averaging block  224  to sample the X signal  216  producing an integral which can be divided by the number of samples to produce an average X signal  230 . 
     Continuing with this example, when the sample and save signal  226  is a “1”, the sample and save signal  226  also controls the saving of the calculated integral within an additional buffer register. The sample and save signal  226  can be “1” indicating a save for one sample clock. In this way, the buffer register always holds the last valid integration result of the X signal  216 , which can be the output of the first averaging block  224  or the average X signal  230 . 
     The average X signal  230  is squared in a first computational block  232 , to produce an X squared signal  234 . Similar to the X signal  216 , the Y signal  218  can be averaged in a second averaging block  236 . 
     That is, the second averaging block  236  can calculate an average of the Y signal  218  over exactly one period of the AC carrier signal  424  with the advantage that the result is available with a delay of one only one period of the AC carrier signal  424 . The sample and save signal  226  controls the integration of samples within the second averaging block  236  by directing the second averaging block  236  to sample the Y signal  218  producing an integral which can be divided by the number of samples to produce an average Y signal  238 . 
     Continuing with this example, when the sample and save signal  226  is a “1”, the sample and save signal  226  also controls the saving of the calculated integral within an additional buffer register. The sample and save signal  226  can be “1” indicating a save for one sample clock. In this way, the buffer register always holds the last valid integration result of the Y signal  218 , which can be the output of the second averaging block  236 , namely the average Y signal  238 . 
     The average Y signal  238  is the DC offset current amplitude  426 , and can be squared in a second computational block  240 , to produce a Y squared signal  242 . The X squared signal  234  and the Y squared signal  242  can be added within an adder  244  then square-rooted within a third computational block  246  to produce the AC current amplitude  428 . 
     It is contemplated that the AC carrier module  134  can be implemented in special purpose hardware or could utilize the logic gates of the control logic  130  of  FIG. 1  in order to produce the same output values of the AC current amplitude  428  and the DC offset current amplitude  426 , which can be illustrated with the following pseudo-code: 
     
       
         
           
               
               
             
               
                   
               
             
            
               
                  1 
                 void sync_demodulation (int I_ACT, int angle) 
               
            
           
           
               
               
               
            
               
                  2 
                 { 
                 / / inputs: actual current and angle of AC_Scan signal 
               
               
                  3 
                   
                 static long int accu_cos; 
               
               
                  4 
                   
                 static long int accu_sin; 
               
               
                  5 
                   
                 static long int accu_i; 
               
               
                  6 
                   
                 static int cnt; 
               
               
                  7 
               
               
                  8 
                   
                 static int angle_old; 
               
               
                  9 
               
               
                 10 
                   
                 int Y, X; 
               
               
                 11 
               
               
                 12 
                   
                 / / Detect: One Period of AC-Scan signal is done 
               
               
                 13 
                   
                 if (angle_old &lt; 0 &amp;&amp; angle &gt;= 0) 
               
               
                 14 
                   
                 { 
               
               
                 15 
                   
                  Y = accu_sin/cnt; 
               
               
                 16 
                   
                  X = accu_cos/cnt; 
               
               
                 17 
                   
                  I_DC = accu_i/cnt; 
               
               
                 18 
                   
                  cnt = 0; 
               
               
                 19 
               
               
                 20 
                   
                  I_AC = sqrt (Y*Y + X*X); 
               
               
                 21 
               
               
                 22 
                   
                  accu_sin = 0; 
               
               
                 23 
                   
                  accu_cos = 0; 
               
               
                 24 
                   
                  accu_i = 0; 
               
               
                 25 
                   
                 } 
               
               
                 26 
               
               
                 27 
                   
                 accu_cos += cos(angle) * I_ACT; 
               
               
                 28 
                   
                 accu_sin += sin(angle) * I_ACT; 
               
               
                 29 
                   
                 accu_i += I_ACT; 
               
               
                 30 
                   
                 cnt++; 
               
               
                 31 
                   
                 angle_old = angle; 
               
               
                 32 
                 } 
               
               
                   
               
            
           
         
       
     
     As will be appreciated, the AC carrier module  134  can be implemented with minimal complexity and mathematics. Illustratively, only three accumulators are needed as is shown in lines 3 through 5 of the pseudo-code. Furthermore, the AC current amplitude  428  is calculated in line  20  while the DC offset current amplitude  426  is calculated for in line  17 . 
     The AC carrier module  134  can therefore calculate the DC offset current amplitude  426  and the AC current amplitude  428  based on the sense input  202  transmitting the digital current signal  408 . The digital current signal  408  is digitized information requiring digital logic to receive and cannot be understood by the unaided human mind. 
     Furthermore, the AC carrier module  134  can provide the DC offset current amplitude  426  and the AC current amplitude  428  for controlling the technical process and the internal functioning of the solenoids by reducing the input voltage  406  of  FIG. 4  to the coil  106  of  FIG. 1  of the solenoid  102  from the energizing voltage  410  of  FIG. 4  to the hold voltage  412  of  FIG. 4 . Furthermore, the internal function of the solenoid  102  is controlled by generating faults if the DC offset current amplitude threshold  432  of  FIG. 4  is exceeded or triggering other heat reduction measures for the solenoid  102  including powering the solenoid  102  off. 
     Thus, the solenoid system  100  of  FIG. 1  provides systems and methods of precise control and monitoring of the solenoid  102  that provides a full solution for lower power, low cost, and integrated internal position and temperature measurements. 
     Referring now to  FIG. 3 , therein is shown a block diagram of an equivalent circuit  302  for the solenoid system  100  of  FIG. 1 . The equivalent circuit  302  can provide a representation of the solenoid  102  of  FIG. 1  coupled to the integrated solenoid driver  104  of  FIG. 1  and retains the electrical characteristics thereof. The equivalent circuit  302  enables resistances and inductances to be simplified for analysis. 
     The equivalent circuit  302  can provide a voltage represented as a step function, u(t)  304 , across an input terminal  306  and an output terminal  308 . The u(t)  304  is to be understood as the input voltage  406  of  FIG. 4  to the coil  106  of  FIG. 1 , which can be the PWM controlled signal provided by the gate driver  116  of  FIG. 1  from the output of the half bridge  113  of  FIG. 1  including the AC carrier signal  424  of  FIG. 4  from the AC carrier module  134  of  FIG. 1 . 
     The equivalent circuit  302  is also shown including a current i(t)  310  through an equivalent resistor  312 , an equivalent inductor  314  and an equivalent solenoid  316 . The i(t) can be the current through the coil  106  as detected by the current sensor  126  of  FIG. 1  and can include the AC current amplitude  428  together with the DC offset current amplitude  426 , both of  FIG. 4 . 
     The u(t)  304  can be equal to the voltage drop across the equivalent resistor  312  plus the voltage drop across the equivalent inductor  314  plus the BEMF produced by the equivalent solenoid  316  in motion. The BEMF voltage can be represented and calculated by a constant (Kemf) times the flux and speed of the equivalent solenoid  316 . 
     Referring now to  FIG. 4 , therein is shown a first timing diagram  400  for the solenoid system  100  of  FIG. 1 . Movement of the solenoid  102  of  FIG. 1  within the solenoid system  100  can be initiated by a control signal  402  from the control logic  130  of  FIG. 1  and input into the gate driver  116  of  FIG. 1 . The control signal  402  can be a digital pulse specifying an actuation duration  404  during which one of the solenoids  102  will be actuated. The control signal  402  can further control which solenoid will be actuated when multiple solenoids are used. 
     The first timing diagram  400  further depicts an input voltage  406  and a digital current signal  408 . The input voltage  406  can be the signal of voltage or u(t)  304  of  FIG. 3  from the output of the half bridge  113  of  FIG. 1 . The digital current signal  408  can be the signal of current or i(t)  310  of  FIG. 3  through the solenoid  102  as detected by the current sensor  122  of  FIG. 1 . 
     The control signal  402 , the input voltage  406 , and the digital current signal  408  are plotted with respect to a horizontal time axis. The control signal  402  and the input voltage  406  are plotted with respect to a vertical voltage axis, such as the u(t)  304  in the case of the input voltage  406 . The digital current signal  408  is plotted with respect to a vertical current axis, such as the i(t)  310 . 
     The input voltage  406  is shown having an energizing voltage  410 , a hold voltage  412 , and a disable voltage  414 . The energizing voltage  410  can be a large voltage, relative to the voltage ratings of the solenoid  102 . The energizing voltage  410  should be large enough to ensure movement of the solenoid  102 . 
     When parameterizing the solenoid system  100 , the largest energizing voltage  410  required by a solenoid, in a group of solenoids, can be chosen as the energizing voltage  410 . Alternatively, the energizing voltage  410  can be customized for each solenoid  102  individually. 
     The input voltage  406  and the digital current signal  408  can be initiated by a rising edge of the control signal  402 . As the energizing voltage  410  is large, an adjustable ramp  416  can be used to bring the solenoid  102  up from the disable voltage  414  to the energizing voltage  410  without overly stressing the solenoid  102 . The adjustable ramp  416  can be created by varying the PWM signal provided by the gate driver  116 . 
     The hold voltage  412  is shown being between the energizing voltage  410  and the disable voltage  414 . The hold voltage  412  can be a voltage that holds the plunger  108  of  FIG. 1  in position without movement. 
     When a group of solenoids are being parameterized, the hold voltage  412  can be the lowest voltage where all solenoids  102  in a group are restrained from movement. The hold voltage  412  can also be determined individually for each solenoid  102  as the lowest voltage preventing movement of the solenoid  102 . 
     The first timing diagram  400  depicts the operation of the solenoid system  100 . The integrated solenoid driver  104  of  FIG. 1  can initiate the adjustable ramp  416  by providing the control signal  402  to the gate driver  116 . The gate driver  116  can then provide the adjustable ramp  416  to bring the solenoid  102  from an off voltage  418  of zero volts to the energizing voltage  410 . 
     As the adjustable ramp  416  is applied, the plunger  108  will move within the solenoid  102 . In some cases, the plunger  108  can begin to move during the adjustable ramp  416 , in other cases, the plunger  108  will move during the energizing voltage  410 , and in yet other cases the plunger  108  will move during both the adjustable ramp  416  and the energizing voltage  410 . Movement of the plunger  108  will generate a back electromotive force, which can be detected as a drop in current. 
     As the plunger  108  begins to move within the solenoid  102 , the back electromotive forces are generated and the drop in current is detected. The drop in current can be detected by the control logic  130  during the energizing voltage  410  or during the adjustable ramp  416 . 
     The input voltage  406  and the digital current signal  408  can be terminated by a falling edge of the control signal  402 . The input voltage  406  can provide a ramp down  420  at the falling edge of the control signal  402  for bringing the input voltage  406  from the hold voltage  412  down to the disable voltage  414 . 
     The input voltage  406  is depicted including both a digital voltage signal  422  and an AC signal  424 , which is an AC voltage signal or an AC carrier signal. For ease of description, the AC signal  424  will be described herein as the AC carrier signal  424 . The digital voltage signal  422  can be determined by the PWM signal from the PWM ramping module  122  of  FIG. 1  while the AC carrier signal  424  can be provided by the AC carrier module  134  of  FIG. 1  and superimposed on the PWM duty cycle of the digital voltage signal  422 . 
     As shown, the AC carrier signal  424  is shown superimposed on the energizing voltage  410 , the hold voltage  412 , and the disable voltage  414 . Illustratively for example, the frequency of the AC carrier signal  424  can be around 1 Hz to 1 kHz. As shown, the disable voltage  414  should be at least larger than half of the peak-to-peak voltage of the AC carrier signal  424 . 
     The digital current signal  408  can be analyzed by the AC carrier module  134  to determine both attributes of the digital current signal  408 , that is the DC offset current amplitude  426  and the AC current amplitude  428 . The solenoid  102  responds to the AC carrier signal  424  with a sinusoidal response signal, which is detected by the AC carrier module  134  as the AC current amplitude  428 . The AC current amplitude  428  is the maximum value or peak of the sinusoidal response signal as measured from the DC offset current amplitude  426  to the highest positive value or lowest negative value. 
     If AC current amplitude  428  is high, the inductance of the solenoid  102  is low and when the AC current amplitude  428  is low, the inductance of the solenoid  102  is high. That is, the AC carrier module  134  can determine the AC current amplitude  428  is a low AC current amplitude based on the plunger  108  being in a retracted position and determine the AC current amplitude  428  is a high AC current amplitude based on the plunger  108  being in an extended position. 
     The high AC and low AC current amplitude can be determined by an AC amplitude threshold  430  or by comparing the AC current amplitude  428  to a previous value. Based on this determination of high or low values for the AC current amplitude  428 , a binary signal indicating proper plunger  108  position can be determined. The AC amplitude threshold  430  can be programmable trigger levels measured against the AC current amplitude  428  through the coil  106  of  FIG. 1  and used to determine extended or retracted position of the plunger  108 . 
     In one contemplated embodiment, the control logic  130  can instruct the gate driver  116  to modify the PWM signal to provide the hold voltage  412  or for dropping from the energizing voltage  410  to the hold voltage  412  based on the position of the plunger  108  being detected in the actuated position as determined by the AC current amplitude  428 . 
     As will be appreciated, the hold voltage  412  can significantly reduce the power consumption of the solenoid  102 . This is all the more important as the time spent using the hold voltage  412  increases in relation to the energizing voltage  410 . 
     Furthermore, a DC offset current amplitude threshold  432  is shown extending across the digital current signal  408 . The DC offset current amplitude threshold  432  can be used to determine a high resistance through the coil  106 , which indicates a high temperature and the solenoid  102  should be changed. For example, when the digital current signal  408  or the DC offset current amplitude  426  falls below the DC offset current amplitude threshold  432  during the actuation duration  404 , an alarm or a fault can be generated, which indicates that the solenoid  102  should be replaced. The AC amplitude threshold  430  can be a threshold of the AC current amplitude  428  while the DC offset current amplitude threshold  432  can be a lower threshold of the digital current signal  408  or the DC offset current amplitude  426 . 
     Referring now to  FIG. 5 , therein is shown a second timing diagram  500  for the solenoid system  100  of  FIG. 1 . The second timing diagram can depict the input voltage  406  having only the digital voltage signal  422  and without the AC carrier signal  424  of  FIG. 4  applied thereto. 
     Similarly, the current response of the solenoid  102  of  FIG. 1  is shown as the digital current signal  408  having only the DC offset current amplitude  426  and without the AC current amplitude  428  of  FIG. 4 . It has been discovered that detecting the digital voltage signal  422  and the DC offset current amplitude  426  can allow the resistance of the coil  106  of  FIG. 1  to be calculated with minimal additional power or additional components by dividing the digital voltage signal  422  at one specific time by the AC current amplitude  428  detected at the same time. Multiple readings can be taken and averaged to increase signal to noise of the reading. 
     The temperature of the coil  106 , which is proportional to the resistance of the coil  106 , can be used to apply the disable voltage  414  or the off voltage  418  of  FIG. 4  if the temperature rises above a temperature threshold. Furthermore, the temperature can be used to generate a fault or a temperature reading as an output of the solenoid system  100 . 
     The DC offset current amplitude threshold  432  can be utilized, for example, to detect a low DC offset current amplitude  426  during the energizing voltage  410  or the hold voltage  412 . If the DC offset current amplitude  426  drops below the DC offset current amplitude threshold  432 , the low DC offset current amplitude  426  would indicate a large resistance and therefore that the solenoid  102  is operating at a high temperature that is not operating with regard to predefined specification requirements. 
     Notably, when the AC carrier signal  424  is not included as a component of the digital voltage signal  422 , the disable voltage  414  can be lower, even zero volts, and is not restricted to being greater than half the peak-to-peak voltage of the AC carrier signal  424  as is the case when the AC carrier signal  424  is included with the digital voltage signal  422 . 
     Referring now to  FIG. 6 , therein is shown a third timing diagram  600  for the solenoid system  100  of  FIG. 1 . The third timing diagram  600  depicts the input voltage  406  of  FIG. 4  to the coil  106  of the solenoid  102 , both of  FIG. 1 , and which includes the AC carrier signal  424  superimposed onto the digital voltage signal  422 . 
     The digital voltage signal  422  is shown providing both the disable voltage  414  and the energizing voltage  410 . The voltage amplitude of the AC carrier signal  424  is half the peak-to-peak value while the period can be one divided by the frequency of the AC carrier signal  424 . 
     Referring now to  FIG. 7 , therein is shown a fourth timing diagram  700  for the solenoid system  100  of  FIG. 1 . The input voltage  406  and the digital current signal  408  are depicted with respect to time along the horizontal axis. The input voltage  406  can include the digital voltage signal  422  having the AC carrier signal  424  superimposed thereon. 
     The input voltage  406  can begin at the hold voltage  412  and then increase to the energizing voltage  410 . As will be appreciated, the digital voltage signal  422  can increase from 6 volts during the hold voltage  412  to 7 volts while in the energizing voltage  410 . 
     The AC carrier signal  424  can oscillate between about 5.5 volts to about 6.5 volts during the hold voltage  412  and can oscillate between about 6.5 volts to about 7.5 volts during the energizing voltage  410 . The AC carrier signal  424  can therefore have a voltage amplitude of about 0.5 volts and a frequency of about 1 Hz to about 1 kHz making the period of the AC carrier signal  424  between 1 second per cycle and 1 millisecond per cycle. 
     The digital current signal  408  is shown having both the DC offset current amplitude  426  and the AC current amplitude  428  response of the solenoid  102  of  FIG. 1  to the input voltage  406 . Illustratively, for example, the DC offset current amplitude  426  is shown centered at around 370 mA during the response to the hold voltage  412  and around 435 mA during the response to the energizing voltage  410 ; however, it should be understood that the DC offset current amplitude  426  will depend on the electrical characteristics of the coil  106  of  FIG. 1  for the specific solenoid  102  used. 
     Continuing with the illustrative example, the AC current amplitude  428  can range from about 180 mA to 190 mA during the hold voltage  412  and range from about 215 mA to 220 mA during the energizing voltage  410 . It will be appreciated that the AC current amplitude  428  is smaller when the energizing voltage  410  is applied to the solenoid  102  and that the AC current amplitude  428  will depend on the electrical characteristics of the coil  106  for the specific solenoid  102  used. 
     The present example depicts the AC current amplitude  428  decreasing from a value of about 10 mA during the hold voltage  412  to about 5 mA during the energizing voltage  410 . A low AC current amplitude can indicate that the plunger  108  of  FIG. 1  has retracted into the solenoid  102 . That is, the solenoid  102  is activated in the retracted position based on the energizing voltage  410  being applied and low AC current amplitude resulting. 
     In one contemplated embodiment, the AC amplitude threshold  430  can be used to determine the low AC current amplitude. That is, if the AC current amplitude  428  is less than the AC amplitude threshold  430  during the energizing voltage  410 , a low AC current amplitude can be identified and the position of the plunger  108  as retracted can also be determined. 
     Alternatively, a high AC current amplitude can be determined if the AC current amplitude  428  is greater than the AC amplitude threshold  430  during the energizing voltage  410 . The high AC current amplitude can indicate the position of the plunger  108  in an extended position. 
     Referring now to  FIG. 8 , therein is shown a fifth timing diagram  800  for the solenoid system  100  of  FIG. 1 . The input voltage  406  and the digital current signal  408  are depicted with respect to time along the horizontal axis. The input voltage  406  can include the digital voltage signal  422  having the AC carrier signal  424  superimposed thereon. 
     The AC carrier signal  424  can be superimposed on the disable voltage  414 , which is presently depicted as the off voltage  418  of  FIG. 4 , the energizing voltage  410 , the hold voltage  412 , as well as the adjustable ramp  416 . The AC carrier signal  424  is shown having a similar amplitude across all regions of the digital voltage signal  422 . 
     The disable voltage  414  can be at zero volts or the off voltage  418 . The AC current amplitude  428  response during the disable voltage  414  is shown to be zero. When the AC current amplitude  428  is required to be detected during the disable voltage  414 , the disable voltage  414  should be at least greater than the voltage amplitude of the AC carrier signal  424 . As depicted, the AC current amplitude  428  is detected on the DC offset current amplitude  426  in areas that correspond in time to the adjustable ramp  416 , the energizing voltage  410 , and the hold voltage  412 . 
     In the present example, the digital voltage signal  422  is zero volts at the disable voltage  414 , ramps to 10 volts at the energizing voltage  410 , falls to 8 volts at the hold voltage  412 , and falls back to 0 volts at the disable voltage  414 . The AC carrier signal  424  can have an amplitude of about one volt when applied to each of the disable voltage  414 , the energizing voltage  410 , the hold voltage  412 , and the adjustable ramp  416 . 
     The DC offset current amplitude  426  is shown at 0 mA when the disable voltage  414  is applied to the coil  106  of the solenoid  102 , both of  FIG. 1 , and can ramp up to 550 mA during the adjustable ramp  416 . A dip in current is the result of back electromotive forces, or the result of the plunger  108  of  FIG. 1  moving within the coil  106 . The AC current amplitude  428  can be approximately 10 mA when the energizing voltage  410  is applied and can fall to a little less during the hold voltage  412 . It will be understood that the digital voltage signal  422 , the AC carrier signal  424 , the AC current amplitude  428 , and the DC offset current amplitude  426  will depend on the electrical characteristics of the coil  106  within the specific solenoid  102  used. 
     Referring now to  FIG. 9 , therein is shown a sixth timing diagram  900  for the solenoid system  100  of  FIG. 1 . The input voltage  406  and the digital current signal  408  are shown together with respect to time on the horizontal axis. 
     The input voltage  406  is shown at the off voltage  418  prior to applying the adjustable ramp  416  until the energizing voltage  410  is reached, then dropping from the energizing voltage  410  to the hold voltage  412 . Lastly, the input voltage  406  is shown dropping to the disable voltage  414  prior to again being placed in the off voltage  418 . 
     The digital current signal  408  is shown having a DC current dip  902  caused by a back electromotive force from the plunger  108  of  FIG. 1  moving within the coil  106  of  FIG. 1 . The DC current dip  902  can be determined by the digital current signal  408  rising above the DC offset current amplitude threshold  432  and falling below the DC offset current amplitude threshold  432  during the adjustable ramp  416  or the energizing voltage  410 . 
     Once the DC current dip  902  is detected, the plunger  108  has moved and the hold voltage  412  can be applied to the coil  106  of the solenoid  102  of  FIG. 1 . The AC carrier signal  424  is shown applied to the digital voltage signal  422  during the hold voltage  412 . Similarly, the AC current amplitude  428  is shown riding on the DC offset current amplitude  426  during the hold voltage  412 . 
     The AC current amplitude  428  can be used to determine the position of the plunger  108  within the solenoid  102  in order to ensure proper placement and actuation of the plunger  108 . The disable voltage  414  can be greater than the amplitude of the AC carrier signal  424  so as to ensure the AC carrier signal  424  is propagated through the coil  106  during the disable voltage  414 . A current spike in the DC offset current amplitude  426  can indicate a second movement of the plunger  108  back to the rest position. 
     Referring now to  FIG. 10 , therein is shown a seventh timing diagram  1000  for the solenoid system  100  of  FIG. 1 . The input voltage  406  and the digital current signal  408  are shown together with respect to time on the horizontal axis. 
     The input voltage  406  is shown at the off voltage  418  prior to applying the adjustable ramp  416  until the energizing voltage  410  is reached. The input voltage  406  is then dropped from the energizing voltage  410  to the hold voltage  412 . 
     The digital current signal  408  is shown having the DC current dip  902  caused by a back electromotive force from the plunger  108  of  FIG. 1  moving within the coil  106  of  FIG. 1 . The DC current dip  902  can be determined by the digital current signal  408  rising above the DC offset current amplitude threshold  432  of  FIG. 4  and falling below the DC offset current amplitude threshold  432  during the adjustable ramp  416  or the energizing voltage  410 . 
     The AC carrier signal  424  is shown applied to the digital voltage signal  422  during energizing voltage  410  and the hold voltage  412 . Similarly, the AC current amplitude  428  is shown riding on the DC offset current amplitude  426  during the energizing voltage  410  and the hold voltage  412 . The AC current amplitude  428  can be used to determine the position of the plunger  108  within the solenoid  102  in order to ensure proper placement and actuation of the plunger  108 . 
     Referring now to  FIG. 11 , therein is shown an eighth timing diagram  1100  for the solenoid system  100  of  FIG. 1 . The input voltage  406  and the digital current signal  408  are shown together with respect to time on the horizontal axis. 
     The input voltage  406  is shown at the off voltage  418  prior to applying the adjustable ramp  416  until the energizing voltage  410  is reached, then dropping from the energizing voltage  410  to the hold voltage  412 . 
     The digital current signal  408  is shown having the DC current dip  902  caused by a back electromotive force from the plunger  108  of  FIG. 1  moving within the coil  106  of  FIG. 1 . The DC current dip  902  can be determined by determining a local high voltage  1102  and a local low voltage  1104  of the digital current signal  408  being larger than a back electromotive force threshold  1106 . Alternatively, the DC current dip  902  can be detected as the digital current signal  408  rising above the DC offset current amplitude threshold  432  of  FIG. 4  and falling below the DC offset current amplitude threshold  432  during the adjustable ramp  416  or the energizing voltage  410 . 
     Once the DC current dip  902  is detected, the plunger  108  has moved and the hold voltage  412  can be applied to the coil  106  of the solenoid  102  of  FIG. 1 . The AC carrier signal  424  is shown applied to the digital voltage signal  422  during the hold voltage  412 . Similarly, the AC current amplitude  428  is shown riding on the DC offset current amplitude  426  during the hold voltage  412 . The AC current amplitude  428  can be used to determine the position of the plunger  108  within the solenoid  102  in order to ensure proper placement and actuation of the plunger  108 . 
     Referring now to  FIG. 12 , therein is shown a control flow  1200  of a method for operating the solenoid system  100 . The method can include providing an energizing voltage to a coil of a solenoid with a switch controller coupled thereto in a block  1202 ; providing an AC signal with a control logic coupled to the switch controller, the AC signal being superimposed onto the energizing voltage in a block  1204 ; detecting current through the coil with a current sensor coupled thereto, the current through the coil including an AC current amplitude induced by the AC signal and including a DC offset current amplitude in a block  1206 ; determining the AC current amplitude is a low AC current amplitude based on an armature within the solenoid being in a retracted position or determining the AC current amplitude is a high AC current amplitude based on the armature being in an extended position with the control logic, and where the AC current amplitude is determined utilizing the AC signal for synchronous demodulation in a block  1208 ; and determining a temperature fault based on the DC offset current amplitude falling below a DC offset current amplitude threshold in a block  1210 . 
     Thus, it has been discovered that the solenoid system furnishes important and heretofore unknown and unavailable solutions, capabilities, and functional aspects. The resulting configurations are straightforward, cost-effective, uncomplicated, highly versatile, accurate, sensitive, and effective, and can be implemented by adapting known components for ready, efficient, and economical manufacturing, application, and utilization. 
     Illustratively, for example the AC carrier signal  424  superimposed onto the energizing voltage  410 , the hold voltage  412 , and the digital voltage signal  422  can be used to sense the current through the coil  106  of the solenoid  102  including the AC current amplitude  428  and the DC offset current amplitude  426  which provides systems and methods of precise control and monitoring of the solenoid  102  that provides a full solution for lower power, low cost, and highly integrated internal position and temperature measurements, a solution not previously available in the electronic solenoid industry. 
     This solution unexpectedly provides a very low power solution allowing synchronous demodulation of the sense input. Furthermore, the DC offset current amplitude  426  and the AC current amplitude  428  can be calculated using multiple readings and averaging the results which provides an unexpectedly large signal to noise ratio allowing even smaller AC carrier signal  424  amplitudes to be used and greatly reducing power consumption. 
     Yet still further, in addition to measuring the inductance, the AC carrier signal  424  can be used as a dithering signal to overcome breakaway torques due to static friction. This can be useful for valves, but also for DC motors with brushes for smooth starting at low speeds. 
     Thus, the solenoid system  100  provides systems and methods of precise control and monitoring of the solenoid  102  that provides a full solution for lower power, low cost, and integrated internal position measurements. The solenoid system  100  further provides systems and methods of precise control and monitoring of the solenoid  102  temperature measurements in that the DC offset current amplitude  426  can be precisely calculated and used to divide the input voltage  406  in determining the resistance of the coil  106  and thereby the temperature of the coil  106 . 
     While the solenoid system has been described in conjunction with a specific best mode, it is to be understood that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the preceding description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations, which fall within the scope of the included claims. All matters set forth herein or shown in the accompanying drawings are to be interpreted in an illustrative and non-limiting sense. 
     Referring now to  FIG. 13 , therein is shown a block diagram of the solenoid system  1300  in a low power embodiment. The low power embodiment relates to electric solenoids, more particularly to electric solenoids implementing a motion triggered low power mode. 
     It is contemplated that the low power embodiment could be implemented with the position and temperature detection embodiment of  FIG. 1  or could be implemented independently. As an extension of the electronics industry, electronic solenoids have come under ever-increasing commercial competitive pressures demanding miniaturized, feature rich, low cost, and low power solenoids. 
     Chief among current technical problems constraining electric solenoids is high electric power consumption. This technical problem hinders remote installations, miniaturized applications, battery power applications, and greatly increases the operating costs across the board. 
     Of the many design requirements, power consumption has become a primary concern for next generation electric solenoids as many future electronic systems are designed to rely on battery power alone; or when designs are not reliant on battery power, consumers are demanding lower power systems for operational cost savings. High power consumption presents follow on technical problems in that solenoids operating under high power regimes will have greater wear limiting operational lifespan and increasing risk of malfunction. 
     The technical problem of high power usage arises due to the criticality of electronic solenoids functioning every time. Because of this criticality, a large initial energizing voltage is used to ensure and initiate solenoid movement. However, this large initial energizing voltage is a significant source of power usage. 
     Furthermore, these large energizing voltages used by prior solutions are also used to maintain the electronic solenoid in position while in use. These large maintenance voltages also contribute to a significant source of power usage of prior solutions. 
     Some prior solutions focused on detecting solenoid plunger motion in order to determine health of a solenoid and enable faulty solenoids to be replaced without requiring even higher drive voltages. However, these previous attempts continue to rely on high power operation and have failed to provide a technical solution for lowering power consumption, a solution that the industry demands. 
     In view of the ever-increasing commercial competitive pressures, along with growing consumer expectations and the diminishing opportunities for meaningful product differentiation in the marketplace, it is critical that answers be found for these problems. Thus, a need remains for electronic solenoid systems with significantly lower power consumption. Solutions to these technical problems have been long sought but prior developments have not taught or suggested any technical solutions and, thus, solutions to these problems have long eluded those skilled in the art. 
     The solenoid system  1300  is depicted having a solenoid  1302  coupled to an integrated solenoid driver  1304 . 
     The solenoid  1302  can be an electromechanical component comprising a coil  1306  with an armature  1308  that moves or otherwise imparts mechanical force in response to a magnetic field generated by passing current through the coil  1306 . One skilled in the art will appreciate that other words may be used to describe the armature  1308  including but not limited to a piston, an actuator, a movable core, a movable slug, and a plunger. For descriptive clarity, hereinafter the armature  1308  will be referred to as plunger  1308 . 
     When the coil  1306  is energized by applying a voltage across the solenoid  1302 , the plunger  1308  is either extended out of the coil  1306  or retracted into the coil  1306  depending on current direction and system assembly. The solenoid  1302  is shown having a first connection  1310  and a second connection  1311 . The first connection  1310  can be coupled to VM, which can be a motor drive voltage larger than supply voltage Vdd  1312 , while the second connection  1311  can be coupled to a half bridge  1313  contained within the integrated solenoid driver  1304 . 
     Although the first connection  1310  of the solenoid  1302  is described as connected to VM, it is contemplated that the first connection  1310  could alternatively be connected to ground when other half bridge configurations are used. Still further, it is contemplated that the first connection  1310  could alternatively be connected to a second half bridge to form a full H-bridge for the coil  1306 . 
     The solenoid  1302  can further include a spring  1314  for providing mechanical resistance against the motion of the plunger  1308  and to limit the retraction of the plunger  1308  within the solenoid  1302  during excitation. Both extension and retraction types of solenoids are contemplated and can be adapted. These types of solenoids differ in the location of the spring  1314  and design of the plunger  1308 . Rotary solenoids are yet a further contemplated implementation, again differing in the location and design of the spring  1314  and also in the type of movement produced. 
     The integrated solenoid driver  1304  can include a switch controller  1316  coupled to the solenoid  1302  through a half bridge  1313 . The switch controller  1316  is to be understood herein as a physical structural component at least having structural low power inputs and higher power outputs. Isolation for protecting delicate control circuitry is also a common structural component of switch controllers  1316 . The switch controller  1316  is typically referred to as a gate driver and for ease of description, the switch controller  1316  will be referred to hereinafter as gate driver  1316 . 
     Illustratively for example, the gate driver  1316  is depicted as a high-side low-side PWM driver. The gate driver  1316  can control the half bridge  1313  with a pulse-width modulated (PWM) signal. The gate driver  1316  can be implemented as dedicated ICs, discrete transistors, or transformers. The gate driver  1316  can also be integrated within a larger IC or IC package. 
     The half bridge  1313  is depicted having a high side N-Channel Depletion MOSFET and a low side N-Channel Depletion MOSFET. It is alternatively contemplated that the half bridge  1313  could also be implemented using insulated-gate bipolar transistors (IGBTs) or one low side N-Channel Depletion MOSFET and one high side P-Channel Depletion MOSFET, for example. The solenoid  1302  can be coupled to the source of the high side MOSFET and coupled to the drain of the low side MOSFET. 
     The N-Channel Depletion MOSFET is a depletion-mode MOSFET device which can be doped so that a channel exists with zero volts between the gate and the source. To control the channel, a negative voltage is applied to the gate, which functions as a normally closed switch. The half bridge  1313  and the solenoid  1302  can further be coupled to an open load  1318 . 
     The gate driver  1316  can provide the PWM signal to the half bridge  1313 . The PWM signal can provide a duty cycle proportional to an energizing voltage  1506 , a hold voltage  1508 , and a disable voltage  1510 , all of  FIG. 15 , below, to the coil  1306 . The gate driver  1316  can also provide an adjustable ramp  1512  of  FIG. 15  from the disable voltage  1510  to the energizing voltage  1506  to the coil  1306  by varying the PWM signal. 
     The drain of the high side N-Channel Depletion MOSFET can be coupled to VM in order to drive the high side N-Channel Depletion MOSFET positive with respect to the supply voltage Vdd  1312 . A charge pump  1320  can optionally drive the high side of the half bridge  1313 . 
     The integrated solenoid driver  1304  can further include a current sensor  1322  coupled to the solenoid  1302 . The current sensor  1322  can detect current through the coil  1306  of the solenoid  1302  as an analog current signal. 
     The current sensor  1322  is to be understood herein as a physical structural component at least having structural input and output connections. However, many forms of the current sensor  1322  are contemplated including Hall effect linear sensors, galvanically isolated sensors, or GMR-based sensors. Yet other forms are contemplated including fluxgate sensors, shunt resistors, and even fiber optic interferometer based sensors. 
     The integrated solenoid driver  1304  can further include an analog-to-digital converter  1324  for converting the analog current signal to a digital current signal  1504 , of  FIG. 15 , prior to distributing the digital current signal  1504  to control logic  1326 . The control logic  1326  can be a digital computational block for performing Voltage Divider Rule (VDR) and Current Divider Rule (CDR) based calculations. 
     The half bridge  1313 , the gate driver  1316 , the open load  1318 , the current sensor  1322 , and the analog-to-digital converter  1324  can be reproduced for multiple solenoids  1302 . As shown, the half bridge  1313 , the gate driver  1316 , the open load  1318 , the current sensor  1322 , and the analog-to-digital converter  1324  are reproduced for coupling to four solenoids  1302 . 
     The control logic  1326  is to be understood herein as a physical structural component at least having transistor logic gates for providing computation and control. Furthermore, the control logic  1326  includes structural inputs and outputs typically operating between zero and five volts. It is contemplated that the control logic  1326  can be a TTL or CMOS based architecture but could also include other logic families including RTL, DTL, and ECL, for example. 
     The control logic  1326  can be coupled to the current sensor  1322  through the analog-to-digital converter  1324 . The control logic  1326  can compare the digital current signal  1504  with a reference current  1328  to provide a highly accurate current reading. 
     The control logic  1326  can detect the drop in current  1514  of  FIG. 15 . The drop in current  1514  is generated by movement of the plunger  1308 . More particularly, movement of the plunger  1308  within the solenoid  1302  produces a back electromotive force which is detected as the drop in current  1514  during the energizing voltage  1506 , or during the ramp  1512  to the energizing voltage  1506 . 
     The drop in current  1514  indicates movement of the plunger  1308  and can be detected during the energizing voltage  1506 , or during the ramp  1512  to the energizing voltage  1506 . The control logic  1326  can be coupled to and control the gate driver  1316  with a control signal indicating a voltage level. 
     The control logic  1326  can compare the drop in current  1514  with a current drop threshold  1520  of  FIG. 15 . When the drop in current  1514  does not exceed the current drop threshold  1520 , the control logic  1326  can provide an error indicating improper movement or no movement of the plunger  1308 . 
     When the control logic  1326  detects the drop in current  1514 , the control logic  1326  can direct the gate driver  1316  to provide the hold voltage  1508  to the coil  1306 . Furthermore, the control logic  1326  can delay the hold voltage  1508  until a wait time has elapsed. 
     The wait time can be a programable variable and can be measured with an oscillator  1330 , which can provide a clock pulse. The control logic  1326  can further direct the gate driver  1316  to provide the disable voltage  1510  to the coil  1306  in order to place the solenoid  1302  in a non-actuated state where the position of the plunger  1308  is based on the force of the spring  1314  rather than based on voltages provided by the gate driver  1316 . 
     The gate driver  1316  providing the hold voltage  1508  to the coil  1306  of the solenoid  1302  based on the control logic detecting the drop in the current reflects an unexpected improvement in the functioning of solenoid systems by reducing power and wear during use while still allowing the solenoid  1302  to remain in an actuated state, a combination previously unknown, unexpected, and untested. As such the solution is necessarily rooted in electronics technology in order to overcome a problem, of high power usage specifically arising in the realm of electronic solenoids, by technical means. 
     The drop in current  1514  detected and measured within the control logic  1326  by way of the current sensor  1322  and the analog-to-digital converter  1324  is used to control the technical process and the internal functioning of the control logic  1326  itself together with its interfaces including the gate driver  1316  and the solenoid  1302 . Thus, the drop in current  1514  and subsequent application of the hold voltage  1508  controls the operation of the solenoid system  1300  and inherently comprises and reflects, corresponding technical features of the control logic  1326 , the current sensor  1322 , the analog-to-digital converter  1324 , and the gate driver  1316 . 
     The drop in current  1514  provides a robust indication of plunger  1308  movement and reducing voltage to coil  1306  of the solenoid  1302 , from the energizing voltage  1506  to the hold voltage  1508  based on this drop in current  1514 , greatly reduces power consumption of the solenoid to the point where the solenoid  1302  could be implemented in remote battery powered systems, such as door locks with extremely low power requirements. In this way power saving is optimized as energizing voltage apply time is minimized. 
     The information of successful movement can be displayed to a user as can the duration between the initial voltage applied to the coil  1306  of the solenoid  1302  to the drop in current  1514 . The integrated solenoid driver  1304  is further shown including input output modules for providing the movement and duration information. 
     Illustratively, the input output modules can include a control interface  1332  having multiple control pins. The input output modules can also include a serial peripheral interface  1334  for providing movement and duration information. 
     Another example of the input output modules can include a voltage input and output  1336  having a linear voltage regulator and coupled to the control logic  1326  with an enable control line. The control logic  1326  can also be coupled to and monitor the supply voltage Vdd  1312  through an analog-to-digital converter  1338 . 
     The control logic  1326  can detect faults in the supply voltage Vdd  1312  including under voltage lockout faults and over voltage threshold faults. The control logic  1326  can also detect over current faults as well as faults based on an i(t)  1410  of  FIG. 14  not having a drop large enough to satisfy the current drop threshold  1520  of  FIG. 15  or based on the i(t)  1410  not rising above and falling below the current drop threshold  1620  of  FIG. 16 , both of which would indicate improper plunger  1308  movement. 
     These faults can be output with a fault interface  1340  coupled to the control logic  1326 . As yet another example of the input output modules, the control logic could be coupled to a multiplexed interface  1342  having multiplexed input and output pins. 
     Referring now to  FIG. 14 , therein is shown a block diagram for an equivalent circuit  1402  of the solenoid system  1300  of  FIG. 13 . The equivalent circuit  1402  can provide a representation of the solenoid  1302  of  FIG. 13  coupled to the integrated solenoid driver  1304  of  FIG. 13  and retains the electrical characteristics thereof. The equivalent circuit  1402  enables resistances and inductances to be simplified for analysis. 
     The equivalent circuit  1402  can provide a voltage represented as a step function, u(t)  1404 , across an input terminal  1406  and an output terminal  1408 . The u(t)  1404  can represent the PWM controlled signal provided by the gate driver  1316  of  FIG. 13  from the output of the half bridge  1313  of  FIG. 13  to the coil  1306  of  FIG. 13 . The equivalent circuit  1402  is also shown including a current i(t)  1410  through an equivalent resistor  1412 , an equivalent inductor  1414  and an equivalent solenoid  1416 . The i(t)  1410  can be the current through the coil  1306  as detected by the current sensor  1322  of  FIG. 13 . 
     The u(t)  1404  can be equal to the voltage drop across the equivalent resistor  1412  plus the voltage drop across the equivalent inductor  1414  plus the back emf produced by the equivalent solenoid  1416  in motion. The BEMF voltage can be represented and calculated by a constant (Kemf) times the flux and speed of the equivalent solenoid  1416 . 
     Referring now to  FIG. 15 , therein is shown a first timing diagram for the solenoid system  1300  of  FIG. 13 . The first timing diagram depicts a digital voltage signal  1502  and a digital current signal  1504 . The digital voltage signal  1502  can be the signal of voltage or u(t)  1404  of  FIG. 14  from the output of the half bridge  1313  of  FIG. 13  to the coil  1306  of  FIG. 13 . The digital current signal  1504  can be the signal of current or i(t)  1410  of  FIG. 14  through the solenoid  1302  of  FIG. 13  as detected by the current sensor  1322  of  FIG. 13 . 
     The digital voltage signal  1502  and the digital current signal  1504  are plotted with respect to a horizontal time axis. The digital voltage signal  1502  is plotted with respect to a vertical voltage axis, such as the u(t)  1404 . The digital current signal  1504  is plotted with respect to a vertical current axis, such as the i(t)  1410 . 
     The digital voltage signal  1502  is shown having an energizing voltage  1506 , a hold voltage  1508 , and a disable voltage  1510 . The energizing voltage  1506  can be a large voltage, relative to the voltage ratings of the solenoid  1302 . The energizing voltage  1506  should be large enough to ensure movement of the solenoid  1302 . 
     When parameterizing the solenoid system  1300 , the largest energizing voltage  1506  required by a solenoid, in a group of solenoids, can be chosen as the energizing voltage  1506 . Alternatively, the energizing voltage  1506  can be customized for each solenoid  1302  individually. 
     As the energizing voltage  1506  is large, an adjustable voltage ramp, such as the adjustable ramp  1512 , can be used to bring the solenoid  1302  up from the disable voltage  1510  to the energizing voltage  1506  without overly stressing the solenoid  1302 . The adjustable ramp  1512  can be created by varying the PWM signal provided by the gate driver  1316  of  FIG. 13 . 
     The hold voltage  1508  is shown being between the energizing voltage  1506  and the disable voltage  1510 . The hold voltage  1508  can be a voltage that holds the plunger  1308  of  FIG. 13  in position without movement. 
     When a group of solenoids are being parameterized, the hold voltage  1508  can be the lowest voltage where all solenoids  1302  in a group are restrained from movement. The hold voltage  1508  can also be determined individually for each solenoid  1302  as the lowest voltage preventing movement of the solenoid  1302 . 
     The first timing diagram depicts the operation of the solenoid system  1300 . Starting with the disable voltage  1510 , which is usually 0 volts, the integrated solenoid driver  1304  of  FIG. 13  can initiate the adjustable ramp  1512  to bring the voltage to the coil  1306  of the solenoid  1302  from the disable voltage  1510  to the energizing voltage  1506 . 
     As the adjustable ramp  1512  is applied and the energizing voltage  1506  is reached, the plunger  1308  will move within the solenoid  1302 . In some cases, the plunger  1308  can begin to move during the adjustable ramp  1512 , in other cases, the plunger  1308  will move during the energizing voltage  1506 . Movement of the plunger  1308  will generate a back electromotive force, which can be detected as a drop in current  1514 . 
     As the plunger  1308  begins to move within the solenoid  1302 , the back electromotive forces are generated and the drop in current  1514  is detected. The drop in current  1514  can be detected by the control logic  1326  of  FIG. 13  during the energizing voltage  1506  and during the adjustable ramp  1512 . 
     The drop in current  1514  can be measured between a local current maximum  1516  and a local current minimum  1518 , both detected by the control logic  1326 . The control logic  1326  can measure the drop in current  1514  against a current drop threshold  1520 , which can be an absolute value of the change in current. 
     If the drop in current  1514  is larger than the current drop threshold  1520 , motion of the plunger  1308  is recognized and the integrated solenoid driver  1304  can then reduce the u(t)  1404  from the energizing voltage  1506  to the hold voltage  1508 . Although the current drop threshold  1520  is depicted as an amount of the i(t)  1410  change required to detect the drop in current  1514 , it is alternatively contemplated that the current drop threshold  1520  could also be a single current value and the drop in current  1514  could be determined by first detecting the i(t)  1410  rising above the current drop threshold  1520  and then the i(t)  1410  falling below the current drop threshold  1520  due to the back electromotive force of the plunger  1308 . 
     In the present embodiment, the hold voltage  1508  is applied after a wait time  1522  had elapsed. The wait time  1522  can allow slower or sticky solenoids to complete their motion before the power saving hold voltage  1508  is applied. 
     As will be appreciated, the hold voltage  1508  can significantly reduce the power consumption of the solenoid  1302 . This is all the more important as the time spent using the hold voltage  1508  increases in relation to the energizing voltage  1506 . 
     When the solenoid  1302  needs to be disabled, the gate driver  1316  can apply the disable voltage  1510 , allowing the current and the voltage to fall to zero. The control logic  1326  can determine a motion time  1524  between energizing, which is the application of the adjustable voltage ramp  1512 , and the drop in current  1514  indicating plunger motion based on BEMF. Specifically, the motion time  1524  can be from the initial adjustable ramp  1512  application to the back electromotive force detected as the drop in current  1514 . 
     Referring now to  FIG. 16 , therein is shown a second timing diagram for the solenoid system  1300  of  FIG. 13 . The second timing diagram depicts a digital voltage signal  1602  and a digital current signal  1604 . The digital voltage signal  1602  can be the signal of voltage or u(t)  1404  of  FIG. 14  from the output of the half bridge  1313  of  FIG. 13  to the coil  1306  of  FIG. 13 . The digital current signal  1604  can be the signal of current or i(t)  1410  of  FIG. 14  through the solenoid  1302  of  FIG. 13  as detected by the current sensor  1322  of  FIG. 13 . 
     The digital voltage signal  1602  and the digital current signal  1604  are plotted with respect to a horizontal time axis. The digital voltage signal  1602  is plotted with respect to a vertical voltage axis, such as the u(t)  1404 . The digital current signal  1604  is plotted with respect to a vertical current axis, such as the i(t)  1410 . 
     The digital voltage signal  1602  is shown having an energizing voltage  1606 , a hold voltage  1608 , and a disable voltage  1610 . The energizing voltage  1606  can be a large voltage, relative to the voltage ratings of the solenoid  1302 . The energizing voltage  1606  should be large enough to ensure movement of the solenoid  1302 . 
     When parameterizing the solenoid system  1300 , the largest energizing voltage  1606  required by a solenoid, in a group of solenoids, can be chosen as the energizing voltage  1606 . Alternatively, the energizing voltage  1606  can be customized for each solenoid  1302  individually. 
     As the energizing voltage  1606  is large, an adjustable ramp  1612  can be used to bring the solenoid  1302  up from the disable voltage  1610  to the energizing voltage  1606  without overly stressing the solenoid  1302 . The adjustable ramp  1612  can be created by varying the PWM signal provided by the gate driver  1316  of  FIG. 13 . 
     The hold voltage  1608  is shown being between the energizing voltage  1606  and the disable voltage  1610 . The hold voltage  1608  can be a voltage that holds the plunger  1308  of  FIG. 13  in position without movement. 
     When a group of solenoids are being parameterized, the hold voltage  1608  can be the lowest voltage where all solenoids  1302  in a group are restrained from movement. The hold voltage  1608  can also be determined individually for each solenoid  1302  as the lowest voltage preventing movement of the solenoid  1302 . 
     The second timing diagram depicts the operation of the solenoid system  1300 . Starting with the disable voltage  1610 , which is usually 0 volts, the integrated solenoid driver  1304  of  FIG. 13  can initiate the adjustable ramp  1612  to bring the solenoid  1302  from the disable voltage  1510  to the energizing voltage  1606 . 
     As the adjustable ramp  1612  is applied and the energizing voltage  1606  is reached, the plunger  1308  will move within the solenoid  1302 . As is shown, the plunger  1308  moves during the adjustable ramp  1612  and is completed prior to reaching the energizing voltage  1606 . Movement of the plunger  1308  will generate a back electromotive force, which can be detected as a drop in current  1614 . 
     As the plunger  1308  begins to move within the solenoid  1302 , the back electromotive forces are generated and the drop in current  1614  is detected. The drop in current  1614  is detected by the control logic  1326  of  FIG. 13  during the adjustable ramp  1612 . 
     The drop in current  1614  can be measured between a local current maximum  1616  and a local current minimum  1618 , both detected by the control logic  1326 . The control logic  1326  can measure the drop in current  1614  against a current drop threshold  1620 . 
     The current drop threshold  1620  is shown as a single current value by which the drop in current  1514  is determined by first detecting the i(t)  1410  rising above the current drop threshold  1520  of  FIG. 15  and then the i(t)  1410  falling below the current drop threshold  1520  due to the back electromotive force of the plunger  1308 . Alternatively, the current drop threshold  1520  could be an amount of the i(t)  1410  change required to detect the drop in current  1514 . If the drop in current  1514  is detected, motion of the plunger  1308  is recognized and the integrated solenoid driver  1304  can then reduce the u(t)  1404  from the energizing voltage  1606  to the hold voltage  1608 . 
     In the present embodiment, the hold voltage  1608  is not applied after a wait time but is applied immediately once reaching the energizing voltage  1606 . As will be appreciated, the hold voltage  1608  can significantly reduce the power consumption of the solenoid  1302 . This is all the more important as the time spent using the hold voltage  1608  increases in relation to the energizing voltage  1606 , and as is depicted, the energizing voltage  1606  is terminated immediately for increased power savings. 
     When the solenoid  1302  needs to be disabled, the gate driver  1316  can apply the disable voltage  1610 , allowing the current and the voltage to fall to zero. The control logic  1326  can determine a motion time  1624  between energizing and plunger motion based on BEMF. Specifically, the motion time  1624  can be from the beginning of the adjustable ramp  1612  to the back electromotive force detected as the drop in current  1614 . 
     Referring now to  FIG. 17 , therein is shown a control flow  1700  of a method for operating the solenoid system  1300 . The method can include providing an energizing voltage to a coil of a solenoid with a switch controller in a block  1702 ; detecting a current through the coil of the solenoid with a current sensor coupled to the solenoid in a block  1704 ; detecting a drop in the current indicating movement of an armature of the solenoid the drop detected with control logic coupled to the current sensor in a block  1706 ; dropping the energizing voltage to the coil down to a hold voltage with the switch controller based on the control logic detecting the drop in the current, and the hold voltage being below the energizing voltage in a block  1708 ; providing an error based on the drop in the current being less than a current drop threshold in a block  1710 ; and providing a disable voltage to the coil placing the solenoid in a non-actuated state, and the hold voltage is between the energizing voltage and the disable voltage in a block  1712 . 
     Thus, it has been discovered that the solenoid system furnishes important and heretofore unknown and unavailable solutions, capabilities, and functional aspects. The resulting configurations are straightforward, cost-effective, uncomplicated, highly versatile, accurate, sensitive, and effective, and can be implemented by adapting known components for ready, efficient, and economical manufacturing, application, and utilization. 
     Particularly, it has been discovered that providing a hold voltage to a coil of a solenoid based on control logic detecting a drop in the current reflects an unexpected improvement in the functioning of solenoid systems by reducing power and wear during use while still allowing the solenoid to remain in an actuated state, a combination previously unknown, unexpected, and untested. As such the solution is necessarily rooted in electronics technology in order to overcome a problem of high power usage specifically arising in the realm of electronic solenoids by technical means. 
     The drop in current detected and measured within the control logic by way of a current sensor and an analog-to-digital converter is used to control the technical process and the internal functioning of the control logic itself together with its interfaces including the switch controller and the solenoid. Thus, the drop in current and subsequent application of the hold voltage controls the operation of the solenoid system and inherently comprises and reflects, corresponding technical features of the control logic, the current sensor, the analog-to-digital converter, and the switch controller. 
     The drop in current provides a robust indication of armature movement and reducing voltage to the coil, from the energizing voltage to the hold voltage based on this drop in current, greatly reduces power consumption of the solenoid to the point where the solenoid could be implemented in remote battery powered systems, such as door locks with extremely low power requirements. In this way power saving is optimized as energizing voltage apply time is minimized. 
     While the solenoid system has been described in conjunction with a specific best mode, it is to be understood that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the preceding description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations, which fall within the scope of the included claims. All matters set forth herein or shown in the accompanying drawings are to be interpreted in an illustrative and non-limiting sense. 
     The solenoid system  1300  can be a low power solenoid system comprising: a solenoid having a coil; a switch controller coupled to the solenoid, the switch controller provides an energizing voltage and a hold voltage, the hold voltage being below the energizing voltage; a current sensor, coupled to the solenoid, the current sensor detects current through the coil; and control logic coupled to the current sensor, the control logic detects a drop in the current, the switch controller drops the energizing voltage to the coil down to the hold voltage based on the control logic detecting the drop in the current, and the control logic provides an error based on the drop in the current being less than a current drop threshold. 
     Within the low power solenoid system, the control logic compares the current through the coil with a current reference input into the control logic. The low power solenoid system can also include an analog-to-digital converter coupled between the current sensor and the control logic. Within the low power solenoid system, the drop in the current is from a back electromotive force generated by movement of an armature of the solenoid. 
     The solenoid system  1300  can further be a low power solenoid system comprising: a solenoid having an armature and a coil; a switch controller coupled to the solenoid, the switch controller provides an energizing voltage, a hold voltage, and a disable voltage, the hold voltage being between the energizing voltage and the disable voltage; a current sensor, coupled to the solenoid, the current sensor detects current through the coil; and control logic coupled to the current sensor, the control logic detects a drop in the current indicating movement of the armature, the switch controller drops the energizing voltage to the coil down to the hold voltage based on the control logic detecting the drop in the current, the switch controller provides the disable voltage to the coil placing the solenoid in a non-actuated state, and the control logic provides an error based on the drop in the current being less than a current drop threshold. 
     The low power solenoid system can also include an N-channel MOSFET half bridge coupled between the switch controller and the solenoid, the N-channel MOSFET half bridge supplies the energizing voltage, the hold voltage, and the disable voltage to the coil based on a pulse-width modulated signal from the switch controller. Within the low power solenoid system, the control logic determines a time between a beginning of an adjustable voltage ramp to the coil and the drop in the current indicating the movement of the armature. 
     Within the low power solenoid system, the switch controller provides the hold voltage to the coil based on the control logic detecting the drop in the current and based on a wait time elapsing after the drop in the current is detected. Within the low power solenoid system, the switch controller provides an adjustable voltage ramp to the coil from the disable voltage to the energizing voltage. 
     The solenoid system  1300  can be operated by: providing an energizing voltage to a coil of a solenoid with a switch controller; detecting a current through the coil with a current sensor coupled to the solenoid; detecting a drop in the current with control logic coupled to the current sensor; providing an error based on the drop in the current being less than a current drop threshold; and dropping the energizing voltage to the coil down to a hold voltage with the switch controller based on the control logic detecting the drop in the current, and the hold voltage being below the energizing voltage. 
     Operating the low power solenoid system can also include comparing the current through the coil with a current reference input into the control logic. Where detecting the current includes detecting the current with an analog-to-digital converter coupled between the current sensor and the control logic. Where detecting the drop in the current includes detecting the drop in the current from a back electromotive force generated by movement of an armature of the solenoid. 
     Operating the low power solenoid system can also include providing a disable voltage to the coil placing the solenoid in a non-actuated state, the hold voltage being between the energizing voltage and the disable voltage, and wherein detecting the drop in the current indicates movement of an armature of the solenoid. Where providing the energizing voltage, the hold voltage, and the disable voltage includes providing the energizing voltage, the hold voltage, and the disable voltage with an N-channel MOSFET half bridge coupled between the switch controller and the solenoid, and based on a pulse-width modulated signal from the switch controller. 
     Operating the low power solenoid system can also include determining a time between a beginning of an adjustable voltage ramp to the coil and the drop in the current indicating the movement of the armature. Where providing the hold voltage to the coil with the switch controller based on the control logic detecting the drop in the current further includes providing the hold voltage to the coil based on the control logic detecting the drop in the current and based on a wait time elapsing after the drop in the current is detected. Operating the low power solenoid system can also include providing an adjustable voltage ramp to the coil from the disable voltage to the energizing voltage with the switch controller. 
     The solenoid system  1300  can abstractly be described as a method and apparatus that can include: providing an energizing voltage to a coil of a solenoid with a switch controller; detecting a current through the coil of the solenoid with a current sensor coupled to the solenoid; detecting a drop in the current indicating movement of an armature of the solenoid the drop detected with control logic coupled to the current sensor; dropping the energizing voltage to the coil down to a hold voltage with the switch controller based on the control logic detecting the drop in the current, and the hold voltage being below the energizing voltage; and providing a disable voltage to the coil placing the solenoid in a non-actuated state, and the hold voltage is between the energizing voltage and the disable voltage.