Patent Description:
Current sensor control systems are used in a variety of applications that require knowledge of the level of current delivered to one or more loads. As illustrated in <FIG>, conventional current sensor control systems <NUM> typically include a current sensor <NUM> interposed between an input power supply <NUM> and a load <NUM>. The current sensor <NUM> is configured to output a current signal <NUM> indicating a level of current delivered to the load <NUM>.

Traditional current sensors <NUM>, however, are susceptible to current drifting. Namely, the surrounding temperature of the current sensor <NUM> can affect the measurement precision of the current sensor <NUM>. In fact, the current sensor <NUM> may indicate false current readings even when switching control logic <NUM> commands a switch <NUM> into an open state so as to disconnect the input power supply <NUM> from the load <NUM>. These imprecisions and false readings introduce undesirable errors in the output current signal <NUM>. Many applications utilize BIT circuitry <NUM> to diagnose the behavior of the overall system <NUM> including, for example, failure to distinguish between an on state and off state of the load <NUM>. When the BIT circuitry <NUM> is connected directly to the current sensor <NUM> as illustrated in <FIG>, an output current signal <NUM> including drifting errors can cause the BIT circuitry <NUM> to misdiagnose the system. Current sensor calibration is known from <CIT>.

According to a a first aspect there is provided a dynamic calibrating current sensor control system according to claim <NUM>.

According to a second aspect, a method is provided to dynamically calibrate a current sensor control system according to claim <NUM>.

The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:.

At least one embodiment provides a dynamic calibrating current sensor control system including a current sensor interposed between an input power supply and a load. The input power supply generates an input current that drives the load, and the current sensor is configured to output a current signal indicating a current level received by the load. Unlike conventional systems including a current sensor, at least one embodiment of the disclosure provides an electronic drift current suppression circuit. The drift current suppression circuit dynamically applies an offset value to the current signal output from the current sensor so as to generate a corrected current signal. The corrected current signal cancels any drift current existing in the current signal after the input power supply is connected to the load. In this manner, the current signal output by the current sensor is dynamically corrected and calibrated such that a more accurate measurement of the current level received by the load is achieved.

With reference now to <FIG>, a dynamic calibrating current control system <NUM> is illustrated according to a non-limiting embodiment. The dynamic calibrating current control system <NUM> includes an input power supply <NUM> configured to generate an input current (IIN) that drives one or more loads <NUM> such as, for example, a solenoid. The input power supply <NUM> may include, for example, a voltage supply or a current supply. In addition, the voltage supply may include, for example, an alternating current (AC) voltage supply or a direct current (DC) power supply. A switch <NUM> configured to selectively operate in an open state and closed state allows for the input power supply <NUM> to be selectively connected and disconnected to the load <NUM>. Any switch capable of selectively establishing the connection between the input power supply <NUM> and the load <NUM> may be used including, but not limited to, a voltage controlled switch, a current controlled switch, a magnetic switch, and a hydraulic switch. A current sensor <NUM> is interposed between the switch <NUM> and the load <NUM>, and is configured to output at least one current signal <NUM> indicating a level of current delivered to the load <NUM>. The current sensor <NUM> may include various types of current sensors including, but not limited to, a DC current sensor, an AC root-mean-square (ACrms) sensor, and an AC peak-to-peak (ACpp) sensor.

The dynamic calibrating current control system <NUM> further includes an electronic switching control circuit <NUM> and an electronic drift suppression circuit <NUM>. The electronic switching control circuit <NUM> generates at least one switch control signal <NUM> that controls the state of the switch <NUM>. For example, the switch <NUM> is closed in response to receiving the switch control signal <NUM> so as to connect the input power supply <NUM> to the load <NUM>, and is opened when the switch control signal <NUM> is inhibited from reaching the switch <NUM> so as to disconnect the input power supply <NUM> from the load <NUM>.

According to a non-limiting embodiment, the switching control circuit <NUM> includes an electronic switch logic circuit <NUM> and an electronic time delay circuit <NUM>. The switch logic circuit <NUM> is configured to generate the switching signal <NUM> in response to various conditions including, but not limited to, data values exceeding one or more threshold values, or input control signals commanding activation and/or deactivation of the load <NUM>. The time delay circuit <NUM> is configured to halt (i.e., delay) delivery of the switching signal <NUM> to the switch <NUM> for a predetermined time period. The time delay circuit <NUM> may include, but is not limited to, a resistor-capacitor (RC) circuit that generates a time constant matching the predetermined time period, and a digital logic timing circuit having a digital countdown timer set to the predetermined time period. A time delay input of the time delay circuit <NUM> is in signal communication with the switch logic circuit <NUM> and a time delay output is in signal communication with the switch <NUM>. The predetermined time period for halting (i.e., delaying) the switch control signal <NUM> may range, for example, from approximately <NUM> microsecond (µs) to approximately <NUM> milliseconds (ms).

The electronic drift suppression circuit <NUM> is in signal communication with the current sensor <NUM> and the switching control circuit <NUM>. The drift suppression circuit <NUM> is configured to generate a corrected current signal <NUM> in response to applying an offset value <NUM> to the current signal <NUM>. The offset value <NUM> cancels any drift current from the current signal <NUM> in response to connecting the input power supply <NUM> to the load <NUM>. The corrected current signal essentially indicates the actual current level generated by the input power supply <NUM>, and is a different and independent signal with respect to the input current (IIN) used to drive load <NUM>.

According to a non-limiting embodiment, the drift suppression circuit <NUM> stores a first current value output by the current sensor <NUM> when the input power supply <NUM> is disconnected. Since the input power supply <NUM> is disconnected at this time, the first current value essentially indicates the drift current output by the current sensor <NUM>. Accordingly, the drift suppression circuit <NUM> stores the first current value as the offset value which is used to correct and calibrate current signal <NUM> as discussed in greater detail below. When the input power supply <NUM> is connected to the load <NUM>, the drift suppression circuit <NUM> receives a second current value output by the current sensor <NUM>. This second current value is indicative of the current level delivered to the load <NUM>, in addition to any drift current generated by the current sensor <NUM>.

The drift suppression circuit <NUM> includes a sample and hold (S/H) circuit <NUM> and an electronic differential circuit <NUM>. The S/H circuit <NUM> is configured to store the first current value. More specifically, the S/H circuit <NUM> includes a sampling input that shares a connection with the switch logic circuit <NUM> and the time delay input. In this manner, the S/H circuit <NUM> is capable of storing the first current value in response to receiving the switching signal <NUM> but prior to closure of the switch <NUM>.

The electronic differential circuit <NUM> is configured to subtract the stored first current value from the second current value in response to connecting the input power supply to generate the corrected current signal <NUM>. More specifically, the differential circuit <NUM> may be constructed as a differential amplifier <NUM> that includes a positive terminal connected to an output of the current sensor <NUM>, and a negative terminal connected to a sampling output of the S/H circuit <NUM>. In this manner, negative terminal receives the stored first current value (i.e., the offset value), while the positive terminal receives the second current value. The output of the differential amplifier <NUM> is therefore a corrected current signal that excludes any drift current that may have existed in the current signal <NUM>. As described above, the current sensor <NUM> is dynamically calibrated such that any device connected to the drift suppression circuit <NUM> receives a corrected current signal absent any imprecisions or false measurements caused by drifting of the current sensor <NUM>. For example, the system <NUM> may include a BIT analysis circuit <NUM> in signal communication with the output of the differential amplifier <NUM> so as to receive the corrected current signal <NUM>. Accordingly, the BIT analysis circuit <NUM> may properly diagnose the behavior of the system <NUM>. For instance, the BIT analysis circuit <NUM> may properly distinguish between an on state and an off state of the load <NUM>, whereas BIT circuitry included in a conventional system may incorrectly determine a load exists in an on-state due to the additional drift current existing in the output of the conventional current sensor. Accordingly, an output of the BIT circuitry <NUM> can be used to control the operation of the system <NUM>, e.g., can control operation of the load <NUM>.

Referring now to <FIG>, a flow diagram illustrates a method of controlling a dynamic calibrating current sensor according to a non-limiting embodiment. The method begins at operation <NUM>, and at operation <NUM> a state of a switch connecting an input power supply to one or more loads is monitored. When the switch is closed, for example, the method returns to operation <NUM> and continues monitoring the state of the switch. When the switch is open, however, the method proceeds to operation <NUM> to determine whether a switch control signal configured to close the switch has been generated. When the switch control signal is not generated, the method returns to operation <NUM> and continues to determine whether the switch control signal is generated. When the switch control signal is generated, delivery of the switch control signal to the switch is delayed for a predetermined time period at operation <NUM>. At operation <NUM>, a first current value output from a current sensor is stored. The current sensor is disposed, for example, between the input power supply and the load to measure a current level received by the load.

Turning to operation <NUM>, the delay time of the switch control signal is monitored. When the predetermined time period has not expired, the method returns to operation <NUM> and continues monitoring the remaining delay time. When the predetermined time period has expired, however, the switch control signal is delivered to the switch so as to closes the switch at operation <NUM>. Accordingly, the input power supply is connected and drives the load via an input current at operation <NUM>. At operation <NUM>, a second current value is output from the current sensor. At operation <NUM>, the first current value is subtracted from the second current value. In this manner, the second current value is offset by a value equal to the first current value stored prior to connecting the input power supply to the load. At operation <NUM>, a corrected current signal is output which excludes any drift generated by the current sensor. At operation <NUM>, the control system is controlled (e.g., operation of the load is adjusted) based on the corrected current signal, and the method ends at operation <NUM>.

As described above, various non-limiting embodiments provide a dynamic calibrating current sensor control system that includes an electronic drift current suppression circuit. The drift current suppression circuit dynamically applies an offset value to the current signal output from the current sensor so as to generate a corrected current signal. The corrected current signal cancels and removes any drift errors from the current signal after the input power supply is connected to the load. In this manner, the current signal output by the current sensor is dynamically corrected and calibrated such that a more accurate measurement of the current level received by the load is achieved. Furthermore, the current sensor included in the system can be installed in a wide variety of temperature surroundings without concern of outputting a current signal including drift errors caused by changes in the surrounding temperature.

Claim 1:
A dynamic calibrating current sensor control system, comprising:
an input power supply (<NUM>) that generates an input current;
a current sensor (<NUM>) interposed between the input power supply and a load (<NUM>), the current sensor configured to output at least one current signal indicating a level of current delivered to the load;
a switch (<NUM>) interposed between the current sensor (<NUM>) and the input power supply (<NUM>) to selectively deliver the input current to the load;
an electronic switching control circuit (<NUM>) in signal communication with the switch, the electronic switching control circuit (<NUM>) configured to generate a switch control signal that controls the switch (<NUM>) to selectively connect the input power supply to the load and to deliver the switch control signal a predetermined time period after generating the switch control signal;
an electronic drift suppression circuit (<NUM>) in signal communication with the current sensor and the switching control circuit, the drift suppression circuit configured to generate a corrected current signal in response to applying an offset value to the current signal, the offset value cancelling drift current from the current signal in response to connecting the input power supply to the load, the drift suppression circuit (<NUM>) configured to store different current values output by the current sensor based on the connection state of the input power supply to the load;
wherein the electronic drift suppression circuit (<NUM>) includes an electronic differential circuit (<NUM>) configured to store, as the offset value, a first current value output by the current sensor after generating the switch control signal but prior to closing the switch such that the input power supply is disconnected from the load, and after storing the offset value, is configured to receive a second current value output by the current sensor in response to delivering the switch signal to close the switch (<NUM>) connecting the power supply to the load such that the input power supply is connected and drives the load, and to subtract the first current value from the second current value in response to connecting the input power supply to drive the load; and further comprising:
an electronic BIT analysis circuit (<NUM>) that is configured to receive the corrected current signal excluding drift current from the drift suppression circuit, and to determine an on-state or an off-state of the load based on the corrected current signal.