# Patent

## Title
Hall effect measurement instrument with temperature compensation

## Abstract

Disclosed is a Hall Effect instrument with the capability of compensating for temperature drift consistently, accurately and in real time of operation. The instrument embodies a four-point ohmmeter circuit measuring Hall Effect sensor resistance and tracking the effect of temperature on the Hall Effect sensor. The instrument takes into account a relationship between the temperature and a temperature compensation index on a per probe basis, which has exhibited a deterministic difference observed by the present inventor.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a Continuation-in-Part of co-pending U.S. application Ser. No. 14/077,322 entitled A HALL EFFECT MEASUREMENT DEVICE WITH TEMPERATURE COMPENSATION and filed Nov. 12, 2013, which is herein incorporated by reference.


FIELD OF THE INVENTION
The present invention relates to non-destructive testing and non-destructive instruments (NDT/NDI) and more particularly to a Hall Effect probe and measurement device with compensation of measurement drift caused by temperature change.
BACKGROUND OF THE INVENTION
Hall Effect sensors have been used in measurement devices such as thickness gages (e.g. Olympus NDT Magna Mike 8500) to accurately measure thickness of nonferrous materials. One of the most often seen applications is thickness measurement on plastic bottles. A Hall Effect sensor typically comprises a probe that has magnet(s) generating a primary magnetic field. Measurements are performed by holding the device's magnetic probe to one surface of the test material and placing a small steel target ball on the opposite surface. The target ball, in responding to the primary magnetic field, generates a secondary magnetic field, which varies according to the distance between the probe and the steel target ball. A Hall-effect sensor, which measures the strength of the secondary magnetic field, built into the probe measures the distance between the probe tip and target ball. Typically measurements are instantly displayed as easy-to-read digital readings on the device display panel.
One unique challenge encountered and overcome by the present disclosure involves a hall sensor that is not part of an integrated circuit on board the instrument. As required by many Hall Effect instruments or applications, a major portion of the circuitry is assembled on the main body of the instrument, which is coupled to the Hall Effect sensor or probe via wires or cables with a length that meets the operator's needs, e.g. 1 meter. This physical distance between the Hall Effect sensor and the instrument presents an unknown wiring and connector resistance. As the Hall Effect sensor is located in the probe and sensitive to temperature changes, it presents a unique challenge for the instrument to compensate the temperature of the probe assembly including both magnetic parts and the Hall effect sensor.
It also presents more unique challenges when the operation of a Hall effect sensor based instrument involves interchange of Hall sensor probes and gage and maintaining an accurate and temperature compensated system.
However, it's been widely observed that the accuracy of a measurement from a Hall effect thickness gage drifts with temperature quite noticeably. It is also known that the resistance of the Hall Effect sensor varies with temperature. Because the measurement is directly related to the resistance of the Hall Effect sensor, a change in temperature would result in a change in the Hall Effect resistance and a change in the result of the magnetic measurement. This is also called measurement drift due to temperature.
An existing effort made in an attempt to reduce this effect was to re-calibrate the instrument whenever the instrument is in a condition called “Ball-Off condition”, i.e. whenever there are no targets. By re-calibrating, adjustment is made so that the sensor is calibrated to the current testing conditions, including temperature. However, since this Ball-Off condition does not always occur, or occur frequently enough, the measurement could drift with temperature change without the knowledge of measurement taker or operator.
Another existing effort has been seen in U.S. Pat. No. 5,055,768 in which a temperature sensitive current source is deployed to solve the problem of Hall effect sensor sensitivity to temperature. This current source is intended to be part of the Hall effect sensor. However, the circuit as disclosed is limited to compensating temperature effects inside the Hall sensor residing on the same chip.
Yet another existing effort seen in U.S. Pat. No. 6,281,679 involves a system that uses a magnet and a Hall Effect sensor to measure distance. However, the magnets and the Hall sensor move in relation to each other. It teaches a method by which two Hall sensors are matched so that temperature is not a factor. It also addresses methods of regulating the temperature of the magnet and Hall sensors by auxiliary temperature control, including using circulated air. Yet, it failed to mention the challenge brought by and hence the solution to the issue of temperature variation between the locals of Hall probe and the processing circuit, which is located in the instrument.
U.S. Pat. No. 8,274,287 uses a magnet and a Hall sensor to detect disturbances in the field. It also employs a temperature sensor to control the temperature compensation of its measurement on quantity of metallic debris. However, the patent did not make use of the unique property and the subsequent advantages presented by Hall sensors' sensitivity to temperature. It did not make any effort in measuring changes of Hall sensors circuitry reading attributed to temperature change. In addition, it explicitly regards the temperature response as linear, which is not an accurate representation of this line of Hall sensor devices.
U.S. Pat. No. 6,154,027A uses a temperature reference circuit to control the current flow from a temperature-variable current source to a Hall-effect element according to sensed temperature conditions. It in a way compensates the temperature drift reflected in the current source. However, it does not, in Applicant's opinion, directly compensate the temperature effect within the Hall Effect sensor.
In U.S. Pat. No. 4,327,416 ('416), the temperature of the Hall element is measured by a thermistor to develop a temperature dependent voltage. In one embodiment, the Hall element voltage and temperature dependent voltage are digitalized and supplied to address the ROM to generate a temperature compensated Hall voltage. In another embodiment, the ROM is addressed by only the temperature dependent voltage to generate a correction voltage that is added to the Hall element voltage for temperature compensation. However, in Applicant's opinion, '416 does not take into account that the source of temperature change is from both the temperature drift within the Hall Effect sensor, and within the magnetic source, noting that it only relies on the thermistor to gauge the instant temperature. In addition, this effort does not use a second pair of voltage measurement from the Hall sensor, which could lead to temperature compensation with higher fidelity.
US Patent 2008/0074108 also relies reading from a temperature sensor to compensate on Hall Effect measurement. It does not use the voltage measurement of a second pair from the Hall Sensor as the basis to the calculation of temperature effect directly on the Hall Sensor itself, not just on the magnetic fields.
SUMMARY OF THE INVENTION
It is therefore a primary objective of the present disclosure to provide a Hall Effect instrument with the capability of compensating for temperature drift consistently, accurately and in real time of operation.
It is another objective of the present disclosure to accurately measure the Hall Effect sensor resistance via a four-point ohmmeter circuit to track the effect of temperature on the Hall Effect sensor.
It is yet another objective of the present disclosure to provide a Hall Effect instrument configured to constantly measure the change in Hall sensor resistance due to change in temperature and to derive a relationship between the temperature and the compensation index on a per probe basis, which has exhibited a deterministic difference observed by the present inventor.
It is yet another objective of the present disclosure to provide a Hall Effect instrument configured to make compensation of the measurement result based on system-wide temperature changes, including temperature changes caused by locale distance between the Hall sensor and the magnets, the Hall sensor (Hall probe) the processing circuit (the instrument), etc.



BRIEF DESCRIPTION TO DRAWINGS
FIG. 1 is a block/flow diagram presenting the Hall Effect instrument with Temperature Compensation using a four-wire ohmmeter circuit technique according to present disclosure.
FIG. 2 is schematic diagram depicting the components of a Hall sensor probe (101) for thickness measurement embodying a temperature sensor according to the present disclosure.
FIGS. 3a and 3b are schematic circuit diagrams depicting the two-wire or four-wire ohmmeter circuit, respectively, used in the present disclosure to accurately measure the Hall Effect sensor resistance, which is highly sensitive to temperature change.
FIG. 4 is a flowchart depicting a data acquisition and processing module (103). It shows how the measurements taken from a Hall Effect sensor (203) are acquired and processed before the measurements are used for temperature compensation.
FIG. 5 is a flowchart elaborating a temperature compensation module (104). It further comprises three modules, one for probe parameter compensation and one for slope compensation and the third module for calculating the Temperature Compensation Index.
FIG. 6 is a flowchart depicting how a probe parameter temperature compensation module (501) calculates probe parameter temperature compensation, voltage, and VCOMP_P.
FIG. 7 is a graph showing relationship of VCOMP versus Temperature, which is used to determine the temperature compensation slope for the exemplary probe.
FIG. 8 is a flow chart depicting a probe slope temperature compensation module (502) calculating probe slope temperature compensation voltage and VCOMP_S.
FIG. 9 is yet another flow chart representing how a probe temperature compensation index calculation module (503) calculates the Temperature Compensated Index.
FIG. 10 is a flow chart depicting steps through which the Temperature Compensated Measurement is determined from the Temperature Compensated Index.
FIG. 11 is a block/flow diagram presenting an alternative embodiment of the Hall Effect instrument with Temperature Compensation using a four-wire ohmmeter circuit technique according to the present disclosure.
FIG. 12 is schematic diagram depicting the components of Hall sensor probe (101) in the alternative embodiment for thickness measurement embodying a temperature sensor according to the present disclosure.



DETAILED DESCRIPTION OF THE INVENTION
It should also be noted that some terms commonly used in the industry are interchangeably used in the present disclosure to denote the Hall Effect sensor. For example, “Hall Effect sensor”, “Hall probe” and “Hall sensor”, etc., all denote to the Hall Effect sensor shown as 203 in FIG. 2. It should also be noted that “Hall Effect instrument” or “Hall sensor instrument” denotes to the whole measurement system including the Hall probe, data acquisition circuitry and the whole logic and processing circuitry (not shown). Such variations in the usage of these terms do not affect the scope of the present disclosure.
Referring to FIG. 1, a block diagram of the presently disclosed temperature compensated Hall Effect Sensor Measurement System using a four-wire ohmmeter circuit technique is presented. As can be seen the Hall sensor measurement system includes mainly five modules or five steps used for compensating measurement drift caused by the effect of changes of operational temperature. Each of the five modules is further elaborated to provide more details in subsequent figures.
According to FIG. 1, the Hall-Effect measurement instrument with temperature compensation in the present disclosure comprises a Hall sensor probe 101, a Hall Effect measurement circuit 102, a data acquisition and processing module 103, a temperature compensation module 104 and a measurement conversion module 105.
As can be seen in FIG. 1 that signals acquired by Hall sensor probe 101, including VSNS_PIN, VMON_PIN and temperature at the probe are measured and fed into Hall Effect measurement circuit 102 which accurately captures three pairs of differential signals from the Hall Effect sensor to produce the three Hall Effect Sensor Temperature Uncompensated Raw Data for data acquisition and processing module 103. The three pairs of differential signals including VSNS_PIN, VMON_PIN are further elaborated in the subsequent description. Temperature un-compensated data is then sent to temperature compensation module 104 which operates to combined thermostat reading from Hall sensor probe 101 and the probe slope from an EEPROM 208 (described later) and a temperature compensation algorithm to produce Temperature Compensated Index. The measurement conversion module 105 then determines the correct Hall Effect measurement, such as corrected thickness, with the information from compensation module 104.
It should be appreciated that the temperature compensation function as novel aspect of the Hall instrument is largely carried out and executed concurrently with other normal operational functions of the Hall instrument, and can be built within the same components that otherwise serve other functions of the Hall sensor instrument. For instance, Hall sensor probe 101 both serves for Hall Effect measurement and temperature measurement with a temperature sensor 207. Data acquisition and processing module mainly serves the processing need for the Hall Effect measurement, and also provides the data processing need for temperature compensation as described in the present disclosure. In other words, the steps and or modules embodied in the present disclosure can largely co-use hardware components of the Hall effect instrument that are designed for the main purpose of the Hall Effect measurement, i.e., thickness measurement.
Optionally, the Hall Effect measurement system can be coupled with two types of probes in separate measurement sessions, the first type of probes includes temperature sensor 207, the second probe does not include any temperature sensor. Accordingly, data acquisition and processing module 103 optionally includes a mode selection module 1100, selecting modes between the first type of probes is coupled or the second type of probes is coupled. The mode selection can be done either automatically based on probe identification, which is an existing practice, or manually by means of operator input. The embodiment of the measurement system to be without temperature sensor 207 is described in details later associated with FIGS. 11 and 12.
It should also be appreciated that any of the steps or modules shown in FIG. 1 can alternatively resides in and be executed by other stand-alone or add-on components so that the method of temperature compensation on Hall Effect measurement can be used in combination of existing Hall Effect instrument. The alternatively devised add-on components are also within the framework of the present disclosure.
Reference now is turned to FIG. 2. According to FIG. 2, the Hall measurement system firstly embodies Hall sensor probe 101. Hall sensor probe 101 further comprises a Hall Effect sensor 203, magnets 206 providing the primary magnetic field source, a temperature sensor 207, an electrical erasable type of memory device such as EEPROM 208, and a probe casing 209.
A thickness measurement is taken by placing Hall sensor probe 101 between a nonferrous material to be measured and a target ball 201. Hall Effect sensor 203 measures the magnetic field between target ball 201 and Hall sensor probe 101. Magnets 206 encased in probe casing 209 generate a magnetic field between the probe and the target ball. This magnetic field is detected by Hall Effect sensor 203. It then sends the Hall Effect sensor measurement signals, the Probe Slope (described later) from the EEPROM 208 and the temperature from temperature sensor 207 into the data processing circuitry of the measurement system residing on the instrument for further processing.
In addition, temperature sensor 207 provides the temperature of the magnets Tmag for temperature compensation module 104. Lastly, Hall sensor probe 101 uses memory EEPROM 208 to record the probe specific information, such as the Probe Slope (described later) used in the temperature compensation module 104 and other probe identification parameters common to existing practice. How the Probe Slope was derived is subsequently explained in relation to FIGS. 7a and 7b. 
Referring to FIGS. 3a and 3b, Hall Effect measurement circuit 102 can be devised with two alternative embodiments, one detailed as using a four-wire ohmmeter with a drive current monitoring circuit 310 in FIG. 3a; the other as using a four-wire ohmmeter with a constant current source ISRC (without circuit 310) in FIG. 3b. 
According to FIG. 3a, Hall Effect measurement circuit 102 embodies a sub-circuit similar to that of four-wire ohm meter and drive current monitoring circuit 310. Hall Effect measurement circuit 102 further embodies components producing three pairs of differential Hall Effect sensor signals which are accurately measured to produce three Temperature Uncompensated Raw Data for data acquisition and processing module 103. Hall Effect sensor 203 via Hall Effect measurement circuit 102, as shown in FIG. 3a, produces three pairs of differential signals for further processing.
The three differential pairs of Hall Effect Sensor signals are defined as:

    
    
        a. VSNS_PIN—Positive Hall Effect Sense Voltage—positive differential input to an amplifier 302;
        b. VSNS_NIN—Negative Hall Effect Sense Voltage—negative differential input to amplifier 302;
        c. VMON_PIN—Positive Hall Effect Monitor Voltage—positive differential input to a differential amplifier 304;
        d. VMON_NIN—Negative Hall Effect Monitor Voltage—negative differential input to differential amplifier 304;
        e. VIMON_PIN—Positive Hall Effect Voltage modulated with current stability, VIMON—positive differential input to an amplifier 306;
        f. VIMON_PIN—Negative Hall Effect voltage modulated with current stability, VIMON—negative differential input to an amplifier 306.
    
    


Continuing to the right-hand side of FIG. 3a, Hall Effect measurement circuit 102 produces three Temperature Uncompensated Raw Data outputs defined as:

    
    
        g. VSNS_R—Hall Effect Raw Digital Sense Voltage—digital output from an analog to digital converter 303;
        h. VMON_R—Hall Effect Raw Digital Monitor Voltage—digital output from an analog to digital converter 305;
        i. VIMON_R—Hall Effect Raw Digital voltage modulated for current stability, VIMOD,—digital output from an analog to digital converter 307.
    
    


It should be noted that the Hall Effect measurement circuit includes a sub-circuit that happens to be the same as that used in the existing practice involving a four-wire ohmmeter. One of the novel aspects of the present disclosure is to repurpose the four-wire circuit for Hall Effect measurement. The temperature compensation aspect of the operation also uses the signals retrieved from the four-wire circuit. It can therefore be understood that the four-wire ohmmeter itself had existed in prior practice. However, the use of such circuit for Hall Effect measurement, thickness measurement and for further making temperature compensation of such measurements are considered novel by the present disclosure.
Still referring to FIG. 3a, the methodology involved in the usage of Hall Effect measurement circuit 102 is herein described. Starting at the lower left-hand corner of FIG. 3a, a (constant) voltage source 309 is used to provide a constant current ISRC that goes across a resistor 308. This constant current, ISRC, is the same constant current that goes across the Hall Effect sensor from Point 3 to Point 4. The constant current, ISRC, continues and sinks into an amplifier 301. A constant current, ISRC, is provided across the Hall Effect Sensor and a Kelvin connection at Points 1 and 2 are made to ensure proper and accurate measurement of a resistor.
With the accurate measurement of the Hall Effect sensor resistance by measuring the voltage across Points 1 and 2, we have VMON_PIN and VMON_NIN. These two differential signals, VMON_PIN and VMON_NIN, can be measured by connecting them to differential amplifier 304, followed by analog to digital converter 305. The resultant digital signal, VMON_R, represents the voltage across the Hall Effect sensor.
Continuing with FIG. 3a, by Ohm's Law, the resistance of the Hall Effect sensor can be expressed as VMON_R/ISRC. Since ISRC is a constant current, then VMON_R is proportional to the resistance of the Hall Effect Sensor. Since the resistance of the Hall Effect sensor is also proportional to temperature, we now have a measurement, VMON_R, which is proportional to temperature. This is one of several signals used to compensate measurement due to temperature drift.
Similarly, the Hall Effect sensor voltage, VSNS_R, via the differential signals, VSNS_PIN and VSNS_NIN, are measured via amplifier 302, and analog to digital converter 303, to produce VSNS_R.
And the constant current, ISRC, via VIMOD_PIN and VIMON_NIN are measured by amplifier 306, and analog to digital converter 307, to produce VIMOD_R.
Lastly VMON_R, VSNS_R, VIMOD_R, as well as temperature of the magnets and Probe Slope (later described) can be used to further determine how to compensate for temperature drift.
Reference is now made to FIG. 3b. An alternative implementation can be viewed by substituting another design for FIG. 3a. As for the embodiment shown in FIG. 3a, the origin of VIMOD_R is the voltage across resistor 308. In this way VIMOD—R monitors the performance of the constant current drive circuit. Components 301, 308 and 309 make a constant current source used to drive a current through the Hall Effect sensor 203. If voltage source 309 changes for any reason, VIMOD_R will detect this and be used to compensate for the matching changes in Vmon and Vsns.
It should be noted that voltage source 309 can be an AC or DC source, bearing in mind that drive current monitoring circuit 310 is effective when AC is used.
As voltage source 309 does not need to be extremely stable for excellent instrument performance, VIMOD is used to compensate or performance limitations of circuits inside the gage only in this preferred embodiment shown in FIG. 3a. VIMOD does not compensate the probe. In other words, VIMOD is not a must needed component in order for the system in the present disclosure to function as intended. It should be appreciated that with or without the usage of VIMOD and its associated components are all within the scope of the present disclosure.
As an example, referring to FIG. 3b, an alternative embodiment is shown to be without VIMOD. A constant current source forcing a current Isrc through probe casing 209 Point 3 to Point 4. It should be noted that when referring to FIG. 3b as a replacement for FIG. 3a, the value Isrc can be used to substitute the use of VIMOD in the subsequent implementations. In this regard, Isrc can be assumed as a constant, which in an exemplary case, to be about 1 mA.
Reference is now turned to FIG. 4 which presents a more detailed diagram of data acquisition and processing module 103. This module further comprises two modules: a data acquisition module 401, and a signal processing module 402. Data acquisition module 401 takes in the three inputs VMON_R, VSNS_R, and VIMON_R or Isrc from circuits shown in FIGS. 3a and 3b, and, through a magnitude detection circuit, produces three signals, VMON_DA, VSNS_DA, and IDA. In FIG. 4, the three temperature Uncompensated Raw Data from circuits shown in FIGS. 3a and 3b are acquired and processed to produce the three temperature Uncompensated Filtered Data for temperature compensation module 104.
Three signals, VMON_DA, VSNS_DA, IDA, then go to signal processing module 402, where they get filtered to produce three final signal magnitudes, VMON_F, VSNS_F, and VIMON_F, for the next stage, temperature compensation module 104.
The three Temperature Uncompensated Filtered Data outputs are defined as:

    
    
        j. VSNS_F—Hall Effect Filtered Digital Sense Voltage—filtered output from signal processing module 402;
        k. VMON_F—Hall Effect Filtered Digital Monitor Voltage—filtered output from signal processing module 402;
        l. VIMON_F Hall Effect Filtered Digital VIMOD Voltage modulated with current stability filtered output from signal processing module 402.
    
    


Reference is now made to FIG. 5, with a more detailed diagram of temperature compensation module 104 of FIG. 1. Temperature compensation module 104 further comprises three modules: probe parameter temperature compensation module 501, probe slope temperature compensation module 502, and probe temperature compensation index calculation module 503. In this stage, the three Temperature Uncompensated Filtered Data, along with the magnet temperature reading from temperature sensor 207, and the Probe Slope from EEPROM 208, are used to calculate the Temperature Compensated Index.
Probe parameter temperature compensation module 501 receives four inputs: VMON_F, VSNS_F, and VIMON_F from 103 and temperature (Tmag) from temperature sensor 207. This module then produces a first compensation factor VCOMP_P. For more details, refer to FIG. 6.
Probe slope temperature compensation module 502 receives two inputs: temperature (Tmag) from temperature sensor 207, and Probe Slope from EEPROM 208. This module 502 then produces a second compensation factor VCOMP_S. For more details, refer to FIG. 8.
Probe temperature compensation index calculation module 503 receives two inputs: VCOMP_P and VCOMP_S. This module then produces the Temperature Compensated Index. For more details, refer to FIG. 9.
Referring now to FIG. 6, a more detailed diagram of probe parameter temperature compensation module 501 of FIG. 5 is presented. The four inputs, VMON_F, VSNS_F, and VIMON_F from 103 and Tmag from 207 are received through parameter input 510, and sent to probe parameter temperature compensation calculator 512, which produces the product of probe parameter temperature compensation module 501. As can be seen below, probe parameter temperature compensation calculator 512 can be configured to carry out calculations in one of the following two equations, Eq. 1 or Eq. 2.

VCOMP_P=VSNS_F+VMON_F*(α+VSNS_F*β)+Tmag*(γ+VSNS_F*δ)  Eq. 1

wherein, Tmag is the temperature from temperature sensor 207;
α, β, γ and δ are constants based upon the manufacturing tolerances of Hall sensor probe 101. They can be obtained by those skilled in the art according to Eq. 1, and empirical data from conducting experiments on the probe of each probe type, yielding readings of the VSNS_F, VMON_F, ISRC from the corresponding four-wire ohmmeter and the temperature reading, Tmag, for the probe.
Once VCOMP_P is calculated, it goes through a probe parameter temperature voltage output 514, and is sent to probe temperature compensation index calculation module 503 of FIG. 5.
As can be seen, the temperature compensation calculation according to Eq. 1 reflects temperature changes both in the Hall sensor, through reading VMON_F and VSNS_F, and near the magnets, through Tmag.
It should be noted that in Eq. 1, it is assumed that ISRC is a constant and the factor represented by VIMON_R is not reflected in it. Therefore Eq. 1 is suitable to be used for the embodiment presented in FIG. 3b, wherein the embodiment shown in FIG. 3a does not include a sub-circuit for monitoring the stability of ISRC.
It should be noted in connection to FIG. 3a that VIMON_F is used to monitor how stable the constant current, ISRC, is and to factor in the stability of ISRC into the temperature compensation.
For the embodiment of the measurement circuit 310 with voltage source monitoring (FIG. 3a),

VCOMP_P=(((VSNS_F)+((VMON_F−VIMON_F)*A)+(((VMON_F−VIMON_F)*(VSNS_F)*B)/(VIMON_F))+((Tmag−22)*(VIMON_F)*C)+((Tmag−22)*(VSNS_F)*D))/(VIMON_F))  Eq. 2

wherein there are six major contributing parts to VCOMP_P:

    i) VSNS_F is the factor involving the Hall Effect Filtered Digital Sense Voltage;
    ii) ((VMON_F−VIMON_F)*A) provides temperature compensation based on the Hall sensor temperature as indicated by VMON_F, with coefficient A modulating the magnitude of this portion of the temperature compensation, which is intended to correct the “ball-off” situation, but has an equal impact on “ball-on” situation;
    iii) ((VMON_F−VIMON_F)*(VSNS_F)*B)/(VIMON_F)) is a scalar temperature compensation factor based on the Hall sensor temperature as indicated by VMON_F, and wherein coefficient B modulates the amount of correction, which is intended to correct the ball-off situation and accounts for manufacturing tolerances of the Probe and Hall Effect sensor;
    iv) ((Tmag−22)*(VIMON_F)*C) provides offset temperature compensation based on the magnet temperature as indicated by Tmag, and wherein C is the factor involving the Tmag from Temperature Sensor 207 and accounts for the specific probe manufacturing tolerances;
    v) ((Tmag−22)*(VSNS_F)*D) provides scalar temperature compensation based on the magnet temperature as indicated by Tmag, and wherein D is a factor involving the Tmag from Temperature Sensor 207 and accounts for the specific probe manufacturing tolerances.


It should be noted that reference temperature herein used in the equation (22° C.) is an exemplary ambient temperature. Different values can be used when calibration is done differently.
A, B, C and D are constants based upon the manufacturing tolerances of Hall sensor probe 101. They can be obtained by those skilled in the art according to Eq. 2, and empirical data from conducting experiments on the probe of each probe type, yielding readings of the VSNS_F, VMON_F, VIMON_F from the corresponding four-wire ohmmeter and the temperature reading Tmag for the probe used in the experiment.
Once the VCOMP_P is calculated, it goes through probe parameter temperature voltage output 514, and is sent to probe temperature compensation index calculation module 503.
Again it can be noted that Eq. 1 compensates measurement inaccuracies due to temperature drift quite well without using the factor related to VIMON_F. VIMON_F is used solely to monitor how stable the constant current ISCR is.
Eq. 2 provides better temperature compensation taking into account when ISCR varies. In addition, measurement variation due to interdependencies between the four inputs (VSNS_F, VMON_F, VIMON_F, Temperature) are compensated via Eq. 2's factors ii) through v).
Reference is now made to FIG. 7 which present a methodology herein employed to determine the per probe relationship between Temperature and VCOMP slope called VCOMP-S.
FIG. 7 represents an exemplary probe-specific slope drawing by using experimental data from a case collected from the probe for various temperature settings. The exemplary Hall Effect measurement circuit for the specific probe as shown in FIG. 3a is measured with various temperatures. VMON_F, VSNS_F and VIMON_F are drawn from the measurement and VCOMP_P is calculated by using Eq. 2. FIG. 7 is then plotted representing the relationship between Temperature and VCOMP_S.
The Probe Slope derived from the experimental data graph similar to FIG. 7 using a linear curve fit is stored in EEPROM 208, to be retrieved for FIG. 8.
FIG. 8 presents a more detailed diagram of probe slope temperature compensation module 502.
In parallel to the calculation of VCOMP_P, VCOMP_S is calculated in this module. The Probe Slope, from EEPROM 208, and the magnet's temperature from temperature sensor 207, are received through a parameter input 520, and sent to probe slope temperature compensation calculator 522. The calculator used is in the following format:

VCOMP_S=Probe Slope*(Tmag−Reference Temperature)  Eq. 3

    
    
        where VCOMP_S adjusts the overall VCOMP based upon the probe's response to magnet's temperature.
    
    


Once VCOMP_S is calculated, it goes through a probe slope temperature voltage output 524, and is sent to probe temperature compensation index calculation module 503.
FIG. 9 presents a more detailed diagram of probe temperature compensation index calculation module 503.
The VCOMP_P from 501 and VCOMP_S from probe slope temperature compensation module 502 are received through a parameter input 530, and sent to a temperature compensated index calculator 532. The calculator used is in the following format:

Temperature Compensation Index=VCOMP_P−VCOMP_S  Eq. 4

Once the Temperature Compensated Index is calculated, it goes through a temperature compensated index output 534, and is sent to measurement conversion module 105.
FIG. 10 provides a more detailed exhibit of measurement conversion module 105 showing how the temperature compensated thickness measurement is converted from the Temperature Compensated Index. In order to use the temperature compensated index Vcomp (right column in FIG. 10) for a specific probe, a specific target is used in experiments to derive measured thickness at the reference ambient temperature (22° C.).
Temperature Compensated Index, or compensated Hall Effect reading Vcomp, is then fed into measurement conversion module 105 and converted by a probe-target specific conversion, such as shown in FIG. 10. It is known to those skilled in the art to obtain empirical data between a Hall Effect reading and a thickness measurement for any specific set of probe and target. The novel aspect of the invention herein presented is that the effect of temperature change to Hall Effect reading is compensated and presented as “compensated index Vcomp”. The temperature compensated or corrected measurement (thickness) is therefrom accurately produced. In the exemplary conversion used in FIG. 10, Temperature Compensated Index Vcomp is provided to measurement conversion module 105. Based on the Vcomp and through linear interpolation, an accurate measurement is produced by measurement conversion module 105.
Reference now is made to FIGS. 11 and 12 which present an alternative embodiment in the present Continuation-in-Part application.
The alternative embodiment herein presented shares the same principle as presented in the parent co-pending U.S. application Ser. No. 14/077,322 of providing accurately measure the Hall Effect sensor resistance via a four-point ohmmeter circuit to track the effect of temperature on the Hall Effect sensor. However, as shown in FIGS. 11 and 12, the alternative embodiment of the Hall Effect sensor does not use, nor depend on the usage of a temperature sensor, such as temperature sensor 207 as shown in FIGS. 1 and 2.
Therefore, as shown in FIGS. 11 and 12, and in FIGS. 3a, 3b, 4 ̃10, the alternative embodiment of the Hall Effect measurement instrument with temperature compensation in the present Continuation-in-part disclosure comprises Hall sensor probe 101, Hall Effect measurement circuit 102, data acquisition and processing module 103, temperature compensation module 104 and measurement conversion module 105. Probe 101 further comprises Hall Effect sensor 203, magnets 206 providing the primary magnetic field source, an electrical erasable type of memory device such as EEPROM 208 and probe casing 209.
In this alternative embodiment, Hall Effect measurement circuit 102 is the same as that of in the co-pending U.S. application Ser. No. 14/077,322. For temperature compensation module 104, there is no signal feed from a temperature sensor. Therefore, for this alternative embodiment, there is no temperature sensor 207 and its associated temperature signal feed in FIGS. 5, 6, 7, 8 and 9.
Subsequently, for this alternative embodiment without magnet temperature sensor, Eq. 1 is changed to:

VCOMP_P=VSNS_F+VMON_F*(α+VSNS_F*β)  Eq. 5

wherein, α, β, γ and δ are constants based upon the manufacturing tolerances of probe 101. They can be obtained by those skilled in the art according to Eq. 3, and empirical data from conducting experiments on the probe of each probe type, yielding readings of the VSNS_F, VMON_F, ISRC from the corresponding four-wire ohmmeter in FIGS. 3a and 3b. 

Further for this alternative embodiment without magnet temperature sensor, for circuit 310 in FIGS. 3a and 3b, constant coefficients C and D are both zero in Eq. 2.
It should be appreciated by those skilled in the art that various implementations can be achieve for embodiments with or without the usage of magnet temperature sensor. All of such implementations are within the scope of the present disclosure.
For example, one can design the Hall Effect measurement instrument by coding data acquisition and processing module 103 with only one set of equations Eq. 1 to 4 for both embodiments suiting for probes with or without the magnet temperature sensor, providing an option-toggle key of either a virtue or physical button allowing users to choose between the embodiments. The toggle function can also be automatically triggered once the probe is plugged in based on the probe identification, which is an existing practice to those skilled in the art. When option is chosen to be without the magnet temperature sensor, the coefficient C and D are set to zero in Eq. 2, and Tmag is automatically set to be 22° C. in Eq. 3. The toggle function can be implemented by mode selection module 1100 described in association with FIG. 1.
It should be noted that usually when Hall sensor probes are relatively small with smaller magnets for applications of making thickness gages on thinner material, the temperature difference between the end of magnets and the tip of the Hall sensor can be negated. In this case, a Hall sensor probe without magnet temperature sensor can be used.
An alternative example would be for one to design the Hall Effect measurement instrument only for using probes without magnet temperature sensor. In this case, Eqs. 1-4 are correspondingly modified as follows and coded to data acquisition and processing module 103.

VCOMP_P=VSNS_F+VMON_F*(α+VSNS_F*β)  Eq. 5 (corresponding to Eq. 1)

VCOMP_P=(((VSNS_F)+((VMON_F−VIMON_F)*A)+(((VMON_F−VIMON_F)*(VSNS_F)*B)/(VIMON_F))  Eq. 6 (corresponding to Eq. 2)

Temperature Compensation Index=VCOMP_P  Eq. 7 (corresponding to Eq. 4)

Subsequently, there is no input or consideration for Vcomp_S and there is therefore no equation corresponding to Eq. 3 for the embodiment of without magnet temperature sensor.
Further, for the instrument designed only for probes without magnet temperature sensor, the following elements are removed from data acquisition and processing module 103 in the following manner:

    
    
        in FIG. 5, temperature sensor input from temperature sensor 207, probe slope temperature compensation module 502 and input VCOMP_S;
        in FIG. 6, temperature input from temperature sensor 207;
        in FIG. 7, the probe slope;
        in FIG. 8, temperature input from temperature sensor 207;
        in FIG. 9, VCOMP_S;
    
    


Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention not be limited by the specific disclosure herein.

## Claims

1. An instrument measuring Hall Effect of at least one Hall sensor magnetically coupled with a target during a measurement session, comprising:
a probe including the Hall sensor and a magnetic field source,
a data processing and display console coupled with the probe with an electronic coupling means, the console further comprising,
a Hall Effect measurement circuit connected with the Hall sensor via the coupling means, the Hall Effect measurement circuitry further including at least partially a four-wire ohmmeter circuit, which captures at least two pairs of differential signals from the Hall Effect sensor,
a data acquisition and processing module configured to receive signals from the Hall Effect measurement circuit and provide at least two pairs of uncompensated raw signals based on the differential signals;
a temperature compensation module configured to compute based on the at least two pairs of uncompensated raw data to produce a temperature compensation index;
a measurement conversion module configured to provide a corrected Hall Effect measurement data by correcting the raw signal data using information corresponding to the temperature compensation index.

2. The instrument of claim 1 further comprises an electronic erasable memory for storing specific information in the probe.

3. The instrument of claim 1 is configured to measure thickness according to the strength of the Hall Effect measurement.

4. The instrument of claim 1, wherein the compensation index is a result of dynamically compensating the Hall Effect measurement of the probe with the temperature change in the Hall sensor.

5. The instrument of claim 1, wherein the two pairs of the uncompensated raw data, including raw Hall Effect Sense Voltage, VSNS_R and raw Hall Effect Monitor Voltage, VMON_R, respectively, wherein VSNS_R and VMON_R is each fed to the data acquisition and processing module.

6. The instrument of claim 5 wherein the data acquisition and processing module further comprises a data acquisition module and a signal processing module, wherein the signal processing module producing Hall Effect filtered digital sense voltage VSNS_F from the VSNS_R and filtered digital monitor voltage VMON_F from the VMON_R.

7. The instrument of claim 6, wherein the temperature compensation module further comprises a probe parameter temperature compensation module producing a first compensating factor VCOMP_P and a probe temperature compensation index calculation module producing a temperature compensation index VCOMP.

8. The instrument of claim 6, wherein the Hall Effect measurement circuitry further comprises a voltage source providing substantially constant current source ISRC to the four-wire ohmmeter circuit.

9. The instrument of claim 8, wherein the probe parameter temperature compensation module further comprises probe parameter temperature compensation calculator producing the factor VCOMP_P substantially according to the following:


VCOMP_P=VSNS_F+VMON_F*(α+VSNS_F*β)  Eq. 5.

10. The instrument of claim 9, wherein α and β are obtained according to Eq. 5, and empirical data from conducting experiments on the probe of each probe type, yielding readings of the VSNS_F, VMON_F, ISRC from the corresponding four-wire ohmmeter.

11. The instrument of claim 7, wherein the Hall Effect measurement circuitry further comprises a voltage source and a voltage source current stability monitoring circuit, providing a raw voltage differential data VIMON_R factored by the current monitoring circuit, wherein VIMON_R is further provided to the data acquisition and processing module.

12. The instrument of claim 11, wherein the signal processing module further provides a filtered differential voltage data VIMON_F factored by the current monitoring circuit, based on the Hall Effect measurement value of raw voltage VIMON_R.

13. The instrument of claim 12, wherein the probe parameter temperature compensation module further comprises an a probe parameter temperature compensation calculator producing the factor VCOMP_P substantially according to the following:


VCOMP_P=(((VSNS_F)+((VMON_F−VIMON_F)*A)+(((VMON_F−VIMON_F)*(VSNS_F)*B)/(VIMON_F))  Eq. 6

wherein A and B are all coefficient accounting for manufacturing tolerances of the probe and the Hall Effect sensor.

14. The instrument of claim 8, wherein the temperature compensation index calculation module calculates the temperature compensation index, deriving from the first compensation factor VCOMP_P according to


Temperature Compensation Index VCOMP=VCOMP_P  Eq. 7.

15. The instrument of claim 14, wherein the measurement conversion module is configured to produce the corrected Hall Effect measurement data based on the temperature compensation index VCOMP for the probe and the target.

16. An instrument measuring Hall Effect of at least one Hall sensor magnetically coupled with a target during a measurement session and a first probe including the Hall sensor and a first magnetic field source, or a second probe including the Hall sensor, a magnetic field source and a temperature sensor,
a data processing and display console coupled with the first or the second probe, one at a time, with an electronic coupling means, the console further comprising,
a Hall Effect measurement circuit connected with the first or the second Hall sensor respectively via the coupling means, the Hall Effect measurement circuitry further including at least partially a four-wire ohmmeter circuit, which captures at least two pairs of differential signals from the Hall Effect sensor,
a data acquisition and processing module configured to receive signals from the Hall Effect measurement circuit and provide at least two pairs of uncompensated raw based on the differential signals;
a mode selection module operable to be switched to a first mode or a second mode corresponding either the first probe or the second probe is coupled;
a temperature compensation module configured to compute based on the at least two pairs of uncompensated raw data and the temperature reading and a probe slope associated with the probe to produce a temperature compensation index;
a measurement conversion module configured to provide a corrected Hall Effect measurement data by correcting the raw signal data using information corresponding to the temperature compensation index.

17. The instrument of claim 16 further comprises an electronic erasable memory for storing specific information in the probe.

18. The instrument of claim 16, wherein the compensation index is a result of dynamically compensating the Hall Effect measurement of the probe with the temperature change in the Hall sensor and/or at the magnetic source.

19. The instrument of claim 16, wherein the two pairs of the uncompensated raw data, including raw Hall Effect Sense Voltage, VSNS_R and raw Hall Effect Monitor Voltage, VMON_R, respectively, wherein VSNS_R and VMON_R is each fed to the data acquisition and processing module,
and the data acquisition and processing module further comprises a data acquisition module and a signal processing module, wherein the signal processing module producing Hall Effect filtered digital sense voltage VSNS_F from the VSNS_R and filtered digital monitor voltage VMON_F from the VMON_R, and,
the temperature compensation module further comprises a probe parameter temperature compensation module producing a first compensating factor VCOMP_P, a probe slope temperature compensation module producing a second compensation factor VCOMP_S and a probe temperature compensation index calculation module producing a temperature compensation index VCOMP, and,
the Hall Effect measurement circuitry further comprises a voltage source and a voltage source current stability monitoring circuit, providing a raw voltage differential data VIMON_R factored by the current monitoring circuit, wherein VIMON_R is further provided to the data acquisition and processing module, and,
the signal processing module further provides a filtered differential voltage data VIMON_F factored by the current monitoring circuit 310, based on the Hall Effect measurement value of raw voltage VIMON_R, and,
the probe parameter temperature compensation module further comprises an a probe parameter temperature compensation calculator producing the factor VCOMP_P substantially according to the following:


VCOMP_P=(((VSNS_F)+((VMON_F−VIMON_F)*A)+(((VMON_F−VIMON_F)*(VSNS_F)*B)/(VIMON_F))+((Tmag−22)*(VIMON_F)*C)+((Tmag−22)*(VSNS_F)*D))/(VIMON_F))  Eq. 2


wherein A, B, C and D are all coefficient accounting for manufacturing tolerances of the probe and the Hall Effect sensor, and,
the probe parameter temperature compensation module further comprises a probe slope temperature compensation calculator producing the factor VCOMP_S according to a probe slope derived according to experimental data collected on the probe,


VCOMP_S=Probe Slope*(Tmag−Reference Temperature)  Eq. 3


and,
the temperature compensation index calculation module calculates the temperature compensation index, deriving from the first compensation factor VCOMP_P and the second compensation factor VCOMP_S according to,


Temperature Compensation Index VCOMP=VCOMP_P−VCOMP_S  Eq. 4


and, the measurement conversion module is configured to produce the corrected Hall Effect measurement data based on the temperature compensation index VCOMP_P for the first probe or the second probe and the target.

20. The instrument of claim 19, wherein when the mode selection module is switched to the first mode when the first probe is coupled with the instrument, Tmag=reference temperature in Eq. 2, and constant coefficients in Eq. 2, C=0, and D=0.