Patent Application
20210102918
This invention relates to a method and apparatus to compensate for zero signal errors in a material characterisation process.
In many forms of instrumentation associated with the characterisation of materials, there can be a signal “signature” that underlies the characteristics that are measured. This signature can be specific to a particular characterisation technique, or indeed a specific instrument. The signature is referred to as a zero signal because when the instrument is used in a normal characterisation process, without a sample of material, a signature is still obtained.
It is common practice to mathematically subtract this zero signal from the characterisation measurement cycle data to obtain a resulting characteristic that has greater integrity. Sometimes the zero signal can be small with respect to the sampled signal, but in the case of, say, small samples, or weak measurement data, the zero signal can be quite significant due to the limitations of the sample size/volume, or instrumentation. The zero signal can also change with temperature or other physical effects.
One such characterisation technique is pulsed field magnetometry or PFM, which is typically used to magnetically characterise permanent magnet materials. Due to the fundamental physics of the characterisation technique, when a measurement is made without a measurement sample there is a zero signal. In the case of PFM, the zero signal is dependent upon the electrical characteristics of the immediate magnetic environment, temperature and mechanical factors. The normal process during a material characterisation measurement is to take two measurements cycles, one with the material sample (measurement) and one without (zero signal). The measurement data is, in reality, a combination of the material characteristic and the unknown, zero signal. It is then assumed that the zero signal cycle measurement (without the sample) is identical to what it was during the measurement cycle, but this is not always the case. The temperature of the components of the magnetic environment may not be the same in the two measurement cycles. Mechanical movement may also occur between the measurement cycles. These and other factors can all produce significant changes in the zero signal, causing significant inaccuracies in the corrected data.
In practical applications of PFM, the mechanical arrangements are normally designed for good short term stability, and the zero signal measurement it attempted when the magnetic environment is at the same temperature as it was during the measurement cycle. Nevertheless, unknown errors can still exist which affect the accuracy of the corrected measurement.
In general, disadvantages of the existing approach can be summarised as follows:—
The length of the characterisation process can be reduced by saving a zero signal that is applied to all measurement cycles. Inevitably the longer term mechanical arrangements will “creep.” The effect of which is to change the true, underlying zero signal, reducing overall accuracy.
The method of performing a material characterisation process which is described herein uses a technique where a zero signal is not measured as part of the measurement cycle, and is not a saved zero signal, but is instead deduced from the data present in a characterisation measurement, and is mathematically removed without the need for a separate zero signal cycle.
The following description and the accompanying drawings referred to therein are included by way of non-limiting example in order to illustrate how the invention may be put into practice. In the drawings:
The following method is suitable to be performed by material characterisation apparatus such as PFM apparatus. The subject method involves first constructing a synthesised zero signal which is expressed with a range of appropriate variable parameters. The synthesised zero signal is not one particular signature, but is expressed with a range of variables which can be independently adjusted to tune the synthesised signal through a wide spectrum of possible signatures.
The well-documented physics of PFM determines how the variables may impact on the zero signal through
The synthesised zero signal function can be determined through theoretical physics considerations, or built empirically using large amounts of data for known zero signals while changing the variables.
When a measurement cycle is performed on a sample of material to be characterised the resulting stored data will contain an unknown zero signal. By way of illustrative example,
The underlying signature of the synthesised zero signal will have a relationship to the unknown zero signal, but the values of the variables which describe the precise relationship are unknown. In order to ascertain the values of the variables the synthesised zero signal is mathematically superimposed on the stored measurement data and the variables are adjusted until a best fit is determined. By way of illustration, a superimposed signal which is related to the unwanted signal shown in
In the case of the PFM, the initial zero signal transient, overall magnitude and phase are modeled, adjusted, and compared to the measurement cycle data. An optimum synthesised zero signal is determined and then mathematically subtracted from the measurement cycle data.
The advantages of the method are:—
The effect of this is to enable characterisation of materials at a higher rate than the conventional technique, with better accuracy in conditions that may be variable. (Temperature, mechanical etc.)
Whilst the above description places emphasis on the areas which are believed to be new and addresses specific problems which have been identified, it is intended that the features disclosed herein may be used in any combination which is capable of providing a new and useful advance in the art.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1805405.6 | Apr 2018 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2019/050942 | 4/1/2019 | WO | 00 |
