Calibration method for neonatal scales

Abstract

The present invention discloses a calibration method for a neonatal scale. The method comprises the following steps: determining the maximum error H of a weighing sampling circuit through a two-point calibration experiment; determining the minimum number of calibration segments based on the ratio of the maximum error H to the standard accuracy G of the neonatal scale; and selecting the optimal number n of calibration segments. The measuring range of the neonatal scale is divided into n segments, and the nominal weight increments at adjacent calibration points are ensured to be equal. The slope of each calibration segment is determined by recording the sampling values of the weighing sampling circuit at the zero point and each calibration point. The advantage of the present invention is that the scale is calibrated using a multi-segment calibration method, and the calibration points use standard theoretical values instead of measured sampling values, effectively reducing the maximum value of possible system error accumulation, avoiding the use of hardware for linear compensation of the sensor, and having a high cost-effectiveness ratio.

Description

Technical Field

[0001] The present invention relates to the field of neonatal scales, and in particular to a calibration method for neonatal scales. Background Art

[0002] A neonatal scale is a measuring instrument for measuring the weight of newborns. It has a wide range (0-12kg) and high accuracy (1g). The calibration method of the neonatal scale determines the size of the neonatal scale's error. Figure 1 As shown, the calibration of neonatal scales is usually done by using software to calculate w / m, i.e. slope K, under the premise that the hardware ensures the linear output of the sensor. Then, the corresponding value w and the true value m are restored, or the intercept (b) is directly changed to make the displayed value correspond to the true value, as shown in the following example. Figure 1 The straight line 1 in the figure is used to make the output of any calibration object coincide with the pre-fixed straight line by changing the intercept b. Figure 1 Line 2 in the figure has a fixed slope k determined by table lookup or hardware circuitry. However, in practical applications, the discrete slope of inexpensive load cells seriously affects the accuracy of neonatal scales. Summary of the Invention

[0003] The present invention aims to provide a calibration method for a neonatal scale.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] The calibration method of the neonatal scale of the present invention comprises the following steps:

[0006] S1, linear compensation of the load cell output by hardware;

[0007] S2, determine the maximum error H of the weighing sampling circuit through a two-point calibration experiment;

[0008] S3, after determining the minimum number of calibration segments based on the ratio of the maximum error H to the standard accuracy G of the neonatal scale, selecting the optimal number n of calibration segments;

[0009] S4, dividing the measuring range of the neonatal scale into n segments according to the optimal number n of calibration segments, determining intersections of adjacent calibration segments as calibration points, and ensuring that the nominal weight increases at adjacent calibration points are equal;

[0010] S5, recording the sampling values of the weighing sampling circuit at the zero point and each calibration point, and determining the slope of each calibration section.

[0011] Furthermore, the minimum number of calibration segments is the ratio of the maximum error H to the standard accuracy G of the neonatal scale, rounded up.

[0012] Furthermore, the optimal number of calibration segments is greater than or equal to the minimum number of calibration segments and is determined according to user needs.

[0013] Furthermore, for any sampling value of the weighing sampling circuit , determine the indicated value according to the following formula :

[0014]

[0015] in, is the slope of the i-th segment; is the sampling value of the i-1th calibration point; m is the nominal weight increase at the adjacent calibration point; i is Integer; and determine according to the range from large to small The calibration section to which it belongs determines the value of i.

[0016] The advantage of the present invention is that the scale is calibrated by using a multi-stage calibration method, and the calibration points are replaced by standard theoretical values instead of measured sampling values, which effectively reduces the maximum value of possible system error accumulation, avoids the use of hardware to perform linear compensation on the sensor, and has a high cost-effectiveness. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a schematic diagram of the calibration principle of a common neonatal scale according to the present invention.

[0018] Figure 2 The figure is a schematic diagram showing the principle of the method for calibrating a neonatal scale by calculating the slope according to the present invention.

[0019] Figure 3 It is a schematic diagram of the principle of the two-stage calibration method of the present invention.

[0020] Figure 4 is a flow chart of the method of the present invention.

[0021] Figure 5 This is a circuit diagram of a weighing and sampling circuit in the method of the present invention.

[0022] Figure 6 It is a flow chart of the calibration of the fourth section of a specific embodiment of the method of the present invention.

[0023] Figure 7 It is a schematic diagram of the calibration of the fourth section of a specific embodiment of the method of the present invention.

[0024] Figure 8 This is a flow chart of weighing a scale in the fourth section of a specific embodiment of the method of the present invention. DETAILED DESCRIPTION

[0025] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts are within the scope of protection of the present invention.

[0026] The existing method for calibrating a neonatal scale is to calculate the slope. The basic principle is formula 1:

[0027] Formula (1)

[0028] in, is the tare weight of the scale (i.e. the sampling output of the weighing sensor when no object is placed), It is the sampling output of the weighing sensor after the weight is placed on the scale. is the standard weight value when the mass of the weight is zero, is the standard weight value when the mass of the weight is m.

[0029] According to formula 1, the sampling value of any weighing sensor , its value is calculated as shown in formula 2:

[0030] Formula (2)

[0031] in, is the sampling value of any weighing sensor Corresponding indication value; This is the standard weight value for the neonatal scale weighing mass at this time.

[0032] The method of calibrating the neonatal scale by calculating the slope is very simple, but due to the discreteness of the weighing sensor parameters, it is difficult for the hardware to ensure that the sensor has a linear output, which ultimately leads to excessive error in the indication. Figure 2 shown. Figure 2 China-Israel 、 、 、 A straight line with a slope of k is determined. For this straight line, any standard weight value The corresponding weighing sensor sampling value should be , but in fact the output of the weighing sensor is not linear, but Figure 2 The curve shown in , therefore, any standard weight value The corresponding weighing sensor sampling value is actually , and The difference To reduce the indication error, it is necessary to perform linear compensation on the output of the weighing sensor through hardware, which will increase the cost of the neonatal weighing scale and reduce the cost-effectiveness.

[0033] Therefore, the calibration method of the neonatal scale described in the present invention proposes a segmented calibration method. It uses general hardware to perform conventional linear compensation on the output of the weighing sensor. For the sake of mass production and cost-effectiveness, it does not overemphasize that the sensor output is infinitely close to the linear output. After the hardware linear compensation, the remaining nonlinear output is calibrated by the program segmented method to reduce the indication error. Figure 3 As shown in the figure, it is the relevant curve diagram of 2-segment calibration. Figure 3 middle,

[0034] Formula (3)

[0035] Formula (4)

[0036] When the sampling value of the weighing sensor , then its indicated value for:

[0037] Formula (5)

[0038] From the above, we can see that, in theory, the more calibration segments there are, the smaller the absolute error. However, when calculating the slope k of each calibration segment, errors are inevitable, and the accumulated errors may exceed the error requirements of the neonatal scale. To solve this problem, the calibration method of the neonatal scale described in the present invention is as follows: Figure 4 As shown, the following steps are included:

[0039] S1, determine the R value in the weighing sampling circuit; the sampling circuit is as follows Figure 5 As shown, Rt is a thermistor or a thermistor probe. The sampling circuit is determined according to the characteristic parameters of the thermistor or thermistor probe and the connection method in the circuit. R The value is set so that the sampling value of the thermistor or thermistor probe, that is, the output value Uo, is linearly related to the weighing weight. That is, the output of the weighing sensor is linearly compensated by hardware.

[0040] In step S2, determine the maximum error H of the weighing sampling circuit through a two-point calibration experiment. Building on step S1, further improve the sampling accuracy of the load cell through a multi-stage calibration method. Perform a two-stage calibration experiment on a sample of thermistors or thermosensitive probes to determine the maximum error H of the weighing sampling circuit from the experimental results.

[0041] S3. After determining the minimum number of calibration segments based on the ratio of the maximum error H to the standard accuracy G of the neonatal scale, an optimal number n of calibration segments is selected. The minimum number of calibration segments is the ratio of the maximum error H to the standard accuracy G of the neonatal scale, rounded upward. The optimal number of calibration segments must be greater than or equal to the minimum number of calibration segments and is determined based on user requirements, such as the neonatal scale's range, nominal weight, and calibration convenience.

[0042] S4, divide the range of the neonatal scale into n segments according to the optimal number n of calibration segments, determine the intersection of adjacent calibration segments as the calibration point, and ensure that the increase in the nominal weight of the calibration segment is equal; that is,

[0043] Formula (6)

[0044] in, is the sampling value of the weighing sensor at the zero point; 、 、 、 is the sampling value of the weighing sensor at the intersection of adjacent calibration sections; 、 、 is the slope of the calibration segment.

[0045] The essential meaning of formula (6) is that the increase in the nominal weight at adjacent calibration points is Equal, that is

[0046] Formula (7)

[0047] Combining formula (5) and formula (7), we can see that any sampling value of the symmetrical resampling circuit , indicating value for:

[0048] Formula (8)

[0049] in, is the slope of the i-th segment; is the sampling value of the i-1th calibration point; m is the nominal weight increase at the adjacent calibration point; i is Integer; and determine according to the range from large to small The calibration section to which it belongs determines the value of i.

[0050] In this way, the inevitable error accumulation can be limited to a minimum when calculating the slope k of each calibration segment.

[0051] S5, record the sampling values of the weighing sampling circuit at the zero point and each calibration point, and determine the slope of each calibration section. Figure 6 The flowchart of the 4-segment calibration is shown. Figure 7The diagram is a four-section calibration diagram. The entire range of the neonatal scale is divided into 4 sections, and the nominal weight increase in each section is .

[0052] First, weigh and sample without putting weights, that is, record the sampling value of the weighing sampling circuit at zero point , increase the nominal weight at adjacent calibration points by one times , that is, a weight of 1m is weighed and sampled, and the sampling value of the weighing sampling circuit is recorded , record and calculate the slope of the first calibration section Then weigh the weight of 2m and record the sampling value of the weighing sampling circuit. , record and calculate the slope of the second calibration section Weigh and sample the weight of a 3m weight and record the sampling value of the weighing sampling circuit , record and calculate the slope of the third calibration section Weigh and sample the weight of a 4m weight and record the sampling value of the weighing sampling circuit. , record and calculate the slope of the 4th calibration section At this point, the calibration of the entire neonatal scale is completed. 、 、 、 is the sampling value of the calibration point. is the sampling value at zero point.

[0053] When in use, when the newborn scale is weighing, any sample value of the weighing sampling circuit , determine the indicated value according to the following formula :

[0054] Formula (8)

[0055] in, is the slope of the i-th segment; is the sampling value of the i-1th calibration point; m is the nominal weight increase at the adjacent calibration point; i is Integer; and determine according to the range from large to small The calibration section to which it belongs determines the value of i.

[0056] Specific as Figure 8 As shown, still taking the use of the 4-segment calibrated neonatal scale as an example, the symmetrical resampling circuit is explained to obtain any sampled value. , how to determine the indication.

[0057] First, judge Whether it is zero, that is, determine it from large to small according to the range Belong to the calibration section, if If the value is true, it means that the weight to be weighed has exceeded the total range of the neonatal scale, and it will be handled as over-range. If not, continue to judge Is it established? Is it greater than Less than If the judgment is established, it means In the 4th calibration section, the value calculated according to formula (8) is:

[0058]

[0059] That is, i in formula (8) is 4, and w is .

[0060] like If not, continue to judge Is it established? Is it greater than Less than If the judgment is established, it means In the third calibration section, the value calculated according to formula 8 is:

[0061]

[0062] That is, i in formula (8) is 3, and w is .

[0063] like If not, continue to judge Is it established? Is it greater than Less than If the judgment is established, it means In the second calibration section, the indicated value is calculated according to formula (8):

[0064]

[0065] That is, i in formula (8) is 2, and w is .

[0066] like If not, continue to judge Is it established? Is it greater than Less than If the judgment is established, it means In the first calibration section, the indicated value is calculated according to formula (8):

[0067]

[0068] That is, i in formula (8) is 1, and w is .

[0069] like If not, the displayed value is 0.

Claims

1. A method for calibrating a neonatal scale, characterized by: The following steps are involved: S1, linear compensation is performed on the output of the weighing sensor through hardware; specifically, the R value in the weighing sampling circuit is determined; the weighing sampling circuit is composed of a resistor R and a thermistor or thermistor probe Rt in series; the R value in the weighing sampling circuit is determined based on the characteristic parameters of the thermistor or thermistor probe and the connection method in the weighing sampling circuit, so that the sampling value of the thermistor or thermistor probe, i.e., the output value Uo, is linearly related to the weighing weight; S2, determine the maximum error H of the weighing sampling circuit through a two-point calibration experiment; specifically, based on step S1, further improve the sampling accuracy of the weighing sensor through a multi-stage calibration method; perform a two-point calibration experiment on a sample of thermal elements or thermal sensor probes to determine the maximum error H of the weighing sampling circuit in the experimental results; S3, after determining the minimum number of calibration segments based on the ratio of the maximum error H to the standard accuracy G of the neonatal scale, selecting the optimal number n of calibration segments; S4, dividing the measuring range of the neonatal scale into n segments according to the optimal number n of calibration segments, determining intersections of adjacent calibration segments as calibration points, and ensuring that the nominal weight increases at adjacent calibration points are equal; S5, record the sampling values of the weighing sampling circuit at the zero point and each calibration point, and determine the slope of each calibration section; for any sampling value of the weighing sampling circuit , determine the indicated value according to the following formula : in, is the slope of the i-th segment; is the sampling value of the i-1th calibration point; m is the nominal weight increase at the adjacent calibration point; i is Integer; and determine according to the range from large to small The calibration section to which it belongs determines the value of i; The minimum number of the calibration section is the ratio of the maximum error H to the standard accuracy G of the neonatal scale rounded up; the optimal number of the calibration section is greater than or equal to the minimum number of the calibration section and is determined according to user needs.

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