Calibration method of trace friction balance

Abstract

The invention discloses a calibration method of a micro friction balance, and belongs to the technical field of aerodynamics. Horizontally placing the balance, and loading by using a weight suspension method to obtain an intermediate balance formula; and respectively recording reading outputs of the balance in a vertical state and a horizontal state, and substituting a difference value of the two readings into an intermediate balance formula to obtain the equivalent dead weight of the balance. The balance is inclined for a series of angles from a vertical state, and the reading output at each angle is recorded. The downward component of the balance dead weight along the sensing surface at each angle can be known from the balance equivalent dead weight and the inclination angle, the component can be regarded as an equivalent friction load, and the equivalent friction load corresponding to each inclination angle and balance reading output are fitted to obtain a balance formula. According to the invention, the problem that the actual calibration load is far greater than the load to be calibrated due to the existence of the self weight when the balance is horizontally placed by using a weight suspension method is effectively solved, the calibration state and the use state of the balance are ensured to be consistent, and the fine loading of the micro friction balance is realized.

Description

Technical Field

[0001] The invention relates to a calibration method for a micro-friction balance and belongs to the technical field of aerodynamics. Background Art

[0002] For high-altitude friction measurement, a micro friction balance is usually required. The measurement load of this type of balance is very small, and its range is generally within 1 Pa. When conducting static calibration, the calibration load needs to be small, and the calibration accuracy requirement is also very high, which greatly increases the difficulty of calibration.

[0003] When the weight suspension method is used to calibrate the friction balance, the balance needs to be placed horizontally at 90° and then the weights are suspended on the sensing surface with a thin wire for loading. However, in ground wind tunnel tests, the balance is usually placed vertically at 0°, which results in inconsistency between its calibration state and its usage state. For conventional friction balances, the range is relatively large, and this difference can be ignored. For micro-friction balances, since the friction value it measures is very small (usually less than 1g), the weight of the balance itself is much greater than the friction load after it is placed horizontally, resulting in the actual calibration load of the balance being much greater than the load to be calibrated. Therefore, the use of the weight suspension method to calibrate a micro-friction balance has certain limitations, and a calibration method suitable for a micro-friction balance is needed. Summary of the invention

[0004] The technical problem to be solved by the present invention is: to overcome the shortcomings of the prior art and solve the problem that when a micro-friction balance is calibrated using a weight suspension method, the calibration state is inconsistent with the usage state, resulting in the existence of the balance's own weight making the actual calibration load much larger than the load to be calibrated.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A method for calibrating a micro friction balance comprises the following steps:

[0007] S1: The balance is placed horizontally and loaded using the conventional calibration method, i.e., the weight hanging method;

[0008] Fix the balance horizontally, adjust the balance sensing surface to be perpendicular to the horizontal plane, and use the weight suspension method to load the balance with a single component.

[0009] S2: Get the intermediate balance formula;

[0010] Perform data processing according to the balance calibration specification and obtain the balance formula, which is recorded as the intermediate balance formula:

[0011] F 1 =f 1 (ΔU)

[0012] Among them, F 1is the weight of the hanging weight, ΔU is the increment of the balance reading before and after the weight is loaded, and f 1 It is the intermediate balance formula function.

[0013] S3: Record the reading output of the balance in the vertical state and the horizontal state respectively.

[0014] Fix the balance vertically and adjust the balance sensing surface to be parallel to the horizontal plane. This state is recorded as the 0° state. Record the balance reading output U at this time. α0 Fix the balance horizontally, adjust the balance sensing surface to be perpendicular to the horizontal plane, this state is recorded as the 90° state, and record the balance output U at this time. α90 .

[0015] S4: Substitute the difference between the readings of the two states into the intermediate balance formula to obtain the equivalent deadweight;

[0016] The difference between the readings at 0° and 90° on the balance is ΔU = |U α90 -U α0 |Substitute the intermediate balance formula and calculate the load to be recorded as the equivalent deadweight G 0 .

[0017] S5: Tilt the balance from a vertical position to a series of angles and record the readings;

[0018] Fix the balance vertically on the angle platform, and adjust the balance sensing surface to be parallel to the horizontal plane, that is, 0° state. Adjust the angle platform to tilt a series of angles α starting from 0°, and record the reading output at each angle.

[0019] S6: Calculate the equivalent friction load at each angle based on the balance inclination angle and equivalent deadweight;

[0020] The downward component of the balance's deadweight along its sensing surface can be equivalent to the friction load applied to the balance, that is, the equivalent friction load F f , by the natural effect of self-weight G 0 and the inclination angle α, the equivalent friction load F f The expression is:

[0021] F f =G 0 sinα

[0022] S7: The balance formula is obtained by fitting the equivalent friction load and the corresponding reading output increment at each inclination angle.

[0023] The equivalent friction load at each inclination angle is used as the calibration load, and the balance formula is obtained by fitting the reading output increment at the corresponding inclination angle:

[0024] F f =f 2 (ΔUα )

[0025] Among them, ΔU α is the reading increment at different inclination angles of the balance, f 2 is the final balance formula function.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) A calibration method for a micro-friction balance of the present invention utilizes the component of the balance's own weight downward along the balance's sensing surface at different inclination angles as a calibration load for loading, thereby ensuring the consistency between the calibration state and the usage state of the balance. This effectively solves the problem that in the process of calibrating the balance using the traditional weight suspension method, the actual calibration load is much larger than the load to be calibrated due to the existence of the balance's own weight when placed horizontally, thereby achieving refined loading of the micro-friction balance.

[0028] (2) The weight suspension method is used to calibrate and obtain the intermediate balance formula. Combined with the reading output of the balance at 0° and 90° inclination angles, accurate balance equivalent deadweight data can be obtained.

[0029] (3) The angle platform is used to control the tilt angle of the balance, which can conveniently and continuously obtain the standard tilt angle and obtain the effective reading output of the balance at each tilt angle.

[0030] (4) The balance formula is obtained by fitting the components of the effective deadweight of a balance and the increment of the readings at each inclination angle. Compared with the balance formula obtained by the traditional weight suspension method, this formula can achieve higher accuracy in calculating micro-friction loads. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is a flow chart of the method of the present invention;

[0032] Figure 2 It is a schematic diagram of the structure of the micro friction balance of the present invention;

[0033] Figure 3 It is a schematic diagram of the weight suspension calibration method of the present invention;

[0034] Figure 4 It is a schematic diagram of the tilting method of the balance of the present invention;

[0035] Figure numerals: 1 - micro friction balance, 101 - sensing surface, 102 - strain gauge, 2 - fine wire, 3 - weight, 4 - angle platform. DETAILED DESCRIPTION

[0036] To make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0037] A calibration method for a micro friction balance, the simplified schematic diagram of the balance used is as follows Figure 2 As shown, it includes a micro friction balance 1, a sensing surface 101, and a strain gauge 102. The sensing surface 101 is located above the entire balance and is used to sense the friction load. The balance used in this embodiment is a single-component friction balance, and its direction is the incoming flow direction in the figure. The calibration direction should be consistent with the incoming flow direction. The strain gauge 102 is pasted to the sensitive beam at the root of the balance to form a Wheatstone bridge. When subjected to the friction load, the strain gauge 102 deforms with the sensitive beam and outputs an electrical signal to achieve friction measurement.

[0038] The design load of the balance in this embodiment is 0.2g.

[0039] like Figure 1 As shown, a calibration method of a micro friction balance in this embodiment includes the following steps:

[0040] S1: The balance is placed horizontally and loaded using the conventional calibration method, i.e., the weight hanging method;

[0041] like Figure 3 As shown, the balance is fixed horizontally, the sensing surface 101 is adjusted to be perpendicular to the horizontal plane, and a thin wire 2 is pasted at the center of the sensing surface for hanging the weight 3. In this embodiment, loading is performed according to the load table shown in Table 1 below:

[0042] Table 1

[0043] Serial number Load / g 1 0 2 0.5 3 1 4 1.5 5 2 6 1.5 7 1 8 0.5 9 0

[0044] S2: Get the intermediate balance formula;

[0045] After loading is completed, data processing is performed according to the balance calibration specification, and the balance formula is obtained and recorded as the intermediate balance formula:

[0046] F 1 =f 1 (ΔU)

[0047] Among them, F 1 is the weight of the hanging weight, and ΔU is the increment of the balance reading before and after the weight is loaded.

[0048] The intermediate balance formula obtained by calibrating the micro-friction balance used in this embodiment is as follows:

[0049] F 1 =16.289ΔU+0.0005

[0050] Among them, F 1 The unit is g, and the unit of ΔU is mV / V.

[0051] S3: Record the reading output of the balance in the vertical state and the horizontal state respectively.

[0052] Fix the balance vertically and adjust the sensing surface 101 to be parallel to the horizontal plane. This state is recorded as the 0° state. Record the reading output U of the balance at this time. α0 Fix the balance horizontally, adjust the sensing surface 101 to be perpendicular to the horizontal plane, this state is recorded as the 90° state, and record the reading output U of the balance at this time. α90 The above steps were repeated three times. The data obtained by the micro friction balance used in this embodiment are shown in Table 2 below:

[0053] Table 2

[0054] Serial number Angle / ° Reading (mV / V) 1 0 -0.17534 2 90 0.07648 3 0 -0.17495 4 90 0.07603 5 0 -0.17431 6 90 0.07636

[0055] S4: Substitute the difference between the readings of the two states into the intermediate balance formula to obtain the equivalent deadweight;

[0056] The reading difference between the 0° state and the 90° state of the three sets of balances is ΔU=|U α90 -U α0 |Substitute the intermediate balance formula to calculate three sets of loads, and take the average value as the equivalent deadweight G 0 In this embodiment, the effective deadweight G of the balance is calculated. 0 It is 4.09g.

[0057] S5: Tilt the balance from a vertical position to a series of angles and record the readings;

[0058] like Figure 4 As shown, the balance is fixed vertically on the angle platform 4, and the sensing surface 101 is adjusted to be parallel to the horizontal plane, that is, the 0° state. The angle platform is adjusted to tilt a series of angles α from 0°, and the reading output at each angle is recorded. In this embodiment, the balance tilt angle, the reading output at each tilt angle, and the reading increment ΔU at each tilt angle are calculated α As shown in Table 3 below:

[0059] Table 3

[0060] Serial number Rotation angle / ° Reading (mV / V) <![CDATA[ΔU α (mV / V)]]> 1 0 -0.17538 0 2 0.2 -0.17426 0.00112 3 0.4 -0.17348 0.00190 4 0.6 -0.17265 0.00273 5 0.8 -0.17171 0.00367 6 1 -0.17078 0.00460 7 1.2 -0.16995 0.00543 8 1.4 -0.16905 0.00633 9 1.6 -0.16820 0.00718 10 1.8 -0.16725 0.00813 11 2 -0.16629 0.00909

[0061] S6: Calculate the equivalent friction load at each angle based on the balance inclination angle and equivalent deadweight;

[0062] The component of the balance's deadweight along its sensing surface downward is equivalent to the friction load applied to the balance, that is, the equivalent friction load F f , by the natural effect of self-weight G 0 The equivalent friction load F can be calculated by the following formula: f :

[0063] F f =G 0sinα

[0064] The equivalent friction loads at various inclination angles in this embodiment are shown in Table 4 below:

[0065] Table 4

[0066] Serial number α / ° <![CDATA[F f (g)]]> 1 0 0 2 0.2 0.01428 3 0.4 0.02856 4 0.6 0.04284 5 0.8 0.05712 6 1 0.07140 7 1.2 0.08568 8 1.4 0.09996 9 1.6 0.11424 10 1.8 0.12851 11 2 0.14279

[0067] S7: The equivalent friction load at each inclination angle and the corresponding reading output are fitted to obtain the balance formula.

[0068] The equivalent friction load F at each inclination angle f As the calibration load, the output increment ΔU is corresponding to the reading at the inclination angle α The balance formula is obtained by fitting:

[0069] F f =f 2 (ΔU α )

[0070] The balance formula obtained in this embodiment is as follows:

[0071] F f =15.974ΔU α -0.0015

[0072] Among them, F f The unit is g, ΔU α The unit is mV / V.

[0073] The contents not described in detail in the specification of the present invention belong to the common knowledge of those skilled in the art.

[0074] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for calibrating a micro friction balance, characterized in that: include: S1: The balance is placed horizontally and loaded using the weight suspension method; S2: Get the intermediate balance formula; S3: Record the reading output of the balance in the vertical state and the horizontal state respectively; S4: Substitute the difference between the readings of the two states into the intermediate balance formula to obtain the equivalent deadweight; S5: Tilt the balance from a vertical position to a series of preset angles and record the reading outputs respectively; S6: Calculate the equivalent friction load at each inclination angle based on the balance inclination angle and equivalent deadweight; S7: The balance formula is obtained by fitting the equivalent friction load at each inclination angle and the corresponding reading output.

2. The micro-friction balance calibration method according to claim 1, characterized in that: In S1, the balance is fixed horizontally, the sensing surface of the balance is adjusted to be perpendicular to the horizontal plane, and the balance is loaded with a single component using the weight suspension method.

3. The micro-friction balance calibration method according to claim 1, characterized in that: In S2, data processing is performed according to the balance calibration specification, and the balance formula is obtained and recorded as the intermediate balance formula: F1=f1(ΔU) Among them, F1 is the weight of the hanging weight, ΔU is the increment of the balance reading before and after the weight is loaded, and f1 is the intermediate balance formula function.

4. The micro-friction balance calibration method according to claim 1, characterized in that: In S3, fix the balance vertically and adjust the balance sensing surface to be parallel to the horizontal plane. This state is recorded as the 0° state. Record the balance reading output U at this time. α0 ; Fix the balance horizontally, adjust the balance sensing surface to be perpendicular to the horizontal plane, this state is recorded as the 90° state, and record the balance reading output U at this time α90 .

5. The micro-friction balance calibration method according to claim 4, characterized in that: In S4, the difference between the readings at 0° and 90° on the balance is ΔU = |U α90 -U α0 |Substitute into the intermediate balance formula and calculate the load to be recorded as the equivalent deadweight G0.

6. The micro-friction balance calibration method according to claim 1, characterized in that: In S5, the balance is fixed vertically on the angle platform, and the sensing surface of the balance is adjusted to be parallel to the horizontal plane, that is, the 0° state; the angle platform is adjusted to tilt a series of preset angles α starting from 0°, and the reading output at each angle is recorded.

7. The micro-friction balance calibration method according to claim 1, characterized in that: In S6, the downward component of the balance's deadweight along its sensing surface can be equivalent to the friction load applied to the balance, that is, the equivalent friction load F f The equivalent friction load F is obtained from the equivalent deadweight G0 of the balance and the inclination angle α. f The expression is: F f =G0sinα。 8. The micro-friction balance calibration method according to claim 7, characterized in that: In S7, the equivalent friction load at each inclination angle is used as the calibration load, and the balance formula is obtained by fitting the reading output increment at the corresponding inclination angle: F f =f2(ΔU α )。 Among them, ΔU α is the reading increment at different inclination angles of the balance, and f2 is the final balance formula function.

9. The micro-friction balance calibration method according to claim 1, characterized in that: In S1, load according to the load table in the following table:

10. The micro-friction balance calibration method according to claim 1, characterized in that: In S5, a series of preset angles for tilting the balance from the vertical position are shown in the table below:

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