CN104267364A - Method for calibrating large-current sensor - Google Patents

Abstract

The invention relates to a calibration method of a large current sensor, the steps of which are: (1) appearance inspection; (2) power-on inspection; (3) withstand voltage test; (4) insulation resistance inspection; (5) selection of calibration points; (6) basic error measurement; (7) relative error measurement. The calibration method of the large current sensor provided by the present invention has good applicability, and the relative error can be measured and calibrated by using a large current source or a standard small resistance method, both of which have high measurement and calibration accuracy.

Description

A Calibration Method for Large Current Sensor

technical field

The invention belongs to the field of electrical testing equipment, in particular to a calibration method for a large current sensor.

Background technique

Large current sensor is a device that converts large current into small voltage output according to a certain ratio, such as Rogowski coil, current comparator, Hall transformer, etc., so as to realize real-time measurement of large current.

High-current sensors are widely used, but the calibration lacks certain norms and operation standardization and unified steps, which has caused great obstacles to the operator in the actual calibration process, not only affecting work efficiency, but also causing many test benches to be more complicated. The difference error is large, and even cause damage to the test bench. Therefore, an urgent problem to be solved is to seek a calibration method for large current sensors with better applicability.

Contents of the invention

The purpose of the present invention is to overcome the disadvantages of the prior art, and provide a calibration method of a large current sensor with small relative error and good applicability.

The present invention solves its technical problem and realizes by taking the following technical solutions:

A calibration method for a large current sensor, the steps of which are:

(1) Appearance inspection;

⑵Power-on inspection;

⑶ withstand voltage test;

⑷Insulation resistance inspection;

⑸ Selection of calibration points:

The principle of selecting the calibration point of the sensor is to select no less than 5 calibration points evenly from the lower limit to the upper limit, and select 10%, 30%, 50%, 80% and 100% of the range respectively.

⑹Basic error measurement:

① The sensor to be calibrated shall be placed in the calibration environment for no less than 2 hours;

② When measuring, except for the current-carrying wire, the distance between all other current-carrying conductors and the sensor to be calibrated should be greater than 0.5m;

③ The sensor to be calibrated should be placed at the horizontal and vertical geometric center of the current wire;

④After the value is stable for 5s, read each calibration point;

⑺ Relative error measurement:

A large current source method is used to measure the relative error of the conversion ratio of the large current sensor.

Moreover, in the large current source method, the relative error calculation formula of the conversion ratio of the large current sensor is:

$\mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 100</span>}<span\; class="notranslate">\; \%</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 100</span>}<span\; class="notranslate">\; \%</span>$

In the above formula: γ—the relative error of the output conversion ratio

V ₁ —Standard multimeter display value

I ₁ —Standard current source display value

k ₁ —actually measured value of conversion proportional coefficient, unit mV/A

k ₀ —The nominal value of the conversion ratio of the large current sensor, the unit is mV/A.

Advantage and positive effect of the present invention are:

The calibration method of the large current sensor provided by the present invention has good applicability, and a large current source can be used for measurement and calibration for relative errors, and both methods have high measurement and calibration accuracy.

Description of drawings

Fig. 1 is a schematic diagram of the wiring structure for measuring the relative error of a large current sensor in the present invention.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and through specific embodiments. The following embodiments are only descriptive, not restrictive, and cannot limit the protection scope of the present invention.

A calibration method for a large current sensor, the steps of which are:

⑴Appearance inspection

The calibrated high-current sensor should be equipped with instructions and corresponding information; it should have a product qualification certificate and all necessary accessories. The shape and structure of the large current sensor should be intact. Switches, buttons, buttons, etc., are flexible and reliable in operation, with clear signs, and the exposed parts should not be loose or mechanically damaged. Its nameplate or shell should indicate its name, model, serial number, date of manufacture and manufacturer. The sign of the power supply and the indication of the voltage and frequency range are clear.

⑵Power-on inspection

After visual inspection, power on the standard equipment to preheat according to the instruction manual.

⑶ withstand voltage test

Steadily raise the test voltage from zero to the specified value (please refer to the product manual for the specified voltage value), keep it for 1min, and then drop the test voltage to zero at the same speed. During the test, there should be no breakdown of the insulation.

⑷Insulation resistance inspection

The insulation resistance of the two ends of the connection of the sensor circuit to be calibrated can be measured with a 500V insulation resistance meter under the calibration environment.

⑸ Selection of calibration points

The principle of selecting the calibration point of the sensor is to select no less than 5 calibration points evenly from the lower limit to the upper limit, and select 10%, 30%, 50%, 80% and 100% of the range respectively.

⑹Basic error measurement

a) The sensor to be calibrated shall be placed in the calibration environment for no less than 2 hours;

b) When measuring, except for the live wire, the distance between all other current-carrying conductors and the sensor to be calibrated should be greater than 0.5m;

c) The sensor to be calibrated should be placed at the horizontal and vertical geometric center of the current wire;

d) After the value is stable for 5s, read each calibration point;

⑺ Relative error measurement

The relative error measurement of the conversion ratio of the large current sensor adopts the large current source method:

The wiring of the large current source method is shown in Figure 1. The relative error calculation formula of the conversion ratio of the large current sensor is:

$\mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 100</span>}<span\; class="notranslate">\; \%</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 100</span>}<span\; class="notranslate">\; \%</span>$

In the above formula: γ—the relative error of the output conversion ratio

V ₁ —Standard multimeter display value

I ₁ —Standard current source display value

k ₁ —actually measured value of conversion proportional coefficient, unit mV/A

k ₀ —The nominal value of the conversion ratio of the large current sensor, in mV/A

data processing

The calibration data of the standard device should be recorded in the calibration original record. The maximum basic error of the large current sensor and the data of the actual value must be calculated first, and then rounded off. The number of digits after calculation should be one more than the number of digits before calculation, and the rounding of data follows the rule of rounding to even numbers.

The recommended calibration period for large current sensors is 1 year.

Example 1

Checked product information

Equipment Name: Loop Current Tester

Model specification: i3000s

Factory number: 95310102

Production unit: FLUKE

Calibration date: June 26, 2014

Output current range: 0-3000A, this example chooses to measure 100A as the calibration point

Output current accuracy: ±5%

Transformation ratio: select according to the measurement point, select 10mV/A at 100A

Ratio accuracy: ±1%

⑴ Appearance and accessories inspection

The shape and structure of the large current sensor should be intact. Switches, buttons, buttons, etc., are flexible and reliable in operation, with clear signs and no loose or mechanical damage to exposed parts. Its nameplate or shell should indicate its name, model, serial number, date of manufacture and manufacturer. The sign of the power supply and the indication of the voltage and frequency range are clear.

⑵Power-on inspection

The high-current sensor has been placed for more than 24 hours under the environmental conditions of a temperature of 22°C and a humidity of 60%RH.

After visual inspection, power on the standard equipment to preheat according to the instruction manual.

⑶ withstand voltage test

Measuring instrument used: pressure tester MS2670F

Manufacturer: Nanjing Minsheng Electronic Instrument Co., Ltd.

Measurement method: Increase the test voltage from zero to the specified value steadily (please refer to the product manual for the specified voltage value), keep it for 1min, and then drop the test voltage to zero at the same speed.

Measurement results: There should be no breakdown of the insulation during the test

⑷Insulation resistance measurement

Measuring instrument: insulation resistance meter ZV25-3

Manufacturer: Nanjing Jinchuan Meter Manufacturing Co., Ltd.

Measurement method: measure the insulation resistance between the circuit and exposed conductive parts, between the circuit and the ground

Measurement results: the voltage is 500V, the insulation resistance is 100MΩ, which meets the requirements

⑸Measurement of basic error

Using standard instrument information

a. Standard current and voltage source

Equipment Name: Multifunctional Calibrator

Device model: 5720A

Production unit: Fluke

Current maximum output value: 2.2A (expandable to 120A)

Current uncertainty: ±140ppm

Voltage maximum output value: 1100V

Voltage uncertainty: ±45ppm

b. Standard digital multimeter

Name: Digital Multimeter

Model: 8508A

Production unit: Fluke

Current measurement range: 0～20A

Current measurement uncertainty: ±(250ppm output+100ppm range)

Voltage measurement range: 0 ~ 1050V

Voltage measurement uncertainty: ±(65ppm output+10ppm range)

⑹ Relative error measurement

Measurement methods:

According to the large current source method wiring (as shown in Figure 1), the relative error of the conversion ratio of the large current sensor is measured by wiring. The relative error calculation formula of the conversion ratio of the large current sensor is:

$\mathrm{<span\; class="notranslate">\; \&gamma;</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 100</span>}<span\; class="notranslate">\; \%</span><span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 100</span>}<span\; class="notranslate">\; \%</span>$

In the above formula: γ—the relative error of the output conversion ratio

V ₁ —Standard multimeter display value

I ₁ —Standard current source display value

k ₁ —actually measured value of conversion proportional coefficient, unit mV/A

k ₀ —The nominal value of the conversion ratio of the large current sensor, the unit is mV/A.

Put the high-current sensor on the output circuit of the high-current source, select the 10mV/A range, adjust the high-current source to output an AC signal of 100A, and connect a digital multimeter to display the converted voltage signal.

measurement result

Large current source output current value: 100A

Voltage value measured by digital multimeter: 0.999981V

Transformation ratio displayed by loop current tester: 10mV/A

Therefore, the transformation ratio measured by the loop current tester: 0.999981V/100A＝9.99981mV/A.

Although the embodiments and drawings of the present invention are disclosed for the purpose of illustration, those skilled in the art can understand that various replacements, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims Therefore, the scope of the present invention is not limited to what is disclosed in the embodiments and drawings.

Claims (2)

1. a calibration steps for great current sensor, is characterized in that: the steps include:

(1) visual examination;

(2) be energized inspection;

(3) withstand voltage test;

(4) insulation resistance inspection;

(5) the choosing of calibration point:

The principle choosing the calibration point of sensor is that lower limit to the upper limit is chosen uniformly and is no less than 5 calibration points, choose 10% of range respectively, 30%, 50%, 80%, 100% place.

(6) fundamental error is measured:

1. 2h is no less than under being placed in calibration environment condition by school sensor;

When 2. measuring except electrified wire, other all current－carrying conductors and should 0.5m be greater than by the distance between the sensor of school;

3. the horizontal vertical geometric center position of current lead should be placed in by school sensor;

4., after numerical stability 5s, reading is carried out to each calibration point;

(7) relative error is measured:

The relative error of great current sensor conversion proportion is measured and adopts big current source method.

2. the calibration steps of great current sensor according to claim 1, is characterized in that: in the method for described big current source, the relative error computing formula of great current sensor conversion proportion is:

$\mathrm{\&gamma;}=\frac{k_1-k_0}{k_0}\&times;100\%=\frac{V_1/I_1-k_0}{k_0}\&times;100\%$

In above formula: the relative error of γ-output conversion proportion

V ₁-standard multimeter displayed value

I ₁-normalized current source displayed value

K ₁the measured value of-conversion proportion coefficient, unit mV/A

K ₀the nominal value of-great current sensor conversion proportion, unit mV/A.