Direct current sensor can be used to determine the basic error of the measurement method and the direct measurement method, direct measurement method, including the double table method, remote measurement, etc..

First, the error of the DC current sensor calibration error

The method can be used to measure the output voltage of the DC current transformer. The difference method can reduce the influence of the current source output fluctuation on the error calibration test.

When the standard is the same as that of the transformer, the standard resistance box is not required. When the output voltage of the transformer is greater than the standard output, the standard resistance box should be moved to the output side of the transformer. Adjust the standard resistance box, the DC current comparator and the ratio of DC current transformer rated ratio equal.

According to the definition of current error, the current ratio error of the DC current transformer is calculated:

In type:

Up - digital voltmeter A shows that the standard output;

U - digital voltmeter B shows the number.

The load error introduced by the standard resistance box should be less than the allowable error of the DC current transformer 1/10.

In order to reduce the influence of the current source output fluctuation on the test, 3 sets of data can be read at each measuring point.

Two, the double table method verification DC current sensor basic error

When the DC current transformer has the analog voltage output, it can be used as a substitute for the difference method. The principle of double table method for verifying the DC current transformer with analog voltage output is shown in figure 3. Synchronous read standard DC current comparator and the detected DC current transformer output Up and Us. It is recommended to use programmable instrument control technology to read the readings of digital voltmeter A and B synchronously.

The schematic diagram of the simulation of the output DC current transformer with double table method

According to the definition of current error, the error formula of current ratio is calculated:

In type:

Krp - DC current comparator ratio;

Kra -- the ratio of DC current transformer;

Up - digital voltage A shows the number of two, the output voltage DC current comparator;

Us - digital voltmeter B shows the number, that is, the detection of DC current transformer two output voltage.

Two digital voltage meter electronic transformer calibrator can replace 2, which contains high precision analog acquisition card to standard DC current comparator and analog output test DC current transformer of synchronous sampling.

Three, electronic transformer calibrator verification with digital output DC current transformer

When the DC current transformer has two digital outputs, it can be used to check the electronic transformer calibrator with the function of clock synchronization. Electronic transformer calibrator verification with digital output of the DC current transformer circuit diagram as shown in the following figure. Electronic transformer calibrator is an output clock control converter DC current transformer test sampling, digital input port read the detected DC current transformer two converter output digital frame, analog voltage output port reading DC current comparator, Up and Is time synchronization is obtained by processing. Among them, Up is two times the output voltage of DC current comparator, Is is a direct current digital frame detect DC current transformer output represents.

Electronic transformer calibrator verification digital output DC current transformer schematic

According to the definition of current error, the error formula of current ratio error is calculated, and the error is calculated automatically by the electronic transformer calibrator.

In type:

Krp - DC current comparator ratio;

Two - Up output voltage direct current comparator;

Is -- the measured output value of the DC current transformer.

Four, remote measurement of DC current sensor calibration error

When the two converter of the DC current transformer is far away from the primary converter, the test method can not be adopted. Remote measurement principle diagram as shown below. The output of the DC current transformer is two times the analog output Us or digital screen display Is.

Schematic diagram of DC current transformer for remote measurement