Operation process of power sensor

With the development of society and the continuous improvement of power electronics technology, which has also led to the arrival of new technological revolutions, the world has begun to enter the information age. The first thing to solve is to obtain accurate and reliable information, and sensors are the main way and means to obtain information in the natural and production fields. Although the sensor is an electronic device, it is different from ordinary devices. Different installation methods and different usage methods will affect the sensor performance.

Such as: converter valves in high-voltage DC transmission, inverters, the core equipment of solar power generation, main converters of wind power generation, high-speed rail traction drive converters, and robot servo drives necessary for intelligent manufacturing. Among these manufacturing and conversion equipment They are all inseparable from the core device sensors for current and voltage measurement. Sensor performance directly affects the optimal operation of the entire device and even the system. After long-term practical experience, the author summarizes the problems and precautions in the practical application of sensors.

First of all, before using the sensor, be sure to verify the working power supply voltage level and whether the measurement range is consistent with the signal being measured! It is best to read the specifications carefully! Avoid the misuse and mixing of different voltages and currents. For ease of reference, the following discusses the correct use of sensors from several aspects.

1. Usage environment

The sensor should be used in an environment free of conductive dust and gases that corrode metal and damage insulation. Otherwise, the sensor may be burned out due to the occurrence of a primary and secondary circuit between conductive dust and objects, or a short circuit between the secondary side power supply and the signal.

1.1 Ambient temperature

The sensor's specification book will stipulate the normal operating ambient temperature range of the sensor, such as -40 to 85 degrees, which varies depending on the product model. It is recommended not to exceed the temperature range specified in the specification and exceed the normal operating temperature range of the sensor. Some internal components will reduce performance due to temperature characteristics, resulting in reduced accuracy, inaccurate output signals, or failure to work.

The sensor should be installed in a place with good ventilation and heat dissipation as much as possible to prevent excessive temperature from affecting the measurement accuracy and life of the sensor.

1.2 Altitude

Usually when designing the sensor, the altitude will be taken into consideration, which is generally 2000 meters. But it is not only applicable to altitudes below 2,000 meters. If the altitude exceeds 2,000 meters in actual use, it will mainly affect the heat dissipation and insulation performance of the sensor. It will reduce the insulation characteristics. Although the insulation can also be improved through external methods, it is difficult to implement and will increase the cost. In actual selection and use, you can refer to the provisions of the IEC 60664-1 standard for derating. For details, see IEC 60664-1 Section 5.1.4, derating factors in Table A.2. Heat dissipation problems can be solved relatively easily through methods such as forced air cooling.

1.3 Installation location

Since the sensor is a non-contact measurement and most detects the magnetic field around the charged conductor, it is not suitable to have strong magnetic fields or devices that easily generate magnetic fields near the sensor. Including transformers, reactors, conductors that carry large currents, etc. Especially in three-phase testing, adjacent sensors should not be installed too close. Spacing should be as large as space allows.

Sometimes it is limited by the cabinet and its internal layout, and it is difficult to leave enough space. In this case, it is recommended that the sensor be installed in a staggered position, especially the HALL principle sensor. The position of the HALL device should be as much as possible so that the magnetic field source is the principle.

2. Sensor installation and fixation

The sensor is fixed in two ways: PCB and disk mounting.

2.1 PCB installation method

Usually the primary side measurement signal of the sensor installed on the PCB is relatively small.

The output end of the sensor uses pin pins or SMD. Welding can be performed according to the welding process of general devices. Since some sensors do not have glue filled inside, try to avoid cleaning.

2.2 Disk installation method

Usually, the primary side measurement signal of the disk-mounted sensor is relatively large and the volume is relatively large.

In the sensor specifications, the spacing and hole diameter of the mounting holes are provided, and the size of the screws used in each mounting hole and the tightening torque are also specified. The recommended torques have been verified and evaluated by the design engineer. During installation, you must strictly follow the recommended torques in the specifications, otherwise the casing may rupture. Especially for glue-filled sensors, once the shell is broken, it cannot be repaired, which will not only cause economic losses but also cause trouble to the construction.

What is the correct way to open the power sensor?

3. Installation direction

3.1 Current sensor

There will be an arrow on the shell of each current sensor. The direction of this arrow represents the flow direction of the measured current. When connecting the measured current to the primary side of the sensor, make sure that the measured current and flow direction are consistent with the arrow shown on the sensor. Same direction. Otherwise, the output signal of the sensor will be reversed.

3.2 Voltage sensor

On the shell of each voltage sensor, there will be a positive and negative pole of the primary voltage, which respectively represent the positive and negative poles used to connect to the measured voltage signal. Some sensors will also have a ground output terminal "E" or "". Usually this terminal is connected to the shielding layer and to the protective ground to play a shielding and anti-interference role. It is worth reminding that although the sensor can be used for both AC and DC, the direction of the primary side connection will also bring about changes in the secondary side output, and the original and secondary side waveforms will be reversed.

4. Primary conductor

For current transducers that measure large currents, the primary side generally has a perforated structure. The corresponding cable or copper bar should be selected according to the shape and size of the perforation to ensure that the original conductor can pass through the perforation smoothly. Do not cause the cross-section of the conductor to be too large. And damage the sensor hole. The through-core conductor should be filled with through-holes as much as possible to ensure measurement accuracy. When cables and copper bars pass through the sensor, there should be fixed supports on both sides and should be centered as much as possible to avoid skewing of the copper bars or cables, which would affect the measurement results. In actual operation, attention should be paid to the temperature of the conductor. It is best not to exceed the nominal allowable temperature to avoid overheating affecting the normal operation of the sensor or damaging the sensor.

5. Sensor wiring

Generally, there will be a wiring diagram in the specification book of the sensor, which clearly shows the serial number of the corresponding output point, which generally includes the positive pole of the power supply Vc+, the negative pole of the power supply Vc-, the output signal terminal M, and OV. The wiring must be according to the definition of the serial number, and no wrong connections are allowed. , missing connection, otherwise the sensor will be damaged.

5.1 pin pin type

When the secondary side of the sensor adopts PCB soldered pin type, the board must be laid out according to the pin number shown on the last page of the specification.

5.2 Connector type

When the secondary side of the sensor is in the form of a connector, the specification book will provide the model and specifications of the connector, as well as the corresponding functions of each connector pin. It is recommended to use special tools to crimp terminals and wires to avoid short circuit or poor contact.

6. Working power supply of sensor

Generally speaking, sensors require an external working power supply. This working power supply is a DC voltage source, which is divided into several specifications, such as +5V, +/-12V, +/-15V or +/-24V, etc. Usually the power supply voltage level Vc is given in the sensor specifications. If the Vc value is +/-, the sensor needs to be powered by dual power supplies. In addition, when choosing a power supply, choose a power supply with stable voltage and small ripple. Also pay attention to the power of the power supply. The loss value Ic of the sensor is usually provided in the sensor specification sheet. This Ic value represents the power consumption of the sensor. When selecting a power supply, at least ensure that the current output by the power supply is greater than Ic to ensure the normal operation of the sensor.

7. Power on the sensor

The sensor is an active device used to measure current and voltage signals. It requires an external DC power supply for the sensor to work.

1) After the wiring on the secondary side of the sensor is correct, first turn on the DC power supply for the sensor to work. If it is a sensor powered by dual power supplies, the power supply is DC +/-12V, +/-15V or +/-24V. If it is a sensor powered by a single power supply, the power supply is DC +5V. The DC power supply for sensor operation must be stable, with fluctuations within +/-5%. Too low or too high will affect the normal operation of the sensor, and too high a voltage may damage the sensor. After the DC power supply of the sensor is turned on, the sensor is in a ready-to-operate state. At this time, there will be a small signal output at the secondary output terminal. As long as it is within the range allowed by the specification, it is normal.

2) After the sensor power supply is turned on, the measured signal from the primary side is passed through.

When the measured signal is input, there will be a corresponding signal output at the output end of the sensor. This output signal will change with the change of the measured signal on the primary side. If the order of powering on the primary and secondary sides is reversed, the sensor may be damaged. Please pay attention to this in practice!

8. Selection of load resistor

The load resistance refers to the resistance connected to the output end of the sensor. Usually the output current signal will limit the maximum value of the load resistance, and the output voltage signal will limit the minimum value of the load resistance.

8.1 Current output sensor

When the output signal of the sensor is a current signal, it usually needs to be converted into a voltage signal during sampling. In this case, a measuring resistor needs to be connected between the output end of the sensor and OV. The selection of the measuring resistor is limited by the size of the sensor power supply voltage and the size of the measured signal, and cannot be selected arbitrarily.

Under the same power supply voltage, the size of the measurement resistance value will affect the range of the primary signal that the sensor can measure. The smaller the resistance value, the larger the measured signal, the larger the measurement range, the larger the resistance value, the smaller the measured signal. , the smaller the maximum measurement range. However, it should be noted that the measurement resistance value of some sensors cannot be reduced infinitely, otherwise the sensor will be damaged. Usually in the specification book, the manufacturer will indicate the range of the measurement resistance, including the minimum and maximum values. As long as the value of this resistor is within the range specified in the specification, the sensor can work normally and meet the parameter indicators promised in the specification.

8.2 Voltage output sensor

When the output signal of the sensor is a voltage signal, in order to ensure that the connection of the load resistor does not affect the attenuation of the sensor output voltage value, there is a minimum limit on the load resistor value. The manufacturer will indicate the size of the load resistor in the specification book, usually in the kiloohm level. Therefore, when the output end of the sensor is connected to the subsequent circuit, it is necessary to ensure that the equivalent resistance value is greater than the allowable load resistance. Otherwise, the output value of the sensor will decrease.

9. Potentiometer

Under the application of new technologies, sensors are calibrated and calibrated using laser resistance adjustment and software resistance adjustment. However, there are still some sensors on the market that use potentiometers. Usually these exposed potentiometers are adjusted by the manufacturer before leaving the factory. It is used for sensor calibration and is used to adjust the zero point and accuracy of the sensor. After adjustment, it is fixed with red glue to prevent the potentiometer from being accidentally touched and changing the resistance value. Please do not adjust the exposed potentiometer at will, otherwise it will affect the measurement accuracy of the sensor. The above is the breakdown of the correct operation process of the power sensor. I hope it can give you some help.