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Home > MEMS / sensing technology > What should be the correct way to open the power sensor?

What should be the correct way to open the power sensor?

Published time: 2020-02-13 12:07:39

With the development of power electronics technology, variable current, frequency conversion and inverter technology are widely used in the new energy industry. With the advent of the new technological revolution, the world begins to enter the information age.In the process of using information, 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 general devices. Different installation methods and different usage methods will affect the performance of the sensor.

sensor

For example, converter valve in HVDC transmission, inverter of core equipment for solar power generation, main converter for wind power generation, high-speed rail traction drive converter and robot servo driver necessary for intelligent manufacturing are inseparable from the sensor of core devices for current and voltage measurement in manufacturing and converter equipment.Sensor performance directly affects the whole equipment and even the best operation of 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 voltage level of the working power supply and whether the measurement range is consistent with the measured signal!Better read the specification carefully!Avoid misapplication and mixing of different voltages and currents.In order to facilitate inspection, the following aspects to explore the correct use of sensors.

1. Use environment

The sensor shall be used in an environment free of conductive dust, corrosive metals and gases that damage the insulation.Otherwise, the sensor will be burnt out due to the short circuit between the conductive dust and the object, or the power supply on the secondary side and the signal.

1.1 ambient temperature

The specification of the sensor will specify the normal operating ambient temperature range of the sensor, such as -40~85 degrees, depending on the product model.It is recommended not to exceed the temperature range specified in the specification, beyond the normal operating temperature range of the sensor, some internal devices will reduce the performance due to the temperature characteristics, resulting in reduced accuracy, inaccurate output signal, or failure to work, etc.

The sensor should be installed in a place with good ventilation and heat dissipation, so as not to affect the measuring accuracy and service life of the sensor.

At an altitude of 1.2

Generally, altitude is taken into consideration when designing the sensor, which is usually 2,000 meters.However, it is not only applicable to the altitude of less than 2000 meters. If the altitude is more than 2000 meters in actual use, it will mainly affect the heat dissipation and insulation performance of the sensor.Although the insulation can also be improved by external means, it is difficult to realize and will increase the cost. In actual selection and use, the reduction can be made by referring to the provisions of IEC 60664-1 standard. For details, please refer to section 5.1.4 of IEC 60664-1, and see table a.2 for the reduction factor.The problem of heat dissipation can be solved by means of forced air cooling.

1.3 installation location

Because the sensor is non-contact measurement, most of the detection is the magnetic field around the live conductor, so near the sensor, there should not be strong magnetic field, and easy to generate magnetic field devices.These include transformers, reactors, conductors that flow through large currents, and so on.Especially in three - phase test, adjacent sensors should not be installed too close.As far as space permits, the spacing should be as large as possible.

Sometimes the cabinet and its internal layout will be limited, it is difficult to leave enough space, in this case it is recommended to install sensor dislocation, especially HALL principle sensor, should make HALL device position principle magnetic field source as far as possible.

2. Sensor installation and fixation

The sensor can be fixed in two ways: PCB and disc mounting

2.1 PCB installation method

Generally, the primary measurement signal of the sensor installed on PCB is relatively small.

The output end of the sensor adopts the method of pin pin or SMD, which can be performed according to the welding process of general devices in welding. Since there is no glue inside some sensors, cleaning is avoided as far as possible.

2.2 disc mounting method

Generally, the primary measurement signal of the disk-mounted sensor is larger and the volume is larger.

In the sensor specification, the spacing and aperture of mounting holes are provided, and the screw size and tightening torque for each mounting hole are specified.The recommended torque is verified and evaluated by the design engineer. During installation, the recommended torque should be operated in strict accordance with the specification, otherwise it is easy to cause the rupture of the shell.In particular, the filler sensor can not be repaired once the shell is broken, which will bring economic losses and also bring trouble to the construction.

3. Installation direction

3.1 current sensor

There is an arrow on the shell of each current sensor. The direction of the arrow represents the direction of the measured current. When the primary side of the sensor is connected to the measured current, the direction of the measured current and the direction of the current should be consistent with the arrow shown on the sensor.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 primary positive and negative voltage pole, which respectively represent the positive and negative poles used to access the voltage signal under test.

Some sensors will also have a grounding output "E" or "", usually this terminal is connected to the shielding layer, to connect with the protective ground, to play a shielding and anti-interference role.

It is worth reminding that although the sensor can be used for ac and dc, the input direction of the primary side will also bring changes in the output of the secondary side, and the waveform of the primary and secondary sides will reverse.

4. Primary conductor

For the transmitter with a large measurement current, the primary side is generally a perforated structure. The corresponding cable or copper row should be selected according to the shape and size of the perforation, so as to ensure that the primary conductor can pass through the perforation smoothly and not damage the sensor perforation due to the large conductor section.

The conductor through the heart should be filled with holes as much as possible to ensure the measurement accuracy.When the cable and copper row pass through the sensor, both sides should have fixed support, try to center, avoid the copper row or cable skew, so as not to affect the measurement effect.

In the actual operation, it is necessary to pay attention to the temperature of the conductor, and it is best not to exceed the nominal allowable temperature, lest overheating affect the normal operation of the sensor or damage the sensor.

5. Sensor wiring

Generally, there is a wiring diagram in the specification of the sensor, indicating the serial number of the corresponding output points, including the positive power source Vc+, the negative power source Vc-, the output signal terminal M, and OV. The wiring must be in accordance with the definition of the serial number. Wrong connection or missed connection is not allowed, otherwise the sensor will be damaged.

5.1 the pin pin type

When the secondary side of the sensor adopts pcb-welded pin pin, the plate shall be arranged according to the serial number of pin pin 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 will provide the model and specification of the connector, as well as the corresponding functions of each connector.It is recommended to use special tools to press the terminals and wires to avoid short circuit or poor contact.

6. Working power supply of sensor

Generally speaking, the sensor needs external power supply. The power supply is dc voltage source, which can be divided into several specifications, such as +5V, +/ -12v, +/ -15v or +/ -24v.

Generally, the specification of the sensor will give the power voltage level Vc. If Vc value is +/-, the sensor needs to have dual power supply.

In addition, in the choice of power supply, to choose stable voltage, ripple small power supply.Also pay attention to the power supply.

The sensor loss value Ic is usually provided in the sensor specification.This Ic value represents the power consumption of the sensor. When selecting the power supply, at least ensure that the output current of the power supply is greater than Ic to ensure the normal operation of the sensor.

7. Energize the sensor

A sensor is an active device for measuring current and voltage signals. It can only work if it is powered by an external dc power supply.

1).After the connection of the secondary side of the sensor is correct, connect the dc power supply of the sensor first.

If the sensor is powered by a dual power supply, the power supply is dc +/ -12v, +/ -15v or +/ -24v.

If the sensor is powered by a single power supply, the power supply is dc +5V.

The dc power supply of the sensor shall be stable, fluctuating up and down within the range of +/-5%.Too low or too high will affect the normal operation of the sensor, the voltage is too high, and may damage the sensor.

When the dc working power supply of the sensor is connected, the sensor is in standby working state. At this point, the secondary output terminal will have a small signal output, which is normal as long as it is within the scope allowed by the specification.

2).After the power supply of the sensor is connected, the measured signal is passed into the original side.

When the measured signal is input, there will be corresponding signal output at the output end of the sensor, which will be resistant to change with the change of the measured signal on the original side.

If the electrical sequence of the original side is reversed, the sensor may be damaged, which we hope to pay attention to in practice!

8. Selection of load resistance

Load resistance refers to the resistance connected to the output of the sensor. Normally, the output current signal will limit the maximum value of the load resistance, while 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 the sampling process. In this case, the measurement resistance needs to be matched between the output of the sensor and OV.The selection of measuring resistance is limited by the power supply voltage of the sensor and the size of the measured signal.

Under the same power supply voltage, the measured resistance value will affect the range of the primary signal measured by the sensor. The smaller the resistance value is, the larger the measured signal will be. The larger the measured range will be, the smaller the measured signal will be, and the smaller the maximum measurement range will be.However, it is important to note that the measured resistance value of some sensors cannot be reduced indefinitely, otherwise the sensor will be damaged.

Usually in the specification, the manufacturer will indicate the range of resistance to be measured, including the minimum and maximum.As long as the value of this resistance is within the range specified in the specification, the sensor can work normally and meet the parameters 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 access of the load resistance does not affect the attenuation of the output voltage value of the sensor, there is a minimum limit on the load resistance value.

In the specification the manufacturer will indicate the size of the load resistance, usually in the thousands of ohms.Therefore, when the output of the sensor is connected to the back-end circuit, the equivalent resistance value should be greater than the allowable load resistance.Otherwise, the output value of the sensor will decrease.

9. Potentiometer

Under the new technology applications, the sensor USES the laser trimming resistor, adjustable resistance to calibration and calibration software, but there are still some sensors on the market with the method of potentiometer, usually these exposed potentiometer manufacturers in the factory are of sensor calibration and used to adjust the zero and accuracy sensors, adjust good with red rubber after fixed to prevent touch change resistance potentiometer by mistake.Then the exposed potentiometer, do not adjust at will, otherwise it will affect the sensor measurement accuracy.

Tag: sensor
 

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