I would like to ask everyone, how do we filter out the interference caused by very low frequency electromagnetic radiation?

晓行夜宿

I would like to ask everyone, how do we filter out the interference caused by very low frequency electromagnetic radiation? [Copy link]

 

The sensor of the test system is subject to electromagnetic interference from the object being tested - an electric motor with a rotation speed between 1 and 30 Hz. The output of the sensor is an alternating voltage. What additional components can solve the problem?

qwqwqw2088

1 to 30 Hz electric motor?

What is the critical power?

Analyze where the interference source is and do isolation and grounding first

Reanalysis and measures

maychang

"An electric motor with a speed between 1 and 30 Hz"

Frequency conversion motor with reducer? How much power does this motor have? What power supply is used?

maychang

"How to filter out interference caused by very low frequency electromagnetic radiation?"

I'm afraid it's not interference in the form of electromagnetic radiation, but interference transmitted through the power supply.

The OP needs to make the question more clear: what type of sensor is your sensor and what are the consequences of interference.

bigbat

Use an isolated power supply to separate the power supply of your sensor and acquisition circuit from the inverter circuit. Please make sure that the inverter circuit is truly grounded! If conditions permit, use a reactor and an isolation transformer to isolate the inverter from the power grid.

晓行夜宿

The motor does have an impact on the power strip, which I also discovered. I connected an oscilloscope to the same power strip, and the square wave signal measured by the oscilloscope was affected. So I connected the tester to another power supply, and tested this power supply with an oscilloscope, and there was no problem. I connected the tester to the new power supply, and there was interference when I put the sensor close to the motor, but I could test it normally when I moved it away. The sensor is a piezoelectric accelerometer. The rated speed of the motor is 1500 rpm. The interference is generally similar to amplitude modulation in the shape of a square wave. I really don't know the power of the motor, I only know that it is as big as a household trash can.

gmchen

If the experiment on the 6th floor is confirmed, then power interference can be ruled out. At this time, we need to find the source of interference. At such a low frequency, the electromagnetic field can be basically ruled out, and there is only the electric field or magnetic field. Another possibility is mechanical vibration. Try to connect the sensor with shielded wire and twisted pair wire to determine whether there is electric field or magnetic field interference.

qwqwqw2088

Xiaoxing Yesu published on 2020-1-4 19:11 The motor does have an impact on the power strip. I also found this. I connected an oscilloscope to the same power strip. The square wave signal measured by the oscilloscope was affected...

This means that if the sensor and the motor use the same power supply, there will be interference, but if they do not share the same motor, there will be no interference.

Refer to the suggestions on the 5th floor and take some measures

晓行夜宿

qwqwqw2088 posted on 2020-1-5 09:23 This means that if the sensor and the motor use the same power supply, there will be interference. If they do not share the same motor, there will be no interference. Refer to the suggestions on the 5th floor, ...

The power supply has been isolated. However, there is interference when the sensor is close to the motor, but no interference when it is not close.

晓行夜宿

bigbat posted on 2020-1-4 18:56 Use an isolated power supply to separate the power supply of your sensor and acquisition circuit from the inverter circuit. Please make sure that the inverter circuit is truly grounded! If...

The power supply has been isolated. However, when using an isolated power supply, there will be interference when the sensor is close to the motor, but there will be no interference when it is moved away.

晓行夜宿

maychang posted on 2020-1-4 18:07 "How to filter out the interference caused by very low frequency electromagnetic radiation?" I'm afraid it's not interference in the form of electromagnetic radiation, but transmitted through the power supply...

The power supply has been isolated. However, when using an isolated power supply, there is interference when the sensor is close to the motor, and there is no interference when it is moved away. The sensor is a piezoelectric accelerometer, and the interference is amplitude modulation similar to a square wave.

晓行夜宿

maychang posted on 2020-1-4 18:05 "An electric motor with a speed between 1 and 30 Hz" Variable frequency motor with reducer? How much power does this motor have? What power supply is used? ...

An isolated power supply has been used. It is indeed a frequency converter with a reducer. The rated speed of the motor is 1500 rpm. I really don't know how much power it has.

晓行夜宿

qwqwqw2088 posted on 2020-1-4 17:18 1 to 30 Hz motor? What is the critical power? Analyze where the interference source is. First isolate and ground it, then analyze and take measures

The power supply has been isolated. However, when using an isolated power supply, there will be interference when the sensor is close to the motor, but there will be no interference when it is moved away.

bigbat

Xiaoxing Yesu published on 2020-1-5 10:11 The power supply has been isolated. However, when using an isolated power supply, there will be interference when the sensor is close to the motor, and there will be no interference when it is moved away.

If conditions permit, install the sensor in an iron shell or use a metal cover. I don't know what kind of sensor it is, if it is a rotary encoder, replace it with a photoelectric one.

maychang

Xiaoxing Yesu published on 2020-1-5 10:09 The power supply has been isolated. However, when using an isolated power supply, there will be interference when the sensor is close to the motor, and there will be no interference when it is moved away. The sensor...

The inverter may generate relatively strong electromagnetic radiation interference.

"When the sensor is close to the motor, there is interference, but when it is moved away, there is no interference." Then you should try adding ferromagnetic shielding to the sensor as mentioned on the 13th post. Note that the iron shell must be well grounded. The motor shell must also be well grounded.

jack4103

During the electromagnetic compatibility test, I have seen the gaps in the motor being wrapped with copper foil.

threetigher

gmchen posted on 2020-1-5 07:59 If the experiment on the 6th floor is confirmed, then the power supply interference can be ruled out. At this time, we need to find the source of interference. At such a low frequency, the electromagnetic field can be basically ruled out, only...

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