Analysis and Interpretation of Interference Sources of Anemometer
There are many sources of interference for anemometers. Usually what we call interference is electrical interference, but in a broad sense thermal noise, temperature effects, chemical effects, vibrations, etc. may affect the measurement and cause interference. During the measurement process, if the influence of these interferences cannot be eliminated, the instrument will not work properly. According to the mode of interference at the input end of the instrument, it can be divided into series mode interference and common mode interference. Series mode interference refers to the interference superimposed on the signal being measured; common mode interference is the interference added between any input terminal of the instrument and the ground.
Analysis of main interference sources:
(1) Electrostatic induction
Electrostatic induction is due to the existence of parasitic capacitance between two branch circuits or components, which causes the charge on one branch to be transferred to the other branch through the parasitic capacitance, so it is also called capacitive coupling.
(2) Electromagnetic induction
When there is mutual inductance between two circuits, changes in current in one circuit are coupled to the other circuit through a magnetic field. This phenomenon is called electromagnetic induction. For example, magnetic leakage of transformers and coils, energized parallel wires, etc.
(3) Leakage current induction
Due to poor insulation of component brackets, terminal posts, printed circuit boards, capacitor internal media or casings inside electronic circuits, especially when sensors are used in high humidity environments, the insulation resistance of the insulator decreases, resulting in an increase in leakage current, which will cause interference. Especially when leakage current flows into the input stage of the measurement circuit, its impact is particularly serious.
2) Additional thermoelectric potential and chemical potential.
It is mainly due to the thermal electric potential generated by different metals and the chemical electric potential generated by metal corrosion. When it is in an electrical circuit, it will become interference. This interference mostly appears in the form of DC. Thermoelectric potential is easily generated at terminal blocks or reed relays.
3) Vibration.
When a wire moves in a magnetic field, it generates an induced electromotive force. Therefore, it is necessary to secure the signal wires in a vibrating environment. The above four types of interference are all connected in series with the signal, that is, they appear in the form of series-mode interference.
4) Interference caused by different ground potentials.
In the earth, there are often potential differences between different points. Especially near high-power electrical equipment, when the insulation performance of these equipment is poor, this potential difference is even greater. In the use of instruments, there are often more than two ground points in the input loop intentionally or unintentionally. This will introduce the potential difference of different grounding points into the instrument. This ground potential difference can sometimes reach more than 1 to 10 volts. It appears on the two signal wires at the same time. Through electrostatic coupling, a common voltage to ground can be induced at the two input terminals, which appears in the form of common mode interference. Since common mode interference does not superimpose with the signal, it does not directly affect the instrument. However, it can form a leakage current to the ground through the measurement system. This leakage current can directly act on the instrument through the coupling of the resistor, causing interference.
5) Radio frequency interference
6) Others
In addition to some pulse voltages that can act on analog circuits, they can also cause interference to digital circuits. The sources of these pulse voltages are inductive loads such as switches, motors, relays, and machines that generate discharges.
