Category
Solenoid Valve Supplier
inquiry@ato.com.cn
Home » Application » Anti-interference of AC & DC Solenoid Valve
Anti-interference of AC & DC Solenoid Valve
In the thermal control debugging process, it is common to find that the microcomputer board card channel or even the whole board card is damaged because of interference of the solenoid valve or relay. With popularization of the microcomputer control system, the thermal control programs of different mechanical units have widely used the computer control. The solenoid valve and relay are indispensable control circuit apparatuses among the control equipment. Therefore, to restrict inference of the solenoid valve or relay is of vital importance to the microcomputer control system.
In the full set of the control system. the output device of the programmable logic controller (PLC) or the computer distributed control system (DCS) is usually adopted to control the solenoid valve or relay. Because of different causes, the anti-interference of the output devices (plate boards) is usually different. Before powering on for debugging, it is necessary to evaluate these circuits. The anti-inference measures should be adopted to avoid damage of the plate board channels or the whole plate board.
The solenoid valve can be divided into the DC solenoid valve and the AC solenoid valve according to the driving power. The solenoid valve is a typical inductive load. After the solenoid valve coil is switched on, the iron core might not yet be closed and its inductance might be very small. Under the condition, the starting current impulse of the AC solenoid valve will also be strong, which is around six folds to ten folds of the current at the steady state. Though the absolute value of the current is not large to cause any interference, it is necessary to fully evaluate whether the plate board volume can bear the current impact.
When the solenoid valve is powered off, there will be high surge voltage on two ends of the coil and the connecting lead, accompanied by damped high-frequency oscillation. This is a very strong transient interference. If no control measures are adopted, not only will the switch parts or contacts be affected, but also the electronic devices’ operation might be influenced or even the electronic elements might be damaged.
Anti-interference of AC solenoid valve
Most often, the AC 220V or AC 110V power-driven AC solenoid valve is adopted. Apart from restricting the transient inference caused by switch-off of the coil, it is also necessary to restrict the interference caused by the low-pressure power. Below are two commonly-seen control modes.
1. Relay control
As shown in Fig. 1, when relay control is adopted, pulse interference caused by bouncing of contacts upon touch will appear, apart from interference caused by the electric arc and discharge upon disconnection.
Generally, RC absorption circuit should be adopted to not only restrict the disturbance of switch-on and switch-off, but also protect the contacts of the relay. Meanwhile, RC absorption circuit can be connected with contacts to better protect them. Nevertheless, when the connecting line is too long, it cannot effectively restrict interference.
In Fig. 1, though the relay plays the role of buffering, its coil can easily cause the interfering inductance coil. Therefore, the optoelectronic isolation should be adopted between the output plate board and the relay. When certain output channel of the controller outputs, current passes the light-emitting diode in the photoelectric coupler of the channel to give out light. The light ensures saturated connection of the photosensitive transistor in the photoelectric coupler. Then, the contacts of the relay coil close. Because of no electric connection between the light-emitting diode and the photosensitive transistor, electric isolation can be realized.
2. Bidirectional thyristor control
The control mode adopts the solid-state relay or AC non-contact relay to control the solenoid valve. Considering switch-on and switch-off characteristics of the bidirectional thyristor, this control mode is only applicable to the AC solenoid valve control. See Fig. 2.
The bidirectional thyristor can be directly connected to the AC load circuit. However, in order to prevent inference caused by switch-off of the load, induction inference of the output line and common-mode interference of power from intruding the inside of the controller, the photoelectricity can be used to separate the components and the inside of the controller. At the same time, the RC absorption circuits should be connected in parallel on the bidirectional thyristor to alleviate voltage changes on the bidirectional thyristor when switch-off.
The solenoid valve features inductive load. The load current is behind the power voltage. When the driving voltage is in a reverse phase, the load circuit starts to reduce and becomes zero after a period of time. At the moment, the bidirectional thyristor starts to switch off. However, the voltage suddenly exerted on the interdict bidirectional thyristor has already been large. The voltage increasing rate is large, which might lead to connection of the bidirectional thyristor to generate wrong actions or even damage. Therefore, RC absorption circuit must be adopted.
The value of R and C is decided by parameters of the circuit and solenoid valve coil. However, under general conditions, R is 100Ω; C is 0.1μF. When C is too large or R is too small, the restrictive effects will be strengthened, but the leakage current upon switch-off of the bidirectional thyristor can be enhanced. As a result, the solenoid valve might be in a dangerous situation where its absorption cannot be effectively released.
Anti-interference of DC solenoid valve
The method shown in Fig. 1 is applicable to the DC solenoid valve, and the transistor control method shown in Fig. 3 is also frequently-used.
The photoelectric coupler receives the output signals from the circuit within the controller and the light-emitting diode is lighted on. The saturated connection of the photoelectric thyristor on the output terminal of the coupler can provide the base current for the driving transistor, and the solenoid valve closes.
Since the switch-off of thyristor is short and the inductive voltage when the coil is switched off is high, the RC circuits, diodes and voltage-regulating tubes can be connected in parallel on the coil.
In the full set of the control system. the output device of the programmable logic controller (PLC) or the computer distributed control system (DCS) is usually adopted to control the solenoid valve or relay. Because of different causes, the anti-interference of the output devices (plate boards) is usually different. Before powering on for debugging, it is necessary to evaluate these circuits. The anti-inference measures should be adopted to avoid damage of the plate board channels or the whole plate board.
The solenoid valve can be divided into the DC solenoid valve and the AC solenoid valve according to the driving power. The solenoid valve is a typical inductive load. After the solenoid valve coil is switched on, the iron core might not yet be closed and its inductance might be very small. Under the condition, the starting current impulse of the AC solenoid valve will also be strong, which is around six folds to ten folds of the current at the steady state. Though the absolute value of the current is not large to cause any interference, it is necessary to fully evaluate whether the plate board volume can bear the current impact.
When the solenoid valve is powered off, there will be high surge voltage on two ends of the coil and the connecting lead, accompanied by damped high-frequency oscillation. This is a very strong transient interference. If no control measures are adopted, not only will the switch parts or contacts be affected, but also the electronic devices’ operation might be influenced or even the electronic elements might be damaged.
Anti-interference of AC solenoid valve
Most often, the AC 220V or AC 110V power-driven AC solenoid valve is adopted. Apart from restricting the transient inference caused by switch-off of the coil, it is also necessary to restrict the interference caused by the low-pressure power. Below are two commonly-seen control modes.
1. Relay control
As shown in Fig. 1, when relay control is adopted, pulse interference caused by bouncing of contacts upon touch will appear, apart from interference caused by the electric arc and discharge upon disconnection.
Generally, RC absorption circuit should be adopted to not only restrict the disturbance of switch-on and switch-off, but also protect the contacts of the relay. Meanwhile, RC absorption circuit can be connected with contacts to better protect them. Nevertheless, when the connecting line is too long, it cannot effectively restrict interference.
In Fig. 1, though the relay plays the role of buffering, its coil can easily cause the interfering inductance coil. Therefore, the optoelectronic isolation should be adopted between the output plate board and the relay. When certain output channel of the controller outputs, current passes the light-emitting diode in the photoelectric coupler of the channel to give out light. The light ensures saturated connection of the photosensitive transistor in the photoelectric coupler. Then, the contacts of the relay coil close. Because of no electric connection between the light-emitting diode and the photosensitive transistor, electric isolation can be realized.
2. Bidirectional thyristor control
The control mode adopts the solid-state relay or AC non-contact relay to control the solenoid valve. Considering switch-on and switch-off characteristics of the bidirectional thyristor, this control mode is only applicable to the AC solenoid valve control. See Fig. 2.
The bidirectional thyristor can be directly connected to the AC load circuit. However, in order to prevent inference caused by switch-off of the load, induction inference of the output line and common-mode interference of power from intruding the inside of the controller, the photoelectricity can be used to separate the components and the inside of the controller. At the same time, the RC absorption circuits should be connected in parallel on the bidirectional thyristor to alleviate voltage changes on the bidirectional thyristor when switch-off.
The solenoid valve features inductive load. The load current is behind the power voltage. When the driving voltage is in a reverse phase, the load circuit starts to reduce and becomes zero after a period of time. At the moment, the bidirectional thyristor starts to switch off. However, the voltage suddenly exerted on the interdict bidirectional thyristor has already been large. The voltage increasing rate is large, which might lead to connection of the bidirectional thyristor to generate wrong actions or even damage. Therefore, RC absorption circuit must be adopted.
The value of R and C is decided by parameters of the circuit and solenoid valve coil. However, under general conditions, R is 100Ω; C is 0.1μF. When C is too large or R is too small, the restrictive effects will be strengthened, but the leakage current upon switch-off of the bidirectional thyristor can be enhanced. As a result, the solenoid valve might be in a dangerous situation where its absorption cannot be effectively released.
Anti-interference of DC solenoid valve
The method shown in Fig. 1 is applicable to the DC solenoid valve, and the transistor control method shown in Fig. 3 is also frequently-used.
The photoelectric coupler receives the output signals from the circuit within the controller and the light-emitting diode is lighted on. The saturated connection of the photoelectric thyristor on the output terminal of the coupler can provide the base current for the driving transistor, and the solenoid valve closes.
Since the switch-off of thyristor is short and the inductive voltage when the coil is switched off is high, the RC circuits, diodes and voltage-regulating tubes can be connected in parallel on the coil.
Post a Comment:
You may also like:
