When a DC solenoid valve is switched on, the current and voltage characteristics are key parameters for assessing the behavior of the solenoid coil. In many applications, the coil is viewed in simplified terms as an idealized L-R series circuit - a combination of a fixed inductance (L) and an ohmic resistance (R) that describes the copper losses of the coil wire.
But what does it look like in reality? Let's take a detailed look at the actual switching process.
1. The idealized view: The L-R series circuit
In a simple model (L-R circuit), the current flow when switching on is as follows:
- The current increases exponentially until it is limited by the series resistance.
- This curve is reproducible and predictable - but only under the assumption that the inductance remains constant.
In practice, however, this is not the case, as a decisive factor changes dynamically: the magnetic core.
2. The real dynamics of the solenoid coil
The solenoid coil of a valve contains a movable magnetic core that undergoes a defined movement during the switch-on process. This movement significantly influences the inductance of the coil and leads to a more complex current flow.
The real sequence can be divided into five steps:
Step 0 - Standby
- The solenoid valve is switched off.
- No current flows through the coil.
Step 1 - Switching on
- The solenoid coil is supplied with voltage.
- The current begins to increase analogous to the idealized model.
Step 2 - Start of movement
- At a certain point, the magnetic core begins to move.
- This movement changes the magnetic properties of the system: the inductance increases.
- The induced counter EMF (electromagnetic force) causes the current to drop briefly despite the constant voltage.
Step 3 - End position reached
- The magnetic core has reached its end position.
- The movement ends, the inductance remains constant.
- The current starts to rise again - this time in a similar way to the idealized process.
Step 4 - Maximum current
- The current reaches its maximum.
- This value is limited by the ohmic resistance of the coil.
Conclusion
The switching process of a DC solenoid valve is more complex than a simple L-R model would suggest. The movement of the solenoid core has a significant effect on the current flow:
- Dynamic inductance due to movement of the core
- Temporary current drop due to counter EMF
- Current increase after the end of movement until the stable final value is reached
A deeper understanding of these processes is essential for the precise design and optimization of solenoid valve systems - especially for special solutions and demanding applications.
