Proportional solenoids

How proportional solenoids work

Proportional solenoids are electromagnetic components for the continiuous control of forces and movements. Their mode of operation is based on the proportional relationship between the applied current and the magnetic force. Compared to switching solenoids, which only switch on/off, proportional solenoids enable fine and linear regulation or control, in which the force or stroke is varied depending on the current supply.

• Power supply: When an electric current is passed through the solenoid coil, a magnetic field is created. This magnetic field generates an attractive force on a moving armature inside the solenoid.
• Proportionality: The decisive aspect of proportional solenoids is that the strength of the magnetic field, and therefore the attractive force on the armature, is directly proportional to the applied current. This means that the more current flows through the coil, the stronger the force generated and the further the armature moves.
• Movement and force control: This proportionality means that the armature of the solenoid can not only switch between two positions (as with a switching solenoid), but can also move continuously. This enables precise control of movements or forces, which is useful in applications such as valve controls or damping systems.
• Restoring force: A restoring force often acts on the armature, for example through a spring. This force is also balanced with the magnetic force so that the armature can be brought into an exact position that corresponds to the applied current.
• Continuous control: By adjusting the current, the solenoid can react in real time and dynamically generate different forces or movements. This continuous control is particularly advantageous in systems that require high precision.

Designs and types of proportional solenoids

• Square proportional solenoids: These solenoids have a rectangular cross-section. Due to their compact design, they are well suited for applications where the available space is limited. They can be easily integrated into the respective customer application and often offer high precision in proportional control.
• Round proportional solenoids: These solenoids have a cylindrical cross-section and are usually more cost-efficient, as they can be manufactured with moulded housing components. The round design ensures a uniform distribution of the magnetic field, which can have a positive effect on the function of the reversing solenoid.

Performance parameters Proportional solenoids

• Rated current: The current at which the proportional solenoid delivers its specified power. Typical range: From a few milliamperes (for small applications) to several amperes (for industrial applications).
• Nominal voltage: The operating voltage at which the proportional solenoid works. It can vary depending on the type of solenoid and application. Typical ranges: 12V, 24V or 48V for industrial applications.

• Stroke : The linear displacement of the magnetic armature, which is directly dependent on the input signal. The stroke is an important measure for motion control. Typical range: From a few millimetres to several centimetres, depending on the application.
• Force-displacement characteristic: The relationship between the applied electrical power (current or voltage) and the resulting mechanical force over the entire stroke. Proportional solenoids are characterised by a uniform, linear or non-linear force development. This characteristic curve describes the accuracy and efficiency of the movement.
• Holding time/holding force: The force that the solenoid can maintain in the active state over a longer period of time without the power decreasing. This is particularly important for applications in which a position must be held stable over a longer period of time. This holding force is influenced by the magnetic field strength and the coil structure.
• Duty cycle: The maximum period during which the proportional solenoid can be operated under load without overheating or overloading. This is specified as a percentage value (ED %). Typical range: 100% ED for continuous duty solenoids, lower values for intermittent applications.
• Magnetic force: The maximum force that the solenoid can generate at maximum electrical power consumption. This is an important parameter for applications where high forces are required. Typical range: From a few newtons to several kilonewtons, depending on the size and design.
• Inductance: The inductance of the solenoid coil influences the dynamics and speed of the control. Higher inductivities lead to slower response times. Typical range: Millihenry to Henry, depending on the design.

Proportional solenoid design

• Housing: The housing protects the internal components and is often made of ferromagnetic material to optimise magnetic field conduction. Depending on the application, additional housings made of steel, aluminium or plastic can be fitted. For precise control, the housing is often also designed for thermal properties.
• Coil: The coil consists of conductive wire, usually copper, which is often wound on a bobbin. The coil arrangement enables a magnetic field that increases in proportion to the current for precise force or movement control. The number of windings and the geometry of the coil influence the force development.
• Armature: The armature moves in proportion to the current supply and strives to minimise the working air gap. In contrast to switching solenoids, the movement of the armature is uniform, which requires a precise design for exact force development.
• Iron core: Made of soft iron, the core concentrates the usable magnetic field strength. The design of the iron core is decisive for the uniform movement of the armature and the proportional control characteristics. Working air gap: The working air gap is decisive for the stroke and force and therefore also has an influence on the control accuracy and uniform control of the armature.

Proportional solenoid applications

• Hydraulics and pneumatics: Proportional solenoids control valves to regulate the flow of liquids or gases. They enable precise pressure and flow control in hydraulic and pneumatic systems.
• Automotive industry: In automatic transmissions, proportional solenoids control the transmission oil flows for smooth gear changes. They also regulate the fuel quantity in injection systems and optimise consumption and emissions.
• Medical technology: In medical devices such as ventilators and infusion pumps, proportional solenoids precisely dose liquids and gases and ensure safety and efficiency.
• Industrial automation: Proportional solenoids control robots and actuators in manufacturing processes for precise movements. They are used in gripper systems and conveyor systems where stepless movements are required.
• Shipbuilding and aviation: Proportional solenoids control hydraulic systems that move rudder flaps, landing flaps and landing gear. Precision is crucial for safety here.
• Agricultural and construction machinery: In construction machinery and cranes, proportional solenoids control hydraulic systems for attachments and booms to move heavy loads with precision.
• Renewable energies: Proportional solenoids control mechanical and hydraulic systems in wind turbines and solar plants, for example to adjust rotor blades or solar panels.

Control and regulation Proportional solenoid

• Control: Proportional solenoids are controlled by special electronic control units that allow the current to be regulated continuously. Here, pulse width modulation (PWM) or analogue signal control is often used to generate the magnetic field in proportion to the current supply and thus generate precise movements.
• Sensor integration: In many applications, proportional solenoids are equipped with sensors that monitor the exact position of the armature. This feedback allows precise control of the movement and ensures accurate control of the system.

Environmental requirements Proportional solenoid

• Temperature range: Proportional solenoids are designed for use in a wide temperature range, often from -40°C to +150°C or more, to ensure precise and reliable operation even under extreme conditions.
• Protection classes: Depending on the application environment, proportional solenoids are equipped with different protection classes (e.g. IP protection classes) to protect them from dust, moisture and other environmental influences and to ensure long-term functionality.