There is a common view that a solenoid is either on or off, open or closed. One position or the other. Indeed in many applications this is the case with power supplies being either open or closed and the solenoid being either open or closed. However, there is a whole world of possibilities introduced when one considers the idea that a solenoid is not a digital, but analogue.
We use digital here as a shorthand expression. What we man in practice is that it not a 0 or a 1 – open or closed – but an analogue wave, with various options available between the two main positions.
If the coil has a spring then it is perfectly possible to use standard 2 quadrant control to very good effect. This will react against the spring and can therefore be used to create an analogue ‘range’ of options from fully open to partially closed to able to hold in a certain position.
If the plunger is free then it is possible to use four quadrant control to create exceptionally accurate control over the way in which the plunger is positioned.
This can be held against light resistance or can be locked if higher pressure is occurring within the system (for example). This can provide huge amounts of control in applications such as flow control applications or related process control projects. Current control can be used to directly tier the solenoid holding power and use the most efficient amount of current for the particular application.
The final option that can be used involves using a solenoid in the same way as normal with the exception that it is controlled in a way that enables switching them on/off quickly. It is quite likely that this will use much less overall power to achieve the same effect, but the flow through the solenoid will have pulsations (high and low pressure) that can damage mechanical components after time.