DC solenoid with an almost horizontal force-stroke characteristic curve in the operating range and which can be controlled in proportion to voltage or current (Figure P 19). The latter is preferred in most cases because of the significantly shorter switching time.
Proportional solenoids may be controlled in respect of force, distance or position. As far as force control is concerned, the magnetic force is directly proportional to the current for a stroke of close to zero (used with pressure valves).
As far as distance control is concerned, the magnetic force acts against a spring with a working stroke of 2 to 3 mm. In order to reduce the relatively large hysteresis (3—6%), there is an option to create a dither signal. The solenoid can also be used, however, in a closed circuit position control system , which may significantly improve the response sensitivity and reversal error too (Figure P 20). Other aspects are the greater stiffness compared with other types of influences and a high level of repetition accuracy, repeatability.
![32d36273921a3560aa6d79af8d6808809c3e7ed4 0001_proportionalmagnet.gif](/fileadmin/smc/files/32d36273921a3560aa6d79af8d6808809c3e7ed4.gif)
Figure P 19: Schematic representation of a characteristic curve for a proportional solenoid and DC solenoid
![2521112d6868075c8a164f9972fb2fe303db025f 0002_proportionalmagnet.gif](/fileadmin/smc/files/2521112d6868075c8a164f9972fb2fe303db025f.gif)
Figure P 20: Proportional solenoid with an internal closed circuit position control system