Solenoid Fundamentals: Operating Speed

The time taken for a Solenoid to complete its energised stroke is measured from the moment a voltage is applied to the time the energised position is achieved. This time is dependent upon the load, duty cycle, input power, stroke and temperature range. When a DC voltage is applied the current will rise to point (a) as illustrated below. This time delay occurs prior to any plunger motion, until sufficient flux is developed to overcome the load. As the plunger moves through its stroke the change in inductance resulting from the closing air gap causes a dip in the current trace until the Solenoid has completed its stroke. From here the current trace begins to rise to a steady state current value which by Ohms law is I = V / R

At point (a) the Solenoid has developed sufficient flux to move the load, as the load increases, more time is required to reach point (c), as shown by the phantom trace. If the load increased beyond the performance value of the Solenoid the coil will build immediately to a steady state current, no dip will occur as no plunger movement has taken place (top curve).