Relay accelerating pull-in circuit a

An additional resistor Rf is connected in series to the relay
circuit. When Rf is equal to the resistance R of the relay KA coil, the time constant can be reduced by half, and the pull-in time can also be reduced accordingly. Figure 6-27 (b)
Connect another capacitor in parallel with Rf . When the power supply is first applied, the capacitor C is equivalent to a short circuit, and all the power supply voltage is applied to both ends of the dry coil, thus
shortening the pull-in time. After the current stabilizes, the capacitor C no longer plays a role, and the stable current remains at its original value. This
method can also be called forced excitation.