DC relay delayed release circuit one c

In order to meet the needs of the control loop, electromagnetic relays or transistor relays are often required to accelerate or delay action, thereby
forming an acceleration or delay action circuit.
  The circuit is shown in Figure 6-23. These types of circuits all use capacitors to charge and discharge the relay coil to delay the release time
. Figure 6-23 (a) ~ (c) are instant pull-in and delayed release circuits; Figure 6-23 (d) is a delayed pull-in and delayed release circuit .
    The maximum delay time of the relay can be estimated as follows:
    t=0. 85R. CX10-6 (s)
where R: - total resistance of the loop , R: = R+RL, 0;
    R-resistance, 0;
    L-relay coil resistance , n;
    C-capacitance, pF.