1.3 Defining Relay Performance

There is a sequence of events in relay pick up (operate) and dropout(release) with respect to current rise and decay. The events are defined in terms of duration of coil current, armature motion, and contact actuation.

Fig. 1.1 Time traces typical of relay pickup.


Fig. 1.2 Time traces typical of relay dropout.


Figures 1.1 and 1.2 show contact performance-as a series of oscillograms-for relay with a normally open contact, a normally closed contact, and a transfer (break-make) contact.

Table 1.3
Preferred Not Preferred Preferred Not Preferred
Hold, measured Nondropout, measured;
Nonrelease, measured
Pickup, specified Operate, specified
Pull-in (or Pull-on)
value, measured
Operate value,
must Maximum pickup
Hold, specified Maximum dropout;
Nondropout, specified;
Nonrelease, specified
Operate Time Pickup (or pull-in)
time
Nonpickup, measured Nonoperate, measured Dropout, measured Release, measured
Nonpickup, specified Minimum pickup Dropout, specified Release, specified
Minimum Dropout
Pickup, measured Operate, measured
Pull-in (or Pull-on)
value, measured Operate
value
Release time
Transfer time
Dropout (or drop
away) time

In Table 1.3 preferred and non-preferred terms relating to relay performance are summarized.
These terms are fully defined in alphabetical sequence in Paragraph 1.7

Fig. 1.4 Relationship of relay performance to definitions.

Figure 1.4 is a graphical presentation of relay performance related definition.

Fig. 1.5 Two typical relay forms with basic parts idenitied.

Figure 1.5 depicts basic relay parts.


Pick Up (Figure 1.1) Upon coil energization, current begins to rise at a decreasing rate, but no armature movement occurs until the power develops sufficiently to operate the contact spring load. This period is sometimes referred to as waiting time. Contact actuation occurs during the armature movement. The final actuation time exceeds the initial actuation time by the amount of the contact bounce. For normally closed contacts, operate time and initial operate time are identical. On break-make contacts, the time interval between initial opening of the normally closed contact and closure of the normally open contact is called transfer time.
Dropout (Figure 1.2) On de-energization of the coil, the magnetic flux does not die out immediately. The length of time it persists depends upon the release characteristics of the coil (fast-to-release, slow-to-release, and the like). The sequence of events described under pickup is essentially reversed under dropout. It will be seen that a normally open contact may be momentarily reclosed as a result of armature rebound off the backstop. This effect, which is not always present, depends on many factors, such as contact spacing, contact spring load, backstop design, and the like.