Time-delay relays are very important for use in industrial control logic circuits.
Some relays are constructed with a kind of "shock absorber" mechanism attached to the armature
which prevents immediate, full motion when the coil is either energized or de-energized. This addition
gives the relay the property of time-delay actuation. Time-delay relays can be constructed to delay
armature motion on coil energization, de-energization, or both.
Time-delay relay contacts must be specified not only as either normally-open or normally-closed,
but whether the delay operates in the direction of closing or in the direction of opening. The
following is a description of the four basic types of time-delay relay contacts.
First we have the normally-open, timed-closed (NOTC) contact. This type of contact is normally
open when the coil is unpowered (de-energized). The contact is closed by the application of power
to the relay coil, but only after the coil has been continuously powered for the speci¯ed amount of
time. In other words, the direction of the contact's motion (either to close or to open) is identical
to a regular NO contact, but there is a delay in closing direction. Because the delay occurs in
the direction of coil energization, this type of contact is alternatively known as a normally-open,
on-delay.
Next we have the normally-open, timed-open (NOTO) contact. Like the NOTC contact, this
type of contact is normally open when the coil is unpowered (de-energized), and closed by the
application of power to the relay coil. However, unlike the NOTC contact, the timing action occurs
upon de-energization of the coil rather than upon energization. Because the delay occurs in the
direction of coil de-energization, this type of contact is alternatively known as a normally-open,
off -delay.
Next we have the normally-closed, timed-open (NCTO) contact. This type of contact is normally
closed when the coil is unpowered (de-energized). The contact is opened with the application of power
to the relay coil, but only after the coil has been continuously powered for the specified amount of
time. In other words, the direction of the contact's motion (either to close or to open) is identical
to a regular NC contact, but there is a delay in the opening direction. Because the delay occurs in
the direction of coil energization, this type of contact is alternatively known as a normally-closed,
on-delay.
Finally we have the normally-closed, timed-closed (NCTC) contact. Like the NCTO contact,
this type of contact is normally closed when the coil is unpowered (de-energized), and opened by
the application of power to the relay coil. However, unlike the NCTO contact, the timing action
occurs upon de-energization of the coil rather than upon energization. Because the delay occurs in
the direction of coil de-energization, this type of contact is alternatively known as a normally-closed,
off -delay.
Some relays are constructed with a kind of "shock absorber" mechanism attached to the armature
which prevents immediate, full motion when the coil is either energized or de-energized. This addition
gives the relay the property of time-delay actuation. Time-delay relays can be constructed to delay
armature motion on coil energization, de-energization, or both.
Time-delay relay contacts must be specified not only as either normally-open or normally-closed,
but whether the delay operates in the direction of closing or in the direction of opening. The
following is a description of the four basic types of time-delay relay contacts.
open when the coil is unpowered (de-energized). The contact is closed by the application of power
to the relay coil, but only after the coil has been continuously powered for the speci¯ed amount of
time. In other words, the direction of the contact's motion (either to close or to open) is identical
to a regular NO contact, but there is a delay in closing direction. Because the delay occurs in
the direction of coil energization, this type of contact is alternatively known as a normally-open,
on-delay.
Next we have the normally-open, timed-open (NOTO) contact. Like the NOTC contact, this
type of contact is normally open when the coil is unpowered (de-energized), and closed by the
application of power to the relay coil. However, unlike the NOTC contact, the timing action occurs
upon de-energization of the coil rather than upon energization. Because the delay occurs in the
direction of coil de-energization, this type of contact is alternatively known as a normally-open,
off -delay.
Next we have the normally-closed, timed-open (NCTO) contact. This type of contact is normally
closed when the coil is unpowered (de-energized). The contact is opened with the application of power
to the relay coil, but only after the coil has been continuously powered for the specified amount of
time. In other words, the direction of the contact's motion (either to close or to open) is identical
to a regular NC contact, but there is a delay in the opening direction. Because the delay occurs in
the direction of coil energization, this type of contact is alternatively known as a normally-closed,
on-delay.
Finally we have the normally-closed, timed-closed (NCTC) contact. Like the NCTO contact,
this type of contact is normally closed when the coil is unpowered (de-energized), and opened by
the application of power to the relay coil. However, unlike the NCTO contact, the timing action
occurs upon de-energization of the coil rather than upon energization. Because the delay occurs in
the direction of coil de-energization, this type of contact is alternatively known as a normally-closed,
off -delay.
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