Cautions For Use - Panasonic

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Safety Structure of SF Relays

This SF relay design ensures that subsequent operations shut down and can automatically return to a safe state when the SF relay suffers overloading and other circuit abnormalities (unforeseen externally caused circuit or device breakdowns, end of life incidents, and noise, surge, and environmental influences) owing to contact welding, spring fusion or, in the worst-case scenario, relay breakdown (coil rupture, faulty operation, faulty return, and fatigue and breakage of the operating spring and return spring), and even in the event of end of life.

Structure

Operation

1. Forced operation method
(2 Form A 2 Form B,
4 Form A 4 Form B types)

The two contacts "a" and "b" are coupled with the same card. The operation of each contact is regulated by the movement of the other contact.

Even when one contact is welded closed, the other maintains a gap of greater than 0.5 mm .020 inch.

In the diagram on the left, the lower contact “b” have welded but the upper contact “a” maintain at a gap of greater than 0.5 mm .020 inch.
Subsequent contact movement is suspended and the weld can be detected

2. Independent operation method
(4 Form A 4 Form B type)

None of four contacts are held in position by the armature. Even though one of the external N.O. contacts has welded, the other three contacts have returned owing to the de-energizing of the coil.

Enables design of safety circuits that allow weld detection and return at an early stage.

As shown at the top right of the diagram on the left, if the external N.O. contact welds, a 0.5 mm .020 inch gap is maintained.
Each of the other contacts returns to N.O. because the coil is no longer energized.

3. Separate chamber method
(2 Form A 2 Form B,
4 Form A 4 Form B types)

In independent chambers, the contacts "a" and "b" are kept apart by a body/ case separator or by the card itself.

Prevents shorting and fusing of springs and spring failure owing to short-circuit current.

As shown on the diagram on the left, even if the operating springs numbered 1 and 2 there is no shorting between “a” and “b” contacts.

4. 2 Form A 2 Form B contact
4 Form A 4 Form B contact

Structure with independent COM contact of 2 Form A 2 Form B and 4 Form A 4 Form B contacts.

Independent COM enables differing pole circuit configurations. This makes it possible to design various kinds of control circuits and safety circuits.

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The Operation of SF Relays (when contacts are welded)

SF relays work to maintain a normal operating state even when the contact welding occur by overloading or short-circuit currents. It is easy to make weld detection circuits and safety circuits in the design to ensure safety even if contacts weld.

1) 2 Form A 2 Form B type

Form “b” Contact Weld

If the form “b” contact (No. 1 and 3) welds, the armature becomes non-operational, the contact gaps at the three form “a” contacts are maintained at greater than 0.5 mm .020 inch. Reliable isolation is thus ensured.

Non-energized

→

Energized (when No. 1 contact is welded)

Example: If the No. 1 contact welds
Each of the three form “a” contacts (No. 2 and 4) maintain a gap of greater than 0.5 mm .020 inch.

Form “a” Contact Weld

When the form “a” contacts (No. 2 or 4) weld, the armature remains in a non-returned state and the contact gap at the two form “b” contact is maintained at greater than 0.5 mm .020 inch. Reliable isolation is thus ensured.

Energized

→

Non-energized (when No. 2 contact is welded)

Example: If the No. 2 contact welds.
The two form “b” contact (No. 1 or 3) maintains a gap of greater than 0.5 mm .020 inch.

Contact Operation Table

Contact No.	No.1	No.2	No.3	No.4
Terminal No.	11-12	7-8	5-6	9-10

The table below shows the state of the other contacts when the current through the welded form “a” contact is 0 V and the rated voltage is applied through the form “b” contact.

		State of other contacts
		1	2	3	4
Welded terminal No.	1	—	>0.5		>0.5
	2	>0.5	—	>0.5
	3		>0.5	—	>0.5
	4	>0.5		>0.5	—

>0.5: contact gap is kept at min. 0.5 mm .020 inch
Empty cells: either closed or open

*	Contact gaps are shown at the initial state. If the contacts change state owing to loading/breaking it is necessary to check the actual loading.

2)4 Form A 4 Form B type

Internal Contacts Weld

When internal contacts (No. 2, No. 3, No. 6 or No. 7) are welded, the armature becomes non-operational and the four form “a” contact gaps are maintained at 0.5 mm .020 inch or greater. Reliable cut-off is thus ensured.

Non-energized

→

Energized (when no. 2 contact is welded)

Example: If the No. 2 contact welds.
Each of the four form “a” contacts (No. 1, 3, 5, and 7) maintains a gap of greater than 0.5 mm .020 inch.

External Contacts Weld

When external contacts (No. 1, No. 4, No. 5 or No. 8) are welded, gaps of 0.5 mm .020 inch and greater are maintained between adjacent contacts and other contacts operate normally by the coil being non-energized.

Energized

→

Non-energized (when no. 1 contact is welded)

Example 1: If the No. 1 contact welds.
The adjacent No. 2 contact maintains a gap of greater than 0.5 mm .020 inch. The other contacts, because the coil is not energized, return to their normal return state; each of form “a” contacts (No. 3, 5, and 7) maintains a contact gap of greater than 0.5 mm .020 inch; each of the form “b” contacts (No. 4, 6, and 8) return to a closed state.

Example 2: If external connections are made in series.
Even if one of the contacts welds, the other contacts operate independently and the contact gaps are maintained at greater than 0.5 mm .020 inch.

Contact Operation Table

Contact No.	No.1	No.2	No.3	No.4	No.5	No.6	No.7	No.8
Terminal No.	20-19	12-11	8-7	16-15	13-14	5-6	9-10	17-18

The table below shows the state of the other contacts when the current through the welded form “a” contact is 0 V and the rated voltage is applied through the form “b” contact.

Contact No.		State of other contacts
Contact No.		1	2	3	4	5	6	7	8
Welded terminal No.	1	—	>0.5	>0.5	≠	>0.5	≠	>0.5	≠
	2	>0.5	—	>0.5		>0.5		>0.5
	3		>0.5	—	>0.5		>0.5		>0.5
	4	≠	>0.5	>0.5	—	≠	>0.5	≠	>0.5
	5	>0.5	≠	>0.5	≠	—	>0.5	>0.5	≠
	6	>0.5		>0.5		>0.5	—	>0.5
	7		>0.5		>0.5		>0.5	—	>0.5
	8	≠	>0.5	≠	>0.5	≠	>0.5	>0.5	—