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> /ac/ae/control/relay/safety/index.jsp?c=search">Safety Relays
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> Cautions For Use
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 (3 Form A 1 Form B types) |
|
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. Separate chamber method (3 Form A 1 Form B types) |
|
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. |
||
| 3. 3 Form A 1 Form B contact | Structure with independent COM contact of (3 Form A 1 Form B), contacts. | Independent COM enables differing pole circuit configurations. This makes it possible to design various kinds of control circuits and safety circuits. |
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.
Form “b” Contact Weld
If the form “b” contact (No. 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.
|
→ |
|
If the No. 3 contact welds.
Each of the three form “a” contacts (No. 1, 2, and 4) maintain a gap of greater than 0.5 mm .020 inch.
Form “a” Contact Weld
When the form “a” contacts (No. 1, 2, or 4) weld, the armature remains in a non-returned state and the contact gap at the single form “b” contact is maintained at greater than 0.5 mm .020 inch. Reliable isolation is thus ensured.
|
→ |
|
If the No. 2 contact welds.
The single form “b” contact (No. 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 | ||
| 2 | — | >0.5 | |||
| 3 | >0.5 | >0.5 | — | >0.5 | |
| 4 | >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. |
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