Safety Limit Switch: Direct Opening Force

Question

What is direct opening force (DOF)?

Answer

Refer to the following table of terms for operating characteristics.

Note 1: For slow-operating safety switches, the operating position (OP) and return position (RP) are almost identical.

Note 2: The DOF, DOT, and DOP values are specified to ensure that the direct opening mechanism (forcibly opened contacts) functions correctly.

Safety Limit Switch: Pretravel

Question

What is pretravel (PT)?

Answer

Refer to the following table of terms for operating characteristics.

Note 1:For slow-operating safety switches, the operating position (OP) and return position (RP) are almost identical.

Note 2:The DOF, DOT, and DOP values were specified to ensure that the direct opening mechanism (forcibly opened contacts) functions correctly.

Processing for Conduit Section and Recommended Connectors

Question

What is the processing for the conduit section, and what are the recommended connectors for D4B-[]N Safety Limit Switch?

Answer
1. OMRON Applicable Connectors and Dimensions

Metal Connectors

Metal Models with O-ring
G1/2
SC-1M to 5M

Metal Models without O-ring
G1/2
SC-21 to 25

Resin Connectors

Resin Models
G1/2
SC-P2

Resin Models
Pg13.5
SC-P3

Resin Models
G1/2
SC-6

2. Tighten the connectors to a torque of 1.77 to 2.16 Nm. (For conduits, use a tightening torque of 0.78 to 0.88 Nm.)

The case may be damaged if the connectors are tightened excessively.

3. If using a 1/2-14NPT conduit, apply sealing tape to the connector conduit opening to conform to IP67.
4. For 3-conduit connections, use the enclosed cap screws on the unused conduit openings and tighten to a torque of 1.27 to 1.67 Nm.

Safety Limit Switch: Form Lock Mechanism

Question

What is a form lock mechanism?

Answer

Safety Limit Switches use inflexible interlocking components, related to the direct opening mechanism (forcibly opened contacts), so that the components will not distort or come apart even if great force is applied to the Actuator by contact welding or other cause.

The following diagram shows an example using a rotating shaft and lever.

Note 1: The lever cannot be mounted backwards because the protrusion and notch interlock so that the lever will not free-turn even if a large force is applied.

Note 2: The Safety Limit Switches with changeable roller levers do not have the form lock mechanism.

Safety Limit Switch: Snap Action

Question

What is a snap action?

Answer
SPST-NC + SPST-NO Contact (Snap Action) Example

The SPST-NC + SPST-NO contact snap action switches have the direct opening mechanism (forcibly opened contacts) defined under EN 60497-5-1. The NC contact side is the only side with a direct opening mechanism (forcibly opened contacts).

1. When contact welding occurs.

2. When contacts are being pulled apart.

Safety cam directly pushes up the movable contact blade.

3. When contacts are completely pulled apart.

Difference between Safety Limit Switch and General Limit Switch

Question

What is the difference between the Safety Limit Switches and the General Limit Switches?

Answer

The Safety Limit Switches are provided with a direct drive positive opening mechanism (positive actuation structure) with which welded portions are forcibly torn even if contact welding occurs, thus stopping a dangerous process (load) without fault and performing safe operation.

On the other hand, the General Limit Switches are not provided with the above mentioned mechanism. Therefore, if contact welding occurs, it keeps conduction state, and thus it cannot reliably stop dangerous process (load) and may perform dangerous operation.

For this reason, use the Safety Limit Switches in applications for safety purposes.

Safety Limit Switch: Direct Opening Travel (DOT)

Question

What is direct opening travel (DOT)?

Answer

Refer to the following table of terms for operating characteristic.

Note 1: For slow-operating safety switches, the operating position (OP) and return position (RP) are almost identical.

Note 2: The DOF, DOT, and DOP values were specified to ensure that the direct opening mechanism (forcibly opened contacts) functions correctly.

Safety Limit Switch: Total Travel (TT)

Question

What is total travel (TT)?

Answer

Refer to the following table of terms for operating characteristics.

Note 1: For slow-operating safety switches, the operating position (OP) and return position (RP) are almost identical.

Note 2: The DOF, DOT, and DOP values were specified to ensure that the direct opening mechanism (forcibly opened contacts) functions correctly.