Selection Criteria
Selection Criteria
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Selection Tips
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Sequential Access Control
A Sequential Access Control system requires that a predetermined sequence of events takes place or that hazards have been reduced before operators can become exposed to them. Prosafe trapped key interlocks are a mechanical system based on coded keys that achieves this via the premise that no single key can be used in two places at once. And because of their mechanical operation, Prosafe trapped key interlocks are widely used in applications where the location of plant, environment or explosive atmospheres make the use of electrical interlock systems unsuitable or expensive to install.
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High Inertia Machine (Long Run Down Time)
A High Inertia Machine is one on which hazardous motion does not cease immediately when the safety measures are engaged. As a result, there is a possibility that an operator can reach the hazard while it is “running down” and is still dangerous. Interlock switches with guard locking reduce the risk that the guard opens during hazardous machine motion.
Alternative measures:
- Install a braking device which stops the machine motion in a shorter time span.
- Increase the distance between the guard door and the hazard such that the operator cannot physically reach the hazard before it has stopped.
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Washdown Environments
In many applications, primarily those in the pharmaceutical and food/beverage industries, frequent washdown of the machinery with water and/or cleaning fluids is common. Therefore, it is important to select a safety switch with the appropriate environmental protection as indicated by the product’s enclosure (Ingress Protection or IP) rating. Non-contact switches have no “traps” where debris can accumulate and are available in fully sealed versions (IP67/IP68/IP69K), making them ideal for washdown applications.
For details on enclosure ratings, refer to the General section of this catalog (IEC Enclosures) and IEC 529.
Other Application Considerations
| Non-Contact Switches | Hinge Switches | Tongue Switches | Limit Switches | |
| Large Door | ü | ü | ü | |
| Vibration | ü | ü | ||
| Misalignment | ü | ü | ||
| Debris | ü | ü | ||
| Washdown | ü | ü | ||
Technology Overview
Tongue Interlock Switches
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Features/Benefits
Tongue interlock switches are the most commonly used technology for door interlocking. They detect the movement of a guard using a key fitted to an opening in the switch body. Available in a variety of packages, contact configurations and degrees of holding force, these switches are generally the lowest-cost solution. The use of flexible keys also enhances tolerance to misalignment to address an even broader range of applications.
Applications
- Wide range of doors
Common Misapplications
- Washdown
- Heavy debris
- Cutting fluids
- Removable guards
Guard Locking Interlock Switches
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Features/Benefits
Guard locking switches employ the same principle of operation as tongue interlocks, but feature an internal solenoid that locks the key—and therefore the guard—in place until the machine’s power is isolated. Ideal for applications requiring controlled access to hazardous areas, guard locking switches are available in a variety of holding forces and with flexible actuators for optimal performance.
Applications
- Printing presses
- Large access doors
- Saws/cutting blades
- High inertia machinery
- Web machines
Common Misapplications
- Wet environments
- Improper holding force selected
Non-Contact Interlock Switches
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Features/Benefits
Since there is no contact between actuator and switch, non-contact switches offer simple setup and alignment, less wear, and superior tamper-resistance as well as reduced installation cost. In addition, the IP67- and IP69K-sealed plastic or stainless steel housings make them ideal for food processing applications and other harsh environments.
Applications
- Hinged doors
- A wide range of doors
Common Misapplications
- Mounted at the door hinge
- Mounted to mild steel
- Exposed to rapid temperature changes
Technology Overview (continued)
Hinge Interlock Switches
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Features/Benefits
Hinge switches are designed to fit at the hinge point of swinging guards. Because they do not use keys which must slide into a slot in the switch body, hinge switches are ideal for machines with misaligned doors or applications with contaminants that could be caught in a key slot. Offering a higher integrity level than standard tongue interlocks, hinge switches are difficult to defeat and can be adjusted for the opening angle of the door.
Applications
- Hinged doors
Common Misapplications
- Large doors
- Doors with poor hinge alignment
Limit Switches
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Features/Benefits
Available in a variety of actuators and contact configurations, safety position (limit) switches satisfy Machinery Directive requirements. 802T limit switches with direct opening action offer positive opening safety contacts in a rugged NEMA-style housing for use in control reliable and other safety applications, while 440P IEC limit switches provide safety function in a compact, economical package.
Applications
- Conveyors
- Slide doors
- Muting sensors
- Robot positioning
Common Misapplications
- Mounting a single limit switch on a guard door
Trapped Key Switches
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Features/Benefits
Prosafe™ trapped-key interlock switches are designed to provide power isolation, key exchange and interlocking for safety applications requiring a pre-defined sequence of operations. Most of these rugged products do not require power to operate, making them ideal for applications in remote or intrinsically safe locations. Stainless steel construction also allows their use in harsh environments for process/valve control.
Applications
- Sequencing/process control
- Intrinsic safety
- 1/4 turn valves
Common Misapplications
- Duplicate coded keys on the plant floor