Catalogs > Safety Products Catalog > Presence Sensing Safety Devices > Selection Criteria
Selection Criteria
Selection Tips
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Is the hazardous area stationary or mobile?
A stationary hazard refers to a fixed machine or work cell where one or more mechanical hazards exist. A mobile hazard is generally a fixed-rail linear transfer mechanism (e.g. a transfer cart or conveyor) or an Automatic Guided Vehicle (AGV). Use of a safety device on a mobile hazard generally relates to collision avoidance with personnel or surrounding machinery.
In the instance that the hazard moves toward the operator (such as with powered doors) as opposed to the operator moving toward the hazard, a pressure sensitive safety edge can be mounted to the leading edge of the door. Any contact between the door and personnel will stop the machine before injury can occur.
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What do we mean by full- versus partial-body access?
Full-body access generally refers to the requirement for a person to be standing or walking in (or have access to) the hazardous area around a machine that does not require frequent interaction between personnel and the hazard during regular operation; generally this is for maintenance and troubleshooting. Full-body perimeter or area access control (PAC or AAC, respectively) is achieved through the use of a vertical or horizontal safety field, either opto-electronic (i.e. a light curtain or scanner) or by contact (safety edges and mats).
Partial-body access, on the other hand, is required for applications where an operator must regularly reach into a machine hazard as part of the process at the point of operation (known as POC or Point of Operation Control). In the case of opto-electronic safety devices such as light curtains and area scanners, full- or partial-body detection is directly related to the resolution of the safety device. Below is the relationship of sensing field resolution to the type of detection:
| Object to be Detected/Protected | Resolution |
| Finger (vertical field) | 14 mm |
| Hand (vertical field) | 30 mm |
| Limb (horizontal field for leg detection) | 50 mm, 70 mm |
| Full Body (horizontal or vertical fields) | 150 mm |
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Blind Spots
In some cases it may be possible for a person to enter the guarded area and be lost from view, potentially allowing the guard door to be shut and the machine started by another person. Often used in conjunction with hard guarding and a gate outfitted with an interlock switch, presence sensing safety devices such as pressure sensitive safety mats, laser scanners and horizontal light curtains can be used to check for the presence of a person anywhere within the enclosed safety area.
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Is the shape of the hazardous area rectangular?
When the hazardous area to be monitored is a rectangle (or a shape consisting of contiguous rectangles), access to the area can be easily—and cost-effectively—controlled with a standard safety mat. When the hazardous area is irregularly shaped a custom mat is a viable option, but not necessarily the most cost-effective or readily available. In such a case, a safety scanner is the best option as its scanning field can be easily programmed to scan irregular areas and ignore obstacles (walls, columns) while detecting moving objects (people, AGVs, etc.) as required.
Other Application Considerations
| Safety Mats | Safety Scanner | Point of Operation Control | Perimeter Access Control | ||
| Partial Body Detection | Finger Detection | 14 mm | |||
| Hand Detection | 30 mm | 30 mm | |||
| Limb Detection | 50/70 mm | 50/70 mm | |||
| Full Body Detection | ü | ü | ü | ||
| Uneven Floor | ü | Horizontally Mounted | Horizontally Mounted | ||
| Corrosive Chemicals | ü | ü | ü | ||
| High Pressure Washdowns | ü | IP 67 Enclosure | IP 67 Enclosure | ||
| Steam, Dust Environment | ü | ||||
| Reflections, Bright Ambient Light | ü | ||||