Glossary · Protective devices and interlocks
Presence-sensing device (PSD)
Also known as: presence-sensing safeguarding device, PSD
In machine safety, a presence-sensing device (PSD) is a device that detects a person or object in or approaching a hazardous zone and initiates a protective response, such as stopping hazardous motion.
- Machine safety
- USA
In one sentence
A presence-sensing device detects a person in or approaching a hazardous zone and triggers a stop; its placement must allow for the machine's stopping time.
Example
On a mechanical power press, a presence-sensing device across the die opening stops the stroke when the operator's hand enters the point of operation.
How it applies
- USA: “Presence-sensing device” is the common term in OSHA regulations and US practice, for example in the rules for mechanical power presses. In IEC terms, most PSDs are electro-sensitive protective equipment.
- Machine safety: A PSD only protects if the machine stops before the person reaches the hazard. The distance calculation uses the stopping time; see safe distance.
- Limits: A PSD cannot stop a machine that has a mechanical fault, such as a clutch that fails to disengage. Stopping performance monitoring may be required for machines such as presses.
- Technical documentation: When a document is written for US and EU readers, map PSD to the matching IEC terms and name the actual device type.
PSD vs. pressure-sensitive mat
A pressure-sensitive mat detects a person by contact pressure. PSD usually refers to non-contact devices, although some sources include mats.