Annunciated Safety Relays


Thread Starter

Bob Welker

Looking for an annunciated safety relay into which several devices can be input, and (depending on wiring) in addition to providing category 1 through 3 operation, will indicate what device caused the trip.

This thingamabob would have force guided relays, and other amenities of a 'standard' safety relay. Instead of monitoring only a single string of devices it would have multiple inputs (say, in groups of 4 or 8).

LED indicators or some other form of display would indicate which of the monitored devices caused the safety circuit to open up, or indicate if the trip was due to an internal problem (stuck FGR, etc.).

My particular application is a trimpress. This type of machine has cyclic shock loads, and, after time, safety switches in the (currently) traditional series e. stop string become intermittent in ways that aren't always easy to test.

It's kinda possible to do what I want using a whole slew of single safety relays (one for each device), but, at least in this application, way too expensive to consider.

Any thoughts?

Michael Griffin

The usual way of dealing with this is to have an extra contact on each guard
switch (or e-stop button) and to monitor these extra contacts separately from
the safety circuit.

There are safety rated networks (e.g. ASI Safe) which allow monitoring of each
device over the network, but this may be more difficult to add as a retrofit.

Lynn Higgins

Modular safety relay systems may be the solution for you. Pilz makes such a system called the PNOZmulti. The base unit has 20 inputs, for up to 10 dual-channel devices. Individual LEDs allow easier troubleshooting as does optional diagnostic units for direct connection to PLCs or fieldbus systems. Additional modules can be added for more inputs or outputs. I/O is configured using a smartcard and Windows-based software. It is approved for up to category 4 applications.

For more information, see or call 877-PilzUSA (745-9872).