External Device Monitoring (EDM) Safety Solution Guide

What is External Device Monitoring (EDM)?

In safety systems that include a safety relay (mechanically linked/force-guided relay/contactor) that is not self-monitoring, it is necessary to monitor that relay externally. This is known as External Device Monitoring (EDM).

It is strongly recommended that a normally closed (NC), forced-guided monitoring contact from each of two relays/contactors be connected to the EDM input(s). If this is done, proper operation will be verified. Monitoring these contacts is one method of maintaining control reliability (OSHA/ANSI) and Category 3 and 4 (ISO 13849-1).

External device monitoring (EDM) is a means by which a safety device (such as a safety light curtain) actively monitors the state (or status) of external devices that are controlled by the safety device. A lockout of the safety device will result if an unsafe state is detected in the external device. External device(s) may include, but are not limited to: MPCEs (Machine Primary Control Elements), captive contact relays/contactors, and safety modules.

External device monitoring is necessary in safety systems with a non-self-monitoring safety relay. This is achieved by:

• Understanding the device that needs to be monitored
• Selecting a safety device that contains EDM functionality
• Configuring and wiring your device through EDM

EDM requires the use of mechanically linked/force-guided relays/contactors with a normally closed (NC) contact for feedback monitoring. This increases the overall safety of the system by providing an extra layer of protection against potential failures of external components.

Understanding the Device

External Device Monitoring (EDM) works by having a host device with EDM connected to another device that cannot monitor itself. When connected, the host device monitors the electric signals that are either generated by itself or an external 24 V supply. The host device ensures that the EDM input is high before it allows its output to turn on. The host device ensures the EDM input returns to a high state within 250 ms of its output turning off. By monitoring these states, the host device ensures that the devices being monitored have not failed in an ON state.

When the monitored device faults, a contact is welded in the ON state, causing the NC contact to stay open. The host fails to receive its current, which flags that something in the monitored device has occurred.

Devices in a safety monitoring system have three options:

• Device can monitor itself, but does not have EDM capability
• Device can monitor itself and has EDM capability
• Device cannot monitor itself and does not have EDM capability

Selecting a Safety Device with EDM

The following is a synopsis of Banner Engineering products and whether or not they include EDM abilities. Refer to the following list of products to determine if your device has EDM capabilities.

These are not exhaustive lists. There may be other safety devices that can monitor or need monitoring. Always consult the user manual for your device to determine if it features EDM or requires a device with EDM.

EZ-SCREEN Safety Light Curtain Models

Safety Controller Models

Safety Module Models

Configuring and Wiring a Device with EDM

The following example shows a general wiring of a light curtain to an IM module, including an EDM wiring option. Locate the wiring diagrams for the host and/or monitored device.

For this example, the host device is an EZ-SCREEN S4B Light Curtain (product manual p/n 230287) with an 8-pin removable disconnect wired to an IM-T-9A Interface Module (product manual p/n 62822).

Diagram: Generic Wiring Diagram - IM-T-9A Interface Module (1-Channel EDM)

Description of Diagram:

The diagram illustrates the wiring between an 8-pin M12 male connector (face view) and an IM-T-9A Interface Module for a 1-channel EDM setup. The M12 connector has pins labeled: Wh(1) for OSSD2, Bu(7) for 0 V DC, Pk(6) for n.c. (normally closed), Gy(5) for OSSD1, Ye(4) for EDM, Rd(8) for n.c. (normally closed), Gn(3) for Weak Signal, and Bn(2) for +24 V DC.

The IM-T-9A Interface Module has terminals for OSSD2, OSSD1, EDM, Weak Signal, +24 V DC, and 0 V DC. It also includes machine control terminals S1, S2, S3, S4, K1, K2, Y1, Y2, Y3, Y4, and output terminals 13, 14, 23, 24, 33, 34. Machine Primary Control Elements (MPCE) 1 and 2 are also shown.

Wiring Connections:

• M12 Pin Wh(1) connects to OSSD2.
• M12 Pin Bu(7) connects to 0 V DC.
• M12 Pin Pk(6) connects to a normally closed (n.c.) contact.
• M12 Pin Gy(5) connects to OSSD1.
• M12 Pin Ye(4) connects to the EDM input.
• M12 Pin Rd(8) connects to a normally closed (n.c.) contact.
• M12 Pin Gn(3) connects to Weak Signal.
• M12 Pin Bn(2) connects to +24 V DC.
• IM-T-9A +24 V DC terminal connects to S1, S3, and Y1.
• IM-T-9A 0 V DC terminal connects to S2, S4, and Y2.
• IM-T-9A K1 terminal connects to 13, 23, and 33.
• IM-T-9A K2 terminal connects to 14, 24, and 34.
• IM-T-9A Y3 terminal connects to MPCE 1.
• IM-T-9A Y4 terminal connects to MPCE 2.

In this specific configuration, the yellow wire (EDM) from the host device is used for monitoring the IM-T-9A K2 contact by connecting your wire to Y3. A jumper wire is then used from Y4 to Y2 on the IM-T-9A. This jumper wire utilizes the same EDM signal path to monitor the K1 contact when Y1 is connected to +24V. This jumper wire setup can also be used to monitor other devices, represented as Machine Primary Control Elements (MPCE).