SEC402-21

The Yokogawa SEC402-21 is an ESB Bus Coupler Module designed for the ProSafe-RS safety instrumented system. It provides the communication interface between the safety control unit and distributed safety node units through the ESB bus. Its two-port configuration supports upper and lower bus connections, allowing safety nodes to be distributed across separate communication branches.

Function and System Configuration

The SEC402 provides the ESB bus master interface function in the safety control unit. It exchanges I/O module data with safety node units equipped with the corresponding SSB401 ESB Bus Interface Module.

The module is designed for the Yokogawa SSC60S/SSC60D safety control unit. Two SEC402 modules are installed in a dual-redundant configuration, providing redundant ESB communication paths within the ProSafe-RS architecture.

Two-Port ESB Communication

The SEC402 has two independent bus connection ports:

• UPPER (CN1): Connects to the upper ESB bus branch.
• LOWER (CN2): Connects to the lower ESB bus branch.

Each port supports up to 9 connectable safety node units under the standard connection arrangement. The maximum supported total is configuration-dependent; Yokogawa documentation specifies up to 13 safety node units for the applicable SSC60 and S2SC70 configurations.

The ESB bus transmission speed is 128 Mbps for I/O module data transmission. Each upper or lower ESB bus cable has a maximum transmission distance of 10 m. The dedicated YCB301 communication cable is used for the ESB bus connection.

Diagnostic Indicators

The front-panel LEDs provide communication activity information for troubleshooting:

• RCVU: Flashes when response frames are received through the upper ESB port.
• RCVL: Flashes when response frames are received through the lower ESB port.
• SND: Flashes when command frames are transmitted through either port.

These indicators help maintenance personnel distinguish communication activity on the two bus branches when checking node connections. Unused ESB connectors should be covered with the supplied connector caps.

Technical Specifications

Parameter	Specification
Model	SEC402-21
Brand	Yokogawa
Product Type	ESB Bus Coupler Module
System	ProSafe-RS
Communication Interface	ESB Bus
Interface Function	ESB Bus Master
Number of Ports	2 (Upper and Lower)
Transmission Speed	128 Mbps
Maximum Transmission Distance	10 m per port
Connectable Units	Up to 9 per port under standard configuration
Current Consumption	0.5 A
Mounting Position	Slots 7 and 8
Compatible Safety Control Units	SSC60S / SSC60D
Compatible Safety Node Interface	SSB401
Communication Cable	YCB301
Dimensions	129.5 x 129.5 x 32.8 mm
Weight	0.24 kg

Configuration and Selection Notes

The standard connection arrangement supports up to 9 safety node units on each port. A different configuration is documented for S2SC70S/S2SC70D safety control units using SNT4-series modules in a star connection, with a maximum of 12 units per side. This special arrangement requires system revision R4.04 or later. The applicable node count must therefore be checked against the installed controller and system configuration.

The SEC402 is specified for installation in the seventh and eighth slots of the safety control unit. Its communication cable connects to the SSB401 interface in the safety node unit. The ESB bus uses a dual-redundant communication arrangement, so the two bus paths and their corresponding connections must be correctly identified during installation and maintenance.

Frequently Asked Questions

Q: Can the SEC402-21 operate with only one ESB bus port connected?

A: The SEC402 has separate upper and lower ESB connections. Its two-port configuration should be evaluated against the required system communication arrangement. Confirm the intended bus configuration before leaving either port unused.

Q: Which cable is required for the SEC402-21?

A: The specified ESB bus cable is Yokogawa YCB301. It connects the coupler module to the ESB bus interface arrangement of the safety node units.

Q: How can communication activity be checked on the SEC402?

A: Check the RCVU, RCVL and SND indicators. They respectively indicate response reception through the upper port, response reception through the lower port, and command transmission through either port.

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