Abstract: In a redundancy method for Ethernet communication between a plurality of nodes constituting a distributed control system, the nodes are connected to each other in a duplex state through first and second Ethernet communication lines which are independent of each other. A node on the transmission side transmits identical data to both the first and second Ethernet communication lines. A node on the reception side determines one of the identical data received from the node on the transmission side through the first and second Ethernet communication lines which has arrived first as reception data.

Abstract: A housing body of electronic equipment has a square base body having a circumferential wall and a box-like case assembled with the base body. The base body has a built-in printed board assembly including first, second and third printed boards of which the first and second printed boards are arranged above one another, and the third printed board has engaging pawls formed at both its end portions engaged with one side of the first and second printed boards perpendicular thereto. The base body is provided with a plurality of printed board engaging members at an inner side of its circumferential wall, and with first support portions and struts in the vicinity of four corner portions of the base body. Each strut of one pair of struts opposed to each other is provided at its opposed face with a guide groove and with a printed board engaging hole which communicates with the guide groove.