System for monitoring a plurality of sensors

A monitoring system (30) for detecting faults in an apparatus (10), such as a ski lift, employs a communication network (37,38) onto which a sensor bus controller (36) periodically transmits a safety message and receives a echo of each safety message. Different sensors (25) are coupled to sensor adapter modules (31,32,33) that in turn are connected in a series to the communication network. After the last sensor adapter module (33) in the series, each safety message is echoed back along the communication network. Each sensor adapter module (31,32,33), upon receiving a safety message, increments a count in that message and transmits the resultant safety message to another module. When a sensor (25) indicates a fault condition, the associated sensor adapter module (31,32,33) blocks propagation of safety messages along the communication network (37,38). The sensor bus controller determines, in response to a failure to receive the echo and to the count in the echo, whether a fault occurred.