NOVELTY - The system (10) has embedded smart plates (30) receiving operating power from a fuel cell stack (12) via voltage potential from a fuel cell (14) e.g. hydrogen fuel cell, adjacent to a stack plate (20) e.g. bipolar plate. An aggregator device (40) includes an optical transceiver (34) e.g. LED, for initiating communication with the embedded smart plates adjacent to the aggregator device to initiate a series of communications between the embedded smart plates in the fuel cell stack to determine location and measurement data such as fuel cell voltage, collected by the embedded smart plates.    USE - System for communicating measurement data e.g. fuel cell voltage, high frequency resistance and temperature, from a fuel cell (all claimed) e.g. hydrogen fuel cell such as electro-chemical device, and proton exchange membrane fuel cell, in a fuel cell stack of a vehicle.    ADVANTAGE - The aggregator device receives the operating power from a battery instead of from a fuel cell, thus maintaining galvanic isolation between the embedded smart plates and the aggregator device without requiring costly electrical isolation components. The embedded smart plates are electrically coupled to five consecutive stack plates using various interconnection devices, thus allowing measured value of four fuel cells to be determined by a single embedded smart plate. The system allows reversal of direction of communication of the embedded smart plates to relay back a command or modified command to the aggregator device that originates the command, thus detecting failure of the embedded smart plates in an efficient manner. The aggregator device includes a master aggregator transmitting a message to request that a subordinate aggregator issues the command to the embedded smart plates adjacent to the subordinate aggregator at the opposite end of the fuel cell stack when the master aggregator detects a communication failure of the embedded smart plates, thus allowing the fuel cell stack to be interrogated from ends, and hence preventing loss of the measurement data from a portion of the fuel cell stack due to a single failed or inoperative embedded smart plate. The optical transceivers have different spectral emissions and responses, and are employed for upward-bound and downward-bound pulse position modulation (PPM) packets, thus eliminating cross-talk between the optical transceivers.    DETAILED DESCRIPTION - The embedded smart plates include an embedded smart plate printed circuit board having a low-input voltage direct current (DC)-to-DC converter, analog-to-digital converter, microprocessor and a voltage reference.    DESCRIPTION OF DRAWING(S) - The drawing shows a plan view of a fuel cell system including a fuel cell stack that contains a set of fuel cells and embedded smart plates.    Fuel cell's measurement data communicating system (10)    Fuel cell stack (12)    Fuel cell (14)    Stack plate (20)    Embedded smart plates (30)    Optical transceiver (34)    Aggregator device (40)