In a communication system, physical-layer frames for transmission over the physical layer are assembled from link-layer protocol data units by combining several PDU’s into a variable-length first block, and providing the first block with an error detection andor correction code such as a CRC. The invention is particularly useful for synthesis of isotopically enriched sodium or lithium borohydride, MB11H14, and decaborane. A difference between the digitized sampling voltage and the voltage data is calculated and it is determined that abnormality occurs in the AD conversion section when the difference is larger than a threshold.