A powder feed rate sensor includes a surface or diaphragm configured to detect powder feed rate. A control bus for transferring control signals between a main processor and components is separated from a data bus for transferring transmissionreceive signals between processor units including sub-processors and an external interface. The high level priority controller carries out various fine control operations according to a QoS policy and the low level priority controller performs mechanical control operations based on a predetermined simple fixed priority policy. Thereby, the test can be performed with a good timing accuracy even by a low-speed tester. For each link in the VLAN, the count of access switches on the first side of the link is multiplied by the count of access switches on the second side of the link to derive a count of paths that include the link. Among the termination impedances are master impedances arranged to be calibrated by comparison with the standard impedance and slave impedances arranged to be calibrated in accordance with an associated master impedance.