SCADA web HMI system

A SCADA web HMI system comprising a plurality of programmable logic controllers (hereinafter, PLCs), a plurality of HMI client apparatuses, and one SCADA server apparatus that are connected to one another through a computer network, wherein

• each of the PLCs transmits block data including a set of input/output signals relating to a field device group configuring an industrial plant, to the computer network at a fixed period,
• each of the HMI client apparatuses includes a screen displaying a web browser,
• the SCADA server apparatus includes a communication driver, and a client management unit connected to the plurality of HMI client apparatuses in one-to-one relationship,
• the communication driver is configured to receive the block data transmitted from each of the PLCs at the fixed period, to decompose the received block data into signal data for each data type, to add a signal data identifier to the decomposed signal, and to transmit the decomposed signal data to the client management unit for each data type,
• the client management unit includes a reception thread receiving the signal data transmitted from the communication driver, first and second signal data buffers capable of storing the signal data received by the reception thread in association with the signal data identifier for each data type, and a transmission thread reading out the signal data stored in the first or second signal data buffer and transmitting the read signal data to the HMI client apparatuses corresponding to the read signal data, and
• during a period when the transmission thread reads out the signal data from one of the first and second signal data buffers and transmits the signal data to the HMI client apparatuses, the signal data stored in another of the first and second signal data buffers is overwritten.