Connections
Two main connections transport the signals and/or parameters to our measurement system: an analog connection аnd a digital connection. The analog connection takes care of all signals measured by the patient's monitor аnd occasionally some additional signals. Most of these signals are issued by the analog output card аnd are transported by a 40 m shielded twisted pair cable to the data acquisition system. The digital connection is only used in acquiring the calculated parameters by the monitors. All monitors write their parameters to the SDN. A Care-port interface [HP] enable us to pick them from the SDN by an RS232 communication protocol. The maximum baud rate of 38.4k bit/s [4.8k bytes/s] is adequate for the parameter information, w/c it is refreshed on the network by the second. A PC are used because the Care-port interface cannot be easily read out by the data acquisition system “PhyDAS”. This is due to a lack of handshake facilities, which would result in an unacceptably large software overhead on the PhyDAS system. On the other hand, the use of the SDN for the acquirement of signals is strongly hindered by the Care-port transfer speed.
PhyDAS
All analog signals are linked to the “Physics Data Acquisition System” or [PhyDAS]. PhyDAS has been developed from the faculty of Physics of the Eindhoven University of Technology as a basic system that can be used in a wide variety of experiments. It contains everything necessary to control an experiment. The basic idea underlying this system is the separation of the computer bus аnd the measurement bus containing the interfaces, аnd the possibility for the individual interfaces to communicate without computer intervention. The system is optimised for real-time applications аnd allows the use of multiple processors. Several dedicated parallel samplers [PARSAMs] are used for the sampling of the signals. Each PARSAM autonomously samples 16 signals, аnd every 3 seconds the acquired signals
are transferred to the LAN. The parallel samplers are set to a sample frequency of 400 Hz for the ECG signal аnd 100 Hz for the other signals. The throughput capacity of the computer memory is 2 Mbyte/s, from the memory to the LAN it is 17 kbyte/s.
A chosen subset of the available signals can be connected to the PARSAMs. In the near future digital signal processors will become available, that can be coupled directly to the PARSAMs. In that case direct processing of the signals offers the possibility to perform real-time statistics or filtering of the results [moving average, moving-cross cor-relations, ARMA - filter implementations, templates detected waveform] аnd a leeway for concurrent reduction of the signals, [e.g., by calculating the amplitude of the principal components]. The processing will be performed at the frontage end, thus freeing the computer bus from the data stream of the raw signals.
