During a running DAQ job devices like MGCplus, PMX or Spider8 continuously fill sample data into an internal RAM buffer. For other device types (like QuantumX/SomatXR) not featuring an internal buffer, the catman device driver layer will buffer the incoming data. From this buffer, they are fetched by catman Easy/AP at a regular time interval (typically every 100 ms). This usually happens at the same rate as data coming in - i.e. the buffers do not fill up significantly.
If, however, for some reason catman Easy/AP cannot transfer the data fast enough, the buffers start filling up. In that case, the data you observe on the screen are no longer 'real-time': you see past data while the most recent data is still in the buffer. This time difference is denoted as 'Real-time lag' (RT-Lag) and will be displayed in the status bar of catman Easy/AP.
An RT-Lag of several seconds should be taken seriously! The RAM buffers are filled up significantly in that case and might overflow shortly. If that happens the DAQ job is aborted! The following device types feature internal RAM buffers:
- 20,000 samples for Spider8
- 6,000,000 samples for MGCplus CP42 with Standard-RAM (RAM-extensions optionally available)
- 2,000,000 samples for MGCplus CP32 with Standard-RAM (RAM-extensions optionally available)
- 1,000,000 samples for MGCplus CP22 (RAM-extensions not available)
- 5 MB for PMX
The specified number of samples is the sum of all samples from all active channels! For instance, the RAM buffer of an 8-channel Spider8 may hold up to 2,500 samples/channel.
QuantumX/SomatXR don't feature an internal RAM buffer - buffering is done by the catman device driver layer: 5 s buffer, however, at least 30,000 samples.