Format for analogue data logged directly to disk

Development status

NOT IMPLEMENTED YET.

Format for data logged directly to disk (from AnalogueSampleSignal –OutputFile)

Data logged directly to disk is formatted so that it can be interpreted easily by a wide range of software, and can be imported directly into a relational database. The data is in comma-delimited text format, with the first line containing the field names. The following example illustrates a file that has been used for multiple simultaneous AnalogueSampleSignal commands (three independent channels):

SystemDate_YMD,SystemTime_HMS,Time_ms,ChannelLabel,Value_V

2001-11-19,15:24.56,400.0,Bed2_ECG_LeadII,0.045

2001-11-19,15:24.56,400.0,Bed2_ICP,-0.23

2001-11-19,15:24.56,400.0,Bed2_PCWP,0.18

2001-11-19,15:24.56,404.0,Bed2_ECG_LeadII,0.045

2001-11-19,15:24.56,408.0,Bed2_ECG_LeadII,0.048

2001-11-19,15:24.56,410.0,Bed2_PCWP,0.49

2001-11-19,15:24.56,412.0,Bed2_ECG_LeadII,0.057

(For the medically oriented, note that these values aren't representative of real ECG leads and presuppose some amplification has occurred before sampling! Furthermore, Whisker only reports absolute ADC voltage values back; calibration and conversion to real-world pre-amplified voltages/pressures/concentrations/etc. is the client's job.)

Note that the Time_ms field is not the time within the second specified by SystemTime. The SystemDate/SystemTime fields should be considered somewhat independent of the Time_ms field; the system date/time are imprecise while the Time_ms field is a high-precision field. However, having both can be useful.

Note that this field layout generates about 50 bytes of output per sample, depending on the length of the channel label. (Even a more economical single-channel file with just the millisecond timer and the value would occupy ~10 bytes per sample, and a human-unreadable time/value pair wouldn't be much smaller at 6–8 bytes per sample depending on precision.) Similar considerations apply to the TCP output. It is therefore UNWISE to attempt continuous sampling with logging to disk for long periods at very high sample rates, as the disk or network subsystem may be saturated. For example, continuous sampling at 312 kHz would generate 2.5–15 Mbytes·s-1 with any of these data formats.        

See also