HAMPTON TECHNOLOGIES' MASTER CLOCK:
Temporal correlation of collected data is usually an important design consideration. Consequently, we have developed a technique to slave all system instruments and controllers to a master clock. Data collected at a specified time is collected in the same temporal frame, regardless of geographic dispersal -- even world wide.GPS helps achieve this requirement. Each location has a GPS receiver connected to our ClockBoard. This becomes the local master clock. The ClockBoard's custom integrated circuit (ClockChip) is driven by a precision adjustable frequency oscillator. The ClockChip tracks the phase relationship of the GPS time and the precision oscillator. The ClockChip reports its comparison to our HT-DOS operating system.
HT-DOS keeps track of these phase relationships and adjusts the oscillator frequency as appropriate. HT-DOS is mindful that GPS has some phase jitter and its satellite signals can become blocked. Using a precision local oscillator reduces these errors. The scheme provides a local master clock synchronized to UTC (coordinated universal time) to within a few microseconds. This phase-locked precision can be shared with connected equipment.
Our remote terminal units (RTUs) have the same ClockBoard and HT-DOS combination. They are interconnected by HT-LAN. This specialized local area network transmits synchronization pulses from the local master clock, allowing each RTU to slave its time accordingly.
Within each RTU, HT-DOS uses this time to generate TIC interrupts for all requesting software modules. This allows timestamps for all generated data to use exactly the same time. Control signals use this time to coordinate switching.
- One hour of GPS contact allows satellite loss for hours without a phase slip of 15 microsecond.
- A local cluster of RTUs only need one GPS connection.
- The ClockChip/HT-DOS combination provides remarkable temporal software control.
- The ClockChip provides hardware time support for software querries to a resolution of eight microseconds.
- Standard clock accuracy when GPS connected is within eight microseconds of UTC.
- ClockChip provides a watchdog timer and keep track of timeout in hardware.
- ClockChip and HT-DOS detects and records loss of power.