GNSS satellites are equipped with atomic clocks which utilize internal oscillators to deliver timing measurements accurate to 20 ns. This provides system integrators with the world's most precise, stable source of timing information. NovAtel's timing solutions are suited for a wide range of applications where accurate timing is essential in managing workflows and data. Applications for precise GNSS time include:
System time synchronization applications
- Cellular communication networks
- Financial networks
Frequency/phase synchronization applications
- Electricity grids
System time synchronization can be achieved using:
- Logs generated from the GNSS receiver
- Electrical connections from the receiver's programmable time signals (1PPS, VARF)
- Time tagged electrical triggering signals (MARKIN/EVENT) provided to the receiver by external equipment
- Precise 1 Pulse per Second (PPS) and Date/Time of Day timing information to the 20 ns level
- Accurate frequency information locked to the GPS Atomic standard
- Precise time synchronization between 2 or more systems
- The ability of national timing labs to compare their clocks with the clocks of other timing labs for global average UTC type observations
- Seamless and reliable operation with external oscillator input
All of NovAtel receivers' data messages contain time stamped information. This time stamp consists of a GPS reference week number (the week number since January 5th, 1980) and a Time of Week (TOW) value that represents the number of seconds from the Week rollover point at the Saturday night/Sunday morning boundary. The TOW is output with a resolution of 1 ms.
TIME log provides several time related pieces of information including the UTC offset (offset of GPS reference time from UTC time) and the estimated receiver clock offset from GPS reference time.
Binary data can also be easily converted into well recognized industry timing formats. For example: RINEX and the Group on GPS Time Transfer Standards (GGTTS) data format for common view time transfer purposes.
Timing through Strobe Connection:
PPS and Variable Frequency (VARF) Output
- If measurements such as temperature or pressure are required to be in synch with GNSS data, PPS or VARF signals can be used to trigger measurements in other devices. The strobe output produces an electric "pulse" of varying duration depending on the version of hardware utilized.
- Users can adjust the polarity, period and pulse width of the strobe output. VARF signals can generate a frequency up to 50 MHz, while PPS signals can be generated up to 100 pulse per second.
- The leading edge of the PPS signal is synchronous with the receiver's 1 second time tick. The leading edge of the VARF signal can be set to synchronize with the receivers 1 second time ticks on some models of receiver.
- In all cases, the VARF frequency is frequency locked to the receiver's internal clock, that in turn is steered to GPS time by default.
- Timing logs can be generated from EVENT/MARK electric pulse inputs from another device. For example, if you have a user point device, such as a video camera device, it can be connected to the receiver's I/O port. Using a cable that is compatible to the receiver and the device, a MARKIN pulse can be a trigger from the device to the receiver.
- Event/Mark data logs can be enabled or disabled by triggering external electrical signal inputs. The Event/Mark trigger point polarity can be changed and a time bias and guard against extraneous pulses can be added. The result of an Event or Mark input is the generation of the MARKTIME, MARKPOS data message and/or MARKPVA from GPS/INS or GNSS/INS systems.
- The MARKTIME log contains the time of arrival of the received electrical event along with the receiver's current clock health information.
- The MARKPOS log contains the current position of the receiver as well as the time of arrival of the electrical triggered event.
- The MARKPVA log contains the position, velocity and attitude information of the GNSS/INS system and the time of arrival of the electrical triggered event.
External Oscillator Input:
The GPS receiver, by default, steers the internal oscillator. It can also be commanded to control an external reference oscillator. If the receiver is configured for an external reference oscillator and configured to adjust its clock, then the clock steering loop attempts to steer the external reference oscillator through the use of the VARF signal.
A high precision external oscillator can be utilized with a GNSS receiver, with GNSS measurements generated based on the external oscillator time and frequency. In this case, users can monitor the offset and drift of their external oscillator through the analysis of the GPS measurements made using their reference clock and frequency inputs.
Time Synchronization (T-Sync) Circuitry:
NovAtel receivers are designed to accept external clock products (5 or 10 MHz frequency input and 1 PPS) and to lock the internal clock to these signals. The T-Sync Circuitry enables the receiver's internal clock to reliably reinitialize to the external clock products after a power cycle or reset. When the receiver reinitializes from a power cycle or reset, no start-up to start-up bias shift will occur.
When choosing a timing solution, consider the following needs of your application:
- Solution accuracy
- Signal availability
- Solution rate
- Continuity of solution updates
- System exportability
- System price
- System installation constraints
- Real time versus post-processed solution
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