Without the assistance of GPS or other positioning system, position estimates obtained by integrating linear accelerations experience unbounded error growth.  Even after calibration, residual biases and axis misalignments in the accelerometer measurements will quickly grow position estimate errors.  For example, Industrial-grade accelerometers, such as those built-into the VN-100, can yield errors on the order of 100 meters in just 60 seconds.  

We provide a detailed explanation of the difficulties of unaided positioning here:

www.vectornav.com/support/library?id=76#unaided-position-estimate

If measurements from an indoor positioning system are available, we can provide custom filters for an indoor INS system. 

The VN-200 will continue to operate without a GPS fix.  The position and velocity estimates will degrade at a typical acceleration level of 5 cm/s2, which yields an error position of about 50-60 meters in 50 seconds.  VectorNav typically does not recommend using the navigation solution after about 30 seconds of a GPS outage.  The INS solution output by the VN-200 contains a status register to indicate the GPS fix/INS filter mode as well as uncertainty values on the position, velocity, and attitude estimates.

• The GPS module built into the VN-200 does not support GLONASS or SAASM; however, VectorNav is currently developing follow-on products that will.

The VN-200 requires an active antenna to be connected. Both the surface mount and rugged packages can supply 3.0 V and up to 40 mA of current to the antenna. The antenna noise specification should be as low as possible, ideally below 1.5 dB.  In determining the type of antenna and length of cable, we recommend keeping the antenna gain within the range of 20 to 50 dB at the VN-200.  We realize that there are not many aircraft antennas available that can run on anything less than 4.5 V; however, we can recommend the 4G15A-XX-X from ANTCOM Corporation for aircraft applications.  We are currently developing a software selectable feature for the VN-200 Rugged that will allow the user to bias the antenna from the VCC supplied to the unit (up to 17 V).  Customers using the VN-200 surface mount device have installed simple bias circuits to up the voltage and current to the antenna and we can assist with these developments.  We also recommend using LMR-400 cables for long cable runs. 

• Cold start on GPS receiver is 45 seconds
• Hot start is 5 seconds
• INS dynamic alignment time is usually on the order of a few minutes, but depends on the dynamic motion.

Yes, the PPS signal is available from the module (See Section 2 of VN-200 User Manual for pin-out)