Dual Antenna INS Installation
The SPEEDBOX base unit should be mounted inside the vehicle. The base unit can be mounted in any orientation for the SPEEDBOX-INS, since the INS system takes all inertial measurements from the antenna assembly. The base unit should be isolated from excessive vibration, and the supplied power cable should be connected to a power supply between 9 and 30V. Power consumption is approximately 0.4A @ 12V for the INS system, but some additional capacity is required at start-up.
The antenna assembly should then be mounted on the roof of the vehicle in the correct orientation. Please follow the instructions for mounting the INS dual antenna assembly in this section.
Once the base unit and antenna assembly have been correctly fitted, they must be connected using the supplied cable. This cable contains both the data cable for the IMU and the GPS antenna cables. The routeing of the cable from the base unit to the antenna assembly should avoid as far as possible any sources of RF interference, in particular components of the vehicle ignition system, telemetry or radio systems, and in some cases video camera systems.
The data cable from the IMU to the SPEEDBOX base unit connects to the antenna assembly at one end, and to the “Expansion” port of the SPEEDBOX base unit at the other end. Whilst it is possible to connect to either the front or rear expansion port, it is likely that the rear port will be used in order to ensure that the GPS cables integrated into the main cable can reach the GPS connections. Note that the data cable must be connected prior to switching on the INS system in order for the antenna assembly to be correctly detected – if the power is supplied prior to plugging in the IMU cable then the SPEEDBOX will flash an error code to indicate that the IMU is not detected. In this case it is simply necessary to power-cycle the unit after plugging in the IMU cable.
The GPS antenna cables from the INS antenna assembly to the SPEEDBOX unit are colour coded using coloured heatshrink and washers. The red heatshrunk cable connects to GPS Antenna 1 “Base”, and the standard black cable connects to GPS Antenna 2 “Moving”. Antenna 1 “Base” connects to Rf 1 on the SPEEDBOX, and Antenna 2 “Moving” connects to Rf 2 on the SPEEDBOX. Please refer to Figure 1 below for clarification.
Dual Antenna INS Mounting Instructions
It is STRONGLY recommend that you mount the INS antenna assembly on the roof of the vehicle. Mounting the antenna on the bonnet or the boot of the vehicle will give suboptimal results due to the reduced number of satellites in view. This is particularly important due to the fact that any deviation in vehicle heading will change the satellite constellation used.
Fig2. INS antenna assembly mounting position side view
Fig3. INS antenna assembly mounting position top view
For best results the INS antenna assembly should be mounted as close as possible to the centre line of the vehicle.
The telescopic centre section must be fully extended to obtain the most accurate results, and the D-type connector must be facing the rear of the vehicle (direction of travel arrows are engraved on the unit).
Fig4. Suction pad mounting indicator. Pump until the red line can not be seen.
The INS antenna assembly is intended for use with the supplied suction mounts. These mounts are provided with fully articulated ball and socket assemblies, which allow for the antennas to be mounted level and the suction cups to contact the roof of the vehicle effectively. The suction mounts have a red indicator line on the pump, which indicates the suction. If you can see the red line the cup is not secure. Continue to pump until the red line can not be seen. Frequently check the suction mountings to see if the red line is visible.
Once mounted check the following:
- The central telescopic section is fully extended giving an 800mm base line between the antennas.
- The D-type connector is facing the rear of the vehicle and the “direction of travel” arrows are pointing to the front of the vehicle.
- The antennas are mounted as straight and level as possible, and are aligned along the centre line of the vehicle.
- All of the articulated ball and socket arms are tightened securely and the telescopic extension clamp is locked
- All of the suction mounting cups are secure with none of the red warning lines showing.
In view of the importance of the antenna mounting position, the following additional guidelines are set out below:
- The antenna must not be covered with tape
- The antenna must not be subjected to high levels of vibration. To prevent this, isolate the antenna from vibration as much as possible.
- The antenna must be physically remote from sources of electrical noise. By far the biggest source of radio interference is a gasoline engine's ignition system, so keep the antenna away from all aspects of it. Avoid the engine management system, coils, high tension leads and ignition control modules.
- Avoid trapping, pinching or kinking the antenna cables. The RF leads from the GPS antennas to the receiver are special cables and it is not normally practical to repair them. If you do trap, pinch or cut it, then the antenna cables will have to be replaced. Do not attempt to fit the antenna cable into a shut gap, or compress it with a door or window seal.
Alternative mounting points are provided on the unit to allow it to be adaptable when required. 4 x M4 x 7mm deep mounting holes are located on the underside of each antenna assembly base as shown below. These can be used for alternative mountings such as custom brackets, magnets or full mechanical fixing. For an accurate 800mm baseline the hole dimensions are shown below:
Fig5. Alternative mounting hole positions
Setting up the SPEEDBOX Measurement Offset
For firmware newer than v3.7.3 a measurement offset can be set up, allowing the SPEEDBOX unit to model the dynamics of the vehicle, referencing the measurement to a specific point on the vehicle, a separate component such as a laser barrier used for triggering a test, or a reference system for direct comparison. Configuring this function correctly results in increased accuracy.
SPEEDBOX-INS measurement output offset in v4.2.8 or later SPEEDBOX Configuration Utility Software
Note: Measurements shown are only an example, actual values must be measured from your installation.
SPEEDBOX-INS Dual Antenna measurement offset must be made from the rear "Base" antenna, connected to Rf 1.
For the SPEEDBOX-INS measurement offset is taken from the INS antenna assembly to the offset point. Measure the distances below, ahead and right, using negative values for opposite directions, and input these into the configuration software (v4.2.8 or later).