GPS modules

GPS channels are sourced from the GPS connector on the CX23-R/EXRCPU/EXRLCPU. EGPS-200, EGPS-200-Plus and Garmin GPS modules are supported. See GPS channels and www.hbm.com for more information.

The Garmin GPS (model GPS18X-5Hz) module requires the 5 Vdc power option and draws about 0.5 W. EGPS-200 and EGPS-200-Plus modules require the 12 Vdc power option and draw about 2.4 W. On boot up of the main processor, the power is always set to 5 Vdc.

With the power option set to 5 Vdc, the EGPS-200 and EGPS-200-Plus modules operate in a minimal mode that is sufficient to send a message to the processor allowing it to identify the module. When the processor receives this message, it switches to the 12 Vdc power mode.

CAUTION
The Garmin module will be instantly destroyed if it is connected to the GPS connector with the 12 Vdc power option selected! As such, always power off the main processor before connecting a Garmin GPS if an EGPS-200 or EGPS-200-Plus module was previously connected.

Cables and accessories

Order Number Description
1-EGPS-5HZ-2 5 Hz GPS receiver (for use on CX23-R, also order KAB2102-1 in addition)(for an extension cable to EXRCPU/EXRLCPU, also order 1-SAC-EXT-MF-X-2 in addition)
1-EGPS-200-B-2 Precision GPS receiver, Includes (1) Trigger Cable (1-SAC-GPSTRIG-2) and (1) GPS Antenna (1-EGPS-200-ANT-2) (also order a 1-KAB2102-1 to connect to CX23-R) (also order a 1-SAC-EXT-MF-X-2 to connect to EXRCPU/EXRLCPU)
1-EGPS-200-P-2 Precision GPS receiver PLUS Package - IMU and RTK Measurements, Includes (1) Trigger Cable (1-SAC-GPSTRIG-2), (2) GPS Antennas (1-EGPS-200-ANT-2) and (1) Dual Antenna Template (1-EGPS-200-TEM-2) (also order a 1-KAB2102-1 to connect to CX23-R) (also order a 1-SAC-EXT-MF-X-2 to connect to EXRCPU/EXRLCPU)
1-EGPS-200-ANT-2 Antenna for EGPS-200-B-2 or EGPS-200-P-2
1-KAB2102-1 GPS/AUX adapter cable (8-pin M12 to 6-pin M8) 1m.
1-SAC-GPSTRIG-2 Trigger cable for EGPS-200-B-2 or EGPS-200-P-2
1-EGPS-200-TEM-2 Dual Antenna Template for EGPS-200-P-2
1-SAC-EXT-MF-0.4-2
1-SAC-EXT-MF-2-2
1-SAC-EXT-MF-5-2
1-SAC-EXT-MF-10-2
1-SAC-EXT-MF-15-2
Extension Cable - Male/Female Connectors (0.4, 2, 5, 10 or 15 m)

 

EGPS-200 operation and installation

Overview

The EGPS-200 is primarily designed for ground vehicle testing applications. It provides a set of high accuracy vehicle speed output channels (raw 2D, raw 3D, and combined speed). An inertial motion unit (IMU) provides tri-axial (i.e., x-axis, y-axis and z-axis) acceleration output channels. The combined speed channel is computed using the acceleration data combined with the enhanced GPS sourced raw2D and raw3D speed data. In proving grounds test environments where there is a clear view of most of the sky, combined speed accuracy of 0.05 km/hr can typically be achieved for vehicle speeds of 5 km/hr or greater. Speed data can easily be integrated to provide high accuracy distance-travelled data using the Integrator Computed channel.

The EGPS-200 provides the standard GPS receiver time and location fix data with accuracy comparable to GPS receivers in its class – typically within 3 meters or better for latitude and longitude, and 6 meters or better for altitude. GPS position fixes use the latest processing techniques to eliminate jumps in position when the satellite constellation changes, while avoiding any lag in positional update when the unit moves. Note that the EGPS-200 raw speed channels data are computed using either the Doppler shift of the satellites, or the carrier phase of the GPS signal, and as such speed accuracy is not limited by the accuracy of the GPS position fix data.

The EGPS-200 also provides a TTL level trigger input that can be used as a trigger channel in any of the Computed channels such as the Integrator or a DataMode™ that support triggers. This is particularly significant for vehicle testing application such as brake testing, determination of zero-to-speed acceleration marks, etc.

All data channels output from the EGPS-200 are time stamped to ensure data integrity and provide tight synchronization with eDAQ analog and digital channels (acquired from the Bridge, High Level SS, and Digital layers). Typical data synchronization is within a few milliseconds.

The EGPS-200 Plus provides real time kinematic (RTK) channel data and an advanced IMU relative to the EGPS-200 Base product. This IMU provides enhanced tri-axial accelerometer channels and tri-axial gyroscope channels. The RTK option provides pitch, roll, and yaw rate channel data via the IMU gyroscopes, and instantaneous pitch and yaw data sourced from the dual GPS antennae system. This supports the acquisition of quasi real time nominal accuracy vehicle slip and squat data using simple Computed channels.

Cable connection and status LEDs diagram (Top view of 1-EGPS-200-P-2 shown)

EGPS-200 Status LEDs

LED Description
PWR (green) shows power and PPS lock status
Off Unit is not powered.
On Turns on immediately after 12 volt power is applied to the unit, which is typically several seconds after the connected CPU is powered up.
1Hz PPS lock is attained.
STAT (yellow) shows GPS signal status
Off Unit is not powered.
1Hz Unit has acquired enough satellites to get a GPS position fix (i.e., after the fix_quality channel is 1 or higher).
On For the EGPS-200 Plus (1-EGPS-200-P-2) only, RTK lock is attained.
TRIG (blue) shows input from the TRIG connector
Off No connection to the trigger input connector, so trigger channel is pulled high (internally).
On Connection to trigger input connector and the trigger channel input is pulled down to logic 0, when the two wires of the trigger cable pigtail (1-SAC-GPSTRIG-2) are connected to each other.

The EGPS-200 has been developed and optimized for vehicle testing applications in proving grounds quality environments where there is a consistently clear view of most of the sky from horizon to horizon. In such environments, high accuracy combined speed and integrated distance measurements are routinely attainable. Furthermore, short term interruptions of a clear view of the sky (such as passing under an overpass structure) are well tolerated with little or no sacrifice to this high accuracy. However, high accuracy (or even nominal accuracy) measurements are not attainable in environments such as urban areas with high rise buildings, rural areas with dense / tall trees lining the road, canyons in hilly / mountainous areas, etc. Users must be aware of this constraint and plan their vehicle testing programs accordingly.

To obtain maximum EGPS-200 data accuracy and integrity, it is essential that the GPS antennae and the EGPS-200 unit be properly mounted in the test vehicle. The EGPS-200 units require a 3.3V active antenna which must be mounted in a position giving a good view of the sky. The antennae (1-EGPS-200-ANT-2) supplied with the EGPS-200 unit are adequate for most EGPS-200 testing applications. However, for the most demanding applications, the user may want to consider procuring the highest quality antennae available. These are typically larger in size (and typically quite expensive).

EGPS-200 (1-EGPS-200-B-2) Base unit: The single antenna lead is connected to the ANT connector. Mounting the antenna on the top of the vehicle is recommended. The user should be careful not to crush the antenna lead – for example when a vehicle window or door is closed.

EGPS-200 (1-EGPS-200-P-2) Plus unit: Following is a diagram that illustrates the recommended antennae mounting on a test vehicle.

  • It is strongly recommended that the two antennas be mounted on the roof of the vehicle. The (primary GPS measurements) antenna that is connected to ANT1 must be to the rear of the (RTK measurements) antenna that is connected to ANT2.
  • The distance between the two antennae should be as close as possible to the RTK baseline distance of 800 millimeter. The magnetic mounting dual antenna template (1-EGPS-200-TEM-2) is provided to facilitate this. Small deviations on the order of a few millimeters can be tolerated with fairly insignificant loss of accuracy for the RTK channels.
  • The antennae should be mounted parallel to the direction of travel center line. This will minimize the difference between the heading channel data and the rtk_yaw channel data when there is no vehicle slip.
  • The antennae should be mounted so that both are the same distance above the ground. This will minimize the difference between the gradient channel data and the rtk_pitch channel data when there is no vehicle squat (dive).
  • Both antennas should be mounted directly to the metal roof of the vehicle. The metal under the antenna acts as a “ground plane” for the antenna. This is important for optimal satellite signal acquisition. Do not use adhesive tapes or any other material to hold the antennae in place - some adhesive tapes completely block acquisition of the GPS signals.
  • To avoid any possible damage to the car paintwork, clean the metal to remove any dirt or grime before mounting the antenna. This also reduces the possibility that the antenna will move when the vehicle experiences high acceleration rates or encounters strong wind gusts.
  • The antennas should be mounted so the antenna cables point in the same direction – for example mount the antennae such that both cables exit towards the rear of the test vehicle.
  • Both antennas must be of the same make and model. This is critical for acquiring accurate differential GPS data for the RTK channels.

Requirements and recommendations for mounting EGPS-200 units are as follows:

  • Due to the relatively small size of the EGPS-200 unit, mounting it in the test vehicle at the optimal orientation can be somewhat challenging. However, for acquisition of the combined speed, acceleration and gyroscope channels (1-EGPS-200-P-2 only), it is important to make a concerted effort to mount the unit per the following recommendations.
    • The unit should be mounted such that the “direction of travel” arrow on the EGPS-200 lid is parallel to the direction of travel center line, and points to the forward direction.
    • The unit should be mounted such that the XY plane of the unit is parallel to the ground plane. One way to check this is to verify that the X and Y axis accelerometers are centered at zero g’s when the vehicle is parked on flat ground.
    • Ideally, the unit should be mounted such that it sees the same IMU accelerations and angular displacements as the (typically roof mounted) antennae. While this may not be feasible in all situations, it is critical that the unit be rigidly secured to the vehicle chassis to minimize the differences between what the GPS antennae sense and what the IMU senses.
    • Before using the EGPS-200 for formal test data acquisition, the user is strongly advised to perform some check out tests to verify proper antennae and EGPS-200 unit installation.

Mounting diagram (Top view of 1-EGPS-200-P-2 shown)