GPS channels

GPS channels are sourced from the GPS connector on a data processor. EGPS-200, EGPS-200-Plus and Garmin GPS modules are supported.

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 SomatXR/eDAQXR system, 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 SomatXR/eDAQXR data processor allowing it to identify the module. When the data processor receives this message, it switches to the 12 Vdc power mode.

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

All GPS modules source standard NMEA sentences that provide GPS fix position, fix quality, fix date and time and other standard navigational parameters.

NOTE
Position accuracy varies with several factors including, but not limited to, GPS receiver configuration, location (geographic latitude, as it influences HDOP, and surrounding objects possibly blocking reception or causing multi-path reception), satellite constellation status and ionosphere conditions.

  • The Garmin GPS module also sources dilution of precision parameters (i.e., positional, horizontal and vertical). All Garmin channels are sourced at 5 Hz.
  • Both the EGPS-200 and EGPS-200-Plus modules source proprietary NMEA sentences that provide IMU information (i.e., tri-axial acceleration and vehicle yaw rate, roll rate and pitch rate). Both also provide a high accuracy 3D Speed computed channel. All of these channels are sourced at 200 Hz.
  • The EGPS-200-Plus module additionally sources real time kinematic (RTK) parameters (i.e., yaw and pitch) using two antennae that must by properly and accurately mounted on the vehicle. These additional channels are sourced at 20 Hz.

All modules provide GPS PPS time sync pulses that allow the SomatXR/eDAQXR system to align the GPS channel data to be synchronized in phase with other SomatXR/eDAQXR channels (i.e., analog and digital input channels).

Note that this “PPS sync” can only be achieved when the GPS module is providing fix date and time information. This will not be immediately available when the GPS module is first connected to the SomatXR/eDAQXR system, or after the SomatXR/eDAQXR is power cycled, or if the vehicle loses GPS satellite reception for any other reason. The time required for the “PPS sync” to become active is in part module type dependent, but can vary from a few seconds to well over one minute. The system provides a “pps_sync_active” channel; this is a logical channel that is true (1) when the “PPS sync” is active and false (0) when it is not active.

The SomatXR/eDAQXR supports a GPS raw message channel that captures all of the NMEA sentences received from the GPS module. The timestamps for the messages are the times when the messages were received – not the “PPS sync” adjusted times.

ClosedGeneric parameters

  • Connection: A unique hardware identifier created by the system.
  • Reading: Current value of the channel. Show the readings by selecting the desired channels and clicking Live update. Not in edit dialog.
  • Units: For most channel types, the user can enter the physical units as desired; however, for some channel types (i.e., most temperature channels, and any bridge channel that uses the Strain gage scaling mode), the user can only select an option provided in the drop down list box presented.
  • Name: The channel name must be unique and contain valid characters (invalid characters are single and double quotes, '\', '@', '#', '&', '<' and '>'). Invalid channel names are 'true' and 'false' (case sensitive).
  • Description: Enter an optional detailed description of the channel.
  • Measurand: Enter an optional measurement type.
  • Data type: The format of the channel data output (read only).
  • Collect: Select the Collect checkbox to write the channel data to the SIE data file during a test run.
  • Sample rate: Select the desired channel sample rate. If the sample rate changes, all dependent computed channels and DataModes™ are changed automatically.
  • Custom column information: Enter the desired information. The system treats all input as free formatted text. This means it will sort alphabetically, but not alphanumerically (e.g., input values of “1”, “2”, “11”, will be sorted descending as “1”, “11”, “2”). Use leading zeros to realize alphanumeric sorting.
  • Range min / Range max: Enter the desired full scale range min and max values in physical (engineering) units. For all channels, they are used as the default min and max bounds for histogram DataModes.
  • Alarm min / Alarm max: Enter the desired values for min and/or max alarms as a physical units value or as a % of Range min/max value.
  • Warning min / Warning max: Enter the desired values for min and/or max warnings as a physical units value or as a % of Range min/max value.
  • Chart type: Set the default chart type for the channel. Not in edit dialog.
  • Decimals: Select the default decimal places for channel displays. Use the “Auto” option to apply the settings defined in the User Preferences. See User preferences > General > Decimal point handling for more information.
  • Expiration time: Specify the time period in seconds that can elapse without data before data is considered stale and the output is set to the invalid value. The value may be any real number greater than zero.
  • Invalid value: Specify the value to be set when the expiration time has elapsed without any data. The value may be any real number.

ClosedScaling parameters

  • Scaling mode: Set the channel scaling mode.
  • Electrical units: Electrical units of channel input. This is fixed by the system and cannot be changed. The defined sensor scaling is used to convert data from Electrical units to Physical units.
  • Units: Physical units of measurement for the channel.
  • Electrical 1: Specify for Defined two point scaling mode. Automatically set after Experimental two point scaling.
  • Physical 1: Specify for Defined two point scaling mode. Automatically set after Experimental two point scaling.
  • Electrical 2: Specify for Defined two point scaling mode. Automatically set after Experimental two point scaling.
  • Physical 2: Specify for Defined two point scaling mode. Automatically set after Experimental two point scaling.
  • Electrical zero: Specify for Defined zero span scaling mode.
  • Electrical span: Specify for Defined zero span scaling mode.
  • Physical span: Specify for Defined zero span scaling mode.
  • Slope: Specify for Defined slope intercept scaling mode.
  • Intercept: Specify for Defined slope intercept scaling mode.
  • Prerun zero mode: Set to Interactive only to allow channel zeroing.
  • Prerun zero offset: Automatically set after zeroing a channel. The user can edit this, but that is not generally advised.
  • Prerun zero target: Specify the physical value desired for the zero task. Typically, this is 0.0, but not always. For example, this parameter may be set to 1.0 (g) for an accelerometer that senses the force of gravity. In this example, the zero task would result in the channel data being offset so that the current reading is 1.0.
  • Range min and max: Specify the expected extreme values of the channel. These parameters are most significant for the EBRG and EHLS layer channels because they are used to set the signal conditioner gains and offset. For other channel types, they are less significant. However, for all channel types, they are used as defaults for the histogram bounds in applicable data modes, and they can also be used as default y-axis limits for strip chart displays.
  • Warning and Alarm min and max: Specify the desired values for warning and alarm thresholds.
    • Enter a real number that defines the level in physical units, or a real number followed by the ‘%’ character that defines the level as a percent of Range max or min, or leave the cell blank to inhibit the warning or alarm.
    • The percent value must be in the range of 0% to 120%.
    • The % of Range max is independent of Range min and vice-versa. For example, if Range max is set to 1000 and Range min is set to -500 and 90% is used for both alarm levels, the alarms trip when the data value becomes > 900 or <-450. If the user changes the Range min to -600, the Min alarm threshold changes to -540. However, the Max alarm threshold does not change (i.e., it is still 900).
    • The values of the warnings and alarms, in terms of real numbers, must satisfy the following condition for all defined parameters:
      Min alarm threshold < Min warning threshold < Max warning threshold < Max alarm threshold.
    • A min or max warning will show a yellow background for the numbers.
    • A min or max alarm will show a red background for the numbers.
  • Max electrical: This field is applicable to MXB modules only. It is used to set the signal conditioner gain and resultant measurement range.