CAN channels
CAN channels use Vector CAN databases or eDAQ CAN databases to decode specific signal values from incoming CAN messages on an eDAQXR, eDAQXR-lite, CX23-R, MX471B-R or MX840B-R CAN connector.
NOTE
The eDAQ CAN databases are currently supported only by the eDAQXR, eDAQXR-lite and CX23-R CAN interfaces. They are not supported by the MX471B-R or MX840B-R CAN interfaces.
The MX471B-R and MX840B-R support up to 128 CAN channels for each CAN connector. In reality, they cannot support that many channels if the CAN bus load is too high. As such, use caution when assigning CAN channels to these sources.
For the eDAQXR, eDAQXR-lite and CX23-R, there is no fixed limit on the number of CAN channels per CAN port. There is additional support for active queries (SAE® J1939-21 PGN requests) on for up to 75 messages per CAN connector. Furthermore, the default request messages can be edited by the user for special tasks such as J1939 address claiming.
Generic parameters
- Connection: A unique hardware identifier created by the system.
- 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.
- 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.
- Sample rate: Select the desired channel sample rate. If the sample rate changes, all dependent computed channels and DataModes™ are changed automatically.
- Measurand: Enter an optional measurement type.
- Input mode: Select the digital input mode from the options presented. In the channel edit dialog, a wiring diagram for the selected input mode is available for reference.
- 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.
- 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.
- Network node: A CPU serial number shows for a module or camera channel's network node.
- Custom column information: For each column to be used, enter a unique name for the column header. Select either the “Text” or the “Numeric” sorting option.
- 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. For EBRG and EHLS channels, they are used to set the programmable gain and D/A offset to maximize the resolution of the data.
- 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.
Specific parameters
- Input mode: Value is CAN.
- Edit CAN parameters: Click to open a dialog. Dialog information may be changed only if the channel is not calibration locked. Click OK in the dialog to apply changes. See Editing database source channel parameters for more information.
- Expiration time: Specify the time period in seconds that can elapse without data arriving on the CAN bus 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.
- Bit rate: Set the bit rate from the drop-down list of valid values. If the CAN bit rate is changed, all channels on the same port are changed to the same bit rate value automatically.
- Termination: Set the state of the internal termination resistor as true or false. If the termination state is changed, all channels on the same port are changed to the same state automatically.
- Request rate: For unit channels, optionally set the rate for active query requests. When set (not Off), the unit transmits SAE® J1939-21 compliant PGN request messages at the specified rate. Since, request messages are only requests, they may or may not be honored by the connected CAN device. Request messages are only transmitted during a test run.
- Request msg: For unit channels, value is a hexadecimal representation of the SAE® J1939-21 compliant PGN request. This value is read-only and computed based on the CAN message ID. Only applicable when the request rate is set (not Off).
Scaling parameters
-
Scaling mode: Set the channel scaling mode.
- Defined slope intercept: Specify the Slope and Intercept of the scaling line.
- Defined zero span: Specify the Electrical zero of the sensor scaling line. Enter both the Electrical span and the Physical span.
- Defined two point: Specify the Electrical 1, Physical 1, Electrical 2 and Physical 2 points to define the scaling line.
- Experimental two point: Use the Experimental two point scaling option to define the two point parameters based on experimental measurements.
- Electrical units: Electrical units of channel input. The defined sensor scaling is used to convert data from Electrical units to Physical units.
- Calibration date: When using the channel calibration dates and locks option, the UTC calibration date (yyyy-mm-ddThh:mm:ss) is shown when the channel is calibrated. See Calibration options for more information.
- 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.
- 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.
Zero parameters
- Zero mode: Select one of the following options.
- Not applicable: Zeroing is not allowed.
- Interactive only: Interactive zeroing is allowed.
- Normal Test Starts: Zeroing is done automatically on every normal test start. Interactive zeroing is allowed.
NOTE
Normal test start is defined as a test started using the web browser user interface, or a test started using the remote control switch when the Remote control run mode is in use. For tests that use the Cyclic test run mode, only the test started in the user interface is applicable; test cycles started automatically after the previous test cycle are not applicable. Tests restarted on power cycles or error resets are not applicable.
- 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.
- Zero offset: Automatically set after zeroing a channel. The user can edit this, but that is not generally advised.
Database sourced parameters
CAN database sourced parameters can also be viewed and edited. See the topic Editing database source channel parameters for more information.
Technical Note: CAN Message ID Masking
For each signal, a CAN database file specifies which CAN message ID (or IDs) carry the signal, the bit position and length of the signal within the CAN message payload and the format of the signal data, including its endianness, scaling and offset. When a database has been imported into a unit, this information about each signal is displayed in the Databases page accessible in the System view.
In some cases, a signal may be carried in more than one CAN message ID. For example, SAE J1939 designates 8 of the CAN message ID bits as a "source address." SAE J1939 CAN messages transmitted by different source nodes in a CAN network may have different message IDs while still referring to the same SAE J1939 PGN and carrying the same signal. To accommodate such situations, a unit CAN database can specify both a CAN message ID value and an optional bit mask. To decide whether an incoming CAN message carries a particular signal, the bitwise-AND of its ID with the database bit mask is compared to the bitwise-AND of the database message ID value with the bit mask. If a mask is not specified, the message IDs must match exactly.
The eDAQ text database file format allows the user to explicitly specify both the message ID value and the bit mask. When imported into a unit, these values are shown in the Databases view as the "Value" and "Mask," respectively.
The Vector DBC database file format contains information about each message and signal which the unit uses to automatically determine an appropriate bit mask. SAE J1939 messages with a "null" source address value (0xFE) cause the unit to generate a mask which ignores the source address portion of the CAN message ID. SAE J1939 messages with a specific source address value and all non-J1939 messages, cause the unit to omit the mask, so that the specified message ID must be matched exactly. The message ID value and mask determined by the unit are shown in the Databases view as the "Message ID" and "Mask," respectively. The Mask value will be blank if masking is not being used (that is, if the CAN message IDs must match exactly).