CAN Based Data Acquisition

Transcription

1 Introduction This project will convert physical temperature measurements into Controller Area Network (CAN) messages following the Society of Automotive Engineers standard, SAE-J1939, Surface Vehicle Recommended Practice format. The J1939 standard is universally used in the heavy-duty trucking and non-road vehicle industries in North America and Europe for controller to controller communication. Any J1939 compliant data collection device will be able to monitor and record the signals the specific use in this case is the engine test cell automation system at the PACCAR Technical Center. Description The device used for this project is a National Instruments Compact RIO system consisting of a controller, model NI crio-9014, and an 8 port, 3M gate chassis model NI To handle the I/O, 7 thermocouple modules, model NI-9213, and one CAN module, model NI-9853, were installed into the chassis. Each thermocouple module can accept 16 thermocouples and the CAN module has 2 low-speed CAN channels. The CRIO hardware is a real time microcontroller coupled with a Field Programmable Gate Array (FPGA). The CRIO unit plugs into a chassis with up to 8 additional slots for I/O modules, allowing for easy configuration and reconfiguration as necessary. The chassis dimensions are 28 cm x 9 cm x 9 cm, and all modules and the controller fit within this package. See figure 1 for a photo of the hardware. 1 of 10

2 CAN Based Data Acquisition Figure 1 crio unit, complete Hardware Description The crio device consists of 3 main components the real time controller or microprocessor, the chassis which contains the FPGA gates, and the I/O modules which handle the signal conditioning. The controller uses a 400 MHz Freescale MPC5200 real-time processor, 128 MB of internal DRAM and 2 GB of non volatile memory. The controller itself has a power consumption of 6W, and the chassis maximum power is 3W. With a chassis equipped with 8 modules, the recommended power supply is a 24 VDC 48W, as the unit will draw up to 20W during normal operation after the inrush current on startup. The 16 channel thermocouple modules have 24 bit resolution, can sample up to 1200 samples / second with 0.02 C of resolution in high-res mode, and a maximum power consumption of 490mW and thermal dissipation of 840mW. The CAN module has a maximum baud rate of 1 Megabit per second (Mbps), maximum power consumption of 625mW, and thermal dissipation of 1W. As configured, this unit will have a maximum power consumption of W. A basic block diagram of the hardware and signals is in figure 2 below. 2 of 10

3 Figure 2 Hardware Layout 3 of 10

4 Software Requirements National Instruments LabVIEW software was used for this project. LabVIEW is a proprietary graphical programming language used to develop measurement, test and control systems using graphical icons and "wires" connecting the icons, resembling a flowchart. National Instruments hardware is designed to run LabVIEW applications created by the end user, and LabVIEW contains hundreds of built-in libraries to create virtual instrumentation to aid in rapid development of software. The software will run a loop once per second, and will read in all the thermocouples and transmit all necessary CAN messages once per loop. The CAN message can hold up to 8 bytes of data per message, and there are 112 thermocouple channels, which require 2 bytes for each signal, so 28 CAN messages will be required to transmit all the data. A flowchart of the process is below in figure 3. 4 of 10

5 Start Start for loop 1 to 28 Case 1 to 28 Read in 4 thermocouples from FPGA layer Encode CAN message Send CAN message to FIFO buffer End For Loop End Figure 3 Main Software Loop User Interface When programming in LabVIEW, all the signals are automatically placed on the top layer VI, but this project did not make much use of the LabVIEW user interfaces. The primary use of LabVIEW VI was merely troubleshooting the program and signal processing, as the main use of the program was to 5 of 10

6 provide the correct CAN message output. The automation system that will receive the CAN message has a configurable GUI for the test operator and engineer to monitor, and a screenshot of this is in figure 4 - notice the temperature tabular readouts in the lower left corner. The automation system also has data acquisition built in to record all data to a file for postprocessing of the data. Figure 4 PUMA Automation System GUI Communication Protocols The standard SAE J Surface Vehicle Recommended Practice provides in depth requirements for compliance, from the hardware design to the abstract layers of the CAN message format. This project only deals with the software side of the CAN message itself - particularly the encoding and decoding of this message. The speed of this CAN message is 250 kbps with a 29 bit identifier, which consists of a parameter group number (PGN) and a 6 of 10

7 source address, and 8 bytes of data as described in figure 5. The PGN identifies the content of the data field and sets priority of the message. Figure 5 - J1939 Message format The CAN message frame components are: SOF - Start of Frame CAN-ID - 29 bit identifier, consisting of the Parameter Group Number (PGN) and the source address o PGN is 21 bits long, defined in the CAN database and in the SAE J standard Priority field - 3 bits, sets the priority of the message on the network, 0 is highest priority Reserved - for future use, set to zero Data Page - used to expand the maximum number of possible messages 7 of 10

8 PDU Format (PDU-F) - 8 bits, used to determine if the message is intended for a specific device or the entire network PDU Specific (PDU-S) - 8 bits, defined by PDU-F - if intended for a specific device, this is the destination address; if intended for the entire network, it is interpreted as a Group Extension field o Source Address - the address of the device sending the message. Each device on the network must have a unique address RTR - Remote Transmission Request Control - Contains data length code Data Field - up to 8 bytes (64 bits) in single frame, more data can be sent in multiple frame messages o This is where the data is transmitted, in this project 8 bytes are used for 4 thermocouple channels, 2 bytes or 16 bit resolution CRC - Cyclic Redundancy Check ACK - Acknowledge EOF - End of Frame The PGN is used as a reference lookup in the CAN database, which defines the contents of the data field. The CAN database is defined by the SAE J document and describes standard parameters which are grouped together in a message frame and given a PGN. Each parameter is described by its length, resolution, range, type, Suspect Parameter Number (SPN), and the PGN in which the parameter is grouped. Each PGN is described by its transmission rate, data length, data page, PDU-F, PDU-S, priority, and the data parameter bytes (the parameters included in the data field and their byte order). The J document provides a certain number of PGNs for free use, and this project used 28 of those available PGNs to define the CAN messages that I send. 8 of 10

9 Development Plan This project is currently underway to provide this instrumentation for my employer, and the project will be completed long before the Spring quarter. Week#/Year Planned activity 44 / 2010 Hardware arrived, simple assembly and begin writing code 45 / 2010 Set up FPGA for input signals 46 / 2010 Continue FPGA code development 47 / 2010 Write main control loop 48 / 2010 Continue with main control loop 49 / 2010 Set up CAN database 50 / 2010 Continue CAN database 51 / 2010 CAN message encoding 52 / 2010 CAN message encoding 1 / 2011 FIFO buffer system and FPGA configuration for output 2 / 2011 Error checking and debug 3 / 2011 Connect to automation system 4 / 2011 CAN message decoding into automation system data acquisition 5 / 2011 Error checking and debug 6 / 2011 Data collection 7 / 2011 Data collection 16 / 2011 Hardware review with class 18 / 2011 Software system presentation 21 / 2011 Code review 22 / 2011 Project Demonstration I will be using National Instruments LabVIEW for all software code and a CAN analysis software called CANalyzer from Vector Informatik. For the project demonstration, I will bring the crio unit and several thermocouples into the lab and the CAN message transmission can be viewed using CANalyzer. I will also have several posters to show the LabVIEW graphical code and the structure of the crio platform. During the spring quarter for code review and other tollgates, I will present the graphical based National Instruments LabVIEW code. This code will be presented with a pseudo-c equivalent to demonstrate the pros and cons of 9 of 10

10 using LabVIEW. If desired, a simple exercise could be developed for the students to gain exposure to LabVIEW. Industry Standards SAE J1939 Electrical Specifications Range : minimum C Accuracy : +/- 2 C Data transmission rate : all messages sent at minimum 1/sec Power Supply : 24VDC / 50W Operating Temperatures : -40 C to 70 C Maximum Power Consumption : W Part List The price list is current, but the only hardware purchased for this project were the thermocouple I/O modules and connector components, as my employer already had all the other hardware, which was one reason for choosing this option for the data acquisition hardware. All components were purchased from National Instruments. Part Number Description Power Quantity Price Total NI crio-9014 Controller 6W 1 $2699 $2699 NI-9104 Chassis 3W 1 $2899 $2899 NI-9213 Thermocouple I/O 490mW 7 $999 $6993 NI-9853 CAN I/O 625mW 1 $1149 $ Connector block n/a 7 $39 $ Backshell n/a 7 $29 $203 Total Cost of all Hardware $14216 Minus price of available hardware -$6747 Total Project Costs $ of 10