Data acquisition system (DAQ) is the process of measuring an electrical or physical phenomenon like voltage level, current flowing, temperature intensity, pressure amount, or sound intensity with a computer. This data acquisition system consists of sensors to sense, measurement hardware for the readings, and a computer with programmable software. PC-based Data Acquisition systems exploit the processing power of the system, system productivity, result display, connectivity capabilities of industry-standard computers, providing a more powerful solution, flexible, and cost-effective measurement solution.
Data Acquisition System
The Data Acquisition System consists of 3 parts
- DAQ Device
The measurement of a physical phenomenon begins with a sensor. It also called a transducer, converts a physical phenomenon into a measurable electrical signal. Depending on the type of sensor, its output can be a voltage, current, resistance, or any other indicator that varies over time. Sensors may require additional components and circuitry to properly produce a signal that can accurately and safely be read by a DAQ device.
DAQ hardware acts as the interface between a computer and signals from the outside world.Primary function is to digitize the incoming analog signals so that a computer can detect. DAQ will have three components as signal conditioning circuitry, analog-to-digital converter (ADC), and computer bus. This DAQ devices include other functions for automating measurement systems and processes.
The CAN protocol is an international standard defined in the ISO 11898-1. The conformance test for the CAN protocol is defined in the ISO 16845-1, that guarantees the interoperability of the CAN protocol controller chips.
Principles of Data Exchange
CAN protocol is based on the broadcast communication mechanism, by using a message-oriented transmission protocol that defines a message contents rather than stations and station addresses. The Message will have a message identifier, that is unique within the whole network since it defines the content and also the priority of the message. It is important when several stations compete for bus access (bus arbitration). By content-oriented addressing scheme a high degree of system and configuration flexibility is achieved.
So, we can easily add stations to an existing CAN network without making any hardware or software modifications to the present stations as long as the new stations are purely receivers. It allows for a modular concept and also permits the reception of multiple data and the synchronization of distributed process. The Data transmission is not based on the availability of specific types of stations, it allows simple servicing and upgrading of the network.
Real-Time Data Transmission
Real-time process may require different priorities. A message which is transmitted compared to other less urgent message is specified by the identifier of each message. Priorities are laid down during system design in the form of corresponding binary values and cannot be changed dynamically. This identifier with the lowest binary number has the highest priority.
Message Frame Formats
CAN protocol supports two message frame formats. There is only difference in the length of the identifier. CAN base frame supports a length of 11 bits for the identifier whereas the CAN extended frame supports a length of 29 bits for the identifier.
CAN Base Frame Format
CAN base frame message begins with the start bit called Start Of Frame (SOF), followed by the Arbitration field consists of identifiers and Remote Transmission Request (RTR) bit used to distinguish between the data frame and the data request frame called remote frames. Followed Control field contains the IDentifier Extension (IDE) bit to distinguish between the CAN base frame and the CAN extended frame “Data Length Code (DLC)” used to indicate the number of following data bytes in the “Data field”.
A message is used as a remote frame, then DLC contains the number of requested data bytes. A Data field that follows is able to hold up to 8 data bytes. The Integrity of the frame is guaranteed by the following Cyclic Redundant Check (CRC) field. Acknowledge (ACK) field compromises the ACK slot and the ACK delimiter frame.
The ACK slot bit is sent as a recessive bit and is overwritten as a dominant bit by those receivers. Messages are acknowledged by the receivers regardless of the result of the acceptance. End of the message is indicated by End Of Frame (EOF). Intermission Frame Space is the minimum number of bits separating consecutive messages.
CAN Extended Frame Format
The difference between an extended frame format message and a base frame format message is the length of the identifier. 29-bit identifier is made up of the 11-bit identifier (base identifier) and an 18-bit extension (identifier extension). The distinction between CAN base frame format and CAN extended frame format is made by using the IDE bit transmitted as dominant in the case of an 11-bit frame that transmitted as recessive in case of a 29-bit frame.
Two formats have to co-exist on one bus is laid down which message has higher priority on the bus in the case of bus access collision with different formats and the same identifier base identifier and 11-bit message always has priority over the 29-bit message. Extended format has some trade-offs like bus latency time is longer 20 bit-times, the messages in extended format require more bandwidth (about 20 %) that the error detection performance is lower because the chosen polynomial for the 15-bit CRC is optimized for frame length up to 112 bits.
Detecting and Signaling Errors
If CAN protocol does not use, acknowledgement messages, then signal errors immediately occurs. Error detection and the CAN protocol implement three mechanisms at the message level
Cyclic Redundancy Check (CRC) : CRC safeguards the information in the frame by adding a frame check sequence (FCS) at the transmission end. Receiver this FCS is re-computed and tested against the received FCS. There will be a CRC error if they do not match.
Frame check: Frc mechanism verifies the structure of the transmitted frame by checking the bit fields against the fixed format and the size of the frame. The Errors detected by frame checks are designated format errors.
ACK errors: The Receivers of a message acknowledge the received frames. The transmitter does not receive an acknowledgement, then an ACK error is indicated.
Measurement Components of a DAQ Device
Signals from the sensors or the outside world can be noisy or too dangerous to measure directly by physical manner. The Signal conditioning circuitry manipulates a signal into a form that is suitable for input into an ADC device. Signal conditioning circuitry can include amplification of signal, attenuation, signal filtering, and isolation. The DAQ device includes built-in signal conditioning designed for measuring specific types of sensors.
Analog-to-Digital Converter (ADC)
In analog to digital converter, Analog signals from sensors must be converted into digitally before they are manipulated by digital equipment such as a computer and reading devices. The ADC is a chip that provides a digital representation of an analog signal at an instant in time in a practical way, these analog signals continuously vary over time and an ADC takes periodic samples of the signal at a predefined rate. Samples are transferred to a computer over a computer bus where the original signal is reconstructed from the samples in software.
The DAQ devices connect to a computer through a slot or port. This computer bus serves as the communication interface between the DAQ device and computer for passing instructions and measured data over the sensor. The DAQ devices are offered on the most common computer buses that include USB, Ethernet, PCI, PCI Express. Recently, these DAQ devices have become available for 802.11 Wi-Fi for wireless communication purpose. Many types of buses available, and each offers different advantages for different types of applications.
Computer’s Role in a DAQ System
A computer with programmable software controls the operation of the DAQ device and is used for processing data, data visualization and storing measurement data. We use Different types of computers for different types of applications. As we know desktop may be used in a lab for its processing power capacity, a laptop may be used in the field for its convenience and an industrial computer may be used in a manufacturing plant for its ruggedness.
Different Software Components in DAQ
Driver software provides application software to interact with a DAQ device. Device simplifies communication with the DAQ device by abstracting low-level hardware commands and a register-level programming for the device. DAQ driver software exposes an application programming interface (API) that is used within a programming environment to build application software.
Application software facilitates the interaction between the computer and used for acquiring the data, to analyze the data, and presenting measurement data in a better way. DAQ software is either a pre built application with predefined functionality in a programming environment for building applications with custom functionality with requirements. These Custom applications are often used to automate multiple functions of a DAQ device to perform signal-processing algorithms and also display custom user interfaces.
Wireless Data Acquisition System
Wireless Sensor Network
All Sensors are connected to each wireless device. These devices, self-organize into a redundant wireless multi-hop mesh, data will forward to the gateway. Wireless sensors use an innovative low power listening technology to keep up connectivity amongst each other while offering years of autonomous operation from standard batteries.
The gateway connects the sensor network to the Internet via communication technologies such as GPRS or Ethernet. Gateway allows data to flow from the sensor network to the cloud storage, and it configures information and commands from the cloud to the sensor devices.
The cloud-based data storage and analysis application collects the data and stores it in a database. The Cloud provides a convenient user interface to visualize sensor data and allows for device configuration and user notifications in case sensor data exceeds pre-defined thresholds.
EEPROM Stands for Electrically Erasable Programmable Read-Only Memory and is a type of non-volatile memory used in computers and other electronic devices to store small amounts of data that must be saved when power is removed. Individual bytes in a traditional EEPROM can be independently read and erased for re-written.
When larger amounts of static data are to be stored such as in USB flash drives a specific type of EEPROM such as flash memory is more economical than traditional EEPROM devices. These EEPROMs are organized as arrays of floating-gate transistors.
The EPROM usually must be removed from the device for erasing and programming, but EEPROMs can be programmed and erased in-circuit, with applying special programming signals. EEPROMs were limited to single byte operations, that made them slower, these modern EEPROMs allow multi-byte page operations, which also has a limited life – that is, the maximum number of times it could be reprogrammed was limited to tens or hundreds of thousands of times. Delimitation has been extended to a million write operations in modern EEPROMs. An EEPROM that is frequently reprogrammed while the computer is in use, the lifespan of EEPROM can be an important design consideration. For this reason that EEPROMs were used for configuration information than random access memory.
Applications of Data Acquisition System
The Data Acquisition system targets all types of low data rate sensing and applications include
- Energy observation and monitor
- Object tracking at any moment
- Process automation and management
- Conditional maintenance
- Environmental observation and maintenance
- Weather observation and monitoring
- Structural heal observation and monitoring
- Physical safety and perimeter observation and monitoring
- Smart agriculture and irrigation control and management4
The Data acquisition system plays a crucial role in data management. It takes data from the sensors in both wired and wireless manner. It processes the data and stores to analyze. Different hardware and softwares are used while doing process. EEPROM is the one of data carrying device that can be used number times. Furthermore, any queries regarding this article or LABVIEW programming for virtual projects, please give your feedback by commenting in the comment section below.