MATLAB: Does the Data Acquisition Toolbox support real-time closed-loop control

.datdaqData Acquisition Toolboxrealtime

I would like to know if the Data Acquisition Toolbox supports real-time closed-loop control.

Best Answer

The Data Acquisition Toolbox was not designed to support real-time control. The toolbox is specifically designed to bring measured data into MATLAB. The Data Acquisition Toolbox is built on top of MATLAB and operates in a non real-time Microsoft Windows environment. Because of this, it is not possible to achieve deterministic real-time operation.

For real-time control with MATLAB, we suggest that you take a look at the following Products:

- Simulink Coder

https://www.mathworks.com/products/simulink-coder.html

- Simulink Desktop Real time

https://www.mathworks.com/products/simulink-desktop-real-time.html

- Simulink Real Time

https://www.mathworks.com/products/simulink-real-time.html

These products are specifically designed for Real-time Control, and generate C-code that is downloadable to a real-time operating system which will guarantee real-time control simulation, and hardware-in-the-loop simulation of embedded real-time systems.

If deterministic real-time control is not required, it is possible to use the Data Acquisition Toolbox for single-point acquisition and control, however, the toolbox was not designed for such operation and any use of the Data Acquisition Toolbox for these purposes will be at the user's own risk.

When attempting to use the toolbox in this manner, the data acquired goes through all of the following steps:

1. Data is acquired and brought up through the particular hardware vendor's software

2. The data is handed off to the Data Acquisition Toolbox engine.

3. The data is made available in MATLAB.

4. The data is run through whatever control algorithm the user designs in MATLAB.

5. The data is then routed back to the engine and down through the hardware vendor's software into the board.

Because MATLAB and the Data Acquisition Toolbox are operating in a non-real-time environment, each one of the steps stated above presents an opportunity for a higher priority thread to take precedence over the control loop. This introduces the possibility for jitter in your control loop once the data has been acquired and brought into MATLAB; the complexity of the control algorithm further increases the time required to be able to control the system.

Related Solutions

MATLAB: Will the Data Acquisition Toolbox work with Simulink

Starting with Data Acquisition Toolbox 2.9 (R2006b), Simulink blocks to acquire live or measured data directly into your Simulink models are provided as part of the toolbox. Data Acquisition Toolbox block library consists of four Simulink blocks:

1. Analog Input block

2. Analog Output block

3. Digital Input block

4. Digital Output block

Additional information is provided on the Data Acquisition Toolbox product page at: http://www.mathworks.com/products/daq/

Note, Data Acquisition Toolbox was not designed to support real-time control. It is specifically designed to bring measured data into MATLAB and Simulink. Since the toolbox is built to operate inside a non real-time Microsoft Windows environment, it is not possible to achieve deterministic real-time operation.

If deterministic real-time control is not desired, it is possible to use Data Acquisition Toolbox for acquisition and control in Simulink. For deterministic real-time control in Simulink involving data acquisition, you need to use Real-Time Workshop and one of the real-time targets available, such as:

1. Real-Time Windows Target - http://www.mathworks.com/products/rtwt

This runs your model on the same machine as Simulink (task-sharing the processor between a real-time kernel and Windows).

2. xPC Target - http://www.mathworks.com/products/xpctarget

This requires a separate machine, which can range from an Intel 486 to a Pentium 4 or an Athlon based machine.

The target to be used depends on your application and hardware. In general, if speed is not an issue, use Real-Time Windows Target. Otherwise, use a second machine and xPC Target.

MATLAB: National Instruments Data Acquisition Trigger Events & Listeners

MATLAB documentation lists the following example to acquire data in the background by creating a session and adding a listener to access the acquired data using an anonymous function. For a continuous background generation, add a listener event to queue additional data to be output:

      s = daq.createSession('ni');
      s.addAnalogOutputChannel('cDAQ1Mod2', 0, 'Voltage');
      s.IsContinuous = true;
      s.Rate = 10000;
      data =  linspace(-1, 1, 5000)';
      lh = s.addlistener('DataRequired', ...
              @(src,event) src.queueOutputData(data));
      s.queueOutputData(data) 
      s.startBackground();

% perform other MATLAB operations during the generation.

The operation is continuous,

      s.stop();
      delete(lh);

As to how you can add a trigger connection and send data to computer for processing, you can refer to the link provided below: http://www.mathworks.com/help/daq/ref/addtriggerconnection.html#bt_7mfo-1

Best Answer

Related Solutions

MATLAB: Will the Data Acquisition Toolbox work with Simulink

MATLAB: National Instruments Data Acquisition Trigger Events & Listeners

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