SAMPLE DATA CONTROL SYSTEM        

Sample data control system

 control systems are implemented digitally, on platforms that range from large computer systems (e.g. the mainframe of an industrial SCADA system) to small embedded processors. Since computers work with digital signals and the systems they control often live in the analog world, part of the engineered system must be responsible for converting the signals from one domain to another.

In particular, the control engineer should understand the principles of sampling and quantization, and the basics of Analog to Digital and Digital to Analog Converters (ADC and DAC).

Control systems that combine an analog part with some digital components are referred to as sampled-data systems.

In sampled-data systems, the plant to be controlled is an analog system (continuous-time), and measurements about the state of this plant that are initially in the analog domain need to be converted to digital signals. This conversion process from analog to digital signals is generally called sampling done by analog to digital converter.

 

Sampled data control system

The digital controller produces required digital control signals, which need to be transformed into analog signals to actuate the plant. In control systems, this transformation is typically done by a form of signal holding device, most commonly a zero-order hold (ZOH) producing piecewise constant signals and digital to analog converter.

 

Advantages of sampling in control

1. Improved sensitivity

2. Better reliability

3. No drift

4. Less effect due to noise and disturbance

5. More compact and lightweight

6. Less cost

7. More flexibility

why sampling is important?

1. The high degree of accuracy is prerequisite

2. Required for long-distance transmission

3. Pulse amplitude modulated data is easily transmitted (little loss of accuracy) by means of the carrier over a transmission channel and data reconstructed at the receiving end

4. More than one channel of information may be sequentially sampled and transmitted through a single transmission system (time multiplexing) thus decreasing the cost of transmission installation.

5. Reduces power demand, helpful for signals of weak power origin

 Sampled data systems are used

1. When digital computers are used as part of the control loop

2. For time-sharing of control components

3. Whenever a transmission channel forms part of the control loop

4. Whenever the output of a control component is essentially in discrete form