Control system is a collection of so many physical components connected together to achieve certain objective. We have studied about different types of controls systems which are commonly deployed in various processes in our last article, and saw controls such as manual control, automatic control and so forth.
What is a system?
A system is a collection of many objectives with definite relationship between attribute and objective.
Scientific way to represent control system :
- INPUT → CONTROL SYSTEM → OUTPUT
- Manipulated variable → Control system → Controlled variable
The above sequence shows the flow of a control system wherein a variable is controlled using the system to keep the output within a specified range or value, depending on the exact scenario or situation. We shall now see how typically electronic pneumatic controls compare with each other. This will be done by a comparative study of both, listing the drawbacks and advantages of both. After going through both of these, the reader would have a good idea about the relative usefulness and application of both these types of systems.
Electronic Control System
- No time lag or transmission delay
- Linear and quick response and good accuracy
- No entrainment or contamination in control medium
- Integrated control system and easier interconnections
- Low power requirements
- Speed of response is substantially instantaneous
- Complex networks
- Difficult maintenance and test kit requirements
- Not possible for flame-proof areas
- Skilled maintenance regulations
- Expensive layout
- Good and safe wiring layout required
- Susceptible to line fluctuations of voltage and frequency
Image Credit: Tedvollers.com
Pneumatic Control System
- Simplicity of the components and no complex structure
- Easy maintainability
- Useful in flame -proof applications
- Low cost of installation
- Good reliability and reproducibility
- Speed of response is relatively slow but steady
- Limited power capacity for large mass transfer
- Great distance lag can be a crucial setback with pneumatic controls.
- Slow response
- Difficult to operate in sub-normal temperatures
- Copper piping is vulnerable to damage
- Pipe-couplings can give rise to leaks in certain ambient conditions
Image Credit: PAKWHEELS.COM
How Automatic Control Works ?
What ever may be the type of control system, the automatic process will be of the closed loop type; that is to say, it includes both the measuring means as well as the controlling means within the process itself, thereby completing the loop.
These are the steps followed in the automatic control system :
Step 1 :
A detection (measuring) means to sense the value of the process variable known as "primary element ".
Step 2 :
A transmission means of the measured signal to the measuring element .
A measuring element to reckon the actual process variable and display it called as "secondary element ".
A comparison means to detect error with reference to the desired set value .
A computation means to convert the error signal to a proportionate controller output (in phase and magnitude).
Step 6 :
A corrective (regulating) means by which the controller output signal is transmitted by the control medium to the final control element.