Microprocessor-Based Instrumentation System
The microprocessor is a multipurpose programmable, clock-driven, register-based electronic device that reads binary instructions from a storage device called memory, accepts binary data as an input, processes it according to those instructions, and provides results as output.
An instrumentation system is defined as the assembly of various instruments and other components interconnected to measure, analyze, and control physical quantities such as electrical, thermal, mechanical, etc. Instrumentation systems centered around a microprocessor are known as microprocessor-based instrumentation system.
Basic features of a microprocessor-based system
The basic features of a microprocessor-based system are;
- Parallel processing
- User friendly
- Repeatability of readings
- Microprocessor-based instrumentation system comprises three main components: microprocessor, input/output, and memory.
- It has decision-making power based on the previously entered values.
- Timesharing and multiprocessing
- Effective control of multiple equipment on time time-sharing basis.
Types of microprocessor-based system
Any instrumentation system can be controlled by a microprocessor in two ways: An open-loop microprocessor-based system and a closed-loop microprocessor-based system.
- Open-loop microprocessor–based system: In this system, the microprocessor gives output control variables in the form of some display to the human operator then based on the displayed information, the human operator makes changes in the necessary control inputs. It is simple, low-cost, and used when feedback is not critical.
The upper and lower limit of the desired pressure is set. Pressure is converted to digital form to be fed to the microprocessor. The microprocessor compares a sample of pressure measurement with the present pressure limit. If the sample is beyond limits, the microprocessor indicates in the form of some alarm. So according to the output signal, the human operator makes necessary changes.
2. Closed loop microprocessor-based system: In this system, the microprocessor monitors the process variable continuously and then supplies the output signal to the electro-mechanical device, which in turn controls the values of the process variables. It is more accurate and adaptive because no human operator is required, for example, such as an automatic temperature control system in an oven.
In the microprocessor, upper and lower limits of temperature are set. Every sample of temperature measured from the transducer is compared by the processor. If the temperature exceeds the present higher limit, the microprocessor transmits an output signal to a system which in turn turns off the supply to some of the heater elements. If the temperature is less than the present lower limit, the microprocessor transmits a signal to the system so the it turns on the supply the the heating element of the oven.
Here is a table summarizing the differences between open-loop and closed-loop microprocessor-based systems:
| Feature | Open-Loop Microprocessor-Based System | Closed-Loop Microprocessor-Based System |
|---|---|---|
| Control Mechanism | Manual control by human operator | Automatic control by microprocessor |
| Feedback | No feedback from the process | Continuous feedback from the process |
| Accuracy | Less accurate, relies on human intervention | More accurate, due to automatic adjustments |
| Cost | Generally lower cost due to simplicity | Higher cost due to complexity |
| Complexity | Simpler design and operation | More complex design and operation |
| Reliability | Less reliable as it depends on human judgment | More reliable as it automatically corrects deviations |
| Example | Pressure control system where operator adjusts based on displayed data | Automatic temperature control system in an oven |
| Adaptability | Limited adaptability | Highly adaptive to changes in process conditions |
| Human Involvement | Requires human operator to monitor and adjust | Does not require human intervention for process control |
Benefits of Microprocessor-based system
The benefits of a microprocessor-based system are:
- Complete automation
- Added intelligence
- Reduced manpower
- Flexibility to modify
- Economic design
- Reduced circuit complexity
- Reduced operating cost
- Statistical process control capabilities