Introduction to Instrumentation
In engineering, we deal with two primary measurement systems: metric (SI) and imperial. While both serve their purpose, the metric system has significant advantages in engineering applications. Its base-10 structure simplifies calculations and conversions, unlike the imperial system's irregular scaling. For instance, converting between kilometers and meters is a straightforward shift of decimal points, while converting between miles and feet requires memorizing conversion factors.
The SI system, adopted internationally, standardizes the metric system for scientific and engineering work. It consists of seven base units and numerous derived units that form the foundation of all physical measurements. The consistency of the SI system helps prevent costly errors.
When working with instrumentation, we encounter measurement systems comprising sensors, signal conditioners, processors, and output displays. Each component must be carefully selected based on application requirements. Critical factors include measurement range, resolution, environmental conditions, and system response time. For example, when measuring high-temperature processes in a chemical plant, we must consider not just the temperature range but also sensor durability and response characteristics.
Measurement Units
Physical quantities require standardized units for consistent measurement. Common types include base units and derived units, with prefixes (kilo-, milli-, etc.) indicating scale.
The derived units in SI, such as pascals for pressure or watts for power, are combinations of base units that maintain mathematical consistency throughout calculations. This consistency is particularly valuable in complex engineering systems where multiple physical quantities interact
Fundamental SI Units
| Physical Quantity | Unit | Symbol |
|---|---|---|
| Length | meter | m |
| Mass | kilogram | kg |
| Time | second | s |
| Electric Current | ampere | A |
| Temperature | kelvin | K |
| Amount of Substance | mole | mol |
| Luminous Intensity | candela | cd |
Elements of a Measurement System
- Sensor (Primary Sensing Element)
Converts physical measurand into quantifiable output signal (e.g., displacement, voltage). Interfaces directly with measured parameter and initiates signal chain.
- Signal Conditioner (Variable Conversion Element)
Transforms sensor output into standardized signal format while preserving signal integrity. Functions as intermediary transducer for signal standardization and initial processing.
- Signal Processing Unit (Variable Manipulation Element)
Performs signal conditioning operations including amplification, filtering, and linearization. Maintains signal type while optimizing signal-to-noise ratio and measurement resolution.
- Data Communication Interface (Data Transmission Element)
Enables signal routing between distributed system components via standard protocols. Critical for remote operations and distributed control architectures. Implements necessary error checking and signal integrity preservation.
- Human-Machine Interface (Data Presentation Element)
Converts processed signals into human-interpretable format through visualization tools and displays. Enables real-time monitoring, control operations, and data analysis. Implements MOX (Monitoring, Operation, eXamination) functionality for system interaction.
Choosing Appropriate Measuring Instruments
The starting point for selecting the most suitable instrument for measuring a specific quantity in a production plant or other system is the specification of the instrument characteristics required, especially parameters such as the desired measurement accuracy, resolution, sensitivity and dynamic performance.