Measurement Systems in Environmental Management

Measurement Systems in Environmental Management

• Parameters in an EMS (Environmental Management System) must be measured and recorded with the accuracy specified in the EMS manual.
• Accuracy levels vary, some require high accuracy, others are more modest.
• Measurement systems are carefully designed, employing principal components that capture variable magnitude.
• Sensors/transducers capture variable magnitude.
• Variable conversion elements translate output.
• Signal-processing steps improve measurement quality.
• Signal transmission sends signals to a data recorder.
• Some measurement systems may not use all components (e.g., variable conversion or signal processing).
• Commercial instruments often combine multiple measurement system elements.
• Intelligent instruments usually incorporate additional sensors and transducers for measuring and compensating disturbances in environmental conditions.

Choosing Suitable Measuring Instruments

• Instruments must meet EMS requirements and not be affected by operating conditions.
• Understanding instrument types and characteristics is key for selection.
• Instrument types can be classified for easier study. Accuracy, cost, and applicability are crucial attributes to consider.

Deflection/Null-Type Instruments

• Deflection instruments show quantity by pointer movement (e.g. pressure gauge).
• Null instruments balance forces to determine the measured quantity (e.g. dead-weight pressure gauge).
• Null-type instruments are usually more accurate than deflection types due to simpler weight calibration.

Active/Passive Instruments

• Active instruments derive output from an external power source. External signals are modulated by the measured quantity (e.g., petrol tank level indicator).
• Passive instruments receive energy directly from the measured quantity, such as the change in pressure in a pressure gauge.
• Active instruments offer superior control over measurement resolution.

Analogue/Digital Instruments

• Analogue instruments have a continuously varying output that reflects continuous changes in measured quantity.
• Digital instruments offer discrete steps in their output, reflecting changes in the measured quantity.

Intelligent Instruments

• Intelligent instruments combine a digital processor with other measurement components.
• Intelligent instruments often offer automatic compensation for environmental disturbances or provide functions such as switchable ranges, remote control, or self-diagnosis.

Static Instrument Characteristics

• Accuracy measures the extent of possible measurement error (expressed as a percentage of full-scale reading).
• Sensitivity quantifies the responsiveness of an instrument to changes in measured quantities.
• Linearity indicates that instrument output is proportional to input.
• Precision describes instrument freedom from random errors (typically expressed as a range of outputs for the same input).
• Repeatability and reproducibility describe the closeness of output readings when input is repeated under the same conditions.
• Resolution quantifies the smallest change in measured quantity detectable.

Dynamic Instrument Characteristics

• Dynamic characteristics describe instrument behavior during changes in measured variables.
• Instrument response time, time constant (measured quantity for instrument output to reach 63% of final value) are important features of dynamic characteristics.

Calibration of Measuring Instruments

• Calibration procedures require standards of known accuracy to compare output.
• Calibrations are usually performed over the instruments' entire operating range.
• Calibration should be performed regularly or after specific conditions that may affect the instruments' accuracy.
• Calibration records are important as proof that instruments remain reliable.

Primary Reference Standards

• Primary Reference Standards are the most accurate and precise.
• All other measurement standards are calibrated against Primary standards or secondary reference standards.
• Calibration is traceable to assure high accuracy.

Traceability

• Traceability is a chain of comparisons to establish accuracy (e.g., standards to instruments).
• Traceability in measurements and calibration relies on validated and calibrated instruments through an unbroken chain towards the most exact reference measurements.

This quiz explores the various measurement systems used in Environmental Management Systems (EMS). It covers parameters, accuracy levels, and the components involved in designing these systems. Additionally, it addresses the selection of suitable measuring instruments and their roles in ensuring data quality.