When you walk into an industrial site, you’re immediately struck by the scale and complexity of the operation. Turbines spin with precision in power generation sites, conveyor systems transport materials across manufacturing floors, pumps push fluids through intricate water operations, and control systems maintain delicate balances of temperature and pressure.
Amid the hum of motors and the hiss of steam, thousands of sensors vigilantly monitor critical parameters—thermocouples measure temperatures at key process points, pressure transducers detect subtle changes in system conditions, flow meters track the movement of materials, and vibration sensors watch for the earliest signs of mechanical issues.
These measurements form the foundation for understanding equipment operation and performance, and their value can be significantly amplified when combined with calculated tags. By combining existing sensor data with mathematical formulas and logical operations, calculated tags help extract additional insights without installing more physical sensors.
What Are Calculated Tags?
Calculated tags (virtual tags, script tags, or derived points) are custom data points created by applying mathematical formulas, statistical functions, or logical operations to existing sensor data. Unlike physical sensor data that comes directly from equipment, calculated tags exist purely in your data management system or other industrial software systems but work alongside your raw measurements to create a more complete operational picture.
So, why are calculated tags essential for industrial operations? Because they allow you to:
- Measure what matters but can’t be directly sensed (efficiency, performance, reliability)
- Synthesize multiple data points into meaningful information
- Standardize complex calculations across your organization
- Transform raw data into actionable intelligence
- Expand your monitoring capabilities without adding physical sensors
Starting Simple: Building on Raw Data
Let’s start with a basic example to illustrate the concept: your site has sensors measuring the power output of multiple generating units. While knowing individual unit outputs is necessary, having the total plant output readily available simplifies monitoring and reporting for the entire site.
| Raw Sensor Data | Calculated Tag |
| Unit 1 Power Output | Total Plant Output |
| Unit 2 Power Output | (Unit 1 + Unit 2 + Unit 3) |
| Unit 3 Power Output |
This straightforward calculation is just the beginning—a simple demonstration of how calculated tags work. From here, you can develop increasingly sophisticated calculations that provide operational insights across the site.
Types of Calculations for Improved Operations
Advanced industrial operations use calculated tags to create metrics to support decision-making. Here are some examples:
1. Equipment Effectiveness and Utilization
Overall Equipment Effectiveness (OEE) is a widely-used metric for manufacturing evaluation, calculated as:
OEE = Availability × Performance × Quality
Where:
- Availability = Operating Time ÷ Planned Production Time
- Performance = (Total Count ÷ Operating Time) ÷ Ideal Count Rate
- Quality = Good Count ÷ Total Count
Creating calculated tags for each component of OEE allows real-time monitoring of this metric without manual calculations.
2. Process Efficiency and Optimization
Calculating efficiency metrics helps identify optimization opportunities:
- Thermal Efficiency = Net Work Output ÷ Energy Input
- Production Capacity Utilization = Actual Production ÷ Maximum Possible Production
- Cycle Time Analysis = Average time between production stages
3. Statistical and Analytical Functions
Advanced calculated tags can implement more logic:
- Moving Averages: Smooth out noisy sensor data to identify true trends
- Rate of Change Calculations: Identify unexpected acceleration in equipment parameters
- Statistical Processing: Apply standard deviation or variance to understand data spread
- Threshold Detection: Create binary indicators when values exceed critical limits
4. Operational Status Monitoring
Calculated tags can synthesize multiple digital inputs to provide comprehensive status indicators:
- System Readiness: Logical AND of all prerequisite conditions
- Fault Detection: Identifying when multiple parameters indicate potential failure
- Process Stage Monitoring: Tracking progression through defined operational stages
Best Practices for Implementing Calculated Tags
As you expand your use of calculated tags, consider these industry best practices:
Standardize Calculations Across Your Organization
When multiple teams or facilities independently create their own calculated tags, inconsistencies inevitably arise. Establish clear standards for:
- Naming conventions: Make tag names intuitive and consistent
- Calculation methodologies: Define precisely how critical metrics should be calculated
- Documentation requirements: Ensure formulas and logic are well-documented
While the examples above illustrate basic concepts, real-world calculated tags often incorporate complex logic and sophisticated calculations. The assumptions built into these calculations can impact your understanding and the resulting insights. By having everyone on the same page, you can better identify areas for improvement or opportunity across teams, units, and sites.
Quality Assurance for Calculated Data
Remember that calculated tags are only as good as the input data and the formulas used:
- Validate formulas before implementation
- Handle bad-quality input data appropriately (e.g., exclude bad-quality values from calculations)
- Regularly audit calculated tags to ensure they still serve a valuable purpose
- Test with historical data to verify calculation accuracy
Your data historian or industrial software should include validation tools that check formula syntax and logic before implementation. This prevents the propagation of errors that could lead to incorrect operational decisions.
Consider System Integration and Performance
As you build your calculated tag strategy, consider the technical implications:
- Calculation frequency: Determine how often tags need to be calculated
- Data storage requirements: Plan for additional database capacity
- Processing impact: Complex calculations across many tags can impact system performance
Evaluating Data Historian Capabilities for Calculated Tags
When selecting or upgrading your data historian or industrial data platform, carefully evaluate its capabilities for creating and managing calculated tags:
Key Features
- Intuitive formula editor with formula validation capabilities
- Comprehensive function library (statistical, mathematical, logical)
- Quality propagation that handles bad input data appropriately
- Debugging tools to test and validate complex calculations
- Consistent treatment of calculated tags alongside physical sensor data
- No artificial limitations on the number of calculated tags
Enhancing Visibility and Decision-Making
Calculated tags become particularly valuable when integrated into your overall monitoring and analysis systems:
- Interactive dashboards with calculated KPIs that provide real-time operational status
- Automated reports that leverage calculated metrics for consistent performance tracking
- Process insights that highlight efficiency opportunities
- Customized operational metrics tailored to your specific business objectives
Taking a Strategic Approach to Calculated Tags
Rather than creating calculated tags on an ad-hoc basis, leading industrial organizations develop comprehensive calculation strategies that:
- Align with business objectives and KPIs
- Standardize important metrics across the enterprise
- Balance simplicity with sophistication
- Support continuous improvement initiatives
- Enable data-informed decision-making at all levels
By thoughtfully implementing calculated tags as part of your industrial data strategy, you expand the value of your existing sensor infrastructure while creating new insights that can drive operational improvements.
The most effective industrial data strategies leverage both direct measurements and calculated values. Physical sensors provide the essential foundation of reliable data, while calculated tags enhance and extend that foundation with derived insights. Together, they create a more complete operational picture than either could provide alone.
Contact our team today to discover how our industrial data historian makes calculated tags simple to implement and manage.
