Analog Input Scaling on the Emerson ROC800
Key Takeaway
How to scale analog inputs on the ROC800 — 4-20mA to engineering units, Low EU/High EU configuration, wire break detection, and calibration verification.
Quick Answer
ROC800 analog inputs use linear interpolation between Low EU (value at 4mA) and High EU (value at 20mA) to convert raw 4-20mA signals to engineering units. Wire break detection triggers when the input drops below 3.8mA (recommended threshold). Scaled values feed directly into AGA meter run calculations and DNP3/Modbus SCADA reporting.
How Does ROC Analog Scaling Work?
In ROCLINK 800 I/O Points → Analog Inputs, set Low EU (e.g., 0 PSI at 4mA) and High EU (e.g., 1500 PSI at 20mA). The ROC performs: EU = Low EU + (Raw - 4mA) × (High EU - Low EU) / (20mA - 4mA).
How Do You Detect Wire Breaks?
Configure the alarm low threshold below 4mA live zero (3.8mA recommended). When input drops below this threshold, the ROC triggers a wire break alarm mapped to archives and DNP3.
How Do You Calibrate?
- Apply 4mA from a loop calibrator
- Verify ROCLINK reads Low EU value
- Apply 20mA from calibrator
- Verify ROCLINK reads High EU value
- Apply 12mA (midpoint) and verify linearity
For comparison, see SCADAPack analog scaling, Bristol FB300 analog scaling, and ABB Totalflow analog scaling.
Frequently Asked Questions
When the input drops below the wire break threshold (3.8mA recommended), the ROC triggers a sensor fault alarm logged in archives and reportable via DNP3.
Set Low EU = 0 PSI (at 4mA) and High EU = 1500 PSI (at 20mA). The ROC linearly interpolates between these values.
Yes. When a DP input is assigned to an AGA-3 meter run, square root extraction is applied as part of the orifice flow equation.