SOP: Digital Integrity & Calibration

DIGITAL_INTEGRITY_PROTOCOL

Syncing the Physical Twin with the Digital Twin

⚠️ THE DISCONNECT RISK

A SCADA screen is not reality. It is a digital interpretation of a voltage signal.

If the SCADA says "Bearing Temp: 45°C" but the bearing is physically 80°C because of a drifted resistance signal, the machine burns while the screen looks normal. Trust, but Calibrate.

LOOP CHECKING: END-TO-END VALIDATION

Procedure for Analog Signal Verification (4-20mA):

Do not rely on the sensor display alone. You must verify the entire chain: Sensor → PLC Input Card → SCADA Display.

TEST SEQUENCE: GUIDE VANE POSITION 1. Physically measure Guide Vane opening (mm). 2. Calculate theoretical % (e.g., 50mm = 20%). 3. Radio Operator A: "Physical is 20.0%" 4. Radio Operator B (Control Room): "SCADA reads ???" -------------------------------------------------- PASS: 19.9% - 20.1% FAIL: < 19.8% or> 20.2% -> RE-SCALE PLC

The "Deadband" Trap: If SCADA reads 0.0% but the physical valve is cracked open by 2mm, you are wire-drawing the seat. Zero must be ABSOLUTE ZERO.

SENSOR DRIFT PROTOCOL

Pressure Transducers (Strain Gauge)

Drift Cause: Over-pressure spikes (water hammer) deform the diaphragm permanently.

Calibration Check (Atmospheric):

  • Isolate sensor and vent to atmosphere.
  • SCADA must read 0.00 Bar.
  • If reading is > 0.1 Bar (phantom pressure), the zero-point has shifted. Replace or re-zero.

RTD Temperature Sensors (Validation)

Drift Cause: loose terminal screws increase resistance (Ohms), causing artificially HIGH temperature readings.

The "Cold Iron" Check:

  • After 24h shutdown, all RTDs (Bearings, Oil, Water) should read within 1-2°C of each other (Ambient Temp).
  • If Turbine Bearing reads 35°C while surrounding air is 20°C (after cooldown), the sensor loop has high resistance. Check the terminal block for oxidation.
ALARM LOGIC AUDIT

Review and hard-code these safety margins into the PLC Logic.

Component Material Limit Trip (High-High) Setpoint Alarm (High) Setpoint Rationale
Babbitt Bearings 130°C (Melt) 80°C 70°C Sudden failure zone starts > 90°C
Stator Windings (Class F) 155°C 120°C 110°C Maximize insulation life (10° rule)
Hydraulic Oil 60°C (Oxidation) 55°C 50°C Prevent varnish formation
Turbine Overspeed Runaway 115% 110% Centrifugal force limit
DIGITAL SAFETY LOCKS

Forcing Signals:

  • NEVER leave a "Force" active in the PLC code after testing.
  • Audit: Check "Forced Variables" list weekly. A forgotten "Force True" on the Lube Oil Pressure switch will destroy the turbine.
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