LOOP VERIFICATION

Loop Verification gives the expected value at every point of a 4-20mA signal chain from a reading at any one of them, for commissioning and fault-finding on linear, square-root flow, RTD and thermocouple loops.

Capabilities

• Bidirectional conversion between process value, percent of range, milliamps, volts, ADC counts and the sensor’s raw resistance or millivolts.
• Linear and square-root (DP flow) profiles.
• RTD element types Pt100, Pt500, Pt1000, Cu10 and Ni120.
• Thermocouple types B, E, J, K, N, R, S and T, with cold-junction compensation temperature as an input.
• ADC counts at 12-bit and 16-bit resolution simultaneously.
• Live-zero selection between 4-20mA and 0-20mA conventions.

Why the results hold up

RTD conversions use the IEC 60751 Callendar-Van Dusen polynomial for the selected element. Thermocouple conversions use the NIST ITS-90 reference polynomials for each type, corrected for the entered cold-junction temperature. Every conversion is bounded to the sensor’s published valid range.

Verification

ALKANE’s V&V Diagnostics includes an instrumentation suite, which checks the thermocouple conversions against published reference data. Details are on Validation & Verification.

Scope

Results are the values a correctly wired, correctly calibrated loop should produce; the difference from a measured reading isolates the fault to wiring, calibration or sensor. Lead-wire resistance, extension-wire mismatch, calibration drift and ground-loop noise are not modelled. Where a loop forms part of a safety instrumented function, its proof test remains a separate requirement; see the Software & Engineering Disclaimer for the suite-wide statement on safety-critical use.