Calibration / Pressure

Accuracy and Simplified Calibration in Foxboro S Series Pressure Transmitters

Foxboro's S series stores 11 calibration points and automatically selects the right curve for an extended range of inputs.

By Control Staff

Due to the non-linear output of the transducer, a typical pressure transmitter is calibrated and rated for a limited pressure range.  Specifiers and maintenance departments must choose and stock multiple models to cover the various applications in a typical plant, and each application must consider carefully the ramifications of turndowns, start-ups and operating conditions that take the transmitter out of its accurate range.

Foxboro by Schneider Electric has introduced a new series of pressure transmitters that store 11 calibration points in firmware. As the pressure input changes, the transmitter automatically selects the proper calibration curve for that specific input. "We call this patented technology FoxCal," says Patrick Cupo, product manager, pressure and temperature, Foxboro. "The result is a very accurate output that covers three to four ranges of competitive instruments."

S series models cover pressure ranges to 1,000 in.WC (2.5 bar), to 2,000 psi (138 bar), and to 6,000 psi (414 bar). Each is calibrated at 2.5, 5, 10, 20, 30, 40, 50, 60, 70, 85 and 100% of upper range limit (URL). "The FoxCal calibration points are stored in the transmitter firmware forever and cannot be deleted accidentally," says Cupo.

Using this multiple calibration approach, the reference accuracy of the transmitter is maintained even at high turndowns. The accompanying figure shows the effect of FoxCal technology on transmitter accuracy. Common pressure transmitter reference accuracy typically begins degrading at turndowns greater than 10:1. "The S series allows turndowns on the order of 80:1 without sacrificing accuracy," Cupo says. "The customer is no longer forced to use algebraic equations to determine the accuracy at high turndown. The S series offers a simple percent of reading specification."

The benefits to the user are enhanced turndown performance along with fewer sensor ranges required for inventory stock.  "A 2,000-psi S series in-line gauge can be used down to 50 psi and still maintain reference accuracy," says Cupo. "The 6,000-psi S series in-line gauge can be used down to 150 psi.  The 1,000-in.WC differential pressure transmitter is calibrated down to 25 in.WC."

The S series pressure transmitter is available in both in-line gauge (2,000 and 6,000 psi) and differential pressure (200 and 1,000 in.WC). The differential pressure transmitter is available with traditional and low-profile process connections. Wetted material selections include 316ss and Hastelloy, and FM, CSA, ATEX and IECEx safety approvals are available.

Other features include a time-in-service odometer for predictive and preventive maintenance, full configuration from the local display without a handheld and a standard five-year warranty.

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