The iCT is fundamentally a digital device. The capacitance cell forms part of a resonant circuit, such that capacitance changes induced by pressure changes vary the resonant frequency resulting in a direct digital signal. The performance of the sensor under varying pressure and temperature conditions is characterised at the calibration stage. PSM's new pressure/level transmitter design incorporates a number of significant advances, including: digital pressure sensing, capacitive ceramic sensor and dual digital/analog operation.
Mechanically, the pioneering sensor design uses a fully supported ceramic diaphragm, which in addition to being impervious to attack from most chemicals and has high shock and overload resistance. This combination provides both mechanical and electrical freedom from drift, coupled with a substantial 200:1 turndown. One transmitter covers spans from 5 to 1000 kPa, and can be programmed from a PC running PSM's integrated support system (iSS) over a USB port, with zero and span freely selectable.
The transmitter may be used in fully digital mode, where 128 transmitters can be multidropped off an RS485 network, or operated as a conventional 2-wire 4 to 20 mA transmitter. In pure analog mode, a laptop will be required to access digital information. When used for tank level measurement, volume conversion is available through a built-in 20 point strapping table.
The sensor temperature is measured, and can be accessed digitally. Other digital benefits stored in the instrument include service condition records, eg, maximum temperature and pressure exposed to, time in service, and fault monitoring and troubleshooting tools.
The iSS program runs in three modes: Commissioning - which allows configurations settings to be done, including density correction, and loop test procedures executed; Diagnostic - which permits the running of built-in tests; Monitoring in an OLE, Multi Document Interface mode, collecting, presenting and distributing measured data. ISS software is available to OEMs and system integrators.
This is a complete system built around a single sensor, and its makers believe that it provides a degree of flexibility and performance hitherto unknown. The picture shows the mechanical construction of the sensor element.
For more information contact Rod McLeman, Blanes Instruments, 011 397 7365, email@example.com
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