PSM INSTRUMENTATION LTD

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High Performance Dual Mode Liquid Level Transmitter

Intelligent Ceramic Transmitter
Benefits at a glance. Both digital and analogue outputs. 200:1 turndown 20 bar over-range protected PC programmable Marine and I.S. approvals.
PSM has taken the most stable and repeatable materials available for sensor manufacture and drawn upon almost 30 years of global application experience across all industries, to develop a liquid level transmitter that offers the highest possible standards in terms of performance, versatility, functionality and reliability. The instrument’s pioneering capacitive measurement cell utilises a diaphragm manufactured in ceramic, a material impervious to chemical attack for most applications, which, thanks to the unique “close-coupled” structure of the sensor, is fully supported and protected against overload and shock pressure conditions. This ground - breaking design (registered for patent) also provides greatly increased span and sensitivity compared with conventional capacitive devices, allowing a single model to cover all applications from 0.5 to 100 meters WG, all with the same high performance levels. The transmitter body is manufactured from high integrity stainless steel investment castings and employs custom-made elastomer seals, providing a fully submersible construction (to IP68) capable of withstanding the toughest operating conditions. Advanced features are not confined to the mechanical design. The iCT utilises a unique digital processing principle, which employs the varying capacitance of the sensor to control the frequency of an oscillator. An embedded micro-controller monitors this frequency with 16-bit precision a comprehensive range of functions and outputs, all under the user’s control. Analogue Mode The iCT can be operated as a conventional 4-20 mA, two-wire transmitter with an accuracy of 0.25 per cent, over a temperature range of –10 to +85 deg C. The iCT will directly replace PSM’s earlier generation of level transmitters and other conventional instruments. Even when used conventionally, the benefits of digital processing are immediately apparent. Push buttons allow simple calibration for any range from 500mm to 100m. With no potentiometers to adjust, and digital output control, excellent long-term stability and reliability is assured. Digital mode Operated in digital mode the real power of the transmitter becomes apparent. The iCT can communicate directly with a host PC via its industry standard RS485 communications port. With no digital to analogue conversion limiting resolution, the 16 bit arithmetic precision immediately improves measurement accuracy to 0.1% under normal conditions. Up to 128 transmitters can be multi-dropped over a single 2 wire RS 485 network. Connection to the host PC uses a low cost convertor from PSM which utilises the latest USB standard. In digital mode this means an entire network of 128 transmitters can be powered directly from the PC, a single point to point wire cable is all that is required. Even if transmitters are to be operated in both digital and analogue mode, up to 10 can be directly powered by the PC, and an optional supply module extends this possibility still further. In digital mode the power requirement is just 3mA at 6 to 30V DC. This, combined with the setting time of only 150ms means the iCT is ideal for battery powered data logging or remote interrogation. With the addition of a low cost modem, interrogation via the telephone network or internet is possible from anywhere in the world. The digital mode protocol is available to OEM’s and system integrators, allowing access to the full range of calibration, diagnostic, and reporting facilities. Alternatively PSM’s own integrated support system (ISS) is a powerful windows based application created specifically to harness the full functionality of the iCT. Full details of the ISS Digital benefits Remote access. The full functionality of any transmitter in the network can be accessed from any point. Accurate re-ranging and/or zero adjustment simply by keying in new addresses. There is no need to employ external test equipment and pressure generators. The unit does not have to be removed from service. Accurate temperature measurement. The iCT has an integral temperature sensor to correct its own measurement. In digital mode, the current temperature may also be output to the ISS. Monitoring of service conditions and extremes. The unit will record the total hours run and the lowest and highest in service pressures and temperatures it has measured to assist in trouble-shooting. Tank characterisation. The digital output can be linear or corrected for non-linear shaped storage tanks using the programmable 20-point look-up table to provide a direct output in volumetric units. This benefit is also available for the analogue output. The 4-20 mA signal can be corrected using the same look-up table, allowing simple, low-cost indicators to be used for volumetric display. Error reporting. Internal diagnostics continually monitor the health of the iCT. In the event of errors (for example, the 4-20mA output becoming inaccurate), an appropriate error message is sent to the ISS. Rate of change alarms. For the direction of tank leaks. Force zero/span. This fixes analogue output to 4 or 200mA for an actual signal within a defined band of these points. In addition, the analogue output can be forced to a programmable fixed value between 3  and 22.5mA for the indication of faults where the unit is being used conventionally. Analogue output switching. The operator can switch the 4-20mA output to 4, 12, and 20mA via the ISS, irrespective of the actual input pressure, providing a powerful proving and calibration tool for the testing of display equipment. All configuration data is held in a non-volatile memory.  Installation flexibility The standard sensor construction is fully submersible, and a full range of fittings is offered to allow external flanged or threaded mounting, or internal clamped or pole mounting. Standard extension cables with submersible connectors are available, as are a range of hygienic process connections. The iCT’s processing power is contained within its body, allowing direct connection of its cable to monitoring equipment. The optional purpose-designed IP67 stainless steel termination enclosure simplifies multi-drop installations with its provision for “looping through” of the RS485 and power cables. This enclosure also contains the push-button controls for analogue mode calibration of the unit and a connection for a PC running the ISS software. Approvals The iCT is available with Intrinsic Safety Approval for use in hazardous areas, and can be specified as Type Approved by all major marine classification societies.  Applications  The construction materials employed and the wide measurement range mean the iCT is suitable for most tank level applications in the marine, offshore, food, chemical, water, and processing industries. The iCT may also be used for absolute or vacuum measurement applications, if this requirement is specified at time of order. PSM and our agents will be pleased to discuss your application needs.