Pressure transmitter with optional PID feature

March 2005 Pressure Measurement & Control

The LD301 pressure transmitter series uses, as its measuring principle, the field proven technique of capacitance sensing, enhanced by a microprocessor-based electronics. Designed for process control applications, these 2-wire transmitters generate a 4 to 20 mA signal proportional or characterised to the applied differential pressure. This signal can be transmitted over a pair of twisted wires through long distances (limited only by the wire resistance and load). Digital communication for remote calibration and monitoring is also provided, superimposing a HART digital signal on the same pair of wires that carries the current signal.

Notable features of the LD301 series include its high accuracy (within 0,075%), its 120:1 rangeability, compact dimensions, low mass, PID control capability (optional). The transmitter consists of two main parts: The sensor (a capacitance variation cell) and the electronic circuit. Transmitter performance is improved by continuous monitoring of the sensor temperature and corresponding corrections. The transmitter can also operate as a combination of transmitters plus controllers. In this case, the 4 to 20 mA signal is used as the output of a PID control function (optional), while the digital signal may be used for remote monitoring and operation.

The LD301 series was developed according to the international safety standards to attend the functional safety requirements in plants that need safety and reliability to protect people, ambient and assets, etc. The LD301 series has FMEDA analyses allowing all series to work in safety areas according to SIL requirements and making it easier to the user the calculation for Safety Integrity Level (SIL). MTBF is a basic measure of product and it is calculated by adding the MTTR and MTTF. MTTR is the mean time to execute maintenance on all of the removable items in a product. It is the most common measure of maintainability. MTTF is the mean time expected until the first failure of a piece of equipment. It is the inverse of the failure rate.

The LD301 is available as a 4 to 20 mA + Hart communication or Fieldbus or Profibus. If only a 4 to 20 mA device is purchased it can be upgraded to Profibus or Fieldbus by just purchasing a new card.

For more information contact KAB Instruments, 011 435 5380, [email protected], www.kabinstruments.com

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