Differential pressure level measurement of pressurised tanks

April 18, 2016  1164  1164   

Linde currently has 3 000 cold converter tanks with a filling level of less than 3m.  They believe that there is a potential to grow this to 100 000 tanks.   Their stated objective is to set a global standard for their cold converter systems: To measure the filing level and the consumption and report them via GPRS to a central unit, which is then capable of planning the refill-logistics optimally.  This has the enormous advantage that the customer no longer has to order the refilling.  The gas supplier takes over the monitoring of the tanks levels from a central location and is then able to plan ahead for delivery.  Keller’s differential pressure transmitter is used in these systems for the filling and measurement.  The data is transmitted via RS485 interface to the wireless system.  Currently, the transmitter is not used for any safety-related functions such as overpressure and compensating pressure control of the system.  For tanks with a filling level over 3m and not exceeding 20m, the PD-39X differential pressure transmitters were used.

Ongoing development of Keller’s PD-33X differential pressure transmitter, resulted in the PRD33X, which features a second integrated pressure sensor, which means that the line, or common mode pressure can now be measured along with the differential pressure.  Several extra features not found in traditional differential pressure transmitters are now available.  An example of which is the compensation for line pressure effect now accomplished during factory calibration. Moreover, both differential and line (absolute) pressure may be read by the user. In addition, the PRD-33 X features high differential overload resistance; e.g., ± 35 bar with a differential measuring range of only 350 mbar (100:1).  The floating sensor assembly guarantees maximum decoupling from external mechanical forces.

Another notable feature of the Series PRD-33 X is the robust digital RS485 bi-directional communication interface. Information such as serial number, pressure range, filter settings and process values for both differential and line (absolute) pressures and their temperatures are easily obtained. This combination of features enables certain measurements not possible with traditional differential pressure transmitters. For example, filling levels in liquefied gas storage tanks, inclu¬ding oxygen, nitrogen, carbon dioxide and argon can now be measured safely and accurately.

The Series PRD-33 X Features

• High-accuracy differential pressure measurement with compensated line pressure dependency
• Pressure- and temperature-compensated
• Independent line (absolute) pressure output
• High overload resistance
• RS485 communication interface
• Configurable via RS485 interface
• Compact structural design

Typical applications

• Level measurement of technical gases in liquefied gas tanks
• Differential pressure measurement in case of high unilateral overload resistance

Instrotech – a Comtest Group Company - distributes and manufactures a range of process control instrumentation and specialized systems which are sold locally and internationally through a number of designated distributors.

For more information on Keller’s PRD-33X Series 33x differential pressure transmitters, contact Instrotech on 011 462 1920, sales@instrotech.co.za or visit www.instrotech.co.za