The new Deltapilot S, incorporating the patented ConTite measuring cell, overcomes the shortcomings of using a conventional pressure or differential pressure (dp) transmitter to monitor liquid levels in the food, beverage and pharmaceutical industries.
Typically in these industries, the processes are run in batches, and at the end of each batch the equipment is cleaned/sterilised using CIP (Clean In Place) or SIP (Steam In Place) techniques. The batch, considering brewing for instance, may be stored at +4oC, and the CIP cycle can run at +120oC, causing the equipment to experience big temperature variations, and even ‘thermal shock’.
Despite these extreme changes, food, beverage and pharmaceutical processes require stable and reliable level measurement to ensure that each batch is the same time after time. The resulting thermal expansion and contraction produces conditions that affect the ability of conventional pressure sensors to deliver the reliable measurements required by the process.
So, what are the effects of these temperature ‘shocks’?
The first thermal effect relates to atmospheric pressure compensation which has to be included for accurate hydrostatic pressure level measurement. This compensation is achieved by connecting the low pressure side of the measuring cell via a thin capillary and gortex filter to atmosphere. The expansion and contraction due to temperature changes results in small volumes of air being exchanged in the capillary and moisture present in the air will be drawn in with the air. Moisture at the opening is in the form of condensate where products are stored at low temperatures, and also from plant wash down.
The amount of air movement is very small and typically ignored by most vendors, but in the short to medium term this moisture interferes with the compensation, and finally damages the electronics. The patented Contite seal combats all these effects with a large capillary diameter and a completely hermetically sealed compensation chamber.
Secondly, all pressure sensors use a fill fluid to transmit the pressure changes between the stainless steel diaphragm that is contact with the liquid being measured, and the measuring electronics in the transmitter. Because the thermal coefficient of expansion of the fill fluid is far greater than that of the steel confining it, temperature changes alone will cause the level reading to ‘drift’ up and down, when in fact the level is constant.
For example, a pressure gauge with 2-inch (25.5mm) triclamp diaphragm seal will create a 1 – 2mm H2O pressure change per degree C temperature change. This means that during sterilisation at +60oC, a deviation of 60 to120mm H2O, and in a 1m high tank, this translates to a massive 6 – 12% error. In contrast, the Deltapilot S under the same conditions would deviate only 3.5mm H2O, resulting in only 0.35% error.
The Deltapilot S also boasts dual ingress protection rating of IP66 and IP68 protecting it against water hose-downs and flooding. Common to processes with CIP and SIP is the chloride attack on the thin stainless steel diaphragm, but with Deltapilot S the process is faced with a corrosion-resistant Alloy 276 direct-coupled membrane, available with Ra<0.4 micron surface roughness and 3.1B material certification, 3A and EHEDG approvals.
The Deltapilot S with ConTite cell is available with 4…20mA HART technology, Profibus PA and FieldbusFoundation interfaces and all industry standard process connections.
“ConTite has proven outstandingly accurate, convenient and reliable for over two decades,” says John Immelman, Managing Director of Endress+Hauser Australia. “It’s an investment that brings excellent returns in terms of reduced downtime and wastage and the advantages of batch-to-batch stability. Now with ConTite you get all that, plus chips as well! This is unquestionably the level measurement technology of choice for the brewing and dairy industries.”
For more information contact:
Endress+Hauser Australia Pty Ltd