An innovation in pressure

'Are users giving up pressure transmitters?' asked industry analyst Wil Chin only three months ago. As director of field devices for the ARC Advisory Group, Chin is well qualified to give an answer.

Introducing his updated ARC study Pressure Transmitter Worldwide Outlook to 2005, he said 'the resilient pressure transmitter market that lumbered along for years with little change was caught by surprise as the dotcom crash ended the decade-long economic expansion, accelerating the contraction.'

Well, Chin himself might have been caught by surprise at the recent ISA Show in Houston, Texas. There he was given a sneak preview by Emerson Process Management of Rosemount's new 3051S series of pressure measurement instrumentation, which had its European launch last month in Montreux, Switzerland.

Commenting on what he saw, Chin said: 'The 3051S series is as creative as it is functional. Completely new thinking has gone into the location of the electronic transmitter. With the help of microelectronics, the package has been miniaturised to fit in a small box integral with the pressure sensor. This radical approach results in an extremely small package that will fit anywhere, enabling new installation practices including the elimination of problematic impulse lines.'

Equally effusive, although understandably so after investing $25million on its three-year development, Rosemount describes the 3051S series as 'the first measurement platform to enable flexible best practices for pressure, level and flow from one instrument.'

The European launch (to be followed later by ones in the US and Asia) follows a major development programme that included 18 months of field trails at major customer sites across the chemical and process industries.

According to Mark Schumacher, v-p and general manager for Rosemount's pressure business unit, 'one of our goals was to meet customer demands for stability with differential pressure (DP) measurements.'

'Innovative design' he says, 'makes the 3051S the world's first truly scaleable measurement platform that meets every plant need today while providing the path to future automation architectures.' For a measurement technique that, as ARC has identified, is under pressure itself from flow devices such as ultrasonics, magmeters, vortex meters, and level devices like ultrasonics again and radar, that is a confident assertion to say the least. So, how justified is it?

All-in-one module

The design is certainly innovative. At its heart lies a 'compact, robust and flexible design platform' known as the 3051S SuperModule (shown in cutaway form). This is the 'small box' identified by Chin as containing the transmitter's electronics along with the pressure sensor itself.

It comprises an all-welded, hermetically sealed 316 stainless steel housing that can withstand the harshest field environments; the Saturn glass/metal sensing technology; patented ASIC technology and single circuit board; and a multi-bus output offering Hart, 4-20mA analogue and built-in high-speed digital bus for fieldbus communications. As part of Emerson's extensive plant automation capabilities, the SuperModule also features advanced PlantWeb diagnostic, measurement and control functionality.

The net result, says Rosemount, is that the 3051S offers twice the performance and twice the reliability of traditional measurement technology. This is quantified as 0.04 per cent accuracy, 10-year stability, a limited lifetime warranty, 200:1 turndown, and 100millisecond response time. Partly, this improved performance comes from developments in the glass/metal capacitive sensor. Now incorporating a secondary sensing ring, this has almost eliminated hysteresis, with a tenfold improvement in this and overpressure capability.

Covered by no fewer than 22 patents, the SuperModule is available in two versions - one for DP measurements and the other for gauge pressure. Both feature the 'scaleability' that Schumacher says is pioneered by the 3051S. This is not scaleability in the 'one size fits all' sense, but rather the ability to deliver flow, level and pressure measurement from the common platform.

What this means for DP flow measurement, according to Schumacher, is the availability of a fully integrated DP flowmeter - replacing with just one device the 30 or so separate components needed before (for example, the orifice plate or pitot tube, the impulse lines, the transmitter, the connectors, and so on).

Rosemount anticipates the new design will bring significant cost savings in the areas of design and procurement, installation and commissioning, maintenance and troubleshooting, and inventory and replacement costs. Upfront prices may carry a 5-6 per cent premium over the 13-year old 3051C instruments but, according to Rosemount's marketing and sales v-p Ron Migliorini, 'the real value has soared'.

With Schumacher estimating that DP measurement still accounts for around half of all flow loops in use today, ARC's Chin could be right when he says 'this product will forever change the way we look at pressure measurement.'