Challenge Gems with your most demanding applications

07 January 2018

Gems understand that standard products are not always the best solution. The company provides outsourced design and development services including custom components and feasibility studies. A Gems program manager structures each project to meet individual needs, timing and budget, making the company the ideal partner for your next development cycle.

Gems designs and manufactures electro-optic, liquid level, flow, magnetically actuated reed switches and pressure sensors, solid-state relays and barriers, liquid and pneumatic miniature solenoid valves, and pre-assembled fluidic systems, with facilities in North America and North UK. It is a division of Fortive Corporation, a Fortune 500 company with global presence.

Its experience spans a wide range of markets and applications in fields such as medical, oil and gas, marine, HVAC/R and general industry.

The company is proud of its latest design in the Liquid level indicators range. The LED Suresite provides a clearly visible indication from more than 100ft. It requires no power and is unaffected by extreme thermal changes. It can also be easily mounted to the exterior of tanks and is widely used in marine applications, where quick visual communication of tank contents is critical. The LED suresite is built to withstand constant vibration and shock while operating.

Gems has been a level sensing expert since the early 1990’s, using the widest range of material compatibility in the industry with durable and reliable performance. It has a large portfolio in flow switches and meters designed specifically for versatility performance, and quality, using corrosion-resistant materials.

At its Basingstoke office in the UK the company manufactures and assembles its pressure product range. Gems has been manufacturing on this site for around for 52 years. Today the facility employs 70 people working in various areas of the business. The site has a dedicated ‘Innovations’ and engineering team, production and operations including customer service and finance, all of whom share a passion to drive the business forward.

The 22/2600 series from the CVD range and the high-performance 4000 series from the thin film range are manufactured at the site, for use in a wide range of test and measurement applications. Electronic switches are also manufactured on site along with assembly of the 5000 series, 9600 series and the slimline borehole 3700 series for all water applications.

Gems is believed to be the only European sensor manufacturer to offer such a broad range of products and to provide comprehensive technical, application and product support. Continuous product development, supported by consultation with customer in a range of industry sectors, ensures that the company’s technology continues to be cutting-edge, with innovative solutions, developed to support customers changing requirements, being introduced on a regular basis.

Pressure solutions?
Pressure transducers are widely used in process and industrial applications, where they often have to withstand aggressive operating conditions, ranging from high pressure hydraulic spikes to extremes of temperature, mechanical shock and vibration. However, within each ruggedly designed transducer there is, typically, an extremely sensitive pressure sensing mechanism, combined with a sophisticated electronics package. Together these can provide accuracies of better than 0.25% of full scale output, with almost zero drift over time, yet with a response to changes in pressure of 1msec or less, and an operating life in excess of 100 million cycles.

These levels of performance are possible thanks to a number of highly innovative and carefully controlled methods of construction. Three of these make use of advanced strain gauge technology: sputtered thin film, chemical vapour deposition (CVD) and micro-machined silicon (MMS); while a fourth uses capacitance as a method of detecting changes in pressure.

Atomically bonded
Sputtered thin-film technology evolved from the manufacturing processes used by the electronics sector for the production of integrated circuits. The production technique, although relatively straightforward, requires advanced engineering systems and carefully controlled conditions to create an atomically bonded strain gauge sensor on a stainless steel diaphragm.

This construction is extremely robust, with the diaphragm being suitable for direct contact with almost all liquids, oils and gasses. In addition, the materials of construction for both the sensor mechanism and the transducer as a whole are thermally compatible to minimise non-repeatable errors for hysteresis and thermal stability, and to ensure that coefficients for thermal zero and shifts in sensitivity remain constant across a wide temperature band.

Volume production
Although thin-film pressure transducers provide exceptional levels of performance and long term stability, the mechanical complexities of the ‘first generation’ sensors, mean they could be relatively expensive to manufacture in large volumes. It was to address this need that the chemical vapour deposition process was originally pioneered, using semiconductor manufacturing processes to produce multiple sensors at lower cost, while retaining many of the benefits and performance characteristics of thin film devices.

CVD sensors are produced on wafers in large batches, using polysilicon deposited on a stainless steel substrate, with the strain gauge patterns being chemically milled. The wafer is then divided to produce individual sensor beams, which are laser-welded to a stainless steel summing diaphragm and pressure port, before being connected to internal electronics for signal conditioning and amplification.

This process enables sensor assemblies to be produced in volume and at low unit cost. Each sensor generates a high electrical output from a small mechanical deflection, thereby simplifying signal processing, and is inherently stable with an accuracy to within 0.5%. It also offers a long operating life with excellent resistance to pressure shocks and mechanical vibration. Additionally, the use of high temperature vacuum brazing of the stainless steel during sensor production creates a structure with low hysteresis and creep, together with high strength and corrosion resistance.

Smaller solutions
By comparison, micro-machined silicon (MMS) sensors are produced with similar technology to that used in the manufacture of integrated circuits on silicon wafers, with ion implantation allowing a strain gauge structure to be diffused into the internal lattice of the silicon. This optimises the unique mechanical and electronic properties of silicon, enabling sensor and diaphragm size to be reduced proportionately, and without adversely affecting factors such as hysteresis, linearity or performance under tough operating conditions. In common with CVD technology, the production methods used for MMS transducers allow larger volumes to be manufactured at lower unit cost, although unlike CVD devices where the diaphragm is in direct contact with the media MMS sensors are generally protected with oil-filled isolation diaphragms.

This need can be met by the use of capacitance sensors, where a flexible ceramic diaphragm and a fixed plate form the two capacitance surfaces. Pressure or vacuum applied to the diaphragm will therefore cause a proportional change in capacitance, with the output signal again being fed directly to integrated electronics for subsequent conditioning and amplification.

Electronics holds the key
In recent years there have been developments in manufacturing processes for all of Gems sensing solutions, which combined with detail changes in design and materials of construction, has led to a steady improvement in areas such as performance, stability and reliability.

The most important developments have been in the electronic packages that are increasingly being supplied with pressure transducers. In particular, many of the latest devices such as Gems’ CVD and thin film transducers incorporate advanced application specific integrated circuits (ASIC) technology, which enables the performance and functionality of each transducer to be tuned to meet the specific requirements of a market, application or customer.

Gems MMS transducers, where they are used for hydrostatic level monitoring with liquids with changing densities, the use of micro processor technology allows both temperature and pressure to be monitored and the results to be processed with a known specific gravity, to produce an extremely accurate level reading.

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