Test fixture pressure sensors – Pressure measurement in the aircraft engine compartment

Test fixture pressure sensors – Pressure measurement in the aircraft engine compartment

As many engineers have found to their chagrin, dealing with pressure measurements in the engine compartment of an aircraft can be a delicate and frustrating experience. The heat, vibrations, orientation, and a multitude of other factors come into play. So how can we hope to develop a method for consistent and accurate readings? Well naturally, we’re left with hours, days, and most likely months of testing! However, we still need a test sensor that can rise to the occasion, function through all these changing conditions, and continually produce correct and repeatable results. We are engineers after all, and repeatable results are an occupational necessity. Thankfully for us, STS has stepped up to the plate to provide a complete series of pressure sensors to meet all of our testing needs. Where those needs can range from specific temperature requirements, size constraints, sealing material, and electrical output signals. All of these requirements will be covered in the following article as we address STS pressure transmitter usage for our testing needs.

Continuing with our engine compartment example, let’s zero in on the oil pressure. One of the first concerns while selecting a pressure sensor for this test is temperature resistance. Naturally, it gets quite warm next to an aircraft engine; therefore, we must ask ourselves, can the sensor be mounted alone or does it need a heat shield? More importantly, will the sensor even function properly when the components begin to heat up? Erratic oil pressure readings are very low on the wish list for a pilot! Therefore, both are valid points; but don’t fret too much. The STS line of pressure sensors include excellent temperature resistance, up to 125° C. This, in most cases, takes care of our initial temperature concerns and allows the sensor to be mounted it the most logical position in the engine compartment without the need to worry about temperature interference. Furthermore, we can fiddle, finagle, and fine-tune the test sensor’s location without constantly looking over our shoulder to see if the increased temperature will manipulate our results.  This provides us with a great deal of flexibility when constructing our test plan. 

Along the same subject of mounting locations, the size of the sensor is also crucial. Trying to wedge an ungainly box next to your sleek engine for a series of oil pressure tests would undoubtedly result in a few raised eyebrows amongst all those concerned. Additionally, space in this area is constantly at a premium. However, that is one bridge you don’t have to cross as STS has produced a very compact and low profile pressure sensor that makes for convenient mounting throughout your testing area of operations. Thanks to the advanced customization options, which we’ll discuss later, the exact dimensions vary from sensor to sensor. However, they tend to fall within the 50-60mm (2.0-2.4”) range. This small size allows for easy fixturing using common Adel clamps or any other off the shelf bracket without spending the time to design a custom mounting scheme, or trying to dream up a new overly complicated fixturing method every time the sensor has to be relocated to find the optimal position for oil pressure readings. All in all, this is certainly a time saver when we are focused on a timely and efficient series of tests.  

The last factor that we’ll touch on that can be invaluable for our pressure testing is customization. More often than not, the pressure sensors that are readily available on the market for such a test have a well-defined scope that they operate in. A single configuration that works best in ‘this’ pressure range, for ‘that’ frequency of collection, and it all comes with just ‘this’ product design. However, STS pressure sensors offer several options and customizations that give us the freedom to not limit our test based on our sensor’s individual capabilities.  

For our example, we of course must have a sealing material that with neither contaminate the oils, nor degrades with constant exposure. Well, we have several options for the sensor seals that can accomplish just that, including EPDM and Viton to ensure that the sensor is operating at peak performance for the entire test. Or, conversely, we can opt for a metallic sealing option to ensure proper test results. What’s more, perhaps we need a frontal diaphragm connection, with a PUR cable, along with 20 mA output signal. STS can deliver exactly that, along with any number of other combinations to ensure that the process connection, electrical and output signals, pressure connection, and seals are exactly what we need. In essence the sensor is cherry picked for our test and not simply some component we need to shoehorn into the test setup.  

To recap, we are required to design a series of oil pressure tests; and as with most tests, many of the factors will be manipulated. The heat, mounting method, pressure range and a mind-numbingly large number of other issues will all be changing constantly over the course of the test. To cap it all off, we need a test pressure transmitter that can fit into this envelope and consistently produce accurate results. Well we can at least nip that problem in the bud straight away by incorporating an STS pressure transmitter for our testing regimen. The high temperature and pressure ranges, combined with custom seals, process connections, electrical and signal outputs, and overall design ensure that this is a sensor that can pre-configured to slide seamlessly into your testing apparatus, and not require that your entire system by reconfigured to suit the sensor.

Pressure measurement of fuels – Material selection is decisive

Pressure measurement of fuels – Material selection is decisive

Aggressive liquids and gases pose a particular challenge to the pressure-sensing technology employed. For this reason, sensors are required which can be flexibly adjusted to the particular requirements. With the ATM.1ST product series, you will always remain on the safe side. 

A significant product characteristic of pressure transmitters is their modular construction. A variety of mechanical and electrical components can be co-assembled, according to application, to:

  1. optimally maintain the usage of matched pressure transmitters, and
  2. ensure a rapid implementation of the measurement setup.

Figure 1: Assembly of a pressure sensor with O-ring measuring cell

The basis for this are high-quality measuring cells of a piezoresistive nature, which are sealed using O-rings. This construction allows for a multitude of combinations. Dependent upon usage within the pressurized medium, various O-ring materials are employed (Viton, EPDM or Kalrez) to optimally tailor the pressure sensors to that particular application.

Figure 2: Example of a metal-seating pressure measurement cell

For application in aggressive media such as fuels (diesel, gasoline, …) or in high-pressure operations, however, sealing with O-rings becomes unsuitable. In such environments, the measuring cell has to be welded together with the pressure port. For this reason, an elastomer-free metal-sealing variant was developed for applications in fuels: The ATM.1ST product range.

These elastomer-free (metal-sealing) versions can be offered in the most diverse of mechanical designs. In the accuracy class of 0.05% FS, the pressure transmitter is available in nominal pressure ranges from 0…20  bar up to 0…100 bar and with an output signal from 4 – 20 mA.

In the 0.1% accuracy class, the pressure sensors are offered in nominal pressure ranges from 0…20 bar up to 0…700 bar and in versions of 4-20 mA or 0 – 5/10 V.

The analog transmitters are calibrated in two temperature ranges, -25…125°C (standard) or -40…125°C (optional). Across both temperature ranges, a Total Error Band of < 0.4% FS is guaranteed.

Featuring a shortened form, robust housing and a very high flexibility, the ATM.1ST product range allows end users to configure these pressure sensors according to the prevailing requirements. Regardless of pressure port or electrical connection, a broad range of possibilities for mechanical mounting are available.

With this convincing technical specification, these pressure sensors are ideally suited to various fields of application in measurement technology or plant and mechanical engineering, as well as in the equipping of test beds or calibration facilities.

Pressure measurement of fuels – Material selection is decisive

Minimizing pollutant emissions using pressure-sensing technology

Recall actions in the automobile industry have widespread consequences. Manufacturers have to contend with a huge image loss, as well as higher costs. Vehicle owners, on the other hand, react with anger and uncertainty. A particularly major stir has welled up over the past year with the scandal surrounding manipulated emissions figures. Politics has in turn reacted and signaled towards new testing procedures.

The automobile industry has triggered a true recall-crisis over the last two years. In the USA alone, some 51 million vehicles were ordered for recall during 2015 by the National Highway Traffic Safety Administration (NHTSA). This far exceeds the number actually sold in that same year, even though the vehicles recalled were not all connected to manipulated emissions figures. Some 11 million of these vehicles originate alone from the “Dieselgate” scandal involving the manufacturer Volkswagen. The losses involved are enormous.

Cost pressure and an increasing complexity of the systems built into vehicles are associated with heightened error susceptibilities and their resultant recall actions. This challenge is to be met primarily through improved and even more reliable control systems – on the part of manufacturers and suppliers, as well as government supervisory bodies responsible for legal specifications monitoring. High-grade measurement equipment is therefore needed, which can deliver the most precise of results under varying conditions and thus secure an optimal standards qualification (or post-qualification). A major backlog demand has since opened up in this respect.

The best pressure measurement technology for the best combustion engines

In the development of combustion engines, high-precision pressure transmitters are required, which, during combustion analysis, can facilitate the exact measurement of cylinder pressures, as well as intake and exhaust pressures. Absolute pressure sensors (gas exchange) and high-pressure sensors (injection pressure measurement) must also be of the highest-grade, since, in the latter instance especially, the potential for pollutant minimization is enormous. In this regard, particulates from gasoline engines can be reduced through an increase in injection pressure. Some suppliers are already working on increasing injection pressures to 350 bar or even higher.

Mobile emissions measurement is on the way

The standardized “New European Driving Cycle (NEDC)” is currently being introduced for exhaust and consumption measurements by state regulatory agencies. As we have witnessed, test procedures have given manufacturers all the freedom to influence measurements to their own advantage, since the vehicle is examined only in a test facility rather than under real-world conditions.

Once the manipulations became known, the Committee of Experts from the European Union decided in May 2015 that emissions during type approval are to be tested from late 2017 under practical driving conditions – known as Real Driving Emissions (RDE). The laboratory conditions for conventional checks will be supplemented by a procedure that prevents the use of cut-off devices during testing. The vehicle to be tested will be examined on an open track and thus subjected to variable conditions. Furthermore, random braking and accelerating procedures will also be performed.

Meeting new challenges – using modular pressure-sensor solutions

The RDE procedure obviously poses particular challenges to the measurement technology deployed. In the optimization of emissions figures for combustion engines, initial emphasis falls upon absolute and relative pressure measurement. With the new measurement procedures in mind, these need to perform reliably across a broad temperature range. Whether in the depths of winter or the heights of summer, measured values must be absolutely reliable to reflect a realistic picture of the true exhaust figures. It is also evident that operation at higher pressures can achieve significant reductions. For this reason, higher pressures must also be measurable. The fact that the pressure sensing technology employed operates without failure in mobile applications, given the new procedures, goes largely without saying.

Standard solutions cannot achieve this objective. Even more than that, they are actually part of the problem. Individual challenges require individual solutions. Also required are instruments that are precise as well as flexible enough to perform reliably in differing applications. Only by following this path can cost-efficiency and precisions be reconciled. It is clear that modular systems would be ideal in this context. In coordination with the manufacturer, these can be adapted to individual requirements and thus deliver highly reliable results. This represents a particular advantage in the development of new engines, since the adaptations can be made both straightforwardly and also promptly.

An experience that our customers have been making daily – and for almost 30 years now. As a leading manufacturer of customer-specific, modular measurement systems, we can provide tailored pressure measuring solutions within a short timeframe and in a proficient cooperation with manufacturers. Viewed from a measurements perspective, there exist no obstacles to the development of new, fuel-efficient engines, as well as to their testing under real-world practical conditions.

Pressure sensors in motorsport: Where a fraction of a horsepower is decisive

Pressure sensors in motorsport: Where a fraction of a horsepower is decisive

“The winner takes it all!” The world of motor racing is divided into winners and losers, with the successful driver enjoying the champagne shower. The preliminary outcome, however, takes place on the engine development test bed, with high-performance pressure sensors representing the decisive competitive advantage.

STS supplies pressure sensors to customers from the world of motorsport, including participants in Formula 1 and NASCAR. Both of these racing series, despite all their differences, have one thing in common. Every horsepower counts and embodies the decisive advantage on the track. When every tenth of a horsepower is to be wrestled from extensive analysis on engine testbeds, the end results have to be absolutely reliable down to last decimal place.

Pressure measurement technology in Formula 1 engine development

The current engine regulations in Formula 1 were introduced in 2014. V-layout engines of six cylinders, 1.6 liters displacement and a single turbocharger are driven. The rev speeds reach up to 15,000 min−1. The Kinetic Energy Recovery System (KERS), an electrical system for recovering energy under braking first introduced in 2009, has now been replaced by the Energy Recovery System (ERS). In modern Formula 1, the engines involved are thus of a hybrid type. The future of Formula 1, for this reason, has long since become the present. The perhaps most successful racing series worldwide is also a testing laboratory for the road. From disc brakes to computer diagnostics, many technologies now found in everyday road traffic have their origins in the development centers of Formula 1.

The prevailing engine regulations, which evenly delineate the parameters for all teams, make thorough research on the testbed essential to carving out the decisive advantage. Every single horsepower counts. In comparison to tests for vehicles in normal road traffic, different requirements, to some extent, are applied. Oil and water pressures are higher, as are their arising temperatures. When improved fuel economy and increased performance is the aim, then extensive testing under racing conditions is essential. Furthermore, the precision of measured results across the required temperature range is of great significance. In Formula 1, major leaps in terms of horsepower are often not the case – improvements even in the decimal regions are a reason for celebration at this elevated performance level.

In light of these challenges, a well known racing team from Formula 1 approached STS, since the hitherto employed sensor technology failed to meet their high requirements. The measuring instruments used were too big and too heavy. Even more serious, however, was the problem that additional cooling technology had to be built into the testbed, since the sensor temperatures would otherwise rapidly escalate above the maximum. Measured results under this scenario would thus be worthless.

The aim of the developers was to acquire pressure sensors that permit standardization and make additional cooling elements obsolete. The topics of weight and size also play a role, since these factors influence the performance of the speeding car.

STS provided the racing team with a new sensor from the ATM series, available on the market from the fall of this year. This sensor scored not only in its desired precision across the required temperature range, but also delivered a further decisive advantage which could enduringly optimize engine development. With the previously used sensors from another manufacturer, there were malfunctions when switching to the hybrid systems employed since 2014. The results were that the testbed would shut itself down and longer term measurements were practically impossible. The ATM sensors from STS are fail-safe and thus allow for extensive testing on the road to the victory podium.

Pressure measurement technology in NASCAR engine development

Although hybrid engines are not built into NASCAR stock cars, extensive testing is still required to attain the optimum in performance. In this sport also, a well known engine manufacturer has opted for the pressure measurement technology from STS. During extensive tests, some 200 ATM.1ST pressure transmitters have been keeping an eye on oil, water, fuel and air pressures. From air pressures reaching the engine right through to improvements in oil flow, the aim is to precisely examine various factors to attain even the slightest increase in performance (involved here is ca. 900 PS). As with Formula 1, the highest of precision is required. The scope here amounts to just a tenth of a horsepower!

The manufacturer choice went to the ATM.1ST pressure transmitter, since it is largely unrivalled in its required performance characteristics.

  • The modularity of STS sensors also allows the manufacturer to connect a special pressure adapter.
  • A total error of ≤ ± 0.30 % FS permits meaningful analyses for improving engine performance.
  • Long-term stability considerably minimizes the need for calibration.
  • The pressure measuring range from 100 mbar…1,000 bar is well suited to those pressures arising during engine development.
  • Outstanding temperature compensation allows for precise results across a broad temperature range – a decisive criteria for the sharply rising temperatures during performance testing at these highest levels.

Whether in Formula 1 or NASCAR, the path to the victory podium leads through engine testbeds. In the high-performance motorsport field in particular, high-precision sensors are required for monitoring all of the important data from oil and water pressures to fuel and air pressures. Besides precision, fail-safe capability also plays an important role in being able to conduct essential long-term testing that yields reliable results.