Devising and creating an aircraft is a daunting task, and no small feat by any means. The endless calculations, designing, simulations, and re-designing seems to be a perpetual process; however, we will eventually reach the milestone of intensive testing! This is a very exciting process, all the 3D parts you’ve designed, the systems you’ve pieced together, and all the components are now sitting right in front of you. It is time to prove to yourself, and your managers, that everything will operate flawlessly, but don’t get ahead of yourself! To do that, we need top-notch data recording equipment to verify our system’s performance. What’s more, we need test sensors that can function in the most extreme conditions both inside and outside the aircraft. Well, that is why STS is here, to furnish us with reliable pressure measurement transmitters to ensure that our rounds of pressure testing work just as smoothly as the system we designed. We’ll spend the rest of this article presenting a step by step guide to fully acquaint you with the full range of options that STS offers and how to integrate those into our system.
Step one, we need to take a close look at the aircraft system we’re testing, and determine the precision required for our data collection. For example, the hydraulic system that controls the aircraft’s brakes often operates within a specific pressure range, and this range is large enough that extraordinary precision is not a requirement when selecting a test sensor. Therefore the STS option of ± 0.25% FS would be a suitable option. On the other end of the spectrum, the oil pressure must be monitored much more judiciously when compared to the brake hydraulics. With that in mind, we can select the STS option for a high precision pressure transmitter with the highest degree of accuracy available, namely ± 0.05% FS to ensure that the oil pressure remains at its peak level throughout the engine system.
Now that we’ve established the required accuracy for our application, let’s move on to integrating the pressure sensor into our test aircraft system. Naturally, the pressure oriented systems on an aircraft are exceptionally diverse in terms of size, operating temperature, and pressure medium; consequently, we need the freedom to cherry-pick every one of these features for our sensor.
For the next step in the selection process, let us turn our attention to the operating temperature. In an aircraft, your test pressure sensor could potentially be recording data within the sweltering confines of the engine compartment. Conversely, it could be located externally, measuring the Pitot pressure or perhaps the de-icing fluid pressure in which case the operating temperature will be drastically lower than the engine compartment. Never fear, STS offers an impressive range of operating temperatures from -25 to 125° C. This base range will by and large cover the majority of our aerospace pressure needs. To sweeten the deal, all STS sensors are manufactured to include a compensated temperature range, meaning the inherent measurement error is drastically lower within the limits specified above. This is an exceptionally beneficial feature when completing intensive testing on our pressure systems!
The aforementioned temperature range is by no means set in stone. When the need arises, we can opt to have our sensor outfitted with cooling fins to boost to max temperature to 150° C. Such a need might arise if the sensor was to be located next to the engine exhaust system which can radiate a significantly large amount of heat. Furthermore, we can choose for our sensor’s minimum temperature to be lowered -40° C if the sensor was to be exposed to a particularly high altitude. That covers the selection process for your sensor’s temperature resistance; always keep your operating environment in mind!
As previously mentioned, the sizes and gauges of the different pressure systems within an aircraft are far from constant. Therefore, the next step in our selection process is to determine the optimal location for the sensor, and select a connector that will allow the sensor to fit in that particular location. For example, take an aircraft brake system. The hydraulic system will consist of various tube sizes and components, but once you have selected the exact location for your sensor, the process connection can be chosen. STS offers a range of sizes and diaphragms including G ¼ M and G ½ M with the additional choice for Hastelloy and frontal diaphragms, amongst other choices. This wide range of possible selections ensures that we can order a sensor that will slide into our test system perfect without any special retrofitting in order to install, which lowers the workload for us!
The final major component of our test sensor that we’ll cover is the sealing materials that are available to us. As with the process connector, the material to select to seal your sensor is highly dependent on the fluid that makes up your pressure system. Luckily for us in the aerospace field, our pressure systems will seldom experience corrosive, acidic, or other unsavory fluids. Nevertheless, we still must give some thought to our seals. In the case of our hydraulic system for landing gear, the standard choice is Nitrile (NBR) as our seal. This rubber-like material is ideally suited for this application in addition to being resistant to oils and other lubrication materials. However, if we’re expecting high temperatures or other harsh conditions that are present in an engine compartment then Viton would be a much more suitable choice with its improved temperature resistance and durability. Last but not least, EPDM rubber has a proven track record when dealing with brake fluids. These are only three of the many sealing options that STS offers, with the main takeaway being that not all seals are interchangeable. Research your system, the options available, and make the best choice to ensure optimal sensor results!
Now you are fully prepared to begin the pressure sensor selection process for your aerospace testing! We’ve covered the level of accuracy required for your sensor, which is dependent on the exact system in which the sensor is located. We then moved on to determining the correct level of temperature resistance required for our individual applications. Followed by the process connection where we can select various sizes and diaphragms to ensure that the sensor is always tailored to our exact needs. Our last point was to explain the primary differences between the many seal options that are available to you, and the ideal application of each one. With this information, you can look at the primary components of your test pressure sensor and make the best selections to ensure that your sensor is quite literally made just for your use!