Applications –

Pressure sensors play a crucial role in modern industry, especially in environments where aggressive gases are processed, transported or stored. These sensors must not only withstand extreme conditions, but also resist the corrosive effects of the gases to ensure accurate and reliable measurements. This guide provides a comprehensive overview of the selection and application of pressure sensors for aggressive gases, with a particular focus on material selection for durability and safety.

Carbon dioxide, also known as R744, is experiencing a renaissance as a refrigerant in vehicle air conditioning. This gas, with a long history in refrigeration dating back to the 19th century, offers numerous advantages, such as no ozone depletion potential. Its special properties make CO2 an attractive alternative to conventional refrigerants like R134a and R1234yf.

Optimized thermal management systems for electric vehicles contribute to energy-efficient, economical and comfortable mobility. Turbine flow measurement systems made by DDM are a tailor-made measurement technology for on vehicle thermal management testing. 

Most vehicles will be powered by electric motors in the future. The coming years will show whether the necessary energy will be stored in batteries or as hydrogen.

Both systems, BEV (Battery Electric Vehicle) and FCEV (Fuel Cell Electric Vehicle), require a sophisticated thermal management. These systems have batteries of different sizes that need perfect temperature control to achieve the highest possible capacity and service life. The powerful electric motors and their power electronics must be cooled. The interior should be air-conditioned to comfortable temperatures for the passengers. All these different temperature levels have to be conditioned according to the situation.

The flow rate and temperature of the coolant must be measured to read and tune the system components. DDM turbine meters are highly miniaturized to measure flow rate and medium temperature simultaneously at high accuracy in real time.

DDM have further developed the turbine flow meter (VCT) for testing and evaluation of the complex thermal management in electric vehicles with development goals as below.

Miniaturization

The turbine flow meters (VCT) are particularly small and lightweight. They can be fitted where space is very limited, not to say where no space is available. Thanks to the weight reduction, no additional brackets are required. The coolant hose is able to safely support the turbine weight.

Dynamics

The turbine flow meters (VCT) are high dynamic flow meters and detect flow changes very quickly. Since temperature can fluctuate within the thermal management circuit a media exposed fast response thermocouple is integrated in the VCT housing. This provides faster and thus more accurate viscosity correction of the turbine flow meter.

Transmission reliability

Electric vehicles operate at high voltage and current levels. They could interfere with low level RF carrier frequencies used on traditional flow turbine meters. To overcome that potential risk the communication between turbine (VCT) and flow computer (VCA) is digitalized and raised to a new level in terms of EMC Interference immunity.

Linearization and viscosity correction           

Valves in thermal management circuits may operate very quickly to control the different temperature levels. Therefore, a flow rate averaging, predefined by the manufacturer, may not perfectly match the measurement task. The flow computer (VCA) is user adjustable. It is possible to operate the flow computer in a “live mode” where the actual linearized and viscosity-corrected flow rate is available virtually without delay. Of course any other averaging between1ms to 5sec can be set.

Media independence

By nature all turbine flow meters are affected by fluid viscosity changes. Each medium or mixtures of those have different viscosity characteristics. So it is quite common to change the fluid in the thermal management to evaluate a different water/glycol ratio. The adaption of the flow measurement system to the media in service is quick and very simple. Up to 10 media characteristics are stored in the flow computer (VCA), which can be toolless selected by means of an RFID tag.

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Hydrogen has become an indispensable part of the future energy mix. Our team supported a large research laboratory in the development of new and more efficient fuel cells. In the context of a long-term test carried out over 4 months of a low-temperature polymer electrolyte membrane fuel cell stack, DDM pressure sensors were used in the anode path of the stack. The media compositions at the pressure sensors corresponded to realistic compositions. The involved medium consisted of different concentrations of hydrogen, nitrogen, water vapor and liquid water. The sensing element and pressure connections of our hydrogen-compatible pressure sensors are made from 316L stainless steel. The construction is fully welded and 100% helium leak tested. Each sensor is supplied against a manufacturer declaration for hydrogen use.

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In some cases, existing turbine flow meters that are still running well are taken out of service because the associated instrumentation system does not perform with reliable flow readings any more. These faults, for example indicate readings at now flow and the other way round. More serious are flow rate readings with increased uncertainty. Malfunctions are more likely caused by the electronic part of the measurement system rather than by the turbine flow meters itself.

RF (radio frequency) pickoffs are very common on the market to detect the turbine rotor speed. They engage, in comparison to magnetic pickoffs, no drag to the turbine rotor. However to operate an RF pickoff, a specific driver circuit is required. To keep the turbine flow meter small and to protect the driver circuit electronics from harsh environment the electronics are fitted remote very often. Due to the resulting cable length which may easily be up to 10 meters the oscillating driver circuit is exposed to interference which could affect the performance and reliability of the low pulse output signal.

The new DDM Smart Pickoff ideally overcome this potential failure source. The RF (radio frequency) circuit is highly miniaturized integrated in the DDM Smart Pickoff. The low signal pulse is amplified to an high level TTL digital output. The digital open-collector TTL pulse output can be transmitted safely to DDM flow computers (VCA & VCA-T) for linearization and viscosity correction.

Turbine flow meters in general are viscosity-dependent. To compensate for this, a type-T thermocouple is built into the DDM Smart-Pickoff also. The thermocouple is used to determine the media temperature and transmit digital readings to flow computers connected. Up to 10 media characteristics (viscosity by temperature) can be stored in any DDM flow computer (VCA & VCA-T). User may easily select the appropriate media tool free by means of an RFID tag. Together with the actual media temperature the flow computer calculates the fluid viscosity and corrects the flow rate output signal in real time.

An ”old” turbine flow measurement system susceptible to interference effects is transformed into a very robust, reliable, linearized and viscosity-corrected measurement system by using DDM smart pickoffs and flow computers (VCA or VCA-T). The turbine retains its value and is upgraded to the current state of the art.

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Even in modern hybrid or electric vehicles, heat is produced as a waste product, or heat and cold are required to supply the power electronics, the drive, the battery and also the passenger compartment with the optimum temperature in each case.

To coordinate these extensive tasks of the cooling system, an elaborate and complex thermal management system is required.

Due to the large number of tasks, a correspondingly large number of components are involved here. The difficulty is that various pressure drops occur at each component involved and in the piping system. However, in order to keep efficiency high, the cooling system is operated with the lowest possible system pressure, which in turn means that any pressure drop disrupts this system.

The thermal management of a vehicle is designed by means of complex CFD simulations. This design is based on manufacturer specifications for the individual components installed in the thermal management system, such as radiators, power electronics, motors and many more.

In order to be able to precisely examine all components and lines regarding their influence in the cooling system, DDM has developed a differential pressure sensor suitable for road tests.

The PV 2722 is compact, media resistant on both sides and temperature compensated, so that it can be used in the temperature range from -40°C to +125°C at almost any location in the vehicle and test bench.

Pelton wheel flow meters are small and cost-effective flow meters for liquids and are suitable for batching processes and dispensing applications particularly within the food and beverage, chemical and laboratory sectors.

We supply with our partner Titan Enterprises Pelton wheel flow meters Series 800 with NSF certificate for beverage dispensing, as ‘equipment for food and drinks products’.

• Wine
• Beer
• Gin
• Whisky
• Fruit Juices
• Other drinks

The excellent chemical resistance, even for ultrapure water, is due to the careful selection of wetted parts materials.

The NSF-approved Flowmeter is overing six d different flow ranges from 0.05 to 15l/min and two temperature options 125°C or 60°C. The good accuracy of 1% FSD and repeatability of 0.1% characterize the Pelton wheel flow meter.

The radially driven Pelton wheel is equipped with robust, smooth-running sapphire bearings.

The filling of complex systems requires a sophisticated filling process. A time-optimised process with short cycle times is crucial when it is about economic efficiency. To permit the most rapid filling a number of process steps are required. Their dynamic sequence is determined by the geometry of the unit to be filled and by the fluid properties of the filling medium itself. The typical areas of application are refrigerators, air conditioning systems, heat pumps, systems for braking, cooling, air conditioning, engines, gearboxes, hydraulics or windshield wiper systems. The most important parameter for a short cycle is the process pressure. It is crucial that the pressure sensor is fully integrated within the hydraulic system to respond immediate for any pressure change.

The highlight: Our team has developed miniaturized, customer-specific pressure sensors which permit a direct integration into the filling adapter. In addition to the individual design, the electrical interfaces were designed customer customer specific also.

Depending on the application, pressures can vary between 1 mbar and 125 bar. Fast response time was achieved by flush diaphragm pressure sensing design. Every DDM pressure sensor is equipped with a TEDS memory. The stored data provides default data like TAG number, Serial number, Pressure range, Calibration data which is automatically read at system power up.

Maximised customer benefit: a product with a unique character, exclusively developed and manufactured.

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Vehicles product quality is perceived via various human senses: In addition to smell, optics and haptics, acoustics also influence the perceived driving comfort and the sense of well-being when driving.

Among others one important factor, is the pressure impulse that occurs when the doors of a vehicle are slammed. If this peak pressure is too high, it can be very unpleasant for the ears. In addition, too much pressure inside the vehicle can also prevent closing and the doors completely.

To ensure health and safety, most vehicles have pressure equalization flaps installed in their body. They ensure the pressure is dissipated promptly to the outside. It is important that these flaps dissipate the pressure impulse to the outside, but at the same time no noise or smell is conducted from the out to the inside. Extensive tests are required to proof the car is passing this requirement.

In order to measure the pressure pulse level and duration, fast response and very precise differential pressure sensors are used.

The DDM differential pressure sensor PV 2722 is placed in the vehicle interior. Via a pressure compensation tube routed from the negative pressure connection to the outside, it is possible to measure the peak pressure pulses within milliseconds at various points inside the vehicle. This provides precise and rapid data for product development.

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The calibration of flow meters is a complex process. Generally speaking, this work is carried out by calibration laboratories having the appropriate technical equipment. In addition to the calibration costs, there is the downtime which may be significant for the customer.

To minimize calibration cost and downtime we developed a customer specific flow calibration rig. The rig is easy to operate and the calibration routine runs automatically. The devices under test (DUT) are flowmeters with ranges up to 30 liters per minute. In order to match calibration fluid with application specific viscosity a special calibration fuild was used. To maintain that viscosity constant, the fluid temperature was controled at a defined level. A variable speed positive displacement pump runs the fluid within a closed loop. Thanks to this pump technology, calibration liquids up to 1,000 cSt may be used. Within the closed loop there is a master flow meter to compare the flow rate readings with the readings from DUT. The handling is easy and requires no special knowledge. Just fit the DUT chose the approbriate calibration routine and press the start buttom. The whole calibration process runs automatically and generates a pass/fail message.

Targets of cost saving and minimizing of downtime where achieved perfectly.

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Various experiments of a biological, chemical or physical nature are carried out at an almost daily basis on the ISS space laboratory. Reliabilty of instrumentation is the most important factor. Therefore some of the experiments were tested on Earth under weightlessness simulated. This is why those instruments are temporary brought into the orbit with small rockets. In this context, for the measurement of various electrical and physical parametres, highly precise and reliable sensors are essential. Therefore the DDM pressure sensor PV 15 series was selected and proven to perform as expected.

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To be able to operate agricultural cultivation economically, you have to use fertilizers and pesticides.

An excessively high dosage is costly, damages the soil and groundwater.

Liquid fertilizers and pesticides can be applied in a more targeted manner according to the soil behavier.

DDM flow meters are robust and media-resistant. They measure the flow rate in real time, allowing exact dosing at high driving speed and documentation of the amounts of plant agents applied.

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Turbine flow meters are dependent on the viscosity of the medium. In order to compensate for this effect, the fluid temperature is measured in the best case in contact with the medium. With the aid of a stored temperature to viscosity characteristic curve, the current media viscosity is calculated.

The wetted temperature measuring point in a measuring turbine is realized either by means of a Pt100/1000 resistance thermometer or via a thermocouple. These two temperature measurement methods are common in the industry and are used in many ways.

The following table compares the performance of these two temperature measurement methods in the application area of a turbine measurement system. Afterwards, the most important parameters accuracy, dynamics, installation space and cabling will be discussed in detail in the comparison. In addition, you will learn all about the added value of our in-house developed DDM turbine flow measurement system with thermocouple VCT.