Accuracy pressure sensors

Another method to process and detect faulty responses of the redundant sensor signal is called the likelihood test. The likelihood test used is borrowed from nuclear reactor safety for pressure sensors deciding shutdown or no shutdown. Instead of shutdown or no shutdown for this case, the sensor reading would be rejected or accepted. For accuracy of the readings, the test chosen needs to reject readings that have even the smallest likelihood of being false and leading to the patient s inappropriate response.36... 

It is also interesting to briefly consider online measurements of variables different from temperature [5], Since pressure is defined as the normal force per unit area exerted by a fluid on a surface, the relevant measurements are usually based on the effects deriving from deformation of a proper device. The most common pressure sensors are piezoresistive sensors or strain gages, which exploit the change in electric resistance of a stressed material, and the capacitive sensors, which exploit the deformation of an element of a capacitor. Both these sensors can guarantee an accuracy better than 0.1 percent of the full scale, even if strain gages are temperature sensitive. 

Mass-flow sensors are used to measure air intake. Their advantage over pressure sensors in the same application is primarily higher accuracy. The growth of this sector is moderate and mainly due to increasingly strict environmental legislation. 

Tab. 7.3.2 Operating temperature and accuracy requirements for automotive pressure sensors...

The automotive pressure sensor is characterized by its strict requirements. Tab. 7.3.2 gives sample accuracy requirements for automotive pressure sensors [2]. The pressure sensor used in the engine compartment is required to operate over a temperature range from -30 to 120 °C, and the pressure sensor for air-condi-... 

To improve the fuel vapor-pressure sensor accuracy, we reduced the mechanical strain conveyed from the package to the sensor device. Fig. 7.3.14 shows the structure of the fuel vapor-pressure sensor for 5 kPa. We chose a relatively thin silicon diaphragm, 14 pm, to achieve the sensitivity required for 5 kPa detection. That makes the sensor device more susceptible to the mechanical strain conveyed from the resin package. To solve that problem, we analyzed the effect of the mechanical strain from the package by FEM. 

Fig. 7.3.15 shows the analysis results. The key factors for improving the accuracy of the low-pressure sensor for 5 kPa are as follows. 

These measures allow reduction in the effect of mechanical strain on the sensing element, resulting in a pressure sensor with a high accuracy of 2% FSD at 5 kPa. 

Hydraulic sensor selects CYAT type pressure sensor, which has high measuring accuracy, stable and reliable performance, good sealing performance. 

Flow and pressure sensors A very important parameter that is often measured in most industrial process streams is flow rate. The range of flow sensors that are available for measuring liquid and gas flow rate in industrial process streams is summarized in Table 2. Of these, the accuracy, resolution, and cost of ultrasonic flow sensors are attractive and comparable to other flow sensors. Furthermore, it is now possible to use this flow sensor to monitor process... 

Accuracies achievable for measurements in the ocean are 0.002 mK for T, 0.05 % for P and 0.002 for S. Temperature and pressure sensors are calibrated in the laboratory. In situ comparison of the laboratory calibrations of these sensors only makes sense if additional sensors with digital output can be attached to the CTD. Die accuracy and stability of reversing thermometers and pressure sensors sometimes attached to rosette bottles is not suffi-... 

In electronic balances the force exercised by the load on the base is measured with a force measurement cell (for example, an electrical strain gauge) and transformed into an electrical signal. This signal is processed within the balance in a digital or analog fashion and is then displayed. These systems can be calibrated and used in fully automatic installations. As force measurement cells one can use pressure sensors with lower requirements for accuracy. These are installations in which the weight is transformed into pressure pneumatically or hydraulically one can determine levels in tanks or reaction vessels by this method, which can also be used to meter automatically the main ingredients of a batch process, for example the water and monomer phase in an emulsion or suspension polymerization. 

A series of tests showed the pressure sensors checked within their calibration accuracies when readings from these gages were compared to load cell data which was used as the standard. Since these tests confirmed basic calibration accuracies, we concluded the strain gage pressure cell would provide the more accurate and reliable data for propellant loading within the i 1/2 per cent required by one missile manufacturer. 

Differential pressure sensors are special pressure sensors with two chambers separated by a membrane. The pressure difference between those two chambers is detected. This setup allows determination of pressure differences significantly smaller than either one of the applied pressures with high accuracy. Fields of application are the pressure losses over certain unit operations such as separation columns or the use of differential pressure to monitor two other process parameters flow and level. The latter applications are discussed in the subsequent chapter. In high-pressure technology, two aspects have to be observed closely. First, the maximum allowable differential pressure of the transducer can easily be exceeded due to high system pressures, thus destroying or offsetting the sensor. Second, fluid... 

As shown by curve(2) in Figure 10, the maximum of the measurement error due to bearing deformation was approximately 2MPa at most or less than 5%. This means, the twin-arc type pressure sensor, as shown in Figure 1(b) and Figure 5, can be used as a pressure sensor without correction, though it may depend on the measurement accuracy required. 

Outlet Volumetric Flow The nominal volumetric flow of 0.15 m /sec (corresponding to a mass flow of 3.08 kg/sec) for the four loop non-optimized Brayton system of Section 6 is assumed. The range 0.01-1 m /sec has been selected to cover a sufficiently wide range of operation to provide for plant startup at reduced flows, full power operation, and casualty performance. The accuracy of 0.0025 m /sec typifies the accuracy of 0.25% of point found in gas industry ultrasonic flow metering equipment The time constant of 1 second typifies high precision pressure sensor with digital instrumentation. 

Before the performance of the loading we have to apply 5 up to 12 sensors, according their size, on the cylindrical part of the drums and after a short check of the required sensitivity and the wave propagation the pneumatic pressure test monitored by AE can be performed. The selection of the sensors and their positions was performed earlier in pre-tests under the postulate, that the complete cylinder can be tested with the same sensitivity, reliability and that furthermore the localisation accuracy of defects in the on-line- and the post analysis is sufficient for the required purpose. For the flat eovers, which will be tested by specific sensors, the geometrical shape is so complicated, that we perform in this case only a defect determination with a kind of zone-location. 

The specific test was made into a specialized bunker of one partner of the CIAPES program. All the vessel was covered by AE sensors to locate witli accuracy AE sources. The corrosion defect was situated on the bottom of the vessel. The service pressure of the vessel was 8 bars, so the vessel was first submitted to a proof test at 12 bars. During this test, the pressure was increased with load holds in order to verify the assessment criteria. After the first hold at 4 bars, a cluster was located at the position of the defect. The number of events located in this cluster increased during all the test (figure 1). 

Process Measurements. The most commonly measured process variables are pressures, flows, levels, and temperatures (see Flow LffiASURELffiNT Liquid-levell asurel nt PressureLffiASURELffiNT Temperaturel asurel nt). When appropriate, other physical properties, chemical properties, and chemical compositions are also measured. The selection of the proper instmmentation for a particular appHcation is dependent on factors such as the type and nature of the fluid or soHd involved relevant process conditions rangeabiHty, accuracy, and repeatabiHty requited response time installed cost and maintainabiHty and reHabiHty. Various handbooks are available that can assist in selecting sensors (qv) for particular appHcations (14—16). 

There are many types of sen.sors used to feed-back the process operating conditions to the switching logistics of an inverter unit. They can be in terms of temperature, pressure, volume, flow, time or any activity on which depends the accuracy and quality of the process. Direct sensing devices used commonly for the control of a drive and used frequently in the following text are speed. sensors, as noted below. 

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