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Digital Interfaces in Measurement Systems
Published in Robert B. Northrop, Introduction to Instrumentation and Measurements, 2018
PXI stands for PC extensions for instrumentation. The PXI standard defines a modular instrumentation platform (hardware modules and operating software) designed specifically for robust measurement and automation applications. PXI peripheral modules are used as remote computer-controlled front ends for Vis. PXI modules generally have only input signal connectors and status LEDs on their narrow front panels; there are generally no control knobs or switches.
Improvement of Real-Time Hybrid Simulation Using Parallel Finite-Element Program
Published in Journal of Earthquake Engineering, 2020
Li-Qiao Lu, Jin-Ting Wang, Fei Zhu
Zhu et al. [2014b] developed a RTHS with dual target computers (D-RTHS). As schematically shown in Fig. 1, the D-RTHS system includes three parts: the distributed real-time calculation system, the shaking table loading system, and the data acquisition and transmission system. (a) The Matlab’s xPC system is used in the distributed real-time calculation system. It splits the calculating task into RAT and SGT [Nakashima and Masaoka, 1999]. The RAT of solving the numerical substructure is implemented on Target Computer 1 with a main time step, and the SGT of using an interpolation algorithm to create the displacement signal with a sub-time step (i.e., to meet the controller’s input demand) is implemented on Target Computer 2. (b) The shaking table loading system includes a shaking table, a 469D digital controller, and the oil source. The controller’s sampling frequency is 2048 Hz. (c) The data acquisition and transmission system consists of the PXI device and the LabVIEW software. The real-time transmission of data is achieved through these three installed SCRAMNet cards. For the details of the system, please refer to Zhu et al. [2014b].
A novel strategy for effectively implementing a typical AVC scheme using finite element model updating
Published in Mechanics Based Design of Structures and Machines, 2019
Poonam Sood, Manu Sharma, Sukesha Sharma, Navin Kumar
The external control voltage that gets applied on the piezoelectric actuator patch placed on element number 11 corresponding to this modal control force is given by (Garrido et al. 2014): where ‘g’ is the gain of the velocity feedback controller, ‘’ is orthonormal modal matrix of first three modes, ‘’ is the capacitance of actuator and ‘’ is vector of electro-mechanics of piezoactuator. Estimation of first three modal displacements and first three modal velocities is done using Kalman filter equations as (Gopal 2012): where ‘’ is the estimated state vector, ‘’ & ‘’ are the discretized system & control matrices respectively. ‘’ & ‘’ are Kalman gains, ‘’ is the sensor voltage, ‘’ is the sensor location vector and ‘’ is the control voltage. To study the effect of FE model updating on the performance of AVC controller two cases are compared. In case 1, the Kalman filter in the controller is based on analytical FE model and in the second case Kalman observer is based on updated FE model. A negative velocity feedback controller is employed to control the first modal displacement of the smart plate. An initial displacement of 2 mm is given to the free edge of the cantilevered smart plate that is parallel to the cantilevered edge of the plate. As can be seen in Fig. 8 sensor signal sensed by a piezoelectric sensor is conditioned and thereafter acquired on to a PXI controller via a data acquisition card. Based on sensor signals and control law, control signals are calculated in real time by the PXI controller. Data acquisition is done using DAQ 6361e card from NI and PXI based quad core controller 8840 is used with a 68 pin terminal block TB 2706 for control. The Kalman filter and control law are coded in Labview software. Two piezoelectric PZT SP-5H patches are bonded at element numbers 11 and 14 to act as actuator and sensor respectively. Figure 9 shows the actual set-up used to actively control the first modal displacement of the plate.
Investigate the full characteristic of a centrifugal pump-as-turbine (PAT) in turbine and reverse pump modes
Published in Engineering Applications of Computational Fluid Mechanics, 2023
Shijie Yang, Puxi Li, Ran Tao, Fangfang Zhang, Ruofu Xiao, Weichao Liu, Fujun Wang
The schematic of the model test rig is shown in Figure 3. Table 2 shows the main parameters of the test rig. Experimental measurements were carried out using the closed loop water circuit to get realistic conditions. Water from the cavitation tank is pumped to the reservation tank and sequentially flow down to the flow stabilisation tanks. The test bench site is shown in Figure 4, and test instrument parameters are listed in Table 3. Before the experiment, we calibrated various parameter sensors to ensure the accuracy of the experimental measurement. All instruments and metres were calibrated using standard gauges with valid qualification certificates, or directly sent to the national metrology department for regular verification. In the actual experimental process, we take the average of multiple measurements to minimise random errors. The experimental PXI system is used for data acquisition and testing, it can provide high-performance modular instrumentation and a rich set of I/Os with dedicated synchronisation and major software functions for fluid machinery measurement applications. The PXI system acquires measurement data from various sensors and then transmits it to the computer for processing. The flow of the inlet and outlet is divided by the section area to obtain the average flow velocity thus the dynamic pressure head. The flow measurement uses an inner diameter of 300 mm electromagnetic flowmeter. The electromagnetic flowmeter uses standard metre method for on line calibration. The speed is measured by an encoder connected to the generator shaft, which is installed directly on the shaft end of the dynamometer motor. When the unit rotational speed is in to steady state, the measured rotational speed frequency is calibrated with a calibrated high precision frequency metre, or the speed is verified with a stroboscope. Energy test is conducted to determine the relationship between head H (m), unit speed n11, unit flow rate Q11 and unit torque M11 under various operating conditions. Several operating conditions located in the S zone are selected to test on the model machine. During the test, the fluctuation value of the rotational speed is Δn≤±0.2%. Each parameter is calculated according to the following formula, the meanings of each symbol in the formula are shown in the Table 4: (1) Head H (m) The reverse pump mode can be replaced by the inlet and outlet in the formula (2) Unit speed n11 (r/min) (3) Unit flow Q11 (m3/s) (4) Unit torque M11 (N·m)