120results about How to "Reduced measurement workload" patented technology

The invention discloses an aviation engine blade profile three-coordinate measuring method which is used for solving the technical problem that an existing blade profile three-coordinate measuring method is low in accuracy. According to the technical scheme, the aviation engine blade profile three-coordinate measuring method comprises the steps of based on extraction of a plurality of curves which can represent the blade profile main-axis direction curvature distribution characteristics, calculating curve control point sets to determine the blade measurement cross sections, based on curvature distribution and tolerance control, planning the minimum control point set of each measurement cross section, and achieving the three-coordinate measurement path planning of the blade profile. According to the aviation engine blade profile three-coordinate measuring method, the blade measurement cross sections are planned according to the blade profile curvature distribution characteristics, the measurement point set of each measurement cross section is planned based on the curvature and the tolerance control, the measurement workloads are reduced, and the measurement accuracy is ensured. The problem that the workloads are greatly increased due to the facts that in the traditional measurement work, the measurement cross sections are planned according to experience and the measurement accuracy is ensured by encrypting the measurement cross sections and the measurement points is solved.

The invention relates to a high-precision cable tension force test method based on model analysis, which comprises the following steps: fixing two or more acceleration sensors on a cable along the cable surface to measure and obtain cable model information; judging the cable model preliminarily, refining the test point arrangement according to a modal identification result, continuously measuring and improving the cable vibration shape, and judging whether a cable modal vibration shape test result forms a complete vibration shape model or not; correcting the sensitivity of the test result of the formed complete vibration shape model, multiplying an identification result by a sensitivity correction coefficient according to the difference of acceleration sensitivities when correcting the sensitivity, obtaining corresponding modal circular frequency omega, and fitting a finally obtained vibration shape curve and obtaining a corresponding vibration shape function, and calculating the actual cable tension force according to the function. Influencing factors controlling the calculation are all obtained by actual measurement, the test error is limited within a certain range, and the calculation result is sure to have extra high reliability.

The invention relates to a method for performing seismograph control and data transmission by using a short message and a short message control and transmission type cableless seismograph. Aiming at solving the problem of no real-time quality control to the prior cableless seismograph, the method for seismograph control and data transmission introduces a mobile phone unit into an acquisition station for the prior cableless seismograph, and utilizes the short message to conduct state control and data transmission to the acquisition station for the cable-less seismograph. The acquisition stationfor the cableless seismograph comprises a main control unit, an acquisition unit, a storage unit, a GPS unit, a power management control unit and a mobile phone unit. The invention has the advantagesthat the work load of measurement can be reduced, the laying of the acquisition equipment is more flexible, simpler and more convenient, the synchronous collection mode for blasting at the fixed timeis convenient, the construction efficiency is favorable for improving, the data recovery is flexible, an SPS file can be automatically generated, the coordinate with cm-level accuracy can be automatically calculated, the difficult problem of no real-time quality control to the cableless seismograph is solved in a simple and inexpensive way, and the application range and the construction efficiency of the cableless seismograph are greatly improved.

The invention relates to a network on-line live line measurement method for the line parameter of a power system. A measuring center performs network on-line live line real-time measurement according to sets of computer networked data and networked instructions organized by a line parameter measuring system on the basis of a specific sequence. The method sequentially comprises the following stepsof: 1) accessing a global positioning system (GPS) signal to a data acquisition device in each transformer substation and correctly running; 2) requesting to establish transmission control protocol (TCP) connection, sending a device configuration information reading command and a real-time data command to the data acquisition device, receiving real-time data and establishing a real-time running chart; 3) actively retrieving the data acquisition device in each transformer station, monitoring the running condition of each line in real time and automatically measuring the line parameter; and 4) storing a line parameter measured value in a database. The data acquisition device which is put into operation and networked on site is utilized, and a new device is not required to be arranged, so that measurement workload can be obviously reduced, measurement cost is saved, power failure frequency is low, and power failure time is short; and the method is easy to operate, and safe and reliable.

The invention discloses a substation type precision compensation for a robot system with an additional external shaft, belongs to the technical field of industrial robot reverse calibration, and aims to solve the difficulty in compensating the error of the external shaft (guide rail) of the industrial robot. According to the method, based on a robot envelope line, the guide rail is divided into a plurality of substations and substation type compensation is performed. The method comprises the steps: a laser tracker is adopted to measure and recognize the error of the external shaft (guide rail) and the robot, and the compensation for the tail end error of the robot is completed through inputting corrected control commands into the robot. During measurement and recognition of the error of the external shaft, an auxiliary coordinate system is introduced so as to allow the measuring process to be simple and quick, and meanwhile to ensure the precision. Through test verification, the method can greatly improve the absolute positioning precision of the robot with the additional external shaft, so as to allow the robot to be suitable for wider applications.

The invention discloses a method for online identification of parameters of a reactive compensation capacitor bank and belongs to the technical field of electric element online monitoring. The method comprises the steps that three-phase voltages and three-phase currents of the reactive compensation capacitor bank at different moments are measured; data are processed, so that sequence components of three-phase voltage fundamental wave phasors and sequence components of three-phase current fundamental wave phasors of the reactive compensation capacitor bank at each moment are obtained and sequence components of three-phase voltage each-time harmonic wave phasors and sequence components of three-phase current each-time harmonic wave phasors are obtained; a positive-sequence component of the voltage fundamental wave phasor of any phase and a positive-sequence component of the current fundamental wave phasor of the same phase at each moment are selected, and the sequence component with the larger content of the voltage each-time harmonic wave phasor of any phase and the sequence component with the larger content of the current each-time harmonic wave phasor of the same phase at each moment are selected; the equivalent resistance value, the capacitance value and the inductance value of an electric reactor of the reactive compensation capacitor bank are calculated through the selected data. According to the method, under the circumstances that a capacitor is not stopped and a connection wire of the capacitor is not detached, online identification of the parameters of the capacitor bank is achieved, and the measurement workload is relieved.

The invention relates to an array type inferior insulator local electric field detector and an inverse diagnosis method of inferior insulators, which comprises the steps of: implementing non-contact type online quantitative monitoring on a circuit insulator, diagnosing the existence of the inferior insulator through the reverse diagnosis method, really reflecting the insulation safety situation of the circuit insulator, building an insulation safety prewarning information system and implementing effective pre-control management on high-tension transmission lines. The array type inferior insulator local electric field detector consists of a field detector and a data processing center; the method is based on 'electric field method' measuring, which applies the basic principle of the charge simulation method to build a corresponding geometric and mathematical equivalent model. The method obtains the actual voltage distribution of an insulator string by working out the solution of an insulator electric field inverse problem, and compares the actual voltage distribution of the insulator string with the international given voltage distribution to judge the existence and position of the interior insulator in the insulator string.

The invention provides a distribution network equipment health degree dynamic diagnosis method involving credibility evaluation. The method comprises the following steps: step (1), obtaining an original feature set of power distribution monitoring quantity; step (2), determining an important status variable through correlation analysis for information of failure equipment and non-failure equipment; step (3), carrying out data quality pretreatment on data of the important status variable determined in the step (2); step (4), marking the important status variable after treated in the step (3); and step (5), inputting a marking result of the important status variable into an evaluation model, and obtaining an evaluation result. The phenomena of data collision and data redundancy appearing in the process of collecting equipment status variables are solved through data credibility evaluation and fusion of different criterial evaluation results, and meanwhile self-updating of the evaluation model is realized through dynamic regulation, so that the method is applicable to power distribution networks with constant development and change.

The invention discloses an automobile noise source acoustic imaging method based on array element random uniform distribution spherical array deconvolution beam forming. The method comprises the stepsof 1, generating a complex sound pressure data matrix p by utilizing sound signals; 2, calculating a cross-spectrum matrix C of the spherical array; 3, dividing a sound source into S observation gridpoints; 4, obtaining a spatial spectrum b; 5, generating a transfer matrix G from S observation grid points to the spherical array; 6, generating a central point propagation function vector psfcentre; 7, generating a Gaussian regularization filtering function vector psi; 8, obtaining an optimal solution of the sound source distribution vector q; 9, solving sound source distribution qJ through iteration; and 10, obtaining a sound source distribution image. According to the invention, high-resolution visual imaging is carried out on spatial distribution of main noise sources of an automobile, and positioning information and relative intensity of the main noise source and the secondary noise source can be accurately obtained from an image.

The invention discloses a device for measuring impedance of a loudspeaker. The device comprises a detector, wherein one end of an output point of the detector is electrically connected with an anode of the loudspeaker to be measured after passing through a power amplifier; the other end of the output point of the detector is serially connected with a sampling resistor and electrically connected with a cathode of the loudspeaker to be measured; the two ends of an input point of the detector are electrically connected with the anode and the cathode of the loudspeaker to be measured respectively; and the two ends of the other input point of the detector are electrically connected with those of the sampling resistor respectively. The invention further discloses a method for measuring the impedance of the loudspeaker. The device and the method are convenient to operate and accurate in measurement results.

The purpose of this invention is to provide a kind of device that can measure the thickness of snow cover and record the geographic location of the measuring point automatically at the same time. A sharp cone is installed at the bottom of the probe rod, a distance detection unit is installed at the top of the probe rod, and a global positioning receiver, microprocessor, power supply, memory module, tilt sensing module and man-machine interface are installed; the measurement process can be operated with one hand and one button; The memory interface saves the measurement data to a USB flash drive, which is convenient for saving in other media. The snow thickness measurement recorder constructed by the present invention has been successfully applied to the Arctic and Antarctic polar scientific surveys. Its ergonomic design can be operated by one person and one hand, reducing the number of personnel for each measurement from 2 to 4 to 1 to 2 people, the measurement workload is greatly reduced, and human error is reduced. Therefore, the snow cover thickness measuring recorder constructed by the present invention has broad promotion prospect.

The invention relates to the field of building of nuclear power stations, and provides an installation method of lower reactor internals in an AP1000 nuclear power station, which aims at decreasing difficulty, shortening time and reducing risk. The installation method comprises the following steps of arranging RV measuring control points and RV measuring points; arranging reactor internal control points and reactor internal measuring points; using a laser tracking instrument to measure the measuring points, establishing a cylinder reference simulation coordination system and a basic model of a pressure container in three-dimensional modeling software according to the measuring data, and establishing an installation model of the lower reactor internals; importing the installation model of the lower reactor internals into the basic model of the pressure container, and performing centering and pipe nozzle pairing; analyzing and calculating to obtain processing data of a positioning embedding block and an energy absorber support column, and processing the positioning embedding block and the energy absorber support column; for the lower reactor internals, lifting in for three times, and lifting out for two times, so as to complete the installation of the lower reactor internals. The installation method of the lower reactor internals in the AP1000 nuclear station has the advantages that the accuracy is high, the difficulty is low, the time is short, and the risk is low.

The invention provides a method for measuring subdistrict beaconing channel wireless quality. In the method, a terminal compares the relation between the variation range and the threshold value of the service subdistrict beaconing channel wireless quality and sets a corresponding timer, and whether the neighboring subdistrict beaconing channel wireless quality is measured is decided. The method for measuring the subdistrict beaconing channel wireless quality can shorten the time of the terminal to measure the neighboring subdistrict beaconing channel wireless quality, reduce the measuring workload of the terminal and save the terminal electric quantity.

The invention discloses a grain quality index prediction method based on an SVM (Support Vector Machine) model. The method comprises the following steps: selecting a part of tth-stage grains as samplegrains; measuring quality index data of the sample grains and taking the quality index data as sample data; constructing an SVM support vector machine model according to the sample data; and measuring the quality index data of the t-th period of grain, and predicting the quality index of the t-th period of grain according to the constructed SVM support vector machine model. The corresponding quality index data of the grains in the same period can be predicted according to the SVM support vector machine model, the measurement workload can be reduced in the whole process, the efficiency is high, and manpower and material resources are saved.

The invention relates to a transformer station grounding network corrosion detecting system based on an earth surface potential, and a method thereof. The transformer station grounding network corrosion detecting system comprises the components of a current injection device which is connected with a random reachable node of the grounding network and injects a sinusoidal AC current that is different from an industrial frequency current, wherein the AC current is injected through the random reachable node of the grounding network; a potential probe which is arranged right above the earth surface of a grounding network conductor and is used for measuring potential distribution on the earth surface right above the earth surface of the conductor, detecting the potential signal of the earth surface and filtering an industrial frequency interference; a signal testing module which is connected with the potential probe and is used for receiving the potential signal that is transmitted by the potential probe, performing filtering and amplification on the potential signal, and calculating and storing a potential component that corresponds with the frequency of the injected current; and an analyzing and displaying terminal which is connected with the signal testing module and is used for receiving potential data that are transmitted by the signal testing module. Compared with the prior art, the transformer station grounding network corrosion detecting system has advantages such as ensuring high safety and stable operation of a transformer station.

The invention relates to an optimize system and a method of hydropower station water turbine design. The optimize method comprises that a parameter database and a model database are called according to characteristic parameters given by a hydropower station, and initialization results of each part of a flow passage of a water turbine are obtained; stability performance simulation is conducted to the whole flow passage, weight of different stability influence factors of each part is calculated, optimize modification opinions and measures of each part of the flow passage are obtained, and optimize design results are sent and saved. The optimize system for achieving the method comprises an overall processing module, a numerical calculation module, a weight analysis module, a data storage module, an influence factor indicator base and a method base. According to the optimize system and the method of the hydropower station water turbine design, comprehensive forecasting and assessment of different factors that influence stability of the water turbine are achieved, time in designing of the water turbine and optimize allocation combination of each part of the flow passage by designers is shortened, and therefore stability of a power station water turbine group and a workshop is improved.

The invention provides a fuel cell water content estimation method. The method comprises the following steps: constructing a cathode two-cavity model, and defining a state variable, an input and an output; constructing an unscented Kalman filter based on the cathode two-cavity model; according to the acquired average current density, average voltage, cathode air supply flow, cathode inlet and outlet voltage difference and cathode back pressure of the fuel cell, calculating an estimated value of a state variable of the cathode two-cavity model by using the unscented Kalman filter; and determining the water content of the fuel cell according to the estimated value of the state variable. In the embodiment of the invention, when the cathode two-cavity model is established, the difference between the gas concentration and the current density along the flow channel direction is considered, which is closer to the real working state, and the estimation precision is favorably improved. And themethod only needs to measure parameters such as voltage, cathode inlet and outlet voltage difference, average current density, cathode air supply flow, cathode back pressure and the like, so that themeasurement workload of the system is reduced.

The invention provides a method and apparatus for measuring configuration, an electronic device and a storage medium. The method comprises the following steps that: according to network performance information of UE to which a measurement content is going to be configured, the measurement content of the UE is determined or if a load of a base station connected to UE to which a measurement contentis going to be configured is determined to be higher than a preset third threshold, the measurement content of the UE is determined based on the load of the base station; and configuration informationincluding the measurement content is sent to the UE and thus the UE performs measurement corresponding to the measurement content, wherein the network performance information of UE includes at leastone of a type of a bearing established by the UE, a service type of an UE application, a data volume transmitted by the UE, inter-network movement information of the UE, a signal strength value of theUE, and frequency information of the UE. With the method provided by the invention, targeted UE indication for measurement is realized; resources needed by sending configuration information to the UEby the base station are saved; and the work load of the UE and the data volume of the measurement report are reduced.

The invention relates to a method and a system for measuring displacement through coordinate change between adjacent monitoring points. The method comprises the following steps: by the relative displacement variation between adjacent monitoring points, the absolute coordinates of all the monitoring points are obtained through coordinate system transformation according to the absolute coordinates of all the monitoring points, only the initial absolute coordinates of all the monitoring points need to be manually measured in the whole monitoring process, the absolute coordinates of all the monitoring points do not need to be measured many times along with the construction progress, and therefore the workload is reduced, and various error accumulation influences are reduced.

The invention discloses a method for testing a deicing effect of a rubber grain bituminous pavement. The dynamic function of a tire to an ice layer can be simulated well; a testing instrument is simple and convenient and low in cost; the time that a steel ball falls down repeatedly can be shortened; a maximum crack length is adopted as the key factor of evaluation indexes; and the measuring working amount is small. The method needs no assistance of an oil jacks or an electric system, and can be used for testing the deicing effect in indoor rubber grain pitch mixing material design.

The invention discloses a device and method for measuring the model flow-induced noise in a working section of a water tunnel, and belongs to the field of optical measurement. The device comprises a gravity-type low-noise water tunnel 1 and a measurement device. The device is characterized in that the gravity-type low-noise water tunnel 1 consists of an upper water tank 10, a straight vertical tube 11, a shrinkage section 12, a working section 13, a diffusion section 14, a water drain pipe 15, and a reverberation box 16; the bottom of the upper water tank 10 is connected with the straight vertical tube 11, and the tail end of the straight vertical tube 11 is sequentially connected with the shrinkage section 12, the working section 13, the diffusion section 14 and the water drain pipe 15; the reverberation box 16 is added to the working section 13; the measurement device comprises a support 2, a damping pad 3, a circular cake-shaped air bag 4, a pulsating pressure sensor 5, a hydrophone6, a signal source 7, a power amplifier 8 and a spherical sound source 9; the signal source 7 emits a single-frequency sine signal, and the single-frequency sine signal passes through the power amplifier 8 to reach the spherical sound source 9; the pulsating pressure sensor 5 and the hydrophone 6 receive the sound signals emitted by the spherical sound source 9.

Dynamic channel allocation (DCA) is adopted in the indention. When new call arrives to system, as long as there is a one vacant channel, mobile control center allocates the channel to the call. After the call is ended, the channel is returned back to central storage area. The invention solves technique issue for quick accessing channel and raises quality of service of mobile communication. Features are: avoiding interference, minimized distance of reusing channel, using wireless resources in high efficiency and increasing system capacity.

The invention discloses a large-scale grounding grid high-frequency characteristic test method using grounding grid current reflow. The method includes the following steps that: the position of a current injection point and a current reflow point are selected from a grounding grid, the current injection point is connected with the positive pole of a high-frequency power source, and the current reflow point is connected with the positive pole of the high-frequency power source; a voltage reference point is selected from a section between the current injection point and the current reflow point;a high-voltage probe is used to measure potential difference between the current injection point and the voltage reference point when high-frequency current is injected into the grounding grid, the effective value of the potential difference is read, namely, ground potential rise of the injection point can be obtained; a current probe is adopted to measure the effective value of the high-frequency current, phase difference between the current and the ground potential rise is obtained through comparison; the high-frequency grounding impedance of the grounding grid under a certain frequency iscalculated according to the ground potential rise, the current and the phase difference; and the frequency of the high-frequency power source is changed, the above steps are repeated, so that the frequency-impedance feature of the grounding grid can be obtained.

The invention discloses a measurement control method based on a distributed strategy for a Femto base station. The HNB periodically detects the state of its own cell and exchanges state information with the neighboring cell HNB, updates the neighboring cell information list in real time according to the state information of the neighboring cell, and sends it to the UE In the measurement object list of the HNB neighbor cell information list, only the cells with light load, little interference or no congestion are configured, and the cells with bad or poor information are not used as the measurement objects of the UE. In this way, cells with insufficient available resources, excessive interference, or congested cells are also avoided as measurement objects, which reduces the number of cells measured by the UE, reduces the measurement burden of the UE, and reduces the time overhead of the measurement process, thereby reducing the handover process. The number of attempts in the process reduces the handover delay and the call drop probability generated during the handover process, and improves the handover success rate.

The invention relates to a bolt test determination method for conditioning reheat cracking sensitive temperature of high-strength steel for a pressure container. The method comprises the following steps: firstly, cutting part of a steel plate to be tested to prepare a plurality of bolt samples and soleplates; then welding the bolt samples and the soleplates to acquire a plurality of groups of combined pieces, then mounting the welded combined pieces onto a high-temperature creep testing machine, carrying out loading test on the combined pieces under different test temperatures, and recording breakdown time, namely the time from when the combined pieces reach a preset load to when the combined pieces break down under the test temperatures, and acquiring the test temperature corresponding to the shortest breakdown time as the reheat cracking sensitive temperature of the steel plate after a lot of breakdown time is acquired. The method disclosed by the invention not only has the advantage that a Y-groove cracking test method can be compared to an actual structure, but also can acquire a relatively accurate test result; meanwhile, the method is small in measurement workload and high in measurement efficiency and is a simple and easy reheat cracking sensitive temperature determination method.

The invention relates to the field of construction of nuclear power stations. In order to reduce the workload, shorten the production time and improve the production precision, the invention provides a method for manufacturing a positioning insert for reactor internals in an AP1000 nuclear power station. The method comprises the following steps: arranging an RV control point and an RV measuring point; arranging a reactor internal control point and a reactor internal measuring point; measuring the measuring points by utilizing a laser tracker, establishing a cylinder reference simulation coordinate system and a base model of a pressure container in three-dimensional modeling software according to the measurement data, and establishing a mounting model of a lower internal; guiding the mounting model of the lower reactor internal into the base model of the pressure container, aligning, and pairing pipe nozzles; and analyzing and calculating processing data of a positioning insert, and processing the positioning insert according to the processing data. The method for manufacturing the positioning insert for the reactor internal in the AP1000 nuclear power station is high in manufacturing precision, small in workload and short in time consumption.

The invention discloses a ballast track laser intelligent track lifting and lining system. The ballast track laser intelligent track lifting and lining system comprises a track lifting and lining tamper (1) and is characterized by further comprising an integrated full-route measurement device, the full-route measurement device comprises a laser transmitting device (4) and an image receiving device (5), the image receiving device (5) is arranged on a front end image receiving trolley (7), and the laser transmitting device (4) is arranged on a laser transmitting movable trolley (2) in a distance. The image receiving device (5) is provided with a two-dimensional automatic tracking mechanism. A construction method includes the steps that route geometrical shape parameters are input, and track lifting and lining are conducted; each time the ballast track laser intelligent track lifting and lining system advances by a set distance, an electrical control system collects front end lifting and lining quantity data, a gva system outputs track lifting and lining quantity data control operation of an operation position, and the gva system feeds back track lifting and lining quantity data of an operation process. By means of the ballast track laser intelligent track lifting and lining system and the construction method, ballast track accurate track lifting and lining measurement workloads are greatly reduced, construction accuracy is improved, the advantages of the full-route measurement system and a large track maintenance machine are given into full play, and the problem of man-made errors occurring in the connection between the measurement procedure and the track lifting and lining construction procedure is thoroughly solved.

The invention relates to a millimeter wave radiator near-field radiation dose measurement method based on far-field plane scanning, which mainly solves the problems of low precision and low efficiencyof the existing millimeter wave radiator near-field radiation dose measurement. According to the invention, the method comprises the steps of measuring and calculating electric field complex amplitude distribution on a far-field scanning plane; converting the far-field electric field complex amplitude into a plane wave spectrum through inverse Fourier transform, decomposing the near-field dose space into near-field planes, converting the plane wave spectrum into the electric field complex amplitude and the magnetic field complex amplitude on each near-field plane through inverse Fourier transform, and calculating the power flow density. According to the method, the power is measured on the scanning plane located in the far field, the near-field radiation dose of the millimeter wave radiator is calculated according to the power, and compared with an existing direct measurement method, the measurement method provided by the invention has the advantages that the measurement precision andthe measurement efficiency are improved.

The invention relates to the technical field of measurement of target position data by applying electromagnetic wave reflection except radio waves, and discloses an underground cavern deformation monitoring method and system, and the method comprises the following measurement processes: selecting a to-be-measured point and a plurality of reference points with known positions in an underground cavern, measuring the distance between the to-be-measured point and each reference point through laser, calculating coordinates of the to-be-measured point according to the distance between the to-be-measured point and each reference point, and calculating deformation of the underground cavern according to coordinate changes of the to-be-measured point. According to the invention, the coordinates of the to-be-measured point are calculated according to the distance between the to-be-measured point and each reference point, and full-automatic operation can be carried out after the device is installed; the space position coordinates of the to-be-measured point are calculated by adopting a four-node three-dimensional space positioning method, only one group of real solutions are calculated each time, manual judgment is not needed, and the calculation process can be fully automatically carried out; and no rotating part is arranged, the problem that the rotating part is greatly influenced by vibration is solved, and the device can be used for occasions with obvious vibration.

The invention relates to a laser beam orientation measuring device and method, and relates to the field of laser beam orientation measuring. The device comprises a beam shrinking lens group M4, a first beam splitter M1, a second beam splitter M2, a backward reflecting mirror M3 and a camera system M5; the primary optical axis of the beam shrinking lens group, the center of the first beam splitterM1 and the center of the second beam splitter M2 are in a straight line; and light spots of incident laser are detected and displayed through the device, the beam orientation is calculated according to coordinate information of continuous light spots, and angle drifts and translation drifts can be calculated simultaneously. Meanwhile, a reflecting mirror is not used, so that errors brought by imprecise adjustment of the reflecting mirror are avoided; and a focusing lens is not used, so that errors brought by the facts that the optical axis is not aligned and a camera cannot be accurately placed at the focus are avoided.