FI114040B - Load measuring system for ship hull, converts structural deformation into electric signal, which is converted into digital signal and processed and processed result is transmitted to central processing unit by bus - Google Patents

Abstract

The system includes a measuring unit (30) removably attached to measurement structure. The measuring unit comprises measuring sensors (302,50) that converts structural deformation into electric signal. The signal is converted to digital signal and processed. The processed result is transmitted to central processing unit (20) over a bus (21). An independent claim is also included for measurement sensor.

Description

114040 System for Measuring Structural Actions and Unit of Measurement - This application is subdivided from application FI-991270.

The present invention relates to a system for measuring loads, stresses and / or material fatigue on a structure. The invention also relates to a measuring unit and a measuring sensor suitable for use with said system. The invention is particularly applicable to the measurement of stresses and stresses on a ship's hull.

The loads on the ship's hull shall be continuously measured to detect any changes in the structures, such as fatigue, before the structures are broken. Similar measurements are also made on other structures, such as other vehicles, bridges and buildings.

Methods of attaching measuring probes to the hull of a ship to measure local deformations of the structure are known in the art. Figure 1 shows a top view of a ship hull main cover 10 and a typical arrangement of gauges 11, 12, 13 and 14 on the ship hull main deck. Measuring transducers typically use steel bars of about 1-2 meters in length, which are permanently secured, for example, by welding the ship's * * * 20 hull main cover so that one end of the bar is fixed and the other can move axially. For example, a motion sensor is located at the junction, which measures the mutual motion. Measuring probe rods must be at least the length mentioned above to allow tan-. · * The relative movement of the sizes would be large enough (typically max. +/- 5 mm) and the deformation measurement would be accurate enough.

* · 25 In prior art methods, a weak signal from the measuring sensors is applied to a central unit of the measuring system, where the signals from the sensors are amplified, digitized and mathematical signal processing is carried out. The standards define various models for processing signals so that critical deformations can be detected from measurement results as reliably as possible. Such models include e.g. frequency domain analysis and so called. Rainflow classification. The Rainflow rating is defined eg. in ASTM E1049-85 (Reapproved 1990).

• · · • · ·

The above-mentioned prior art systems have certain drawbacks. First of all, the systems are designed for a certain number of standard measuring sensors 2 114040, so that the addition of measuring sensors is not possible when the need arises. This is because the computing capacity and interfaces of the system central unit are dimensioned for a predetermined number of measuring sensors. There are situations where the usual number of gauge sensors is insufficient, such as the catamaran 5, for example, the need for gauge sensors may be considerably larger, e.g. in a conventional ship hull, which usually has e.g. 4 gauge sensors.

Second, prior art arrangements have the problem of coupling interference to long measuring lines between the measuring sensors and the central processing unit. This is difficult to avoid by measuring cable shielding because the signals transmitted from the measuring sensors are low-level analog signals.

A further problem with prior art measuring sensors is that they are difficult to calibrate. Namely, removing the large gauge from the hull of the ship is very laborious and, secondly, the behavior of the large gauge when attached to the ship-15 stand may be different than under calibration conditions. Therefore, accurate and reliable calibration is difficult. Similarly, the replacement of a defective measuring transducer is difficult.

It is an object of the present invention to avoid the above-mentioned problems associated with the prior art by means of a novel measurement solution.

It is an idea of the invention that the measuring sensor unit, or * measuring unit, of a measuring system comprises means for processing a signal from the sensor so that the mathematical measurement results can be transmitted from the measuring unit to the central unit. Thus, the central unit does not require a large amount of computing capacity, nor does the central:: unit capacity depend essentially on the number of measuring sensors used.

25 Thus, measuring sensors can be easily added if necessary. In addition, the interference to the cable between the metering unit and the central processing unit is negligible. · · ·. because the transmitted signals are digital and the transmission can be repeated if necessary.

Another idea of the invention is that the measuring sensor is mechanically * * * easy to attach and detach from the structure to be measured.

. · · ·. In this case, the structure to be measured preferably includes a base for mounting the measuring transducer. In this case, the measuring sensor can be calibrated separately from the structure to be measured and: ··: the behavior of the measuring sensor in the structure to be riveted and under calibration conditions *: is exactly the same.

3, 114040

Furthermore, it is an idea of the invention to provide a measuring transducer from the transducer and the strain gauge so that the deformation is transmitted to the strain gauge strip attached to the flexible region in the transducer. The elastic region is preferably formed by a double H-opening in the sensor connection. Further, the transducer preferably comprises a second stretch tab for temperature calibration, which is attached to a non-deformable portion of the transducer. In this case, the measuring sensor is made small in size but still accurate, and can be easily handled, for example, during calibration.

A system for measuring structural loads according to the invention comprising a central unit, at least one measuring unit and a measuring sensor for converting deformations of ship structures into an electrical signal, characterized in that the system further comprises a self-configurable data network, means for converting said signal to a digital form, means for mathematically processing the digital signal, means for transmitting the processing results to the central processing unit, means for connecting the measuring unit to said self-configurable data network, and said central processing unit comprising means for receiving processing data transmitted from at least one measuring unit.

The measuring unit according to the invention for measuring loads on ship structures 25 is characterized in that the measuring transducer for converting deformations of the structure into an electrical signal is encapsulated with signal processing electronics in said measuring unit, and the measuring unit comprises: means for converting means for attaching a measuring unit to a self-configurable computer network;

t t I * '. Preferred embodiments of the invention are disclosed in the dependent claims 35.

i · »· f» t> »» I · 4 114040

The invention will now be described in more detail with reference to the accompanying drawings, in which: Figure 1 is a block diagram of a measuring system according to the invention, Figure 2 is a block diagram of a measurement unit of the invention, Figure 5a shows a top view of a measuring sensor according to the invention and Figure 5b shows a side view of a measuring sensor according to the invention.

Figure 1 was already described above in connection with the prior art description.

Figure 2 is a block diagram of a measuring system according to the invention. It comprises a central unit 20 connected to a digital communication bus 21. A plurality of measurement units 30, 32 and 34 are further connected to the communication bus 21, which are located at suitable measuring points of the structure to be measured.

The central processing unit may comprise, for example, a PC-based computer having, for example, an NT-15 operating system. In this case, the shared memory in Windows NT users may work. mia as an open user interface through which the measurement results are available to the user. ·: ·. and allows the user to control the system. The communication path may advantageously have an Attached Resource Computer NETwork (ARCNET) data network. A feature of the ARCNET data network is that it itself is reconfigurable. This is advantageously utilized in such a way that the addition and ··· * removal of the measuring sensor / unit can be done without any software or other modifications to the system. Each ... * measuring sensor / unit is identified in the system by its unique identifier (e.g., serial number), whereby the data is organized into a user interface (data structure) in the shared NT: memory of Windows NT on the basis of a unique identifier. The ARCNET data network automatically takes care of the communication node IDs every time it is configured at startup. In this case, the crossover as part of the message translation of the central unit may be organized automatically and associate the communication node ID with the unique identifier of the unit. Configuration is thus not required as a user operation.

Figure 3 shows a measuring unit 30 according to the invention. It comprises a Wheatsto-ne bridge 302 in which the first strain gauge and the second strain gauge for temperature compensation are connected in series. The second part of the bridge is formed by fixed resistors.

The measurement signal from the Wheatstone bridge is amplified by an instrumentation amplifier 304, the output signal of which is further filtered by a low-pass filter 306. The measurement frequency band 5 is e.g. 0-150 Hz, and the frequency band is most preferably programmatically selectable. The amplified and filtered analog signal is converted to digital by an analog-to-digital (A / D) converter 308, from which digital samples are directed to microprocessor 310. The A / D converter 308 may also be included in processor 310. Processor 310 stores measurement results in memory 314 . This re-programmable memory 314 has a capacity e.g.

4kB + 32kB. For example, a real-time measurement signal from the last 10 s can be stored in the memory. In addition, calculation parameters can be stored in the memory. Communication interface 316 associated with bus 312 is further connected to system bus 21 which transmits information between the central unit and the measurement units. The transfer of the measurement data from the memory of the 15 measurement units to the central processing unit 314 takes place on the basis of the instructions received from the central unit and the program stored in the measurement unit. At the request of the central unit, the measuring unit may, for example, transfer 10 h of sample history to the central unit.

The measurement unit transmits to the control unit a measurement sample signal at a sample rate 20 which is preferably lower than the sampling rate of the D / A converter. The unit of measurement can also be configured via a communication bus. Thus, it is possible, for example, to select which analysis methods programmed in the measuring unit are performed. Unit: can also send its configuration settings to the central unit at specified intervals. for review. Similarly, the measurement offset can be calibrated and the data sample, ···. The input frequency can be set under the control of the central unit. The unit of measurement also preferably monitors its own operations. For example, the rotation of signal analysis programs can be monitored to prevent overloading the computing capacity of the processor.

The processor 310 preferably comprises an internal, persistent program memory, which may have a capacity of e.g. 128 kB. This program memory stores programs related to the »· · 30 functions of the measuring unit and the data transmission between the central unit and the measuring unit. The necessary signal analyzing algorithm is also stored in program memory; · 'Rhythms, such as:. : ': - Calculation of signal mean,: · · · - Calculation of signal effective value, 35 - Peak expressions: Positive peak, Negative peak and peak to peak value, 6 114040 - Calculation of zero crossings and average frequency of zero crossings, classification and - Calculation of the frequency domain spectrum of the signal by the Fast Fourier Transform (FFT) method.

Preferably, these methods of analysis programmed into the processor of the measuring unit are performed by the measuring unit in real time.

In addition to the aforementioned blocks, the measurement unit may comprise circuits for generating operating voltages from the bus supply voltage (not shown in Figure 3).

Fig. 4 is a flow chart of one method 400 for transmitting data 10 between a measuring unit and a central processing unit according to the invention. First, the measurement unit checks if the message received from the central unit, step 402. If the message has been received, it interprets, 404. Then, the measurement unit receives the new configuration information, step 406. If the new configuration information is received, the measurement unit configuration is set to the new information. Next, it is checked whether the measurement unit has received an instruction to send valid configuration information to the central unit, 410. The instruction may be, for example, a bit / bit string for this purpose in a message addressed to the central processing unit. The command may also come from the sensor timer. If. an instruction is received, configuration information is sent to the central processing unit, 412.

tt: t "20 Next, it is checked whether the instruction received by the measuring unit sends * * · · * 'the mathematically calculated measurement data to the central processing unit, step 414. If said instruction is!!: received, the measuring data is transmitted to the central processing unit, 416. ... 'whether the instruction received by the measuring unit sends a signal history to the central processing unit,]: 418. If the said instruction is received, the signal history is transmitted to the central processing unit, 420.

25 Next, it is checked whether the command received by the measuring unit transmits

• t I

Rainflow Rating for Central Unit, 422. If command received, Rainflow, * · ·. the classification is sent to the central processing unit, 424. Next, it is checked whether the instruction received at the measuring unit transmits the FFT results to the central processing unit, 426. If so, the command sent to the central processing unit, The T command is received, the FFT results are sent to the CPU, 428. Finally, the * 30 is dipped to see if there is data in the signal sample buffer of the measurement unit, step 430. If there is data in the BUF, After these steps, '' '_ returns to step 402, and the above steps are repeated, whereupon the measurement data required by the central unit are transmitted to the central unit in accordance with the instructions of the central unit 7114040. It is to be noted that come not only from the central unit, but also from the timer of the measuring unit.

Figures 5a and 5b show a measuring sensor 50 according to the invention which is suitable for use e.g. in a measuring unit according to the invention. Figure 5a is a top view of a measuring 5 sensor and Figure 5b is a side view of a measuring sensor. The measuring transducer comprises a sensor assembly 502 having rigid portions 504 and 508 at its ends and a resilient portion 506 in the center. The rigid and resilient portion is separated by a dotted line in the figure. The rigid portion of the sensor connector has holes 520 and 522 for attaching the sensor to the structural material to be measured or to the mounting parts in the structural material.

The flexible portion 506 of the sensor assembly has two openings 510 and 512 which are H-shaped, i.e., so-called. double-H opening. The opening makes the flexible part more flexible than the rigid part. Between the two H-shaped openings is attached a first strain gauge sensor 530, which, for example, when coupled to a Wheatstone bridge, produces a signal equal to 15 deformation of the elastic member. In addition, a second strain gauge sensor is attached to the second H-aperture without deformation in the mounting base. The purpose of this second strain gauge sensor is to act as a reference resistor for the Wheatstone bridge and to compensate for changes in resistance due to temperature changes in the first strain gauge sensor.

Preferably, the elastic region (i.e., the elastic limit σΕ) of the material of the sensor joint is selected larger than that of the structural material so that measurable deformations of the structural material do not cause permanent changes in the flexible region of the sensor joint. In addition, : The material of the sensor joint is chosen so that it withstands the load of replacement, like structural material. The twin H-shaped probes on the sensor assembly are rectangular '25 cross-sections whose length does not exceed the buckling length under compressive load. stress load corresponding to the deformation of the structural material over its entire elastic region (σΕ).

:: The bolt mounting of the sensor is advantageously carried out on mounting pieces welded to the construction material, whereby the measuring sensor can be replaced and calibrated. The gauge sensor can also be installed as a standard precision installation job. The transmission from the structural material is made by a frictional joint in which the attachment surfaces of the sensor joint are roughened * · by the cobalt-carbide coating 544 and 548. The carbide crystals of the coating penetrate into the mating surfaces of the fastening elements welded to the structural material.

8 114040

When the measuring unit comprises a sensor according to the invention and the signal processing electronics according to the invention, the unit can be preferably encapsulated so that the bottom part of the housing comprises a measuring sensor and the cover part of the housing comprises signal processing electronics. Further, it is advantageous to use such a joint-5 of the base part and the cover part that the unit is made waterproof. Preferably, the measuring unit uses a solid cable that can be extended in a suitable junction box.

Another possibility is to encase the measurement sensor and signal processing electronics into separate enclosures. Such a solution may be advantageous when the sensor part has to be located in a place with an explosive installation condition. Such locations include, for example, the inside surfaces of various containers. In this case, it is advantageous to place the measuring electronics outside the container, for example.

Some embodiments of the solution according to the invention have been described above. Naturally, the principle of the invention can be modified within the scope of the claims, e.g.

In particular, it should be noted that the invention can be applied to a wide variety of structures in addition to measuring the hull load. It should also be noted that the measuring sensor, measuring unit and measuring method / system according to the invention can also be applied independently of one another.

• «• · t I · • I · • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

Claims (6)

A system for measuring shipbuilding loads, comprising a central unit (20), at least one measuring unit (30, 32, 34) and a measuring transducer for converting the ship's shape changes into an electronic signal, characterized in that the system additionally comprises a self-configuring data network (21), said measuring sensor (302, 50) being encapsulated together with signal processing electronics in said measuring unit (30, 32, 34) and said measuring unit further comprising means (308) for converting said signal into digital form, means (310) for mathematically processing the digital signal, means (316, 21) for transmitting the processing results to the central unit, means for connecting the measuring unit to said self-configuring data network, and said central unit comprising means for receiving and collecting processing results sent from at least one unit of measurement. System according to claim 1, characterized in that the system comprises means for controlling the functions of at least one unit of measurement from the central unit. System according to claim 1 or 2, characterized in that the data transmission between the central unit (20) and the measuring units (30, 32, 34) takes place by means of said self-configuring data network (21), to which has been connected at least two measuring units 30 and to the measurement units logically connect a code specifying the measurement unit, which code is transmitted between the measurement unit and the central unit to identify data transmitted to a specific measurement unit and data transmitted from a specific measuring unit. ». System according to any one of claims 1-3, characterized in that said eating unit has one measuring unit which is removably attached to the structural material to be measured. : 5. Measurement unit (30) for measuring loadings of vessel structures, characteristics •. The sensor (302, 50) for converting the structural shape changes 114040 to an electronic signal is encapsulated together with signal processing electronics in said measuring unit and said measuring unit comprises means (308) for converting said signal into digital form, means (310) for mathematically processing a digital signal, means (316) for transmitting the processing results to the central unit, and means for attaching the measuring unit to the self-configuring data network. Measurement unit according to claim 5, characterized in that it comprises means (520, 522) for being removably attached to the material structure to be measured. »». . · I * k ·