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A tension, depth and speed measurement system based on DSP

Abstract: this system is used to measure parameters such as the tension of the cable, the depth of the oil well and the speed of the cable in the well logging process of the oil field. The system structure and working principle are emphasized. At the same time, the force sensor, depth encoder, system hardware circuit design and software flow are also introduced. The system has high precision, small volume and stable operation. It can not only measure the measured parameters in real time, but also have the function of "black box". It can record the data within 24 hours, provide a reliable basis for accident analysis, and has high engineering application value. It can be used for all occasions of measuring load, length and speed

key words: strain sensor, photoelectric encoder, DSP, CPLD, I2C bus

1 introduction

in the process of oil field logging, ground operators need to know the depth of the oil well, the downhole speed of the cable and the load carried by the cable. Only by mastering these data timely and accurately, can the logging work be carried out smoothly, so as to ensure the safety and reliability of the logging process. Therefore, after any two affirmations, we developed a tension, depth and speed measurement system based on DSP. The system has high accuracy, strong reliability and fast processing speed. It is an ideal monitoring tool for ground operators

2 strain sensor and photoelectric encoder

2.1 strain sensor

the tension on the cable makes the strain sensor. The impact toughness experiment often used in China is to use a u-notch square test bar, place it on the support, and then drop it with a pendulum to produce mechanical deformation of its primary punch. The sensor converts the mechanical deformation into electrical signal output, so as to measure the tension

. Working voltage: DC 12V

Output range: 0 ~ 12mv

Output sensitivity: 1mV/V

2.2 photoelectric encoder

the rotating shaft of the photoelectric encoder is coaxially fixed on the center of the measuring wheel with known circumference. When the equivalent wheel rotates, the encoder rotates synchronously and outputs pulse signals. In this way, a certain length corresponds to a certain number of pulse signals, and the depth value can be converted by calculating the pulse signal. The velocity value is obtained by sampling the depth value per unit time

. Working voltage: from January to October this year, Thailand imported 413 extruders from China, DC 5V

Working current: 40ma

Pulse type: two orthogonal pulse signals, which can identify the rotation direction of the photoelectric encoder and output the depth pulse through the logic circuit

3 system (3) fully automatic fixture: from sample size measurement to clamping structure and working principle

input the millivolt signal generated by the strain sensor to the amplifier for amplification, and then send it to the a/d converter for analog-to-digital conversion, convert it into a binary sequence and send it to DSP for processing. In order to ensure the reliability of a/d conversion, v/f device LM331 is used to realize analog-to-digital conversion and convert voltage signals into frequency signals. This device has high reliability and takes up less resources

two orthogonal signals generated by the photoelectric encoder are input to CPLD and processed to generate two signals. One is direction discrimination pulse, which is used to identify the rotation direction of photoelectric encoder. The other is counting pulse, which is used to complete the conversion of depth parameters. Both pulses are input to DSP. See Figure 1

Figure 1 system hardware implementation block diagram

4 core hardware circuit design

4.1 TMS320VC33 processor

this chip is a 32-bit floating-point high-performance digital signal processor launched by TI company. The instruction cycle is divided into 13ns and 17ns. A single cycle completes 32-bit integer and 40 bit floating-point multiplication. The on-chip 34k 32bitsram is divided into two 16K and two 2K blocks, on which a DMA channel, a synchronous serial port and two 32bit timers are integrated; The total storage space is 16m 32bits, including program, data and i/o space. The address space can be divided according to different requirements; It has the function of program boot. After the system is reset, the program can be loaded from the slow external memory to the fast on-chip RAM for operation; Support IEEE Std 1149.1 (JTAG) standard; 0.18-m process, 1.8V core voltage, 3.2vi/o voltage; Low power consumption(

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