“The design scheme of the underground sensor transmitting probe in the horizontal directional drilling tracking and guiding instrument based on the single chip MSP430F149 and the digital signal processor ADSP2189 is introduced, the hardware and software implementation of the system is given, and the software correction method for the installation error of the system is proposed.
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The design scheme of the underground sensor transmitting probe in the horizontal directional drilling tracking and guiding instrument based on the single chip MSP430F149 and the digital signal processor ADSP2189 is introduced, the hardware and software implementation of the system is given, and the software correction method for the installation error of the system is proposed.
Horizontal directional drilling technology is one of the dominant and fastest growing high-tech in the field of trenchless technology. A new construction method for laying underground pipelines by guiding the guide device to the design position. It is mainly used for laying, updating and repairing various underground pipelines, as well as for geological exploration and resource mining. Measurement while drilling means that the drilling rig continuously detects the information about the hole or the drill bit while drilling, which is realized by the tracking and guiding instrument. Therefore, the tracking and guiding instrument is the necessary measuring equipment for the construction of the horizontal directional drilling rig. A typical tracking and guiding instrument consists of three parts: underground sensor transmitting probe, ground handheld positioning tracker and remote monitoring equipment, and underground sensor transmitting probe is the key to the design of the whole guiding instrument. Aiming at the current situation that all domestic guide instruments rely on imports, the author researches and develops the guide system. This paper mainly introduces the design and implementation of the underground sensor transmitting probe based on the microcontroller MSP430F149 and the digital signal processor ADSP2189.
1 Structural design
The underground sensor emission probe is placed in the cavity of the drilling tool and is limited by the volume. In order to ensure the versatility, the size is φ32cm×380cm which is consistent with similar products in the world. The structure of the probe is shown in Figure 1. It is mainly divided into battery part (two No. 2 batteries), antenna part (coil with magnetic core), modulation and power amplifier part and sensor part.
2 Hardware Design
The underground sensor transmitter probe mainly completes the detection of parameters such as drill bit inclination, tool roll angle, temperature and battery power, as well as the transmission of very low frequency electromagnetic wave signals. Its hardware block diagram is shown in Figure 2. In order to adapt to the characteristics of long-term work in the field, the system hardware adopts a low-power design.
2.1 Selection of controller
MSP430F149 is a Flash-type ultra-low power consumption 16-bit microcontroller produced by TI. It has the characteristics of strong processing capability, fast running speed and high reliability. It can adapt to industrial operating environment, especially suitable for battery applications or handheld devices. This system chooses it as the main controller of the system.
At the same time, the system adopts the special digital signal processor ADSP2189 produced by AD Company. It has the characteristics of fast processing speed (single-cycle instruction execution time is 16ns), convenient interface, and abundant resources. In this system, it mainly realizes precise digital modulation, synchronization and related digital signal processing. In the sleep state, its power consumption is also low.
2.2 Sensor Design
Sensors are selected low-power products. The tilt sensor adopts a new type of MEMS micro-silicon single-axis accelerometer, which has high precision (0.1% ~ 1.0%), high resolution (2% og ~ 5% og), wide dynamic range, low offset and low sensitivity drift, low noise level, and low power consumption. The measurement of the inclination angle is completed by equipping the corresponding processing circuit. The roll angle sensor uses a dual-axis accelerometer, and the output loop converts the analog signal to a digital signal with a pulse width and duty cycle. These digital signals are connected directly to the MSP430F149 timer inputs.
The acquisition of relevant analog signal voltage is completed by MSP430F149. ADCl2 of MSP430F149 is a 12-bit precision A/D conversion module, which has the characteristics of high speed and general purpose. Its maximum sampling rate is 200kSPS, with built-in sampling/holding circuit, software, sampling timer or other on-chip timers can be selected to control the sampling period. The 8 configurable external signal sampling channels of ADCl2 have a variety of conversion modes such as single-channel single, single-channel repeat, and sequence channel single. In this system, sequential channel single conversion mode is used.
2.3 Interface design of MSP430F149 and ADSP2189
The boot, data input and output of ADSP2189 program are all controlled by MSP430F149. ADSP2189 is connected with MSP430F149 by IDMA, as shown in Figure 3. The IDMA interface is a parallel I/O interface with a 16-bit address/data bus. This bus supports access to 16-bit data memory and 24-bit program memory. The read/write access of the IDMA interface is completely asynchronous. When the ADSP2189 runs at full speed, the MSP430F149 can directly access the internal memory of the processor through the IDMA interface, and the hardware connection is simple.
2.4 Design of the source module
The underground sensor transmitter probe is small in size. From the structural design, the probe can only be powered by two AA batteries. In order to meet the needs of long-term work underground, the design of the probe power module is very important. This power supply module needs to provide +3.3V, +2V, ±5V and ±12V to the sensor part, microcontroller part and power amplifier part respectively, and +5V needs to provide 50mA output current, ±12V output current needs to be up to 80mA. Considering the issues of cost, efficiency, output ripple, noise and quiescent current, we finally chose several highly integrated and high conversion efficiency controllable DC-DC converters produced by MAXIM to convert the input of two lithium batteries into for the desired voltage value. When sensors, power amplifiers and other units are dormant, MSP430F149 can simultaneously turn off related power conversion modules to save power. The experimental test proves that the probe can work continuously for 12 hours, and the conversion efficiency of the power module is over 80%.
3 Software Design
In this system, MSP430F149 is used as the main controller to complete the collection of sensor output signals, the guidance of DSP, and the management of power supply modules. The overall software flow is shown in Figure 4. ADSP2189 mainly realizes precise digital modulation, synchronization and related digital signal processing.
3.1 Battery voltage detection
According to the characteristic curve of the battery, the battery voltage obtained by ADCl2 is divided into three grades: 3 (strong), 2 (medium), and 1 (weak). When the battery voltage drops to level 1, the MSP430F149 automatically turns off the power of other functional modules and enters the standby sleep state.
3.2 Communication between MSP430F149 and DSP
DSP guide: activate RESET, set MMAP=0 and BMODE=1 (select IDMA guide); cancel RESET, load ADSP2189 program through IDMA interface. Program execution is blocked until PM (0x0000) is written to address 0 of program memory. ADSP2189 responds to IDMA control signal and provides acknowledgement signal IACK. Write PM(0x0000) to start DSP program execution.
DSP memory read/write: selected by 4 control input pins. When the IDMA interface selects IS and the address latch is enabled (IAL), ADSP2189 writes the address on the address bus into the IDMA control register, and the latched address cannot be read back by the main controller. When the IDMA interface selects IS and the read strobe IRD is valid, ADSP2189 outputs the content of the storage unit pointed to by the IDMA control register to the IDMA data bus. When the IDMA interface selects IS and the write strobe IWR is valid, ADSP2189 writes the input data on the data bus to the storage unit pointed to by the IDMA control register. The access response IACK confirms the completion of the data read/write operation and serves as an indication signal that the IDMA interface is busy.
DSP state detection: store the data to be transmitted in the data area of DSP in a fixed format, and then send an interrupt to the DSP; after the DSP receives the interrupt, the modulation and transmission process will cause the level of DSP-FL0 to MSP430F149-P4.2 Variety. If the change is detected within 1ms, the DSP works normally; if the change is not detected, the DSP does not work normally, and the DSP program guide module is called again.
3.3 Sensor Detection
(1) Inclination angle detection: Under the condition of constant temperature, the output value of the single-axis accelerometer has a linear relationship with the sine value of the inclination angle.
(2) Roll angle detection: The measurement of the dual pulse width output of the dual axis accelerometer is realized by using the two capture/comparison modules of the MSP430F149 timer.
(3) Temperature detection: directly access the temperature sensor through the I/O pin of MSP430F149, read the temperature value, and make corresponding judgments.
In addition, a watchdog timer is also set to prevent the program from running away.
4 System installation error software correction
Due to the misalignment of the axis and the misalignment of the relevant reference lines during the installation of the probe, the inclination sensor and the roll sensor will always produce certain errors. That is to say, when the inclination angle and roll angle of the probe are at absolute zero, the measurement result of the corresponding sensor is not zero, there is a certain deviation, and the initial deviation of different probes is also different. Utilizing the program memory of MSP430F149 is the characteristic of Flash-type on-line programming, and the error correction is realized by software when the whole system is powered on for the first time after the whole system is assembled. The flowchart of the error correction software is shown in Figure 5.
Flash memory is composed of many relatively independent segments, which are mainly divided into information storage area (A, B segment) and main storage area. Programs can be run in one segment, while operations such as erasing or writing data to another segment; It is mainly used to save user programs or important data, information and other data that will not be lost after power failure. In the main storage area, the application program mainly erases and writes data to segment A in the information storage area. When powered on for the first time, the probe is placed on a specific calibration platform, so that the probe’s inclination and roll are at absolute zero. At this time, the probe is powered on, the main program is run, and the data measured by the sensor is the fixed deviation formed by the installation. Write the measured data into the Flash storage module and lock it, so that the program can no longer rewrite the program storage unit in the future, and it will not be erased after power failure. After the probe is powered on, it will judge the data of a specific storage unit, and the above process will not be performed. However, the absolute measurement value is obtained by subtracting the deviation value measured at the first power-on from the data measured by the sensor each time. Before operating the Flash, stop the watchdog to prevent the watchdog timer from overflowing during the operation. The subroutine flow is shown in Figure 6.
The underground sensor transmitting probe uses the single chip MSP430F149 to conveniently realize the acquisition of the sensor output signal, the control and management of the DSP, and the management of the power supply module. At the same time, advanced DSP technology is adopted to realize digital modulation, synchronization and related digital signal processing, which provides a reliable guarantee for ground reception demodulation and positioning sounding. The system has a series of advantages: small size, low cost, high reliability, and low power consumption design. The probe can work continuously for more than ten hours underground, which provides favorable conditions for horizontal directional drilling and longer construction projects.
The Links: LP064V1-LE G150XG01-V0