NMR Power Phase Control Module

Abstract

The invention relates to the technical field of nuclear magnetic resonance logging, and provides a nuclear magnetic resonance logging instrument transmission power phase control module, comprising a transmission circuit. The nuclear magnetic resonance logging instrument transmission power phase control module also comprises a control unit 1 and a DDS direct digital signal synthesis unit 2. The relationship between the amplitude quantity and the phase quantity is established by a software algorithm, thereby simplifying the hardware circuit design, reducing the difficulty of the hardware circuit design, and increasing the reliability.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear magnetic resonance logging and provides a nuclear magnetic resonance logging instrument emission power phase control module. Background Art

[0002] Nuclear magnetic resonance logging technology is currently the only logging method that can directly measure the properties of formation fluids, and has very obvious advantages. Nuclear magnetic resonance logging uses the paramagnetism of H nuclei in formation fluids and the external radio frequency magnetic field of the interaction between H nuclei for logging.

[0003] The radio frequency transmission circuit of the nuclear magnetic resonance logging tool includes a signal reference signal generation circuit, an excitation circuit, a high-power transmitter circuit, an antenna and a discharge circuit thereof, wherein the transmission power control is realized by controlling the phase of the transmission signals of the two high-power transmitter circuits.

[0004] like Figure 1 As shown, the power phase control circuit is mainly composed of four circuit units: control unit 1, DDS direct digital signal synthesis unit 2, D / A digital-to-analog conversion unit 4 and signal excitation unit 3. The function of control unit 1 is to receive instructions and data from the ground, write the instructions and data into DDS direct digital signal synthesis unit 2 through the data line after parsing, and control DDS direct digital signal synthesis unit 2 to generate sin and cos orthogonal reference signals; at the same time, control unit 1 also receives amplitude control data from the ground system, which is converted into analog quantity AM by D / A analog-to-digital conversion unit 4. Finally, the three signals of sin, cos and AM are simultaneously input into signal excitation unit 3, and the circuit in the unit performs analog operation and outputs two signals I and Q. The phase difference between I and Q signals already carries the information of AM amplitude. The two signals I and Q control the high-power transmission circuit to output the amplitude corresponding to the amplitude AM from the ground system. The circuit of excitation circuit unit 3 is complex, the design is difficult, and the reliability is poor. Summary of the invention

[0005] The purpose of the present invention is to use a software algorithm to establish the relationship between the amplitude and the phase, simplify the hardware circuit design, reduce the difficulty of hardware circuit design, and increase reliability, and provide a nuclear magnetic resonance power phase control module, and its technical solution is as follows.

[0006] A nuclear magnetic resonance logging instrument transmission power phase control module includes a transmission circuit, the nuclear magnetic resonance logging instrument transmission power phase control module also includes a control unit 1 and a DDS direct digital signal synthesis unit 2, the control unit 1 is connected to the ground control system for communication, and is used to parse the instructions and data from the ground control system to control the DDS direct digital signal synthesis unit 2, the DDS direct digital signal synthesis unit 2 is connected to the control unit 1 for communication, and is used to receive the instructions and data signals from the control unit 1 and generate two square wave signals I and Q with a specified phase difference under the control of the control unit 1, and the transmission circuit is connected to the DDS direct digital signal synthesis unit 2 for communication, wherein:

[0007] The two signals I and Q control the transmitting circuit to output the RF output signal amplitude corresponding to the RF signal amplitude control amount from the ground control system and used to control the RF output signal amplitude. The RF signal amplitude control amount is converted into a phase difference by the ground control system or the control unit 1. After that, the algorithm between the RF output signal amplitude and the phase difference is first determined, and then the algorithm between the RF output signal amplitude and the phase difference is integrated to establish the relationship between the amplitude amount and the phase amount, so as to control the RF signal output power, wherein,

[0008] The algorithm between the amplitude and phase difference of the RF output signal is as follows. The two orthogonal sinusoidal wave signals are superimposed in opposite phases to obtain:

[0009]

[0010] Where A represents the RF output signal amplitude, t represents time, Represents the phase difference, and its value range is , k represents the gain coefficient of the transmitting circuit;

[0011] Integrating the algorithm between the RF output signal amplitude and phase difference yields:

[0012]

[0013] Fitting a cubic polynomial function between the phase difference and the RF output signal amplitude is as follows:

[0014]

[0015] Among them, a, b, c, d represent constants, and A_rms represents the amplitude of the RF output signal after integration.

[0016] The above-mentioned scheme of the ground control system further includes a nuclear magnetic resonance logging method, which adopts a nuclear magnetic resonance logging instrument transmission power phase control module and includes the following steps:

[0017] (1) Control unit 1 receives commands and data sent by the ground control system;

[0018] (2) The embedded software in the control unit 1 calculates the received instructions and data and converts them into instruction and data signals that can be recognized by the DDS direct digital signal synthesis unit 2 to control the DDS direct digital signal synthesis unit 2;

[0019] (3) The DDS direct digital signal synthesis unit 2 receives the instruction and data signal in step (2) and generates two square wave signals I and Q with a specified phase difference under the control of the control unit 1;

[0020] (4) The transmitting circuit outputs a radio frequency signal of corresponding power according to the signals I and Q generated in step (3).

[0021] The beneficial effects of the present invention are:

[0022] A software algorithm is used to establish the relationship between the amplitude quantity and the phase quantity, which simplifies the hardware circuit design, reduces the difficulty of hardware circuit design, and increases reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a block diagram of the phase-controlled functional module of the prior art, wherein 1 is a control unit, 2 is a DDS direct digital signal synthesis unit, 3 is a digital-to-analog conversion unit, and 4 is an analog operation unit.

[0024] Figure 2 It is a block diagram of the phase-controlled functional module, where 1 is the control unit and 2 is the DDS direct digital signal synthesis unit.

[0025] Figure 3 It is a graph showing the relationship between amplitude and phase difference. The curve in the graph is the result of theoretical calculation. The horizontal axis is the phase difference and the vertical axis is the amplitude.

[0026] Figure 4 This is a comparison chart of the fitting and theoretical calculation results of the relationship between amplitude and phase difference, where the black line is the theoretical calculation result and the red dotted line is the calculation result of the cubic polynomial fitting function. DETAILED DESCRIPTION

[0027] Reference Figure 1-4 A nuclear magnetic resonance power phase control module, consisting of a control unit 1 and a DDS direct digital signal synthesis unit 2;

[0028] The DDS direct digital signal synthesis unit 2 can receive the command word from the control unit 1 and output square wave signals I and Q of corresponding phases;

[0029] The control unit 1 can receive instructions and data from the ground control system, analyze and control the phase difference between the two output signals (I, Q) of the DDS direct digital signal synthesis unit 2.

[0030] During operation, the control unit 1 receives commands and parameters sent from the ground control system. After the embedded software in the control unit 1 calculates the received parameters and converts them into instructions and parameters that can be recognized by the DDS direct digital signal synthesis unit 2, the control unit 1 sends the instructions and data carrying phase difference information to the DDS digital signal synthesis unit 2, and the DDS direct digital signal synthesis unit 2 outputs two signals I and Q. The two signals I and Q control the transmitting circuit to output the RF output signal amplitude corresponding to the RF signal amplitude control amount AM from the ground control system, thereby realizing the control of the RF signal output power.

[0031] The RF signal amplitude control value AM is a parameter input by the ground engineer through the ground control system for controlling the RF output signal amplitude. The parameter is converted into a phase difference matching the I and Q signals through the software of the ground control system or the software of the control unit 1.

[0032] The algorithm between the amplitude and phase difference of the RF output signal is as follows. The two orthogonal sinusoidal wave signals are superimposed in opposite phases to obtain:

[0033] (1)

[0034] Among them, A---RF output signal amplitude;

[0035] t----time;

[0036] ---Phase difference, the value range is ;

[0037] k---The gain coefficient of the transmitting circuit can be determined by yourself during the system design process.

[0038] Integrating formula (1) yields:

[0039] (2)

[0040] According to formula (2), take k=100, , obtain the correlation between the RF output signal amplitude and phase difference, and then draw a two-dimensional curve of the relationship between the RF signal amplitude control amount AM and the phase difference in the plane coordinate system as shown in Figure 3 shown.

[0041] Simplify the algorithm and fit a function of the relationship between the phase difference and the RF output signal amplitude, for example, fit it to a quadratic or cubic polynomial or other function.

[0042] Fit a cubic polynomial function as follows:

[0043] (3)

[0044] In the formula, a, b, c, d are constants;

[0045] A_rms---RF output signal amplitude after integration;

[0046] ------Phase difference.

[0047] like Figure 4 As shown in the figure, it is a comparison of the characteristic curves of formula (3) and theoretical calculation results. The black one is the theoretical calculation result, and the red dotted line is the result of the cubic polynomial. The two curves are Within the range, there is very good consistency. Formula (3) can be used instead of formula (2), which makes the calculation simpler.

Claims

1. A nuclear magnetic resonance logging instrument transmission power phase control module, comprising a transmission circuit, characterized in that: The nuclear magnetic resonance logging instrument transmission power phase control module also includes a control unit 1 and a DDS direct digital signal synthesis unit 2. The control unit 1 is connected to the ground control system for communication and is used to parse the instructions and data from the ground control system to control the DDS direct digital signal synthesis unit 2. The DDS direct digital signal synthesis unit 2 is connected to the control unit 1 for communication and is used to receive the instructions and data signals from the control unit 1 and generate two square wave signals I and Q with a specified phase difference under the control of the control unit 1. The transmitting circuit is connected to the DDS direct digital signal synthesis unit 2 for communication, wherein: The two signals I and Q control the transmitting circuit to output the RF output signal amplitude corresponding to the RF signal amplitude control amount from the ground control system and used to control the RF output signal amplitude. The RF signal amplitude control amount is converted into a phase difference by the ground control system or the control unit 1. After that, the algorithm between the RF output signal amplitude and the phase difference is first determined, and then the algorithm between the RF output signal amplitude and the phase difference is integrated to establish the relationship between the amplitude amount and the phase amount, so as to control the RF signal output power, wherein, The algorithm between the amplitude and phase difference of the RF output signal is as follows. The two orthogonal sinusoidal wave signals are superimposed in opposite phases to obtain: A=k*(sin(t)-cos(t+θ) ) Among them, A represents the RF output signal amplitude, t represents time, and θ represents the phase difference, and the value range is , k represents the gain coefficient of the transmitting circuit; Integrating the algorithm between the RF output signal amplitude and phase difference yields: Fitting a cubic polynomial function between the phase difference and the RF output signal amplitude is as follows: Among them, a, b, c, d represent constants, and A_rms represents the amplitude of the RF output signal after integration.

2. A nuclear magnetic resonance logging method, characterized in that: The nuclear magnetic resonance logging tool transmission power phase control module as claimed in claim 1 is used and includes the following steps: (1) Control unit 1 receives commands and data sent by the ground control system; (2) The embedded software in the control unit 1 calculates the received instructions and data and converts them into instruction and data signals that can be recognized by the DDS direct digital signal synthesis unit 2 to control the DDS direct digital signal synthesis unit 2; (3) The DDS direct digital signal synthesis unit 2 receives the instruction and data signal in step (2) and generates two square wave signals I and Q with a specified phase difference under the control of the control unit 1; (4) The transmitting circuit outputs a radio frequency signal of corresponding power according to the signals I and Q generated in step (3).

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