A Transmitter Circuit for Transient Field Through-Casing Resistivity Logging System

Abstract

The invention discloses a transient field through-casing resistivity logging system transmitting circuit: comprising a DSP core board, a magnetic coupling isolation circuit, an intelligent power module, a transmitting antenna, a power absorption circuit and a transmitting current acquisition circuit, a DC / DC power supply circuit supplies power to the transmitting circuit, and the intelligent power module comprises a driving circuit, a power amplifier circuit, a protection circuit and a monitoring circuit; the DSP core board generates two PWM square wave signals, which pass through the magnetic coupling isolation circuit and then through the driving circuit to realize the switch control of the MOSFET power amplifier tube of the power amplifier circuit, and the power amplifier circuit is converted into an AC excitation for the transmitting antenna according to the control logic of the driving circuit. The transient field through-casing transmitting circuit abandons the traditional complex transmitting circuit form and adopts an integrated intelligent power module as a bridge power conversion circuit, which integrates the transmitting driving circuit, the power amplifier circuit, the overcurrent, overvoltage, undervoltage and overheating protection circuits, and is simple and easy to control.

Description

Technical Field

[0001] The invention belongs to the field of oilfield logging systems, and in particular relates to a transient field through-casing resistivity logging system transmitting circuit in the field. Background Art

[0002] The transient field passes through the transmitting circuit of the casing resistivity logging system, sends a logic control signal through the DSP, and then passes through the magnetic coupling isolation to control the power bridge circuit, converting the DC signal into a bipolar square wave signal, and then generates a primary field through the transmitting coil to excite the secondary field. Its working principle is as follows Figure 1 shown.

[0003] The transmitting power amplifier circuit adopts a full-bridge inverter power supply topology (H-type topology). When the two A switches in the figure are turned on, the two B switches are turned off, and when the two B switches in the figure are turned on, the two A switches are turned off. Through the turning on and off of the AB switches, a bipolar square wave is finally generated, thereby driving the electromagnetic probe to emit a magnetic field outward.

[0004] The traditional transmitting circuit adopts the design of driving circuit + power amplifier tube and other discrete components and triode cascade drive. The circuit design is complex and not easy to control. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a transmitting circuit for a transient field through-casing resistivity logging system.

[0006] The present invention adopts the following technical solution:

[0007] The invention discloses a transmitting circuit of a transient field through-casing resistivity logging system. The improvement thereof lies in that the transmitting circuit comprises a DSP core board, a magnetic coupling isolation circuit, an intelligent power module, a transmitting antenna, a power absorption circuit and a transmitting current acquisition circuit. The DC / DC power supply circuit supplies power to the transmitting circuit. The intelligent power module comprises a driving circuit, a power amplifier circuit, a protection circuit and a monitoring circuit. The DSP core board generates two PWM square wave signals, which pass through the magnetic coupling isolation circuit and then through the driving circuit to realize switch control of a MOSFET power amplifier tube of the power amplifier circuit. The power amplifier circuit is converted into an AC excitation for the transmitting antenna according to the control logic of the driving circuit.

[0008] Furthermore, the power absorption circuit adopts a passive constant voltage clamp circuit composed of a bidirectional TVS tube. The TVS tube does not work when the transmitting circuit is powered forward and reversely, and the TVS tube continues to flow when the power supply is stopped.

[0009] Furthermore, the transmitting current collection circuit adopts a method of connecting a sampling resistor in series in the transmitting coil.

[0010] Furthermore, two 0.05Ω pure resistors are connected in series.

[0011] The beneficial effects of the present invention are:

[0012] The transient field through-the-casing transmitting circuit abandons the traditional complex transmitting circuit form and adopts an integrated intelligent power module as the bridge power conversion circuit. The transmitting drive circuit, power amplifier circuit, overcurrent, overvoltage, undervoltage and overheating protection circuit are integrated inside it, which is simple and easy to control.

[0013] Taking into account the characteristic of large overshoot at the moment of transmitting and shutting off of the transmitting circuit, a passive constant voltage clamp circuit composed of a bidirectional TVS tube is used for power absorption. This power absorption circuit can not only absorb the overshoot energy and reduce the current shutdown time, but also improve the trailing edge of the transmitting current.

[0014] Traditionally, the emission current is collected by using a current sensor module, but the drawback is that the collected emission waveform is prone to emission distortion. In order to record the emission current waveform at high speed, accurately and without distortion, a sampling resistor is connected in series in the emission coil to collect the current. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is the working principle diagram of the transmitting circuit;

[0016] Figure 2 It is the principle block diagram of the transmitting circuit;

[0017] Figure 3 It is a schematic diagram of the composition of the power absorption circuit;

[0018] Figure 4 It is a schematic diagram of the composition of the emission current collection circuit. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0020] Embodiment 1, this embodiment discloses a transient field through-casing resistivity logging system transmitting circuit, which sends a logic control signal through DSP, and then controls the power bridge through magnetic coupling isolation, converts the DC signal into a bipolar square wave signal, and then generates a primary field through the transmitting coil to excite the secondary field. The transmitting circuit principle and design proposed by the present invention are innovative designs, abandoning the traditional transmitting circuit form, and have the advantages of strong driving capability, low transmitting on-resistance, short transmitting off time, etc.

[0021] Abandoning the traditional transmission circuit form, an integrated intelligent power module is used as the bridge power conversion circuit. The intelligent power module integrates the transmission drive circuit, power amplifier circuit, overcurrent, overvoltage, undervoltage and overheat protection circuits. The circuit is simple and easy to control. The transient field through-casing resistivity logging system transmission circuit is mainly composed of timing signal generation circuit, magnetic coupling isolation circuit, bridge power conversion circuit, power absorption circuit and transmission current acquisition circuit. Its principle block diagram is as follows Figure 2 shown.

[0022] Among them, the DSP core board generates two PWM square wave signals, which pass through the magnetic coupling isolation circuit and then the driving circuit to realize the switching control of the MOSFET power amplifier tube; the power amplifier circuit converts it into AC excitation for the transmitting antenna according to the control logic of the driving circuit; the protection circuit protects the intelligent power module from overvoltage, undervoltage and overcurrent.

[0023] Power absorption circuit: Considering the characteristics of large overshoot in the transmitting circuit when it is turned off, a passive constant voltage clamp circuit composed of a bidirectional TVS tube is used for power absorption. This power absorption circuit can not only absorb the overshoot energy and reduce the current shutdown time, but also improve the trailing edge of the transmitting current. Figure 3 shown.

[0024] The TVS tube does not work when the transmitter circuit is powered forward or reversely, and the TVS tube continues to flow when the power is stopped. When the transmitter stops supplying power, the TVS tube can quickly change from high impedance to low impedance, absorb energy, and clamp the voltage at both ends to a fixed value.

[0025] Assume that the emission current is i0(t), the emission current amplitude is i0(t0), U t is the clamping voltage of the TVS tube. Then the emission current cut-off moment is as follows:

[0026]

[0027] When the emission current is 0, the turn-off time t is obtained. d :

[0028]

[0029] Compared with the inductor, the equivalent resistance of the transmitting coil is very small, and the influence of the equivalent resistance on the off time of the transmitting current can be ignored. The derivative of the formula can be obtained:

[0030]

[0031] Because U tand L are fixed values, so i0'[t] is a constant, and it is assumed that the emission current decreases linearly at the time of shutdown. It can be seen from formula (2) and formula (3) that when the clamping voltage value U of the TVS tube is changed t When the clamping voltage is increased, the slope of the emission current falling edge can be changed. When the clamping voltage value is increased, the emission current turn-off time can be reduced. Therefore, within the range that the electronic switch can withstand, selecting a TVS tube with a sufficiently high clamping voltage can obtain a larger current drop rate and reduce the turn-off time.

[0032] Design of emission current acquisition circuit: In order to record the emission current waveform quickly, accurately and without distortion, the current is collected by inserting a sampling resistor in series in the emission coil. In the transient emission current circuit, two 0.05Ω pure resistors are connected in series to the emission coil. Since the emission coil resistance is very small, if the sampling resistor is large, the emission current will be reduced and the emission efficiency will be reduced. Figure 4 This is the current sampling schematic.

Claims

1. A transient field through-casing resistivity logging system transmitting circuit, characterized in that: It includes a DSP core board, a magnetic coupling isolation circuit, an intelligent power module, a transmitting antenna, a power absorption circuit and a transmitting current acquisition circuit. The DC / DC power supply circuit supplies power to the transmitting circuit. The intelligent power module includes a driving circuit, a power amplifier circuit, a protection circuit and a monitoring circuit. The DSP core board generates two PWM square wave signals, which pass through the magnetic coupling isolation circuit and then through the driving circuit to realize the switching control of the MOSFET power amplifier tube of the power amplifier circuit. The power amplifier circuit is converted into AC excitation for the transmitting antenna according to the control logic of the driving circuit. The power absorption circuit adopts a passive constant voltage clamp circuit composed of a bidirectional TVS tube. The TVS tube does not work when the transmitting circuit is powered forward and reversely, and the TVS tube continues to flow when the power supply is stopped.

2. The transient field through-casing resistivity logging system transmitting circuit according to claim 1 is characterized in that: The transmitting current acquisition circuit adopts the method of inserting a sampling resistor in series in the transmitting coil.

3. The transmitting circuit of the transient field through-casing resistivity logging system according to claim 2 is characterized in that: Two 0.05Ω pure resistors are connected in series.

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