Gamma sensor signal processing circuit

Abstract

The invention discloses a gamma sensor signal processing circuit, which relates to the technical field of signal processing, and is characterized in that a negative current pulse signal output by a gamma sensor is converted into a negative voltage pulse signal by using a precise sampling resistor and a high-precision current induction amplifier; and a square wave signal is output through the hysteresis comparator. A single power supply is adopted for power supply, the power supply scheme of the whole system is optimized, and the power supply mode is simplified; the current induction amplifier is adopted to directly convert negative pulse signals of the gamma sensor into voltage signals, so that the influence of temperature on the electric pulse signals output by the gamma sensor can be effectively reduced; the hysteresis comparator is adopted to reduce false triggering and oscillation of a zero boundary point, so that the accuracy of square wave signal acquisition of the single-chip microcomputer is improved, and the overall reliability of the system is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of signal processing, and particularly relates to a gamma sensor signal processing circuit. BACKGROUND

[0002] The gamma sensor is a key component in a gamma instrument, which can monitor the gamma ray intensity in the environment where the instrument is located and feed back the formation information. The stronger the gamma ray is, the more the electric pulse signals output by the gamma sensor are. The electric pulse signals output by the gamma sensor are converted into square wave signals through a circuit, and a single-chip microcomputer calculates the electric pulse signals in a unit time by collecting the rising edges of the square wave signals, so as to determine the intensity of the gamma ray.

[0003] However, when the gamma sensor works in a high-temperature and strong-vibration environment downhole, the electric pulse signal processing thereof faces the following core problems:

[0004] 1. Temperature influence leads to error increase: the traditional scheme converts the electric pulse signals into voltage signals through resistance grounding, but the resistance value will drift with the change of temperature, leading to unstable voltage signal amplitude; the photomultiplier tube will generate dark current under high-temperature conditions, forming noise pulses and interfering with useful signals; the light-emitting efficiency of the scintillation crystal changes with temperature, affecting the conversion efficiency of gamma rays to photons.

[0005] 2. Vibration interference produces pseudo-pulses: the strong vibration environment downhole will cause mechanical stress of the sensor, leading to parameter drift of electronic components and generation of additional electric pulse signals; the vibration may cause poor contact of the connector, generating transient interference pulses;

[0006] 3. Negative pulse power supply is complex: the electric pulse signals output by the gamma sensor are negative, and a negative voltage power supply circuit is needed, which increases the system complexity and power consumption. SUMMARY

[0007] In view of the above technical problems, the present application provides a gamma sensor signal processing circuit, which directly converts the negative electric pulse signals output by the gamma sensor into voltage signals by using a current sense amplifier, effectively reducing the influence of temperature on the pulse signals of the gamma sensor.

[0008] A gamma sensor signal processing circuit converts the negative polarity current pulse signals output by the gamma sensor into negative polarity voltage pulse signals by using a precision sampling resistor and a high-precision amplifier; and then outputs square wave signals through a hysteresis comparator.

[0009] In an embodiment of the present application, the high-precision amplifier is a current sense amplifier.

[0010] In an embodiment of the present application, the negative polarity current pulse signals output by the gamma sensor are converted into negative polarity voltage pulse signals from the current sense amplifier V IN+ pin input, VIN- Pin output, precision sampling resistor is connected to V IN+ Pin and V IN- Pin, the OUT pin outputs a negative polarity voltage pulse signal.

[0011] In an embodiment of the present application, the negative polarity current pulse signal output by the gamma sensor passes through a protection resistor R120 from the current sensing amplifier V IN+ Pin input, V IN- Pin outputs through a protection resistor R47.

[0012] In an embodiment of the present application, V IN+ Pin and V IN- A capacitor C5 is connected between the pins.

[0013] In an embodiment of the present application, the precision sampling resistor is composed of two precision resistors in parallel.

[0014] In an embodiment of the present application, a voltage follower is set in front of the hysteresis comparator for signal buffering and isolation.

[0015] The beneficial effects of the present application are:

[0016] 1. Single power supply is adopted to optimize the power supply scheme of the entire system and simplify the power supply mode;

[0017] 2. The current sensing amplifier is adopted to directly convert the negative polarity pulse signal of the gamma sensor into a voltage signal, which can effectively reduce the influence of temperature on the output pulse signal of the gamma sensor;

[0018] 3. The hysteresis comparator is adopted to reduce zero point false triggering and oscillation, thereby improving the accuracy of the single-chip microcomputer in collecting square wave signals and further improving the overall reliability of the system. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is a signal conversion and amplification circuit principle diagram based on a current sensing amplifier;

[0020] Figure 2 It is an analog-to-digital conversion circuit principle diagram. DETAILED DESCRIPTION

[0021] The present application will be further described in detail below in conjunction with the drawings and specific embodiments. The embodiments of the present application are given for the purpose of illustration and description, and are not exhaustive or limit the present application to the disclosed forms. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments are chosen and described in order to better explain the principles of the present application and its practical application, and to enable those of ordinary skill in the art to understand the present application so as to design various embodiments with various modifications suitable for specific uses.

[0022] Embodiment 1

[0023] A gamma sensor signal processing circuit, as shown in Figure 1 , converts the negative polarity current pulse signal output by the gamma sensor into a negative polarity voltage pulse signal using a precision sampling resistor and a high-precision amplifier, not only maintaining the polarity characteristics of the original signal, facilitating subsequent circuit identification and processing, but also converting the weak current pulse (milliamp level) into a voltage signal (volt level) suitable for ADC sampling. At the same time, the voltage signal has stronger anti-interference ability than the current signal.

[0024] The high-precision amplifier here is preferably a current sense amplifier. The current sense amplifier internally uses a precision-matched resistor network, with temperature drifts canceling each other out; high common-mode rejection ratio can effectively suppress common-mode interference caused by power voltage fluctuations and temperature changes; the temperature drift of the sampling resistor can also be suppressed by the differential input structure of the high-precision amplifier.

[0025] There are various brands and models of current sense amplifiers to choose from, such as the INA series from Texas Instruments. This embodiment selects INA193 (internal fixed gain of 20V / V), as shown in Figure 1 , the negative polarity current pulse signal output by the gamma sensor passes through the protection resistor R120 from the current sense amplifier V IN+ pin, and the V IN- pin outputs through the protection resistor R47, and the precision sampling resistor is connected between the V IN+ pin and the V IN- pin, with the OUT pin outputting a negative polarity voltage pulse signal SIN_OUT. In addition, the V IN+ pin and the V IN- pin are connected with a filter capacitor C5. The V+ pin is connected to the +5V power supply while being grounded through the decoupling capacitor C10, and the GND pin is grounded.

[0026] When the negative polarity current pulse signal flows through the precision sampling resistor, a voltage drop is generated across the resistor. For negative current, V IN+ potential is lower than V IN- , and the differential voltage generated is amplified 20 times by INA193 to output a negative polarity voltage pulse signal SIN_OUT.

[0027] The protection resistors R120 and R47 have the following functions:

[0028] 1. Current limiting and electrostatic discharge (ESD) protection: R47 limits the current flowing from the signal source (preamplifier circuit) into the positive input terminal of the amplifier, and R120 limits the current flowing from the signal source into the negative input terminal of the amplifier. When voltage spikes, electrostatic discharge, or accidental short circuits occur at the input terminal, these two resistors can limit the inrush current and protect the fragile input differential pair of INA193 transistors.

[0029] 2. Reduce the impact of input bias current: The input bias current of the INA193 is approximately ±0.5μA (typical value). The voltage drop generated by the 100Ω resistor under the input bias current is only 0.05mV, which has almost no impact on the measurement accuracy. Without this resistor, the parasitic capacitance at the input terminal and external interference may form an unstable operating point.

[0030] 3. Low-pass filter with capacitor C5: R47 and C5 (10μF) form a first-order RC low-pass filter with a cutoff frequency of f_c = 1 / (2πRC) ≈ 1 / (2×3.14×100×10×10⁻ 6 (≈160Hz) can effectively filter out high-frequency noise and improve measurement stability.

[0031] See Figure 1 In this embodiment, the precision sampling resistor is composed of two precision resistors R35 and R46 connected in parallel. This is mainly to effectively distribute the power while obtaining an extremely low sampling resistance value, reduce the operating temperature and temperature drift of a single resistor, and improve the long-term reliability and measurement stability of the system in harsh environments such as high temperature.

[0032] Although the negative voltage pulse signal SIN_OUT output by the high-precision amplifier has pulse characteristics (rapid rise, slow fall), it is still an analog voltage waveform and needs to be converted into a digital square wave signal. In this embodiment, a hysteresis comparator is used to convert the analog voltage waveform into a square wave signal for output.

[0033] See Figure 2 A voltage follower is set in the pre-stage of the hysteresis comparator. The high input impedance and low output impedance of the voltage follower are used to buffer and isolate the front and rear stages. This ensures that the high input impedance will not cause a load effect on the high-precision current sensing amplifier in the front stage. At the same time, its low output impedance can stably drive the comparator in the rear stage and prevent signal attenuation.

[0034] Since voltage followers and hysteresis comparators are relatively mature circuit structures, their configurations will not be described in detail here. By setting the upper and lower gate limit voltages VT+ and VT- through the hysteresis comparator, noise and small-amplitude interference in the gamma sensor pulse signal are reduced, while avoiding false triggering and oscillation. This improves the accuracy of the microcontroller in acquiring square wave signals, thereby enhancing the overall reliability of the system.

[0035] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art or related fields based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

Claims

1. A gamma sensor signal processing circuit, characterized in that, The negative polarity current pulse signal output by the gamma sensor is converted into a negative polarity voltage pulse signal using a precision sampling resistor and a high-precision amplifier; then, a square wave signal is output after passing through a hysteresis comparator.

2. The gamma sensor signal processing circuit according to claim 1, characterized in that, The high-precision amplifier uses a current-sensing amplifier.

3. The gamma sensor signal processing circuit according to claim 2, characterized in that, The negative polarity current pulse signal output by the gamma sensor is from the current sensing amplifier V. IN+ Pin input, V IN- Pin output, precision sampling resistor connected to V IN+ pin and V IN- Between the pins, the OUT pin outputs a negative polarity voltage pulse signal.

4. The gamma sensor signal processing circuit according to claim 3, characterized in that, The negative polarity current pulse signal output by the gamma sensor passes through the protection resistor R120 and is then transmitted to the current sensing amplifier V. IN+ Pin input, V IN- The pin outputs through the protection resistor R47.

5. The gamma sensor signal processing circuit according to claim 4, characterized in that, V IN+ pin and V IN- A capacitor C5 is connected between the pins.

6. The gamma sensor signal processing circuit according to any one of claims 1-5, characterized in that, The precision sampling resistor is composed of two precision resistors connected in parallel.

7. The gamma sensor signal processing circuit according to claim 1, characterized in that, A voltage follower is set in the preamplifier stage of the hysteresis comparator for signal buffering and isolation.

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