ICP light source power automatic adjusting device

Abstract

The utility model relates to an ICP (Inductively Coupled Plasma) light source power automatic adjusting device, which comprises a voltage transformer, a current transformer, a phase detector, a control unit and a motor driver, wherein the voltage transformer and the current transformer are connected between the high-frequency oscillator and the load loop; the signal output is used for providing high-frequency voltage and current; the phase detector is used for detecting phase difference data of voltage and current in high-frequency energy input by the load circuit; the control unit calculates a rotation angle required by the variable capacitor for changing the capacity for load loop resonance according to the phase difference data, and further calculates the walking step number of the stepping motor; and the motor driver drives the stepping motor to drive the variable capacitor to rotate by a corresponding angle according to a set direction, so that the load loop is closer to a resonance point output by the high-frequency oscillator. According to the electronic automatic control device, the load loop in the ICP light source is automatically tuned, so that the output efficiency and the stability of the ICP light source are improved.

Description

TECHNICAL FIELD

[0001] The utility model relates to the adjusting device of ICP light source, concretely relates to a kind of ICP light source power automatic regulating device. BACKGROUND

[0002] The light source of ICP (inductively coupled plasma emission spectrometer) is an important component of ICP, which is generally composed of the following parts: high-frequency oscillator, impedance matching network, load circuit (LC resonant circuit) and plasma.

[0003] High-frequency oscillator (high-frequency transmitter): a high-frequency oscillator with high-power electronic tube or semiconductor device as core, which generates and outputs high-frequency electric energy (frequency is mostly 27.12MHz or 40.68MHz, i.e. 2 times or 3 times of 13.56MHz); impedance matching network: connecting high-frequency oscillator and load circuit, completing impedance matching and energy transmission between them; load circuit (LC resonant circuit): receiving high-frequency energy, creating electrical conditions for generating plasma; plasma: under the action of high-frequency electric field provided by load coil, argon gas is introduced through specially designed quartz tube, and high-temperature electric spark of Tesla coil is used to excite, finally forming a unique high-temperature plasma torch.

[0004] The basic process of ICP for sample analysis is as follows: the center temperature of plasma torch is as high as several thousand degrees, and the atomized analysis sample is carried to the center of ion torch flame by carrier gas, and the metal elements in the sample are excited by high temperature to emit their characteristic spectral lines, and the spectral line wavelength represents the type of elements in the sample, and the spectral line intensity represents the content of corresponding elements. Therefore, the efficiency and stability of ICP light source play a key role in the measurement accuracy of ICP and the overall stability of the instrument, and the automatic tuning of the LC oscillation circuit where the load is located is an important measure to ensure the efficiency and stability of ICP light source.

[0005] Due to the influence of power supply or other environmental factors, the output of high-frequency oscillator of ICP in use will produce a certain frequency drift, but the main reason for causing its efficiency fluctuation is still the plasma at the load end. First, the fluctuation of argon gas inlet quantity for forming plasma in use, and the instability of analysis sample loading quantity, etc., will affect the impedance change of plasma; second, in the process of forming stable plasma torch (commonly known as "ignition"), the load characteristics change greatly, not only the resonant frequency of load circuit is offset, but also the impedance characteristics are obviously changed, which leads to a large reflected power. Since this process is short and changes quickly, only through automatic adjustment can the requirements of resonance and impedance matching be better met.

[0006] The inductive reactance of the tank circuit of the load circuit is equal to the capacitive reactance, which is the characteristic of the load circuit in the resonant state, and the phase of the voltage and the current of the load circuit is the same in the resonant state, and the phases of the voltage and the current are represented as Pu and Pi respectively, that is, Pu-Pi=0; similarly, if Pu-Pi>0, the voltage phase leads the current, and the load circuit is inductive; if Pu-Pi<0, the voltage phase lags the current, and the load circuit is capacitive.

[0007] For most self-excited ICP light sources at home and abroad, the load coil is also the coil of the oscillation tank circuit, and forms a series resonant circuit with a variable capacitor, therefore, in order to ensure that the load circuit is always in the resonant state during operation, when the impedance characteristic of the load circuit is inductive, the capacity of the series capacitor needs to be increased, and when the impedance characteristic of the load circuit is capacitive, the capacity of the series capacitor needs to be reduced. In this way, by adjusting the capacity of the variable capacitor, the resonance and impedance matching of the load circuit can be realized. The utility model realizes the automatic adjustment of the capacity of the variable capacitor through the detection result (inductive, capacitive, resistive) of the impedance characteristic of the load circuit. Utility model content

[0008] In most ICPs, the load circuit (coil) obtains energy from a high-frequency oscillator through an LC resonant circuit, and then transmits high-frequency energy to a hollow cylindrical plasma (ionized argon gas formed by means of a quartz torch pipe) in a mutual inductance mode, and finally forms a high-temperature plasma torch flame. For most ICPs, the inductance of the LC resonant circuit is the load coil of the ICP, therefore, if the parameters of the circuit can be automatically tracked and adjusted to keep the LC oscillation circuit in the resonant state during the operation of the ICP, the high-frequency energy generated by the ICP light source can be basically guaranteed to be transmitted to the load efficiently. At the same time, due to the reduction of reflected power after resonance, the safety of the high-frequency oscillator can also be improved.

[0009] The utility model aims at providing a kind of ICP light source power automatic regulating device. It is an electronic automatic control device for improving the output efficiency and stability of ICP light source by automatically tuning the load circuit (LC resonant circuit) in ICP light source.

[0010] The power automatic regulating device comprises a voltage transformer, a current transformer, a phase detector, a control unit and a motor driver.

[0011] The voltage transformer and the current transformer are connected between the high-frequency oscillator and the load circuit, and are used to provide the signal output of high-frequency voltage and current.

[0012] The phase detector is composed of a phase detection chip and a phase shift circuit.

[0013] The phase detector detects the voltage and current phase difference data in the high-frequency energy input to the load circuit through the signals output by the voltage transformer and the current transformer.

[0014] The control unit calculates the angle required for the variable capacitor to change its capacity in order to achieve resonance of the load circuit based on the phase difference, and then calculates the number of steps the stepper motor takes; the direction of the stepper motor is determined based on the sign of the phase difference between voltage and current.

[0015] Finally, the stepper motor is driven by the motor driver to rotate the variable capacitor in a predetermined direction by a corresponding angle, so that the load circuit is closer to the resonant point of the high-frequency oscillator output.

[0016] This invention designs a phase difference detector: a voltage transformer and a current transformer are installed on the transmission line from the high-frequency oscillator to the load circuit to measure the high-frequency voltage and current of the ICP load circuit in real time. The measurement signal is conditioned and then input to the phase detection chip. The phase difference value indicates the degree to which the impedance matching deviates from the resonant point (the resonant state is resistive). The sign of the phase difference value reflects the impedance characteristics (inductive, capacitive, resistive).

[0017] This invention designs an adjustment and control unit: the phase difference value between the high-frequency voltage and current output by the phase detector is multiplied by an operational amplifier, and then sent to the control unit MPU after analog-to-digital conversion. Because the phase difference data alone cannot indicate the sign of the phase difference, i.e., it cannot determine whether the voltage or the current is leading, a phase shift circuit is added. The phase detection chip works in conjunction with this phase shift circuit, and the test comparison is performed under the control of the MPU to determine the sign of the phase difference data, thus confirming the impedance characteristics of the load: Pu-Pi>0 is inductive; Pu-Pi<0 is capacitive; Pu-Pi=0 is resistive.

[0018] The control software obtains the angle data for controlling the rotation of the variable capacitor through PID calculation (generally only PI calculation is needed), and determines the rotation direction of the variable capacitor based on the sign of the phase difference between voltage and current. Then, the stepper motor is rotated through the drive circuit, which drives the moving plate of the variable capacitor to change its capacitance, thereby achieving the purpose of adjusting the resonant point of the load circuit.

[0019] This invention designs high-frequency voltage and current transformers: because it is difficult to purchase suitable voltage and current transformers on the market, a self-made solution is adopted. Since it is used in a high-frequency environment, a nickel-zinc ferrite magnetic ring is used (initial permeability 80, typical operating frequency 30MHz, saturation magnetic flux density 300mT). The current transformer adopts a through-core structure (without a primary coil), and the outputs of the two transformers are adjusted to a range of 3-10V after resistive voltage division. Attached Figure Description

[0020] Figure 1 A schematic diagram of the automatic power adjustment device for the ICP light source provided by this utility model;

[0021] Figure 2 Electrical schematic diagram of the ICP light source power automatic adjustment device provided by this utility model. Detailed Implementation

[0022] The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0023] Example

[0024] This embodiment provides an automatic power adjustment device for an ICP light source.

[0025] like Figure 1 The system block diagram of the ICP light source power automatic adjustment device is shown. This is an embodiment designed according to the present invention. The ICP light source power automatic adjustment device consists of the following parts: 1-voltage transformer and current transformer, 2-phase detector (including phase shifting circuit), 3-motor driver, 4-control unit.

[0026] The voltage and current transformers are connected between the high-frequency oscillator and the load circuit to provide high-frequency voltage and current signals to the phase detector (the current signal is converted into a voltage signal input through the transformer). The phase detector consists of a phase detection chip and a phase shift circuit, which is used to detect the phase difference data between the voltage and current in the high-frequency energy input to the load circuit. The control unit calculates the angle required for the variable capacitor to change its capacity for the load circuit to resonate based on the value of the phase difference, and then calculates the number of steps the stepper motor should take. The direction of the stepper motor is determined based on the sign of the voltage and current phase difference. Finally, the motor driver drives the stepper motor to rotate the variable capacitor in a predetermined direction by a corresponding angle, so that the load circuit is closer to the resonant point output by the high-frequency oscillator.

[0027] like Figure 2The diagram shown is an electrical schematic of an embodiment of this invention. The voltage transformer and current transformer constitute the input signal measurement section. The magnetic core of the transformer is a nickel-zinc ferrite core with a frequency of 30MHz or higher. The current transformer has a transformation ratio of 5 / 1, and the voltage transformer has a transformation ratio of 25 / 1 (since this example uses a high-frequency tube oscillator, which is a high-voltage, low-current system, the appropriate transformation ratio should be selected according to the actual circuit parameters in practical use). The output parameters of both sensors are adjusted to 3-10V through a resistor divider. To eliminate the influence of ordinary resistors on the signal phase, the voltage divider resistors and the matching network resistors are both 2W-3W non-inductive resistors. The connection from the sensor to the control device uses a 50-ohm coaxial cable. Figure 2 The parameters of the matching resistor network shown indicate that the power attenuation from the transformer output to the phase detector input is approximately 10 dB.

[0028] The core component of the phase detector is Analog Devices' AD8302 ( Figure 2 The current transformer (U3) has both amplitude and phase detection functions. Only the phase detection function is used here. The phase detection range is 0-180°, and the upper limit of the detection frequency is 2.7GHz. It is suitable for systems with a characteristic impedance of 50Ω. The two signals extracted from the transformer (voltage SUout, current SAou) are connected to the two input terminals of the AD8302. C301 and C303 are coupling capacitors. A phase-shifting circuit is connected in series between the current signal and the AD8302 (the function of the phase-shifting circuit will be described later).

[0029] Since the phase difference output by the AD8302 is an absolute value, it cannot reflect the true nature of voltage and current phase lead or lag. Therefore, a phase-shifting circuit is connected in series between the current signal and the AD8302, which is composed of an operational amplifier LM308. Figure 2 (U10) and analog switch 74LVC2G55 ( Figure 2The circuit consists of LM308 (U9), resistors R1001, R1002, R1003, and capacitor C901, forming a hysteresis phase-shifting circuit. This means the output signal's phase lags behind the input phase, with the hysteresis depending on the values ​​of R1001 and C901. C901 is connected to the phase-shifting circuit via an analog switch 74LVC2G55. Under the control of the MPU, when C901 is connected, the LM308 output produces a certain phase shift; when C901 is disconnected, the LM308 output does not produce a phase shift. In actual phase measurement, the control unit performs a first measurement with C901 disconnected, obtaining a phase difference Δ1 between voltage and current. Then, a second measurement is performed with C901 connected, obtaining a phase difference Δ2. Because Δ2 is the measurement result under artificially increased current hysteresis, if Δ2 > Δ1, it indicates that Δ1 also shows the current phase lags behind the voltage; conversely, if Δ2 < Δ1, it indicates that Δ1 shows the current phase leads the voltage. Based on this result, the MPU of the control unit can determine whether the impedance characteristics of the load circuit are inductive, capacitive, or resistive, and thus obtain the adjustment strategy that should be adopted for the variable capacitor to make the load circuit closer to the resonant point.

[0030] The phase difference signal output by the phase detector AD8302 is 0-1.8V, which is then passed through the precision operational amplifier LM308 ( Figure 2 The voltage is multiplied to 0-3.6V by U4, and then passed through the 10-bit A / D converter chip TLC1549. Figure 2 After being converted into a digital value, the U5 signal is input to the control unit MPU. Figure 2 (China U1).

[0031] The control unit MPU is selected as AT89C2051 ( Figure 2 The U1 chip is equipped with an external MAX813L automatic reset chip. Figure 2 U2) and crystal oscillator circuit ( Figure 2 Y1). Its automatic adjustment process is as follows: the phase difference signal output by the phase difference detector is read periodically through the A / D conversion chip U5, and the characteristics (sign) of the phase difference detection result are judged by the phase shifting circuit to determine the adjustment direction of the variable capacitor. Then, the angle that the variable capacitor needs to change is calculated through scaling transformation, and then the motor driver THB7128 ( Figure 2 The stepper motor (U6) rotates in a predetermined direction by a corresponding angle, thus completing one adjustment operation.

[0032] The motor driver uses THB7128 ( Figure 2The THB7128 is a two-phase hybrid stepping motor driver chip with built-in subdivision circuit, temperature and over-current protection, simple peripheral circuit and convenient operation, which only needs three signals of clock pulse, direction control and start / stop control. In order to operate reliably, the clock pulse signal is output from the MPU to the THB7128 through the photoelectric coupling chip TLP521-1 (U7). Under the condition of 24V power supply, the motor winding current is set to 0.6A through resistors R601-R604.

[0033] Although the utility model has been described in detail above with general description, specific implementation and test, some modifications or improvements can be made on the basis of the utility model, which is obvious to those skilled in the art. Therefore, these modifications or improvements made on the basis of not deviating from the spirit of the utility model all belong to the scope of protection required by the utility model.

Claims

1. An ICP light source power automatic adjusting device, characterized in that, The application relates to a high-frequency resonant power supply device, which comprises a voltage transformer, a current transformer, a phase detector, a control unit and a motor driver. The voltage transformer and the current transformer are connected between a high-frequency oscillator and a load circuit, and are used for providing signal output of high-frequency voltage and current. The phase detector detects voltage and current phase difference data in high-frequency energy input by the load circuit through signals output by the voltage transformer and the current transformer. The control unit calculates the rotation angle of the variable capacitor required for changing the capacity for the load circuit resonance according to the phase difference data, and further calculates the walking step number of the stepping motor; the rotation direction of the stepping motor is determined according to the sign of the voltage and current phase difference. The motor driver drives the stepping motor to drive the variable capacitor to rotate through a corresponding angle in a predetermined direction, so that the resonance point of the load circuit to the high-frequency oscillator output is closer.

2. The ICP light source power automatic adjustment device according to claim 1, wherein, The phase detector is composed of a phase detection chip and a phase shift circuit.

Images