A TCD constant temperature driving circuit

Abstract

The utility model discloses a TCD constant temperature driving circuit, which relates to the field of electronic technology, and comprises: a driving Q1 and a load, wherein the driving Q1 is an N-type MOSFET, adopts a high-end driving, one end of the N-type MOSFET is connected to a power supply VCC, and the other end is connected to the load, and the load is connected to a GND ground, the load is composed of a resistor R1, a resistor R2, a resistor R3 and a switch K1, the resistance values ​​of the resistors R5, R6, R7 and R8 are much larger than those of the resistors R1, R2 and R3, and the load is mainly composed of the resistors R1, R2, R3 and the switch K1, wherein the resistor R3 is a thermal resistance wire of a TCD detector, and the thermal resistance wire is positively correlated with the temperature. Under normal circumstances, when there is no control signal, the MOSFET is not turned on, and no current flows through the load, that is, the load is in a power-off state; on the contrary, if the control signal is valid, the MOSFET is turned on, so that the current flows from the positive end of the power supply through the high-end MOSFET and then flows out through the load, and the load enters a power-on state, thereby generating a response action.

Description

Technical Field

[0001] The utility model relates to the technical field of electronic products, in particular to a TCD constant temperature driving circuit. Background Art

[0002] Thermal conductivity detector (TCD) is a detector commonly used in gas chromatographs. Its working principle is based on the difference in thermal conductivity between the heat conductor and the gas. In the reference state, the heat conductor passes through the reference gas and maintains a stable temperature. When the sample gas enters, the temperature of the heat conductor changes. This change is measured by the sensor and forms a current signal proportional to the concentration of various components in the sample gas. Subsequently, the system returns to the reference state. TCD is a sensitive, stable and reliable gas detection method, especially suitable for the analysis of light gases.

[0003] The detection circuit of TCD includes a heat conductor, a current source, a sensor, a differential amplifier, an amplifier and a filter, and a data processing unit. The heat conductor is heated by the current source, the sensor measures its temperature change, and generates a voltage signal reflecting the concentration of the sample gas component through the differential amplifier. The signal may be amplified and filtered, and then interpreted by the data processing unit, and finally outputs the concentration information of each component in the sample gas. These components work together to enable the TCD system to analyze gas samples efficiently and accurately. The TCD detection circuits of different manufacturers may have slight differences, but the overall principles are similar.

[0004] Generally speaking, the commonly used TCD detection circuit scheme is a constant current circuit. The constant current TCD detection circuit is a circuit designed to maintain a stable temperature of the thermal conductor. In the constant current TCD detection circuit, first, the current source provides a stable current to generate constant heating through the thermal conductor. The thermal conductor is placed in the channel where the sample gas flows. When the sample gas flows through the thermal conductor, different gas components cause changes in the temperature of the thermal conductor, and this change is detected by the sensor. The temperature change of the thermal conductor measured by the sensor is amplified by a differential amplifier. The differential amplifier compares the thermal conductor with a reference temperature signal to generate a voltage signal related to the concentration of various components in the sample gas. This voltage signal is further amplified and processed, and finally used to output the result or further data analysis.

[0005] In general, the key to the constant current TCD detection circuit is to maintain a stable temperature of the heat conductor so that the thermal conductivity changes of each component in the sample gas can be accurately measured. This design makes TCD perform well in gas analysis and is particularly suitable for application scenarios that require high sensitivity and accuracy.

[0006] The constant current TCD circuit method has some disadvantages. First, it has high requirements on the stability of the current source. If the current source is unstable, it may cause uneven heating of the thermal conductor, thus affecting the measurement accuracy. Second, the constant current circuit may have nonlinear effects when dealing with changes in the resistance of the thermal conductor, which may lead to unpredictable temperature changes, especially in high-sensitivity and low-concentration gas analysis. In addition, the constant current TCD circuit is usually relatively complex, requiring a high-precision current source and a control system with strong stability, so the cost is relatively high. Finally, in some cases, the constant current TCD may have limitations on the concentration range of the gas components in the sample, especially in low-concentration analysis, it may not be as good as other detection circuits.

[0007] Therefore, we propose a TCD constant temperature driving circuit to solve the above problems. Utility Model Content

[0008] 1. Technical issues to be solved

[0009] In view of the deficiencies in the prior art, the utility model provides a TCD constant temperature driving circuit to solve the technical problems of the constant current TCD detection circuit.

[0010] (II) Technical solution

[0011] In order to achieve the above objectives, the present invention is implemented through the following technical solutions:

[0012] A TCD constant temperature driving circuit, the circuit analyzes the gas components in the sample based on the difference in thermal conductivity between the heat conductor and the gas, comprising: a driving Q1 and a load,

[0013] The essence of the TCD constant temperature circuit is to control the constant resistance of the thermal resistor. The driver Q1 is an N-type MOSFET (metal-oxide semiconductor field effect transistor), which uses a high-end driver. The advantages of the N-type MOSFET are that the driver uses voltage drive, the drive current is very small, the drive power consumption is low, and the operating frequency can be very high, which is suitable for high-speed control. In addition, the on-resistance of the MOSFET is very low at the milliohm level, and the stable current that can pass through is very large, so it is suitable for high-power drive.

[0014] One end of the N-type MOSFET is connected to the power supply VCC, and the other end is connected to the load, which is then connected to the GND ground. Under normal circumstances, when there is no control signal, the MOSFET is not turned on, and no current flows through the load, that is, the load is in a power-off state; on the contrary, if the control signal is valid, the MOSFET is turned on, so the current flows from the positive end of the power supply through the high-end MOSFET, and then flows out through the load, and the load enters the power-on state, thereby generating a response action.

[0015] The load is composed of resistors R1, R2, R3 and switch K1. The resistance values ​​of resistors R5, R6, R7 and R8 are much larger than those of resistors R1, R2 and R3. The current flowing through these four resistors is very small and can be ignored. The load is mainly composed of resistors R1, R2, R3 and switch K1. Resistor R3 is the thermal resistance wire of the TCD detector. The thermal resistance wire is highly sensitive to temperature and is positively correlated with temperature. The higher the temperature, the greater the resistance value.

[0016] Preferably, when the switch K1 is disconnected, one end of the resistor R1 is connected to one end of the driver Q1 , the other end of the resistor R1 is connected to one end of the resistor R3 , and the other end of the resistor R3 is connected to the ground.

[0017] Preferably, the resistor R1 and the resistor R2 form a voltage divider circuit, the voltage at the connection point between the driver Q1 and the resistor R1 is V1, the voltage at the connection point between the resistor R1 and the resistor R3 is V2, and V2 and V1 are in a certain ratio.

[0018] Preferably, one end of the resistor R4 is connected to the connection point of the resistor R3 and the resistor R1, and the other end of the resistor R4 is connected to the inverting end of U1, and V2 is connected to the reverse end of the operational amplifier U1 through the resistor R4.

[0019] Preferably, the voltage V1 is divided by resistors R5 and R6 at the same time, one end of the resistor R5 is connected to the connection point between the driver Q1 and the resistor R1, and the other end is connected to one end of the resistor R6, and the other end of the resistor R6 is connected to the ground.

[0020] Preferably, the resistor R5 and the resistor R6 divide the voltage of V1, and a voltage V3 is formed at the connection point of the resistor R5 and the resistor R6, and V3 and V1 form a certain ratio.

[0021] Preferably, V3 is then connected to the positive terminal of U1, and the output terminal of U1 is then connected to the control terminal of the driver Q1.

[0022] Preferably, when the circuit just starts working, V2 and V3 enter the operational amplifier for comparison and produce a certain difference, the operational amplifier will output a corresponding voltage, control the driver Q1 to turn on, and current will flow through the resistors R1 and R3. Because the resistor R3 is relatively sensitive to temperature, when current flows through it, the resistance of the resistor R3 will increase, and V2 will also increase accordingly, and eventually V2 and V3 will be equal, thereby achieving constant temperature.

[0023] Preferably, the above is the state when the switch K1 is disconnected. When the switch K1 is closed, the resistor R2 is connected in parallel with the resistor R1, reducing the voltage divider resistance of the resistor R3, so that the circuit can work in both high temperature and low temperature states.

[0024] Preferably, the voltage division of resistors R7 and R8 is used to collect differential signals to obtain voltage information, so as to facilitate inverse calculation of the gas concentration detected by the TCD detector.

[0025] (III) Beneficial effects

[0026] The constant temperature TCD circuit has several significant advantages over the constant current circuit. First, the constant temperature TCD achieves stability by maintaining the temperature of the thermal conductor unchanged, reducing the need for a high-precision current source and alleviating the complexity of the circuit, which helps to improve the reliability of the system, especially helping to stabilize the instrument performance during long-term measurements; second, since there is no need to frequently adjust the current of the thermal conductor, the constant temperature TCD is easier to achieve automated control, improving the instrument's ease of use and operating efficiency; in addition, compared to the constant current TCD, the constant temperature TCD is suitable for a wider range of gas concentrations, making it more flexible and versatile in a variety of application scenarios. Overall, the constant temperature TCD has become a reliable and flexible detection solution in gas analysis through its stability, simplified circuit structure, and suitability for a wide range of gas concentrations. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The above description is only an overview of the technical solution of the utility model. In order to more clearly understand the technical means of the utility model and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the utility model in conjunction with the accompanying drawings.

[0028] Figure 1 The utility model is a circuit diagram of a TCD constant temperature driving circuit. DETAILED DESCRIPTION

[0029] The embodiment of the present application solves the problems of constant current TCD in the prior art by providing a TCD constant temperature drive circuit. The constant temperature TCD achieves stability by maintaining the temperature of the heat conductor unchanged, reduces the demand for high-precision current source, and reduces the complexity of the circuit, which helps to improve the reliability of the system, especially helps to stabilize the performance of the instrument during long-term measurements.

[0030] Example 1

[0031] The technical solution in the embodiment of the present application is to solve the above-mentioned problem of constant current TCD, and the overall idea is as follows:

[0032] In view of the problems existing in the prior art, the utility model provides a TCD constant temperature driving circuit, which analyzes the gas components in the sample based on the difference in thermal conductivity between the heat conductor and the gas, and includes: driving Q1 and the load,

[0033] like Figure 1 As shown, the essence of the TCD constant temperature circuit is to control the constant resistance value of the thermal resistance wire. Figure 1 The middle driver Q1 is an N-type MOSFET (metal-oxide semiconductor field effect transistor), which adopts high-end drive. The advantages of N-type MOSFET are that it adopts voltage drive, small drive current, low drive power consumption, and high operating frequency, which is suitable for high-speed control. In addition, the on-resistance of MOSFET is very low at the milliohm level, and the stable current that can pass through is very large, so it is suitable for high-power drive.

[0034] The principle of high-end switch drive: one end of the N-type MOSFET is connected to the power supply VCC, and the other end is connected to the load, and the load is connected to the GND ground. Under normal circumstances, when there is no control signal, the MOSFET is not turned on, and no current flows through the load, that is, the load is in a power-off state; on the contrary, if the control signal is valid, the MOSFET is turned on, so the current flows from the positive end of the power supply through the high-end MOSFET, and then flows out through the load, and the load enters the power-on state, thereby generating a response action.

[0035] like Figure 1 As shown, the load is composed of resistors R1, R2, R3 and switch K1. The resistance values ​​of resistors R5, R6, R7 and R8 are much larger than those of resistors R1, R2 and R3. The current flowing through these four resistors is very small and can be ignored. The load is mainly composed of resistors R1, R2, R3 and switch K1. Resistor R3 is the thermal resistance wire of the TCD detector. The thermal resistance wire is highly sensitive to temperature and is positively correlated with temperature. The higher the temperature, the greater the resistance value.

[0036] When the switch K1 is turned off, one end of the resistor R1 is connected to one end of the driver Q1 , the other end of the resistor R1 is connected to one end of the resistor R3 , and the other end of the resistor R3 is connected to the ground.

[0037] Resistors R1 and R2 form a voltage divider circuit. The voltage at the connection point between driver Q1 and resistor R1 is V1, and the voltage at the connection point between resistor R1 and resistor R3 is V2. V2 and V1 are in a certain ratio.

[0038] One end of the resistor R4 is connected to the connection point of the resistor R3 and the resistor R1 , and the other end of the resistor R4 is connected to the inverting end of U1 .

[0039] V2 is connected to the inverting terminal of the operational amplifier U1 through the resistor R4.

[0040] The voltage V1 is divided by resistors R5 and R6 at the same time. One end of the resistor R5 is connected to the connection point between the driver Q1 and the resistor R1, and the other end is connected to one end of the resistor R6. The other end of the resistor R6 is connected to the ground.

[0041] The resistor R5 and the resistor R6 divide the voltage V1, and a voltage V3 is formed at the connection point of the resistor R5 and the resistor R6, and V3 and V1 form a certain ratio.

[0042] Then connect V3 to the positive terminal of U1, and then connect the output of U1 to the control terminal of driver Q1.

[0043] When the circuit just starts working, V2 and V3 will enter the operational amplifier for comparison and produce a certain difference. The operational amplifier will output a corresponding voltage, control the driver Q1 to turn on, and current will flow through resistors R1 and R3. Because resistor R3 is relatively sensitive to temperature, when current flows through it, the resistance of resistor R3 will increase, and V2 will also increase accordingly, eventually reaching a state where V2 and V3 are equal, thus achieving constant temperature.

[0044] The above is the state when switch K1 is disconnected. When switch K1 is closed, resistor R2 is connected in parallel with resistor R1, reducing the voltage divider resistance of resistor R3, so that the circuit can work in high temperature and low temperature states. The voltage divider of resistor R7 and resistor R8 is used to collect differential signals to obtain voltage information, which is convenient for inverse calculation of gas concentration detected by TCD detector.

[0045] The constant current TCD detection circuit has the following three advantages:

[0046] 1. When the gas to be tested enters the TCD, the composition of the purge gas changes, and the gas's ability to carry away heat changes. At this time, the current of the drive circuit will also change accordingly, which is used to ensure the stability of the resistance of the hot wire resistor R3. The opening of the drive Q1 changes, and the current through the resistor R3 and the voltage value of point V1 will also change. By detecting the voltage change value of V1, the concentration of the gas to be tested can be inverted.

[0047] 2. The constant temperature TCD driving circuit essentially controls the resistance of the hot wire to be constant. When there is no purge gas, the temperature of the hot wire will rise and the resistance of the hot wire will increase. At this time, due to the effect of negative feedback, the driving current will decrease, and the resistance of the hot wire will return to its original value, that is, the temperature of the hot wire will also return to its original value, and the temperature will remain unchanged. Therefore, even if there is no purge gas, the temperature of the hot wire can be maintained, so the hot wire will not burn out.

[0048] 3. The opening and closing of switch K1 can control TCD to work in high temperature and low temperature modes. When switch K1 is closed, resistor R2 will be connected in parallel at both ends of resistor R1, and the equivalent resistance will decrease. After stabilization, the resistance value of the hot wire resistor R3 will increase. As the resistance R3 increases, the temperature will also increase accordingly, so TCD can work in high temperature mode. When switch K1 is opened, the equivalent resistance value decreases, and the corresponding current flowing through resistor R3 will decrease, and the temperature of resistor R3 will decrease, so the TCD detector can work in the low temperature area.

[0049] Finally, it should be noted that: Obviously, the above embodiments are only examples for clearly explaining the present invention, and are not intended to limit the implementation methods. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the scope of protection of the present invention.

Claims

1. A TCD constant temperature driving circuit, which analyzes the gas composition in the sample based on the difference in thermal conductivity between the heat conductor and the gas, and essentially controls the constant resistance of the thermal resistance wire, including: driving Q1 and the load, Driver Q1 is an N-type MOSFET, which uses high-end drive. One end of the N-type MOSFET is connected to the power supply VCC, and the other end is connected to the load, which is then connected to GND. The load is composed of resistors R1, R2, R3 and switch K1. The resistance values ​​of resistors R5, R6, R7 and R8 are much larger than those of resistors R1, R2 and R3. The load is mainly composed of resistors R1, R2, R3 and switch K1. Resistor R3 is the thermal resistance wire of the TCD detector, which is positively correlated with the temperature. Under normal circumstances, when there is no control signal, the MOSFET is not turned on and no current flows through the load, that is, the load is in a power-off state; on the contrary, if the control signal is valid, the MOSFET is turned on, so the current flows from the positive end of the power supply through the high-end MOSFET, and then flows out through the load, and the load enters the power-on state, thereby generating a response action.

2. A TCD constant temperature driving circuit as claimed in claim 1, characterized in that: When the switch K1 is turned off, one end of the resistor R1 is connected to one end of the driver Q1 , the other end of the resistor R1 is connected to one end of the resistor R3 , and the other end of the resistor R3 is connected to the ground.

3. A TCD constant temperature driving circuit as claimed in claim 2, characterized in that: Resistors R1 and R2 form a voltage divider circuit. The voltage at the connection point between driving Q1 and resistor R1 is V1, and the voltage at the connection point between resistors R1 and R3 is V2. V2 is proportional to V1.

4. A TCD constant temperature driving circuit as claimed in claim 3, characterized in that: One end of the resistor R4 is connected to the connection point of the resistor R3 and the resistor R1, and the other end of the resistor R4 is connected to the inverting end of U1. V2 is connected to the reverse end of the operational amplifier U1 through the resistor R4.

5. A TCD constant temperature driving circuit as claimed in claim 4, characterized in that: The voltage of V1 is divided by resistors R5 and R6 at the same time. One end of resistor R5 is connected to the connection between driver Q1 and resistor R1, and the other end is connected to one end of resistor R6. The other end of resistor R6 is connected to the ground. Resistors R5 and R6 divide the voltage of V1 to form a voltage V3 at the connection between resistors R5 and R6. V3 and V1 form a certain ratio, and then V3 is connected to the positive end of U1, and then the output end of U1 is connected to the control end of driver Q1.

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