Split type circuit module structure of two-wire system anti-explosion water quality monitor

Abstract

The invention discloses a split type circuit module structure of a two-wire system anti-explosion water quality monitor. The split type circuit module structure comprises a 4-20mA output control circuit module integrating a two-wire system 4-20mA output circuit and a power supply circuit, and an external acquisition circuit module used for performing analog acquisition through an MCU and outputting PWM signals for controlling the 4-20mA output circuit through the MCU, the 4-20mA output control circuit module comprises a first connector used for being connected with an external acquisition circuit module, and the external acquisition circuit module comprises a second connector used for being connected with the 4-20mA output control circuit module. And the 4-20mA output control circuit module is connected with the external acquisition circuit module by connecting the first connector and the second connector. Production and assembly are easy, the working efficiency is improved, maintenance is easy, and cost is saved.

Description

Technical Field

[0001] The invention belongs to the technical field of water quality monitors, and in particular relates to a split circuit module structure of a two-wire explosion-proof water quality monitor. Background Art

[0002] Explosion-proof instruments are electric instruments that can be used safely in environments with explosive mixtures. Certain safety technical measures are taken during the design and manufacture of such instruments, which can ensure safe power supply, power consumption, detection and control in places with explosion hazards such as petroleum and chemical industries. Generally, electric instruments may produce sparks, arcs, hot surfaces and burning particles in normal operation or accident conditions, and have a certain amount of energy, becoming a source of fire for igniting flammable gas mixtures in explosive environments. The explosion of explosive gas mixtures must have two conditions: a certain gas concentration and sufficient spark energy. The safety measures taken in electrical equipment are nothing more than making these two conditions not exist at the same time. The sparks and temperatures generated by intrinsically safe circuits in normal and fault conditions will not cause the explosion of explosive gas mixtures. The normal state refers to the working state of electrical equipment under the conditions specified in the design, including normal opening and closing of circuits. The fault state refers to situations such as short circuits, open circuits, grounding and power failures caused by accidents. Modern intrinsically safe explosion-proof refers to the explosion-proof of the entire automation system, such as the DDZ-Ⅲ electric unit combination instrument. The explosion-proof system contains two types of circuits: intrinsically safe and non-intrinsically safe. Intrinsically safe circuits are installed in hazardous places (on-site), and non-intrinsically safe circuits are installed in non-hazardous places (control rooms). An explosion-proof safety barrier is used between the two to prevent excessive energy from entering hazardous places. Two-wire instruments are low-power instruments that can be used in corresponding hazardous places after meeting the corresponding national explosion-proof certification standards and obtaining a certificate. General two-wire explosion-proof instruments are designed with hardware separately. The standby current of the instrument is fixed when it is in standby mode and cannot be adjusted by software. The modularity of the instrument is relatively low. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a two-wire explosion-proof water quality monitor split circuit module structure in view of the deficiencies in the above-mentioned prior art, which is simple to produce and assemble, improves work efficiency, is simple to maintain and saves costs.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a two-wire explosion-proof water quality monitor split circuit module structure, including a 4-20mA output control circuit module integrating a two-wire 4-20mA output circuit and a power supply circuit, and an external acquisition circuit module for analog acquisition through an MCU and for controlling the PWM signal of the 4-20mA output circuit through the MCU output; the 4-20mA output control circuit module includes a first connector for connecting the external acquisition circuit module, the external acquisition circuit module includes a second connector for connecting the 4-20mA output control circuit module, and the 4-20mA output control circuit module is connected to the external acquisition circuit module by connecting the first connector and the second connector.

[0005] The above-mentioned two-wire explosion-proof water quality monitor split circuit module structure, the power supply circuit includes a DCDC step-down circuit module connected to the output end of the 24V power supply through a power protection circuit and an isolated DCDC circuit module connected to the DCDC step-down circuit module.

[0006] The above-mentioned two-wire explosion-proof water quality monitor split circuit module structure, the power protection circuit includes a diode D1, a capacitor C1 and a resistor R1, the anode of the diode D1 is connected to the output end of the 24V power supply, the resistor R1 is connected between the cathode of the diode D1 and the DCDC step-down circuit module U1, and the connection end between the cathode of the diode D1 and the DCDC step-down circuit module U1 is grounded through the capacitor C1.

[0007] The above-mentioned two-wire explosion-proof water quality monitor split circuit module structure, the two-wire 4-20mA output circuit includes a photoelectric isolation chip U4, a logic controller and gate U5, an operational amplifier U6, an operational amplifier U7 and a P-type transistor Q1, the first pin of the photoelectric isolation chip U4 is connected to the PWM signal output end of the MCU in the external acquisition circuit module through a resistor R2, the second pin of the photoelectric isolation chip U4 is grounded, the third pin of the photoelectric isolation chip U4 is grounded through a resistor R4, and the fourth pin of the photoelectric isolation chip U4 is connected to the output end of the DCDC step-down circuit module; the first pin of the logic controller and gate U5 is connected to the output end of the DCDC step-down circuit module through a resistor R5, and is grounded through a capacitor C2; the second pin of the logic controller and gate U5 is connected to the third pin of the photoelectric isolation chip U4, the logic controller The third pin of the logic controller and gate U5 is grounded, the fifth pin of the logic controller and gate U5 is connected to the non-inverting input terminal of the operational amplifier U6 through a resistor R5, the connection end of the resistor R5 and the non-inverting input terminal of the operational amplifier U6 is grounded through a capacitor C3, the inverting input terminal of the operational amplifier U6 is connected to the output terminal and then connected to the non-inverting input terminal of the operational amplifier U7 through a resistor R6, the connection end of the resistor R6 and the non-inverting input terminal of the operational amplifier U7 is grounded through a resistor R7, the inverting input terminal of the operational amplifier U7 is grounded, the output terminal of the operational amplifier U7 is connected to the gate of the P-type transistor Q1, the drain of the P-type transistor Q1 is connected to the cathode of the diode D1 through a resistor R9, the source of the P-type transistor Q1 is grounded through a series-connected resistor R10 and a resistor R8, and the inverting input terminal of the operational amplifier U7 is connected to the connection end of the resistor R10 and the resistor R8.

[0008] In the above-mentioned two-wire explosion-proof water quality monitor split circuit module structure, the analog acquisition includes one or more of PH analog acquisition, DO analog acquisition and conductivity analog acquisition.

[0009] Compared with the prior art, the present invention has the following advantages:

[0010] 1. The circuit design of the present invention is divided into two parts, one part is the 4-20mA output control circuit module, and the other part is the external acquisition circuit module, which is used to control the power consumption flowing through the power supply through PWM, that is, the 4-20mA output current, which can effectively improve the 4-20mA output accuracy of the equipment, and at the same time can be modularly designed. The external acquisition module and the 4-20mA output control only need two plug-ins, U3 and U8, to connect to complete the power supply of the external acquisition module and provide the control signal of the 4-20mA output control, which is easy to use and operate.

[0011] 2. The present invention can control the standby power consumption of the instrument by adjusting the PWM signal output, and make a two-wire explosion-proof instrument with different parameters, which increases the commonality of the module, simplifies assembly, and reduces costs. At the same time, when the on-site equipment fails, it is simple to replace and save costs.

[0012] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a circuit principle block diagram of the present invention;

[0014] Figure 2 This is a circuit schematic diagram of a 4-20mA output control circuit module of the present invention;

[0015] Figure 3 This is a circuit schematic diagram of the external acquisition circuit module of the present invention. DETAILED DESCRIPTION

[0016] like Figure 1 As shown, the split circuit module structure of the two-wire explosion-proof water quality monitor of the present invention includes a 4-20mA output control circuit module integrating a two-wire 4-20mA output circuit and a power supply circuit, and an external acquisition circuit module for performing analog acquisition through an MCU and outputting a PWM signal to control the 4-20mA output circuit through the MCU; the 4-20mA output control circuit module includes a first connector for connecting to the external acquisition circuit module, the external acquisition circuit module includes a second connector for connecting to the 4-20mA output control circuit module, and the 4-20mA output control circuit module is connected to the external acquisition circuit module by connecting the first connector and the second connector.

[0017] In this embodiment, the power supply circuit includes a DCDC step-down circuit module connected to the output end of the 24V power supply through a power supply protection circuit and an isolation DCDC circuit module connected to the DCDC step-down circuit module.

[0018] like Figure 2 As shown, Figure 2In the figure, VCC_24V represents the output end of the 24V power supply, and VCC_24V and GND0 serve as the power supply interface of the split circuit module structure of the two-wire explosion-proof water quality monitor; the DCDC step-down circuit module is the DCDC step-down circuit module U1, and the isolated DCDC circuit module is the isolated DCDC circuit module U2. The power supply of the external acquisition circuit module is stepped down to VCC by the DCDC step-down circuit module U1. Since it is a water quality monitor, the water quality sensor needs to be placed in water. The water quality sensor is very susceptible to interference from the AC220V power supply 50Hz, so an isolated power supply U2 is required for the power supply. VCC isolates DCDC through the isolated DCDC circuit module U2 to generate an isolated power supply VCC1, and the external acquisition circuit module is powered by connectors U3 and U8.

[0019] In this embodiment, the power protection circuit includes a diode D1, a capacitor C1 and a resistor R1. The anode of the diode D1 is connected to the output end of the 24V power supply, the resistor R1 is connected between the cathode of the diode D1 and the DCDC step-down circuit module U1, and the connection end between the cathode of the diode D1 and the DCDC step-down circuit module U1 is grounded through the capacitor C1.

[0020] Among them, diode D1 can prevent the reverse connection of the power supply from damaging the equipment, capacitor C1 is used to filter the power supply to ensure the stability of the power supply; resistor R1 is used as a current limiting resistor to protect the circuit from overcurrent and burning.

[0021] In this embodiment, the two-wire 4-20mA output circuit includes a photoelectric isolation chip U4, a logic controller and gate U5, an operational amplifier U6, an operational amplifier U7 and a P-type transistor Q1. The first pin of the photoelectric isolation chip U4 is connected to the PWM signal output end of the MCU in the external acquisition circuit module through a resistor R2, the second pin of the photoelectric isolation chip U4 is grounded, the third pin of the photoelectric isolation chip U4 is grounded through a resistor R4, and the fourth pin of the photoelectric isolation chip U4 is connected to the output end VCC of the DCDC buck circuit module; the PWM of the MCU controls the on-off of the photoelectric sensing side of the 3rd and 4th pins of the photoelectric isolation chip U4 by connecting the resistor R2 and the photoelectric isolation chip U4; the first pin of the logic controller and gate U5 is connected to the output end VCC of the DCDC buck circuit module through the resistor R5, and is grounded through the capacitor C2; the second pin of the logic controller and gate U5 is connected to the photoelectric isolation The third pin of the off-chip U4 is connected, the third pin of the logic controller and the gate U5 is grounded, the fifth pin of the logic controller and the gate U5 is connected to the non-inverting input terminal of the operational amplifier U6 through the resistor R5, the connection end of the resistor R5 and the non-inverting input terminal of the operational amplifier U6 is grounded through the capacitor C3, the inverting input terminal of the operational amplifier U6 is connected to the non-inverting input terminal of the operational amplifier U7 through the resistor R6 after the inverting input terminal is connected to the output terminal, the connection end of the resistor R6 and the non-inverting input terminal of the operational amplifier U7 is grounded through the resistor R7, the inverting input terminal of the operational amplifier U7 is grounded, the output terminal of the operational amplifier U7 is connected to the gate of the P-type transistor Q1, the drain of the P-type transistor Q1 is connected to the cathode of the diode D1 through the resistor R9, the source of the P-type transistor Q1 is grounded through the series-connected resistors R10 and R8, and the inverting input terminal of the operational amplifier U7 is connected to the connection end of the resistor R10 and R8.

[0022] Specifically, the first pin of the logic controller and gate U5 is its input interface A, and the second pin of the logic controller and gate U5 is its input interface B. A is connected to the pull-up resistor R3, and the capacitor C2 is used as a voltage-stabilizing capacitor, that is, the logic input signal of A is always "1". The input end of B is controlled by the on and off of the photoelectric sensing side of the photoelectric isolation chip U4. When the PWM signal is at a high level, VCC is turned on to the resistor R4, that is, the input interface of the B end is at a high level. When the PWM signal is at a low level, the photoelectric sensing side of the photoelectric isolation chip U4 is cut off, and R4 is connected to GND at a low level. The logic input "0" will appear as follows Figure 2The marked duty cycle is the same as the control signal, with an amplitude of a pulse waveform between 0V and VCC. Assume that the duty cycle of the high level of PWM is D, that is, the duty cycle of the level signal output by the logic controller and gate U5 is also D. The 4th pin of the optoelectronic isolation chip U4 is the output pin Y. The output pin Y of the optoelectronic isolation chip U4 is connected to the resistor R5 and the capacitor C3. The resistor R5 and the capacitor C3 form an RC filter circuit, and finally filter the pulse signal into a DC waveform with an amplitude of D*VCC, so as to ensure that the 4-20mA output is a stable signal without current fluctuations. After filtering is completed, operational amplifier U6 is connected. Operational amplifier U6 isolates the front filtering circuit from the rear current amplification circuit. The inverting input and output of operational amplifier U6 are connected together as a voltage follower, and the output voltage of the output end is D*VCC. Then resistor R1, resistor R7 and operational amplifier U7 are connected. According to the feedback characteristics of the operational amplifier "+" and "-" virtual short and virtual open characteristics, the levels of the inverting input and inverting input of operational amplifier U7 are equal. Because the inverting input of operational amplifier U7 is connected to GND, that is, the level of the inverting input of operational amplifier U7 is also GND, then the current flowing through resistor R6 is I1=D*VCC / R6. The output pin 1 of operational amplifier U7 is connected to P-type transistor Q1, and then connected to resistor R10, and finally grounded GND, which is used to control the opening and closing degree of the channel of P-type transistor Q1 to ensure the stability of output current I2. Since the internal impedance of the inverting input of operational amplifier U7 is very large, I The current of 1 flowing through the in-phase input terminal of U7 is almost 0, that is, the current all flows to R7 and finally flows to GND0; R8 connects GND and R10, and the current flowing through R8 is I2=(GND-GND0) / R8. Since the voltage across R7 is equal to the voltage across R8, that is, the ratio of the current between the two is inversely proportional to R8 / R7, this is actually a current amplifier circuit. The current of the entire power supply flows through VCC_24 through GND and finally flows to GND0. In the circuit, it finally flows to GND0 through the two branches of R7 and R8, that is, the sum of I1+I2 is the 4-20mA output current I, and its calculation formula is I=(D*VCC / R6)*(1+R7 / R8); when setting the standby current, you only need to adjust the duty cycle D to ensure that the current I is less than 4mA and try to keep a relatively large range, so that the output accuracy of the current can be better guaranteed.

[0023] The present invention has made a hardware circuit design in which the standby current can be adjusted by PWM in the design of the 4-20mA output control circuit module, so that the analog acquisition part of the external acquisition circuit module can be made into an acquisition circuit of different analog signals, and only different standby currents need to be set by PWM control for different acquisition signals to meet the detection requirements of various detection parameters. The smaller the standby power consumption, the greater the proportion of 4-20mA output compensation by PWM, and the more accurate the output. In particular, in the numerical value corresponding to the detection parameter corresponding to the 4mA output, if the standby power consumption is too large, due to the small compensation ratio, the resolution of the MCU clock is limited, which leads to inaccurate PWM output compensation, and finally leads to inaccurate output current. The standby current of the device can be set by software to set the output frequency and duty cycle of PWM to greatly improve the 4-20mA output accuracy of the device, and modular design can be made at the same time, and the 4-20mA output control circuit module and the external acquisition circuit module can be made into two assembled split modules.

[0024] In this embodiment, the simulation acquisition includes one or more of pH simulation acquisition, DO simulation acquisition and conductivity simulation acquisition.

[0025] In specific implementation, since the external acquisition circuit module and the sensor probe can be put together through a mechanical shell, the PWM of the MCU on the external acquisition circuit module is used as a 4-20mA output control and also as a standby control signal of the water quality monitor. The analog acquisition part can be designed according to actual conditions, and the standby current only needs to be set according to the power consumption of each monitor for normal operation.

[0026] The principle of the two-wire transmitter is to use the 4-20mA signal to provide itself with power. If the detector's own power consumption is greater than 4mA, it will not be possible to output the lower limit 4mA value. Therefore, it is generally required that the power consumption of the two-wire monitor itself (including all circuits including the sensor) is not greater than 4mA. The standby power consumption refers to the power consumption of the two-wire monitor itself. Due to the different power consumption of different acquisition parameters, for example, the power consumption of the two-wire conductivity is generally greater than that of the two-wire pH, so the standby power consumption is different. If the 4-20mA block is designed separately, the standby power consumption can be set by software, so that there will be a common module between the instruments, which increases the commonality of the module. In this way, the two circuit boards can be made into a card slot structure in the mechanical structure, which is simple to produce and assemble, and improves work efficiency. At the same time, when the equipment fails, only part of the module needs to be replaced, which is simple to maintain and saves costs.

[0027] In summary, the 4-20mA hardware design of the present invention can set the standby power consumption of the two-wire explosion-proof instrument through software, so that the power supply and 4-20mA output part of the two-wire detector can be made into separate modules, and the collection of water quality monitoring parameters can be made into a separate module. New products can be formed by assembly, which improves the operability of the software and can modularize the instrument to reduce production costs.

[0028] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural change made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A two-wire explosion-proof water quality monitor split circuit module structure, characterized in that: It includes a 4-20mA output control circuit module integrating a two-wire 4-20mA output circuit and a power supply circuit, and an external acquisition circuit module for performing analog acquisition through an MCU and outputting a PWM signal to control the 4-20mA output circuit through the MCU; the 4-20mA output control circuit module includes a first connector for connecting to the external acquisition circuit module, the external acquisition circuit module includes a second connector for connecting to the 4-20mA output control circuit module, and the 4-20mA output control circuit module is connected to the external acquisition circuit module by connecting the first connector and the second connector.

2. The two-wire explosion-proof water quality monitor split circuit module structure according to claim 1 is characterized in that: The power supply circuit comprises a DCDC step-down circuit module connected to the output end of a 24V power supply through a power supply protection circuit and an isolation DCDC circuit module connected to the DCDC step-down circuit module.

3. The two-wire explosion-proof water quality monitor split circuit module structure according to claim 2 is characterized in that: The power protection circuit includes a diode D1, a capacitor C1 and a resistor R1. The anode of the diode D1 is connected to the output end of the 24V power supply. The resistor R1 is connected between the cathode of the diode D1 and the DCDC step-down circuit module U1. The connection end between the cathode of the diode D1 and the DCDC step-down circuit module U1 is grounded through the capacitor C1.

4. The two-wire explosion-proof water quality monitor split circuit module structure according to claim 3 is characterized in that: The two-wire 4-20mA output circuit includes a photoelectric isolation chip U4, a logic controller and gate U5, an operational amplifier U6, an operational amplifier U7 and a P-type transistor Q1. The first pin of the photoelectric isolation chip U4 is connected to the PWM signal output end of the MCU in the external acquisition circuit module through a resistor R2, the second pin of the photoelectric isolation chip U4 is grounded, the third pin of the photoelectric isolation chip U4 is grounded through a resistor R4, and the fourth pin of the photoelectric isolation chip U4 is connected to the output end of the DCDC buck circuit module; the first pin of the logic controller and gate U5 is connected to the output end of the DCDC buck circuit module through a resistor R5 and is grounded through a capacitor C2; the second pin of the logic controller and gate U5 is connected to the third pin of the photoelectric isolation chip U4, and the third pin of the logic controller and gate U5 is grounded. The 5th pin of the logic controller and gate U5 is connected to the non-inverting input terminal of the operational amplifier U6 through the resistor R5, and the connection end between the resistor R5 and the non-inverting input terminal of the operational amplifier U6 is grounded through the capacitor C3. The inverting input terminal of the operational amplifier U6 is connected to the output terminal and then connected to the non-inverting input terminal of the operational amplifier U7 through the resistor R6. The connection end between the resistor R6 and the non-inverting input terminal of the operational amplifier U7 is grounded through the resistor R7, and the inverting input terminal of the operational amplifier U7 is grounded. The output terminal of the operational amplifier U7 is connected to the gate of the P-type transistor Q1, the drain of the P-type transistor Q1 is connected to the cathode of the diode D1 through the resistor R9, the source of the P-type transistor Q1 is grounded through the series-connected resistors R10 and R8, and the inverting input terminal of the operational amplifier U7 is connected to the connection end of the resistor R10 and R8.

5. A two-wire explosion-proof water quality monitor split circuit module structure according to any one of claims 1 to 4, characterized in that: The simulation acquisition includes one or more of pH simulation acquisition, DO simulation acquisition and conductivity simulation acquisition.

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