CN216411387U

CN216411387U - Current measuring circuit with electric isolation and range-shiftable

Info

Publication number: CN216411387U
Application number: CN202122084707.3U
Authority: CN
Inventors: 方礼栋
Original assignee: Qingdao Qingzhi Instrument Co ltd
Current assignee: Qingdao Qingzhi Instrument Co ltd
Priority date: 2021-08-31
Filing date: 2021-08-31
Publication date: 2022-04-29
Anticipated expiration: 2031-08-31

Abstract

The utility model relates to the technical field of current measuring circuits, and provides a current measuring circuit with electric isolation and range-shiftable, which mainly comprises a current signal shifting module, a current signal shifting control module and an electric isolation module. After the current measuring circuit adds the high-voltage signal to the current measuring circuit, the main control circuit does not carry the high-voltage signal, so that operators can avoid the possibility of electric shock; the utility model can adopt different measuring ranges for different current signals, and can not cause the disconnection of current in the gear shifting process. If the manual control gear shifting is wrong, the automatic gear shifting circuit can switch the current signal to the corresponding current gear, so that the burning of the sampling circuit and the wave elimination of the current signal are prevented, and the purpose of accurate measurement is achieved.

Description

Current measuring circuit with electric isolation and range-shiftable

Technical Field

The utility model relates to the technical field of current measuring circuits, in particular to a current measuring circuit with electric isolation and a range capable of shifting.

Background

The existing current measuring circuit is mainly only provided with one range gear, and a current shunt converts a current analog signal into a voltage analog signal.

On the other hand, since the main control circuit is directly electrically connected with the current measuring circuit, potential safety hazards may be caused to a person when the main control circuit is operated.

Therefore, with the development of society, industrial automation has rapidly progressed. People put forward higher and higher requirements on the safety and the measurement width of a current measurement circuit, and the traditional non-isolated single current shunt method is not more and more suitable for the current measurement requirements, and is mainly reflected in the following problems:

1. the device has potential safety hazard, and the measuring circuit is not electrically isolated from the main control chip. When measuring current signals exceeding 36V, it is possible to cause excessive damage to the human body.

2. The current measuring range is narrow, for example, the current measuring circuit with the full scale of 15A can only measure 20mA, and for the current signal less than 20mA, the measurement becomes inaccurate, and the data fluctuation is aggravated.

3. The measuring range overload capacity is weak, and for a current signal with a large peak value, the phenomenon of clipping generally occurs, so that the measurement error is large.

SUMMERY OF THE UTILITY MODEL

The utility model aims to solve the problems in the background technology, and adopts the following technical scheme:

a current measuring circuit with electric isolation and range shifting comprises a current signal shifting module, a current signal shifting control module and an electric isolation module, wherein:

the current signaling shift module includes:

the current signal switching circuit is used for switching the current signal between the large current divider and the small current divider under the condition of not switching off the current signal;

the current sampling circuit is used for conditioning 20A or 0.1A input signals and converting the signals into signals within 250mV which can be received by the AD circuit;

the current signal selection and zero calibration circuit is used for selectively inputting two paths of voltage signals output by the current sampling circuit to the AD chip according to different current gears;

the current signaling shift control module includes:

the manual control circuit is used for switching the current signal switching circuit between large current and small current under the control of the main control unit;

the automatic control circuit is used for automatically switching gears according to the magnitude of the applied current signal;

the electrical isolation module includes:

an AD conversion circuit for converting the current analog signal into a current digital signal;

the optical coupling isolation circuit is used for realizing the electrical isolation between the main control circuit and the sampling circuit;

and the sampling control chip is used for transmitting the current digital signal to the main control chip through the optical coupling isolation circuit.

Further, the current signal switching circuit comprises a relay JRC1 and a small shunt U1, wherein the relay JRC1 is connected to the small shunt U1 in parallel, and the relay JRC1 sets a closing threshold and an opening threshold according to the magnitude of the current signal.

Further, the current sampling circuit comprises a large shunt U2 and a small shunt U1, the large shunt U2 is connected with a 4-pole Kelvin shunt resistor, a large current of 20A is input from

ends

1 and 2 of the U2 and is output from

ends

3 and 4, and a rear-stage circuit can receive a small voltage signal of 250mV at most; the small shunt U1 is also connected with a 4-pole Kelvin shunt resistor, 0.1A small current is input from the 1 end and the 2 end of the U1 and output from the 3 end and the 4 end, and a rear-stage circuit can receive a small voltage signal of 250mV at most.

Further, the current signal selection and zero calibration circuit comprises U3 analog switch integrated circuits 74HC4052, R16 and R17 for signal selection.

Further, the manual control circuit comprises a capacitor C1, a Schmidt inverter U4, resistors R2, R3, R4, R5 and a field-effect transistor Q3; the manual control signal is connected to a pin No. 2 of a Schmidt inverter U4 through a capacitor C1, the pin No. 2 of the Schmidt inverter U4 is connected to a pin No. 3 of a field effect transistor Q3 through a resistor R2, a pin No. 4 of the Schmidt inverter U4 is connected to a pin No. 1 of the field effect transistor Q3 through a resistor R5, and the pin No. 1 of the field effect transistor Q3 is connected to a power ground through a resistor R4.

Further, the automatic control circuit comprises a resistor R1, a voltage comparator U5, a resistor R6 and a field effect transistor Q3; the current signal ISH is connected to the pin No. 3 and the pin No. 6 of the voltage comparator U5 through the resistor R1, and the pin No. 1 and the pin No. 7 of the voltage comparator U5 are connected to the pin No. 1 of the fet Q3 through the resistor R6.

Further, the optical coupling isolation circuit comprises resistors R11, R12, R13, a Schmidt inverter U6, a U7, an optical coupler U8 and an optical coupler U9; the communication signal is connected to the No. 11 pin of the Schmitt inverter U6, and the No. 10 pin of the Schmitt inverter U6 is connected to the No. 3 pin of the optocoupler U8; the No. 6 pin of the optocoupler U8 is connected to the No. 5 pin of the Schmidt inverter U7, and the 3.3V-M power supply is connected to the No. 6 pin of the optocoupler U8 through a resistor R11; the communication signal TXD2_ M is connected to a pin No. 13 of a Schmidt inverter U7, a pin No. 12 of the Schmidt inverter U7 is connected to a pin No. 3 of an optical coupler U9, a pin No. 6 of the optical coupler U9 is connected to a pin No. 5 of a Schmidt inverter U6, and a 3.3V power supply is connected to a pin No. 6 of an optical coupler U9 through a resistor R13.

The utility model has the beneficial effects that:

1. the current measuring circuit can realize electrical isolation, and after a high-voltage signal is added to the current measuring circuit, the main control circuit does not carry the high-voltage signal, so that operators can avoid the possibility of electric shock.

2. The current measuring circuit of the utility model can realize range shifting, and is mainly embodied as follows: the current signal switching circuit has two gears, different ranges can be adopted for different current signals, and in the gear shifting process, the current can not be broken. If the manual control gear shifting is wrong, the automatic gear shifting circuit can switch the current signal to the corresponding current gear, so that the burning of the sampling circuit and the wave elimination of the current signal are prevented, and the purpose of accurate measurement is achieved.

3. The circuit design of the utility model can realize the measurement of wide-range current and meet the requirement of the current measuring range of the current users.

4. The circuit design of the utility model can realize the automatic switching of the current gears and meet the requirement of the current user on the automatic gear control.

5. The circuit design of the utility model can realize the manual switching of the current gear and meet the requirement of the current user on the manual control of the gear.

6. The circuit design of the utility model can realize that when the current is shifted, the current signal does not need to be switched off, and the circuit design has no influence on the current signal, thereby meeting the requirement of the current user on simple shift operation.

Drawings

FIG. 1 is a principal topology of the current measurement circuit of the present invention;

FIG. 2 is a circuit diagram of a current signal switching circuit;

FIG. 3 is a circuit configuration diagram of a current sampling circuit;

FIG. 4 is a circuit configuration diagram of a current signal selection and zero calibration circuit;

FIG. 5 is a circuit configuration diagram of the current signaling shift control module;

FIG. 6 is a circuit diagram of an opto-isolator circuit;

fig. 7 is an entire circuit connection circuit diagram of the current measuring circuit.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.

Referring to fig. 1, a current measuring circuit with electric isolation and range-shiftable comprises a current signal shifting module, a current signal shifting control module and an electric isolation module.

Wherein the current signal gear shifting module comprises: the current signal switching circuit is used for switching the current signal between the large current divider and the small current divider under the condition of not switching off the current signal; the current sampling circuit is used for conditioning 20A or 0.1A input signals and converting the signals into signals within 250mV which can be received by the AD circuit; the current signal selection and zero calibration circuit is used for selectively inputting two paths of voltage signals output by the current sampling circuit to the AD chip according to different current gears; the current signaling shift control module includes: the manual control circuit is used for switching the current signal switching circuit between large current and small current under the control of the main control unit; the automatic control circuit is used for automatically switching gears according to the magnitude of the applied current signal; the electrical isolation module includes: an AD conversion circuit for converting the current analog signal into a current digital signal; the optical coupling isolation circuit is used for realizing the electrical isolation between the main control circuit and the sampling circuit; and the sampling control chip is used for transmitting the current digital signal to the main control chip through the optical coupling isolation circuit.

As shown in fig. 2, the current signal switching circuit mainly switches the current signal between the large current divider and the small current divider according to the magnitude of the current signal without turning off the current signal, so that a large current flows through the large current divider and a small current flows through the small current divider. The relay JRC1 is connected in parallel to the small shunt U1, when a current signal is a large-current signal, the relay JRC1 is closed to enable the small shunt U1 to be completely short-circuited, the large current cannot burn the small-current shunt U1, and the current signal cannot be wave-absorbed;

as shown in fig. 3, the current sampling circuit mainly conditions 20A or 0.1A input signals and changes the signals into signals within 250mV that the AD circuit can receive. The large shunt U2 and the small shunt U1 both adopt 4-pole Kelvin shunt resistors, a large shunt U2 sampling circuit mainly realizes that 20-ampere large current is input from the

ends

1 and 2 of the U2, the highest 250mV small voltage signal which can be accepted by a rear-stage circuit is output from the

ends

3 and 4, a small shunt U1 sampling circuit mainly realizes that 0.1-ampere small current is input from the

ends

1 and 2 of the U1, and the highest 250mV small voltage signal which can be accepted by the rear-stage circuit is output from the

ends

3 and 4, the Kelvin structure fully ensures the proportional relation of input and output, and avoids the influence of the rear-stage circuit on the shunt resistors; the resistance is far superior to 2-pole shunt resistance of similar products;

as shown in fig. 4, the current signal selection and zero calibration circuit mainly realizes that two voltage signals output by the current sampling circuit are selectively input to the AD chip according to different current gears. The device mainly comprises a U3 analog switch integrated circuit 74HC4052, R16 and R17; the circuit mainly realizes the selection of signals, during normal measurement, U3 communicates pins 3 of ISH and U3 and pins 13 of ISL and U3 or communicates pins 3 of IBH and U3 and pins 13 of IBL and U3 according to the high and low levels of I _ RNG _ A and I _ RNG _ B control lines of a main control module, and U3 during zero calibration is communicated with

pins

3 and 13 of U3 through R16 and R17 respectively;

the current signal gear shifting control module consists of a manual control circuit and an automatic control circuit.

Referring to fig. 5, the manual control circuit mainly includes a capacitor C1, a schmitt inverter U4, resistors R2, R3, R4, R5, and a field effect transistor Q3. The manual control signal I _ SW _ CTR is connected to a pin 2 of a Schmitt inverter U4 through a capacitor C1, the pin 2 of the Schmitt inverter U4 is connected to a pin 3 of a field effect transistor Q3 through a resistor R2, a pin 4 of the Schmitt inverter U4 is connected to a pin 1 of a field effect transistor Q3 through a resistor R5, and the pin 1 of the field effect transistor Q3 is connected to a power ground through a resistor R4.

The manual control circuit mainly realizes that the current signal switching circuit can be controlled by a main control unit (such as a CPU), so that the current signal switching circuit can switch between large current and small current. When the control signal I _ SW _ CTR changes from high to low, the voltage difference across the capacitor C1 cannot change abruptly, so the voltage level at pin 2 of the schmitt inverter chip U4 is low, and pin 4 of U3 outputs high, and reaches the gate control pin of Q3 through the resistor R5, so that Q3 is turned on. When the Q3 is turned on, the pin 3 of the Q3 goes low, and the low is added to the pin 2 of the U3 through the R2, so that the pin 4 of the U4 always outputs high, and the Q3 maintains a conducting state. The conduction of the Q3 closes a relay JRC1 in the current signal switching circuit, and the current signal switching circuit enters a high-current state. When the control signal I _ SW _ CTR changes from low level to high level, the voltage difference between the two ends of the capacitor C1 cannot change suddenly, so the voltage level at pin 2 of the chip U4 is high level, pin 4 of U4 will output low level, and the Q3 is turned off through the resistor R5 to the gate control pin of the excess Q3. When the Q3 is turned off, the pin 3 of the Q3 goes high, and the high is added to the pin 2 of the U4 through the R2, so that the pin 4 of the U4 always outputs low, and the Q3 maintains the off state. The Q3 judgment can make the relay JRC1 in the current signal switching circuit open, and the current signal switching circuit enters a low current state.

The automatic control circuit mainly realizes automatic switching to a corresponding gear according to the magnitude of the applied current signal, and ensures that the low-current shunt is not burnt and the accuracy of data is ensured under the condition of manual control error.

The automatic control circuit mainly comprises a resistor R1, a voltage comparator U5, a resistor R6 and a field effect transistor Q3. The current signal ISH is connected to the pin No. 3 and the pin No. 6 of the voltage comparator U5 through the resistor R1, and the pin No. 1 and the pin No. 7 of the voltage comparator U5 are connected to the pin No. 1 of the fet Q3 through the resistor R6.

Referring to FIG. 5, when the voltage signal on ISH pin is greater than 0.3V, pin 1 of U5 will output a low level and pin 7 of U5 will output a high impedance state. At this time, the two ends of R6 are low, and Q3 is turned off. The current switching circuit automatically switches to high-grade, when the voltage signal on the ISH pin is smaller than-0.3V, the pin 1 of U5 outputs high impedance state, and the pin 7 of U5 outputs low level. When the voltage across the R6 is low, Q3 is turned off. The current switching circuit is automatically switched to the high grade, so that the current switching circuit can be automatically switched to the high grade as long as the absolute value of a voltage signal on an ISH pin is greater than 0.3V. When the voltage signal on the ISH pin is less than 0.3V and greater than-0.3V, the No. 1 pin and the No. 7 pin of the U5 both output high impedance state, and at this time, the automatic control circuit has no control function on the Q3, and the control right of current signal switching is handed over to manual control.

The electric isolation module mainly comprises an AD conversion circuit, a sampling control chip and an optical coupling isolation circuit.

The AD conversion circuit mainly realizes the conversion from a current analog signal to a current digital signal. We adopt AD chip CS5464 chip to realize

The sampling control chip mainly realizes that a current digital signal is transmitted to the main control chip through the optical coupling isolation circuit, and the sampling control chip is realized by adopting an STM32F103 with a Cortex-M3 core.

The optical coupling isolation circuit mainly realizes the electrical isolation of the main control circuit and the sampling circuit.

As shown in fig. 6, the optical coupler isolation circuit is composed of resistors R11, R12, R13, schmitt inverters U6, U7, and optical couplers U8 and U9. The communication signal TXD2 is connected to pin 11 of the Schmitt inverter U6, and pin 10 of the Schmitt inverter U6 is connected to pin 3 of the optocoupler U8. The No. 6 pin of the optocoupler U8 is connected to the No. 5 pin of the Schmidt inverter U7, and the 3.3V-M power supply is connected to the No. 6 pin of the optocoupler U8 through a resistor R11; the communication signal TXD2_ M is connected to a pin No. 13 of a Schmidt inverter U7, a pin No. 12 of the Schmidt inverter U7 is connected to a pin No. 3 of an optical coupler U9, a pin No. 6 of the optical coupler U9 is connected to a pin No. 5 of a Schmidt inverter U6, and a 3.3V power supply is connected to a pin No. 6 of an optical coupler U9 through a resistor R13.

The data sent by the sampling circuit to the main control circuit is a serial port signal transmitted by a TXD2, the TXD2 serial port signal is shaped by a Schmidt inverter chip U6, is electrically isolated by an optocoupler chip U8 and then is output, and is shaped by the Schmidt inverter chip U7 to become an RXD2-M signal which is output to the main control circuit; the data sent by the main control circuit to the sampling circuit is formed by a TXD2-M serial port signal, a TXD2-M serial port signal is shaped through a Schmidt inverter chip U7, is electrically isolated through an optocoupler chip U9 and then is output, and is shaped through the Schmidt inverter chip U6 to form a TXD2 signal which is output to the sampling circuit.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and equivalent alternatives or modifications according to the technical solution of the present invention and the inventive concept thereof should be covered by the scope of the present invention.

Claims

1. A current measuring circuit with electrical isolation and range shifting, characterized by: including current signal gear shift module, current signal gear shift control module, electrical isolation module, wherein:

the current signaling shift module includes:

the current signaling shift control module includes:

the electrical isolation module includes:

2. The electrically isolated and range shiftable current measurement circuit of claim 1, wherein: the current signal switching circuit comprises a relay JRC1 and a small shunt U1, wherein the relay JRC1 is connected to the small shunt U1 in parallel, and the relay JRC1 sets a closing threshold and an opening threshold according to the magnitude of a current signal.

3. The electrically isolated and range shiftable current measurement circuit of claim 1, wherein: the current sampling circuit comprises a large shunt U2 and a small shunt U1, the large shunt U2 is connected with a 4-pole Kelvin shunt resistor, 20A large current is input from ends 1 and 2 of the U2 and is output from ends 3 and 4, and a rear-stage circuit can receive a small voltage signal of 250mV at most; the small shunt U1 is also connected with a 4-pole Kelvin shunt resistor, 0.1A small current is input from the 1 end and the 2 end of the U1 and output from the 3 end and the 4 end, and a rear-stage circuit can receive a small voltage signal of 250mV at most.

4. The electrically isolated and range shiftable current measurement circuit of claim 1, wherein: the current signal selection and zero correction circuit comprises U3 analog switch integrated circuits 74HC4052, R16 and R17 for realizing signal selection.

5. The electrically isolated and range shiftable current measurement circuit of claim 1, wherein: the manual control circuit comprises a capacitor C1, a Schmidt inverter U4, resistors R2, R3, R4, R5 and a field-effect transistor Q3; the manual control signal is connected to a pin No. 2 of a Schmidt inverter U4 through a capacitor C1, the pin No. 2 of the Schmidt inverter U4 is connected to a pin No. 3 of a field effect transistor Q3 through a resistor R2, a pin No. 4 of the Schmidt inverter U4 is connected to a pin No. 1 of the field effect transistor Q3 through a resistor R5, and the pin No. 1 of the field effect transistor Q3 is connected to a power ground through a resistor R4.

6. The electrically isolated and range shiftable current measurement circuit of claim 1, wherein: the automatic control circuit comprises a resistor R1, a voltage comparator U5, a resistor R6 and a field-effect transistor Q3; the current signal ISH is connected to the pin No. 3 and the pin No. 6 of the voltage comparator U5 through the resistor R1, and the pin No. 1 and the pin No. 7 of the voltage comparator U5 are connected to the pin No. 1 of the fet Q3 through the resistor R6.

7. The electrically isolated and range shiftable current measurement circuit of claim 1, wherein: the optical coupling isolation circuit comprises resistors R11, R12, R13, Schmidt inverters U6 and U7, an optical coupler U8 and an optical coupler U9; the communication signal is connected to the No. 11 pin of the Schmitt inverter U6, and the No. 10 pin of the Schmitt inverter U6 is connected to the No. 3 pin of the optocoupler U8; the No. 6 pin of the optocoupler U8 is connected to the No. 5 pin of the Schmidt inverter U7, and the 3.3V-M power supply is connected to the No. 6 pin of the optocoupler U8 through a resistor R11; the communication signal TXD2_ M is connected to a pin No. 13 of a Schmidt inverter U7, a pin No. 12 of the Schmidt inverter U7 is connected to a pin No. 3 of an optical coupler U9, a pin No. 6 of the optical coupler U9 is connected to a pin No. 5 of a Schmidt inverter U6, and a 3.3V power supply is connected to a pin No. 6 of an optical coupler U9 through a resistor R13.