CN206258503U - A kind of current collector of two-wire system sensor - Google Patents

Abstract

The utility model relates to a current collector for a two-wire sensor, which comprises a precision resistor and an operational amplifier, the precision resistor is connected in series between the first output end and the input end; The other end of the first resistor is connected to the non-inverting input terminal of the operational amplifier, and the other end of the first resistor is also connected to the second output terminal through the second resistor; the inverting input terminal of the operational amplifier is directly grounded, and the output terminal is connected to one end of the sampling resistor; the other end of the sampling resistor is connected to the second output terminal; one end of the sampling resistor is also directly grounded; the resistance value of the precision resistor is much smaller than that of the first resistor and the second resistor resistance value. The utility model enables the current signal of one sensor to be used by two measuring instruments without modifying the measuring instruments.

Description

A current collector for two-wire sensors

technical field

The utility model relates to the technical field of current collection, in particular to a current collector of a two-wire sensor.

Background technique

At present, most sensors are developing towards the two-wire system, and the use of two-wire sensors is becoming more and more extensive. Since the two wires from the two-wire sensor are both power wires and signal wires, the two wires from many measuring instruments provide the voltage required for the sensor to work and can be directly connected to the sensor. Because the price of the sensor is relatively expensive, sometimes it is necessary to reduce the number of sensors as much as possible, and in some special cases, it is necessary to use two measuring instruments to collect the current of one sensor at the same time. Since both measuring instruments provide the voltage required for the sensor to work, this makes it difficult to connect the measuring instrument to the sensor. At present, the signal isolator with one input and two outputs is widely used in the market, which divides the current output by the sensor into two channels at the same time. However, the use of a signal isolator requires the voltage provided by the measuring instrument to be removed, which requires modification of the internal circuit of the measuring instrument, which is cumbersome. Some measuring instruments have complex internal structures, and modifying the circuit may cause damage to the measuring instrument. Therefore, there is a need for a device that enables one sensor to be used by two measuring instruments that supply voltage.

Utility model content

The technical problem to be solved by the utility model is to provide a current collector of a two-wire sensor, so that the current signal of one sensor can be used by two measuring instruments without modifying the measuring instruments.

The technical scheme adopted by the utility model to solve the technical problem is: provide a current collector of a two-wire sensor, including a precision resistor and an operational amplifier, and the precision resistor is connected in series to the first output end of the first measuring instrument Between the two-wire sensor and the input terminal for connecting the two-wire sensor, it is used to convert the current signal of the two-wire sensor into a voltage signal; the positive pole of the voltage signal at both ends of the precision resistor is connected to one end of the first resistor, and the negative pole is grounded; The other end of the first resistor is connected to the non-inverting input end of the operational amplifier, and the other end of the first resistor is also connected to the second output end for connecting the second measuring instrument through the second resistor; The inverting input terminal of the amplifier is directly grounded, and the output terminal is connected to one end of the sampling resistor; the other end of the sampling resistor is connected to the second output terminal; one end of the sampling resistor is also directly grounded; the resistance value of the precision resistor is far less than the resistance values of the first resistor and the second resistor.

The resistance value of the sampling resistor is equal to the resistance value of the precision resistor.

The output terminal of the operational amplifier is also connected with a negative feedback circuit; the negative feedback circuit includes a triode, the base of the triode is connected to the output terminal of the operational amplifier, the emitter is grounded through the third resistor, and the collector is connected to the power supply terminal .

A current limiting resistor and a voltage stabilizing diode are connected in series between the output terminal of the operational amplifier and the ground, and the connection terminals of the current limiting resistor and the voltage stabilizing diode are also connected to the base of the triode.

Both the first output end and the second output end are provided with a full-bridge rectifier.

Both the first output end and the second output end are provided with decoupling capacitors.

A TVS tube is also connected in parallel at both ends of the decoupling capacitor.

Beneficial effect

Due to the adoption of the above-mentioned technical scheme, the utility model has the following advantages and positive effects compared with the prior art: the utility model provides the working voltage of the two-wire sensor with two measuring instruments The output current of the sensor is divided into two channels for the use of two measuring instruments at the same time, and the current collected by the two measuring instruments is the same as the current in the original sensor. This meets the requirement of using two different measuring instruments to simultaneously collect the current in one sensor in some special cases, and also saves the number of sensors used and reduces the cost. The circuit structure of the device is simple, the cost is low, and the error is very small.

Description of drawings

Fig. 1 is a circuit diagram of the utility model;

Fig. 2 is a connection diagram when the utility model is in use.

detailed description

Below in conjunction with specific embodiment, further set forth the utility model. It should be understood that these embodiments are only used to illustrate the present utility model and are not intended to limit the scope of the present utility model. In addition, it should be understood that after reading the content taught by the utility model, those skilled in the art can make various changes or modifications to the utility model, and these equivalent forms also fall within the scope defined by the appended claims of the application.

The embodiment of the present utility model relates to a current collector of a two-wire sensor, as shown in Figure 1, comprising a precision resistor R _c and an operational amplifier, the precision resistor is connected in series to the first output of the first measuring instrument 1 Between the terminal and the input terminal for connecting the two-wire sensor, it is used to convert the current signal of the two-wire sensor into a voltage signal; the positive pole of the voltage signal at both ends of the precision resistor _Rc is connected to _one end of the first resistor R1 , the negative pole is grounded; the other end of the first resistor R ₁ is connected to the positive input of the operational amplifier, and the other end of the first resistor R ₁ is also connected to the second measurement terminal through the second resistor R ₂ The second output terminal of the instrument 2 is connected; the inverting input terminal of the operational amplifier is directly grounded, and the output terminal is connected with one end of the sampling resistor R _s ; the other end of the sampling resistor R _s is connected with the second output terminal; the One end of the sampling resistor R _s is also directly grounded; the resistance value of the precision resistor R _c is much smaller than the resistance values R ₂ of the first resistor R ₁ and the second resistor.

It can be seen that a 150Ω precision resistor is connected in series in the connection circuit between the measuring instrument 1 and the sensor to convert the current in the sensor into a voltage. The positive pole of the voltage is connected to the _first resistor R1, and the negative pole is grounded. The voltage at point B is pulled down to -V0 through the first resistor R ₁ and the second resistor R ₂ with larger resistances and the "virtual short" and "virtual break" characteristics of the operational amplifier, so that through the sampling resistor R _s The current in the sensor is the same as the current in the sensor, and changes with the change of the current output by the sensor.

The output terminal of the operational amplifier is also connected with a negative feedback circuit; the negative feedback circuit includes a triode Q1, the base of the triode Q1 is connected to the output terminal of the operational amplifier, the emitter is grounded through the third resistor _Re , and the collector Connect to the power supply terminal. A current limiting resistor R _m and a voltage stabilizing diode Z ₁ are connected in series between the output terminal of the operational amplifier and the ground, and the connection end of the current limiting resistor R _m and the voltage stabilizing diode Z ₁ is also connected to the base of the transistor Q1 .

In order to prevent the voltage at the non-inverting input terminal of the operational amplifier from rising or falling suddenly, a transistor Q1 is added to the circuit for feedback adjustment to ensure that the voltage at point A is 0. The current limiting resistor R _m and the Zener diode Z1 can also prevent the base voltage _of the transistor Q1 from being too large.

Both the first output end and the second output end are provided with a full-bridge rectifier, so that the measuring instrument can still work normally when the connection is reversed. Both the first output end and the second output end are provided with decoupling capacitors C ₁ and C ₂ , and the decoupling capacitors C ₁ and C ₂ can ensure that the circuit does not oscillate under long-term inductive loads. The _two ends of the decoupling capacitor are also connected in parallel with TVS tubes Z ₂ and Z ₃ , which can absorb the energy _of instantaneous overvoltage and prevent lightning, electrostatic discharge, surge and other energy from damaging the current separator.

Fig. 2 is a connection diagram when the utility model is in use. Among them, the IN3 and OU3 terminals of the current separation device are respectively connected to the positive and negative terminals of the two-wire sensor, the IN1 terminal and OUT1 terminal of the current separation device are respectively connected to the +24V and GND terminals of the measuring device 1, and the IN2 terminal of the current separation device is connected to The OUT2 terminal is respectively connected to the +24V and GND terminals of the measuring device 2 .

Next, the working process of the utility model is described in conjunction with Fig. 1. In Fig. 1, the first resistor R ₁ , the second resistor R ₂ , the current limiting resistor R _m , the third resistor R _e , the precision resistor R _c , and the sampling resistor R _s Color ring resistors are used, among which, the resistance accuracy of the first resistor R ₁ , the second resistor R ₂ , the current limiting resistor R _m , and the third resistor R _e is 1%, and the precision resistor R _c and the sampling resistor R _s are high RJ24 Precision metal film resistors with 0.1% accuracy. The operational amplifier adopts LM358 or LM324 operational amplifier chip. The current-limiting resistor R _m and the Zener diode Z1 are _1N4735 , which can prevent the base voltage of the transistor Q1 from being too large. The decoupling capacitors C ₁ and C ₂ are both 10nF to ensure that the circuit does not oscillate under long-term inductive loads. There is a full-bridge rectifier at the input of both measuring instruments, which works even if the measuring instruments are reversed. TVS tubes Z ₂ and Z ₃ can absorb the energy of instantaneous overvoltage, and prevent lightning strike, electrostatic discharge, surge and other energy from damaging the current separator.

Firstly, the measuring instrument 1 is connected to the sensor. The current flowing through the sensor is I _c , and the current signal is converted into a voltage signal V ₀ through a precision resistor R _c . The process of converting the voltage signal V ₀ into a current I ₂ is analyzed below:

Firstly, the voltage collected by the precision resistor R _c is V ₀ , and the current I _{1 flowing through the first resistor R 1 =} V ₀ /R ₁ , since the input terminal of the operational amplifier cannot absorb current, the current I ₁ all flows through the first resistor R 1 Two resistors R ₂ , then the voltage at point B is V _B =-I ₁ *R ₂ =-V ₀ *R ₂ /R ₁ , when R ₁ =R ₂ , V _B =-V ₀ .

There are only the sampling resistor R _s and the second resistor R ₂ between the negative terminal of the measuring instrument 2 and the entire transmitter circuit, so all the current flows through the sampling resistor R _s and the second resistor R ₂ . The upper end of the second resistor R ₂ is a virtual ground (0V), and the upper end of the sampling resistor R _s is GND. Therefore, the voltages at both ends of the second resistor R ₂ and the sampling resistor R _s are exactly the same, which is equal to the voltage V _B , which is equivalent to connecting the sampling resistor R _s and the second resistor R ₂ in parallel as a current sampling resistor. Therefore, the total circuit current I ₂ =V ₀ /(R _s //R ₂ ), if R ₂ >>R _s is taken, then I ₂ =V ₀ /R _s . Therefore, when R _s =R _c , I ₂ is the same size as I _c . It doesn’t matter if R ₂ >>R _s cannot be satisfied, the sampling resistor R _s and the second resistor R ₂ (R _s //R ₂ ) are fixed values, the current I _s and the voltage V ₀ are still in a linear relationship, and the error proportional coefficient is Can be eliminated during calibration.

In order to ensure that the voltage at point A remains at 0V, a negative feedback circuit is added. The negative feedback process is analyzed below: if point A is higher than 0V for some reason, the output of point 1 of the operational amplifier rises, the voltage across the third resistor Re _e rises, and the current through the third resistor Re _e becomes larger. The current through the sampling resistor R _s also becomes larger, and the voltage at point B becomes lower (more negative). The result is that the voltage at point A is pulled down by the _second resistor R2. Conversely, if point A is lower than 0V for some reason, it will be raised back to 0V by the negative feedback circuit. In short, the result of the negative feedback circuit keeps the virtual short of the operational amplifier, that is, the voltage at point A = 0V.

In addition to the correct circuit, the normal operation of the circuit also requires that the operational amplifier can work with a single power supply, that is, the input terminal can still accept 0V input and work normally without a negative power supply. LM358/324 is the most common and cheapest single-supply op amp, with a power consumption of 400uA per op amp, which is basically acceptable.

It is not difficult to find that the utility model divides the output current of one sensor into two circuits for the use of two measuring instruments at the same time when both measuring instruments provide the working voltage of the two-wire sensor, and the two measuring instruments collect The current is the same as the current in the original sensor. This meets the requirement of using two different measuring instruments to simultaneously collect the current in one sensor in some special cases, and also saves the number of sensors used and reduces the cost. The circuit structure of the device is simple, the cost is low, and the error is very small.

Claims (7)

1. A current collector of a two-wire sensor, characterized in that it includes a precision resistor and an operational amplifier, and the precision resistor is connected in series with the first output terminal for connecting the first measuring instrument and the input for connecting the two-wire sensor Between the terminals, it is used to convert the current signal of the two-wire sensor into a voltage signal; the positive electrode of the voltage signal at both ends of the precision resistor is connected to one end of the first resistor, and the negative electrode is grounded; the other end of the first resistor is connected to the The non-inverting input of the operational amplifier is connected, and the other end of the first resistor is also connected to the second output of the second measuring instrument through a second resistor; the inverting input of the operational amplifier is directly grounded, The output end is connected to one end of the sampling resistor; the other end of the sampling resistor is connected to the second output end; one end of the sampling resistor is also directly grounded; the resistance value of the precision resistor is much smaller than that of the first resistor and the second The resistance value of the resistor. 2 . The current collector for a two-wire sensor according to claim 1 , wherein the resistance value of the sampling resistor is equal to the resistance value of the precision resistor. 3 . 3. the current collector of two-wire sensor according to claim 1, is characterized in that, the output end of described operational amplifier is also connected with negative feedback circuit; Described negative feedback circuit comprises triode, and the base of described triode and The output terminal of the operational amplifier is connected, the emitter is connected to the ground through the third resistor, and the collector is connected to the power supply terminal. 4. The current collector of the two-wire sensor according to claim 3, wherein a current limiting resistor and a voltage stabilizing diode are connected in series between the output terminal of the operational amplifier and the ground, and the current limiting resistor and the voltage stabilizing diode are connected in series. The connecting terminal of the diode is also connected with the base of the triode. 5 . The current collector for a two-wire sensor according to claim 1 , wherein a full-bridge rectifier is provided at the first output end and the second output end. 6 . The current collector for a two-wire sensor according to claim 1 , wherein both the first output terminal and the second output terminal are provided with decoupling capacitors. 7. The current collector of a two-wire sensor according to claim 6, wherein a TVS tube is connected in parallel at both ends of the decoupling capacitor.