CN221261554U - Control circuit for switching voltage and current modes of data acquisition equipment - Google Patents

Abstract

The utility model discloses a control circuit for switching a voltage mode and a current mode of data acquisition equipment. The analog-to-digital converter comprises AN ADC chip, AN analog switch, AN operational amplifier, a first triode and a second triode, wherein AN AN1P terminal pin of the ADC chip is connected with a signal through a third resistor, the AN1P terminal pin of the ADC chip is respectively connected with AN IN terminal pin of the analog switch and AN inverting terminal of the operational amplifier through the first resistor, AN IN-phase terminal of the operational amplifier is grounded, and AN output terminal of the operational amplifier is connected with AN output terminal pin of the analog switch through the second resistor. The utility model mainly utilizes the characteristic of the operational amplifier to skillfully add the function of the analog switch into the operational amplifier, but is not affected by the on-resistance, and combines the advantages of small size and light weight design of the analog switch scheme, and meanwhile, the on-resistance of the relay scheme is not considered, and the design of the push-pull bridge is added on the basis of the two to further enhance the driving capability, so that the amplifier can work in a linear region better and distortion is avoided.

Description

Control circuit for switching voltage and current modes of data acquisition equipment

Technical Field

The utility model relates to the technical field of electronic circuits, in particular to a control circuit for switching a voltage mode and a current mode of data acquisition equipment.

Background

In practical applications, data acquisition devices often face electromagnetic interference problems caused by overlong sensor cables. Particularly in the case of voltage acquisition, the influence of electromagnetic interference on data acquisition is more serious, resulting in uncontrollable errors. To solve this problem, it is a common practice to employ current signaling. By converting the charge signal of the sensor into a current signal and carrying out cable transmission for a longer distance, the influence of electromagnetic interference can be greatly reduced. At the data acquisition equipment end, the transmitted current signals are converted back to voltage signals, and ADC data acquisition is carried out, so that the influence of interference is avoided. Normally, a current signal which is transmitted to the acquisition end and is in the range of 0-20 mA is connected with a 250 omega resistor, a corresponding voltage signal of 0-5V can be obtained, and then the voltage signal is acquired.

In order to realize the diversification of functions, the requirements of different use occasions are met, and the flexibility that the product should have is achieved, so that the switching between the voltage signal acquisition and the current signal acquisition is required to be realized through MCU control. To solve this problem, there are two main approaches currently on the market: one is to use an MCU to control an analog switch to access a 250Ω resistor, and the other is to use a relay control to access a 250Ω resistor. However, both of these methods have some drawbacks. In the method of simulating a switch, the switch itself can introduce on-resistance and on-capacitance, the on-resistance can generate voltage drop, error is increased, and uncontrollable error can be introduced under the influence of temperature; the on-capacitance also causes some hysteresis in the signal, which needs to be avoided as much as possible. On the other hand, the relay method is limited by the fact that the relay is large in volume, and particularly in the occasion of multi-channel use, a large amount of volume is increased, and great influence is brought to application and installation. In addition, the oversized PCB of the data acquisition device can also raise new problems.

In summary, a novel control circuit is designed herein to address the above problems.

Disclosure of utility model

In view of the foregoing deficiencies in the prior art, an object of the present utility model is to provide a control circuit for voltage-current mode switching of a data acquisition device.

In order to achieve the above purpose, the present utility model adopts the following technical scheme:

The utility model provides a control circuit for voltage-current mode switch of data acquisition equipment, includes ADC chip, analog switch, operational amplifier, first triode and second triode, the AN1P end foot of ADC chip passes through the third resistance access signal, the AN1P end foot of ADC chip is connected with analog switch's IN end foot and operational amplifier's inverting terminal respectively through first resistance, operational amplifier's homophase ground connection, operational amplifier's output passes through the second resistance and is connected with analog switch's output foot, the base of first triode and second triode all is connected IN operational amplifier's output and second resistance junction, the power signal is inserted to the collecting electrode of first triode, the projecting pole of first triode and the collecting electrode of second triode are connected with the other end of second resistance, the collecting electrode ground of second triode, analog switch's control end foot all is connected with MCU.

Preferably, the ADC chip is an ADS1278 model.

Preferably, the analog switch is a CD4051B model.

Preferably, the operational amplifier is OPA202 model.

Preferably, the power supply access terminal of the operational amplifier is connected to a power supply through a first inductor and grounded through a first capacitor, and the first capacitor is connected in parallel with a polar capacitor.

By adopting the scheme, the utility model mainly utilizes the characteristics of the operational amplifier to skillfully add the function of the analog switch, but is not affected by the on-resistance, and combines the advantages of small size and light weight design of the analog switch scheme and the non-on-resistance of the relay scheme, and the design of the push-pull bridge is added on the basis of the two to further enhance the driving capability, so that the amplifier can work in a linear region better and distortion is avoided.

Drawings

Fig. 1 is a schematic circuit diagram of an embodiment of the present utility model.

Detailed Description

The present utility model will be described in further detail with reference to the drawings and examples, in order to make the objects, technical solutions and advantages of the present utility model more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the utility model.

In the description of the present utility model, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings are merely for convenience in describing the present utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be configured and operated in a specific orientation, and thus should not be construed as limiting the present utility model. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more of the described features. In the description of the present utility model, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.

In the description of the present utility model, it should be noted that the terms "mounted," "connected," and "coupled" are to be construed broadly, as well as, for example, fixedly coupled, detachably coupled, or integrally coupled, unless otherwise specifically indicated and defined. Either mechanically or electrically. Can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. The specific meaning of the above terms in the present utility model can be understood by those of ordinary skill in the art according to the specific circumstances.

As shown IN fig. 1, the control circuit for switching the voltage and current modes of the data acquisition device provided IN this embodiment includes AN ADC chip U1, AN analog switch U3, AN operational amplifier U2, a first triode Q2 and a second triode Q3, AN1P terminal pin of the ADC chip U1 is connected to a signal through a third resistor R3, AN1P terminal pin of the ADC chip U1 is connected to AN IN terminal pin of the analog switch U3 and AN inverting terminal of the operational amplifier U2 through a first resistor R1, AN IN-phase terminal of the operational amplifier U2 is grounded, AN output terminal of the operational amplifier U2 is connected to AN output terminal pin of the analog switch U3 through a second resistor R2, bases of the first triode Q2 and the second triode Q3 are connected to a junction of the operational amplifier U2, a collector of the first triode Q2 is connected to a power signal, AN emitter of the first triode Q2 and a collector of the second triode Q3 are connected to a second resistor R2, and a collector of the second triode Q3 is connected to AN MCU, and the collector of the second triode Q3 is connected to the ground. The main device model in the circuit can be specifically: the ADC chip U1 is of an ADS1278 model, the analog switch U3 is of a CD4051B model, and the operational amplifier U2 is of an OPA202 model.

The specific circuit of this embodiment works as follows:

The scheme is that an operational amplifier U2 is added, the negative end of a power supply of the operational amplifier U2 is connected with analog ground, and the positive end of the power supply of the operational amplifier U2 is connected with a power supply+. The output end and the inverting end of the operational amplifier U2 are connected by the analog switch U3, the input end and the output end of the analog switch U3 are respectively connected with the output end and the inverting end of the operational amplifier U2, when the analog switch U3 is conducted (the on-off switching can be realized only by using the A, B, C control pins of the MCU to operate the analog switch U3, and the analog switch U3 can also be simultaneously used in a plurality of channels, only one channel is drawn in fig. 1, namely, the analog switch U3 is only connected to the 0 terminal pin, and when the analog switch U3 is specifically used, one of the terminal pins can be connected to 0-7), and an output signal is superposed into a signal of the inverting end of the operational amplifier U2 to play a role of negative feedback. When the analog switch U3 is turned off, according to the "virtual off" characteristic of the operational amplifier U2 (i.e., the input resistance of the operational amplifier U2 is greater than 1gΩ and approaches to the open circuit), the resistance of the third resistor R3 (the resistance value is 250R) is equivalent to suspension, i.e., the circuit is not connected, the circuit equivalent to the third resistor R3 and the circuit on the right thereof is not connected to the acquisition circuit, and only the ADC chip U1 is performing voltage signal acquisition. When current signal acquisition is needed, the analog switch U3 is controlled to be closed through the ADC chip U1, at the moment, the negative feedback circuit is connected, according to the 'virtual short' characteristic (the electric potentials of the two input ends are equal, but are not in fact shorted together and approach to short circuit) of the operational amplifier U2, the resistance of the first resistor R1 (the resistance value is 250R) is equivalent to the voltage of the left end of the grounded ADC chip U1 at the moment, and when the voltage of the left end of the R1 is acquired, the corresponding 0-20 mA current just flows into the grounded first resistor R1, and the obtained voltage at the moment is just 0-5V. The characteristics of short and broken operation of the operational amplifier U2 are skillfully utilized, and although the analog switch U3 is used for control, the on-resistance of the analog switch U3 can not be measured, and meanwhile, the problems of the two schemes are skillfully solved without the influence of the overlarge volume and weight of the relay.

In addition, in the design of the circuit, a push-pull bridge is added, namely, the circuit is composed of a first triode Q2 and a second triode Q3, and the signal amplification effect can be realized immediately after the operational amplifier U2. The push-pull bridge is a complementary output circuit, which conducts the complementary output up and down, has small output impedance and stronger driving capability. The second resistor R2 (the resistance value is 1K) is added in the middle of the push-pull bridge, so that the output signal can be balanced when the voltage of the output signal does not reach the threshold value, the linearity of the signal can be further improved, and the triode can work in a linear region.

In addition, the power supply access terminal of the operational amplifier U2 is connected to a power supply through a first inductor L2 and is grounded to the capacitor C27 through a first capacitor, and the capacitor C27 is connected in parallel with a polar capacitor C28. Therefore, ripple waves caused by current fluctuation during operation of the operational amplifier can be further eliminated, the operational amplifier is ensured to work stably, and the polar capacitor C28 is required to be as close to a power supply pin as possible on wiring.

The foregoing description is only of the preferred embodiments of the present utility model, and is not intended to limit the scope of the utility model, but rather is intended to cover any equivalents of the structures or equivalent processes disclosed herein or in the alternative, which may be employed directly or indirectly in other related arts.

Claims (5)

1. A control circuit for voltage-current mode switching of a data acquisition device, characterized by: the analog-digital conversion circuit comprises AN ADC chip, AN analog switch, AN operational amplifier, a first triode and a second triode, wherein AN1P end pin of the ADC chip is connected with a signal through a third resistor, AN N1P end pin of the ADC chip is respectively connected with AN IN end pin of the analog switch and AN opposite phase end of the operational amplifier through a first resistor, AN IN-phase end of the operational amplifier is grounded, AN output end of the operational amplifier is connected with AN output end pin of the analog switch through a second resistor, bases of the first triode and the second triode are connected to a junction of the output end of the operational amplifier and the second resistor, a collector of the first triode is connected with a power signal, AN emitter of the first triode and a collector of the second triode are connected with the other end of the second resistor, a collector of the second triode is grounded, and control end pins of the analog switch are connected with AN MCU.

2. A control circuit for voltage current mode switching of a data acquisition device as claimed in claim 1, wherein: the ADC chip is of the model ADS 1278.

3. A control circuit for voltage current mode switching of a data acquisition device as claimed in claim 1, wherein: the analog switch is of the model CD 4051B.

4. A control circuit for voltage current mode switching of a data acquisition device as claimed in claim 1, wherein: the operational amplifier is of the OPA202 model.

5. A control circuit for voltage current mode switching of a data acquisition device as claimed in claim 1, wherein: the power supply access end of the operational amplifier is connected to a power supply through a first inductor and grounded through a first capacitor, and the first capacitor is connected in parallel with a polar capacitor.