CN205540217U - Analog input device - Google Patents

Abstract

The utility model discloses an analog input device, including supply circuit, CPU module, communication circuit sum channel acquisition circuit, supply circuit is used for supplying power for whole AI module, passageway acquisition circuit is used for giving the CPU module with on -the -spot signal transmission, the CPU module is used for carrying out the communication through the control station of communication circuit and DCS system, passageway acquisition circuit is equipped with the common mode suppression circuit of height input impedance and common mode rejection ability, common mode suppression circuit is used for carrying out the differential mode to on -the -spot signal and enlargies, realizes the common mode rejection simultaneously. Through the utility model discloses a common mode suppression circuit who takes the common mode rejection can only enlarge the differential mode, and restraines the not too strong problem of AI module moderate resistance common mode interference ability in the solution DCS system to the common mode.

Description

Analog input device

technical field

The utility model relates to the field of DCS control systems, in particular to an analog quantity input device.

Background technique

In the DCS control system, the use of AI analog input modules is very popular. In the field, it is often encountered that the common mode signal is coupled on the transmission signal line due to the poor site environment. When the common mode signal is relatively large, it will have a great impact on the signal, resulting in inaccurate signal detection. The current general method is to add a voltage follower amplifier to the input for signal acquisition, but the voltage follower amplifier cannot suppress the common mode signal, and because of its low input resistance and high requirements on the matching degree of the resistance ratio in the circuit , so the common mode rejection ability is not very strong.

Contents of the invention

The purpose of this utility model is to provide an analog input device for the deficiencies of the prior art. Through the common mode suppression circuit of the present utility model, only the differential mode can be amplified, and the common mode can be suppressed, so as to solve the problem of AI in the DCS system. The problem that the anti-common mode interference ability in the module is not very strong.

The purpose of this utility model is achieved as follows: an analog input device, including a power supply circuit, a CPU module, a communication circuit and a channel acquisition circuit, the power supply circuit is used to supply power to the entire AI module, and the channel acquisition circuit is used for Collect the signal of the field equipment and transmit it to the CPU module. The CPU module is used to communicate correctly with the control station of the DCS system through the communication circuit. The channel collection circuit is provided with a common mode suppression circuit with high input impedance. The common-mode suppression circuit is used for differential-mode amplification of field signals while realizing common-mode suppression. The input end of the common mode suppression circuit is the signal input end of the analog input module.

The common-mode suppression circuit includes a first operational amplifier VC1A, a second operational amplifier VC1C, a third operational amplifier VC1D and several resistors, and the non-inverting input terminal of the second operational amplifier VC1C is used to communicate with the first signal output terminal of the field device connected, the inverting input end of the second operational amplifier VC1C is connected to one end of the fifth resistor R5 and one end of the seventh resistor RG respectively, and the other end of the fifth resistor R5 is connected to the output end of the second operational amplifier VC1C , the other end of the seventh resistor RG is respectively connected to one end of the sixth resistor R6 and the inverting input end of the third op-amp VC1D, and the other end of the sixth resistor R6 is connected to the output end of the third op-amp VC1D , the output end of the second operational amplifier VC1C is connected to one end of the first resistor R1, the other end of the first resistor R1 is respectively connected to one end of the second resistor R2 and the non-inverting input end of the first operational amplifier VC1A, and the second resistor The other end of R2 is connected to the output terminal of the first operational amplifier VC1A, the output terminal of the first operational amplifier VC1A is connected to the channel acquisition circuit, and the non-inverting input terminal of the third operational amplifier VC1D is used to communicate with the second The signal output terminal is connected, the output terminal of the third operational amplifier VC1D is connected with one end of the third resistor R3, and the other end of the third resistor R3 is respectively connected with one end of the fourth resistor R4 and the inverting input terminal of the first operational amplifier VC1A, The other end of the fourth resistor R4 is grounded. The common-mode suppression circuit of the utility model has strong common-mode suppression ability, such as 1-5V input signal, using the traditional differential mode circuit, can only ensure that the common-mode voltage <20mV will not affect the accuracy, but the utility model design The common mode rejection circuit has no effect on the accuracy under the <1V common mode signal. Moreover, the common-mode suppression circuit of the utility model has the function of increasing the input impedance, and the input impedance at both positive and negative ends is particularly large, greater than 10 ⁸ ohms, and the high input impedance has little influence on the signal.

The first operational amplifier VC1A, the second operational amplifier VC1C, and the third operational amplifier VC1D adopt an integrated operational amplifier model LM324A.

The channel acquisition circuit also includes a filter circuit and a sampling circuit, the filter circuit and the sampling circuit are arranged between the common-mode suppression circuit and the CPU module, the input end of the common-mode suppression circuit is used to receive field signals, and the common-mode suppression circuit The output end of the mode suppression circuit is connected with the input end of the filter circuit, the output end of the filter circuit is connected with the input end of the sampling circuit, and the output end of the sampling circuit is connected with the CPU module. The sampling circuit is generally an AD conversion circuit. If the CPU module has its own AD conversion function, then the channel acquisition circuit of the present utility model does not need to be provided with an AD conversion circuit. The filter circuit is to filter out interference such as noise in the signal.

A first isolation circuit is provided between the CPU module and the channel acquisition circuit.

A second isolation circuit is provided between the CPU module and the communication circuit.

Due to the adoption of the above scheme, the channel acquisition circuit of the present invention is provided with a common-mode suppression circuit with high input impedance, and the common-mode suppression circuit is used for differential-mode amplification of field signals and suppression of common-mode. The common mode suppression circuit of the utility model can only amplify the differential mode and suppress the common mode, and the AI input module adopting the circuit has a high common mode suppression ratio and a large input impedance.

Below in conjunction with accompanying drawing and specific embodiment, the utility model is further described.

Description of drawings

Fig. 1 is the functional block diagram of the analog quantity input device of the present utility model;

Fig. 2 is a circuit diagram of the common mode suppression circuit of the present invention.

detailed description

Referring to Fig. 1, an analog quantity input device includes a power supply circuit, a CPU module, a communication circuit and a channel acquisition circuit, the power supply circuit is used to supply power to the entire AI module, the channel acquisition circuit is used to collect field signals, and The field signal is passed to the CPU module. The channel acquisition circuit is provided with a common-mode suppression circuit with high input impedance, and the common-mode suppression circuit is used for differential-mode amplification of field signals while realizing common-mode suppression. The input end of the common mode suppression circuit is the signal input end of the analog input module. The channel acquisition circuit also includes a filter circuit and a sampling circuit, the filter circuit and the sampling circuit are arranged between the common-mode suppression circuit and the CPU module, the input end of the common-mode suppression circuit is used to receive field signals, and the common-mode suppression circuit The output end of the mode suppression circuit is connected with the input end of the filter circuit, the output end of the filter circuit is connected with the input end of the sampling circuit, and the output end of the sampling circuit is connected with the CPU module. The sampling circuit is generally an AD conversion circuit. If the CPU module has its own AD conversion function, then the channel acquisition circuit of the present utility model does not need to be provided with an AD conversion circuit. The filter circuit is to filter out interference such as noise in the signal. The CPU module is connected with an EEPROM access circuit, and can save some setting parameters. A first isolation circuit is provided between the CPU module and the channel acquisition circuit. The CPU module is used for communicating with the control station of the DCS system through the communication circuit. A second isolation circuit is provided between the CPU module and the communication circuit. A communication circuit is a circuit that communicates. Through the communication circuit, the CPU can communicate with the control station. The core of the communication circuit is the communication chip used, such as SP485 and so on. It is connected to the 485 bus outside and the isolation circuit on the other side.

Referring to Fig. 2, the common mode suppression circuit includes a first operational amplifier VC1A, a second operational amplifier VC1C, a third operational amplifier VC1D and several resistors, and the non-inverting input terminal of the second operational amplifier VC1C is used to communicate with the first operational amplifier of the field device A signal output terminal is connected, the inverting input terminal of the second operational amplifier VC1C is connected with one end of the fifth resistor R5 and one end of the seventh resistor RG respectively, and the other end of the fifth resistor R5 is connected with the second operational amplifier VC1C The other end of the seventh resistor RG is connected to one end of the sixth resistor R6 and the inverting input end of the third operational amplifier VC1D respectively, and the other end of the sixth resistor R6 is connected to the third operational amplifier VC1D The output end of the second operational amplifier VC1C is connected to one end of the first resistor R1, and the other end of the first resistor R1 is respectively connected to one end of the second resistor R2 and the non-inverting input end of the first operational amplifier VC1A , the other end of the second resistance R2 is connected with the output terminal of the first operational amplifier VC1A, the output terminal of the first operational amplifier VC1A is connected with the channel acquisition circuit, and the non-inverting input terminal of the third operational amplifier VC1D is used to communicate with the field The second signal output terminal of the device is connected, the output terminal of the third operational amplifier VC1D is connected to one end of the third resistor R3, and the other end of the third resistor R3 is respectively connected to one end of the fourth resistor R4 and the reverse phase of the first operational amplifier VC1A The input end is connected, and the other end of the fourth resistor R4 is grounded. The first operational amplifier VC1A, the second operational amplifier VC1C, and the third operational amplifier VC1D adopt an integrated operational amplifier model LM324A. The common-mode suppression circuit of the utility model has strong common-mode suppression ability, such as 1-5V input signal, using the traditional differential mode circuit, can only ensure that the common-mode voltage <20mV will not affect the accuracy, but the utility model design The common mode rejection circuit has no effect on the accuracy under the <1V common mode signal. Moreover, the common mode suppression circuit of the present invention has the effect of increasing the input impedance, and the input impedance at both positive and negative ends is particularly large, greater than 10 ⁸ .

Referring to Figure 2, set R1=R3, R2=R4, R5=R6. Then according to circuit knowledge, it can be obtained: Uout=-(U _in+ -U _in- )(1+2R ₅ /R _G )R ₂ /R ₁ . According to this deduction formula, it can be seen that the output voltage is only related to the difference of the input voltage. How many times you want to amplify the input difference is the corresponding value. The resistors R _5, R _G R _{2, and} R ₁ are precision resistors that can be matched according to specific needs. In this case, the common mode signal is greatly suppressed in this circuit. The common mode rejection ratio of the AI input module using this circuit is very high. According to our AI module, the common-mode AC suppression voltage can reach 250V.Ac, and the common-mode DC can reach 1V, compared to 40V.ac. 20mV.dc before improvement.

The utility model is not limited to the above-mentioned embodiments, and technical solutions with slight changes without departing from the spirit of the technical solutions of the utility model shall fall into the protection scope of the utility model.

Claims (6)

1. an analog input device, it is characterised in that: include power supply circuits, CPU module, telecommunication circuit and channel acquisition electricity Road, described power supply circuits are for whole AI module for power supply, and described channel acquisition circuit is used for collection site signal, and by scene Signal passes to CPU module, and described CPU module is for carrying out communication by the control station of telecommunication circuit Yu DCS system, described logical Road Acquisition Circuit is provided with the common mode rejection circuit of band high input impedance, and described common mode rejection circuit is for poor to on-site signal Mould amplifies, and realizes common mode inhibition simultaneously.

Analog input device the most according to claim 1, it is characterised in that: described common mode rejection circuit includes the first fortune Putting (VC1A), the second amplifier (VC1C), the 3rd amplifier (VC1D) and some resistance, the homophase of described second amplifier (VC1C) is defeated Entering end to be connected for the first signal output part with field apparatus, the inverting input of described second amplifier (VC1C) is respectively with the One end of five resistance (R5), one end of the 7th resistance (RG) connect, the other end of described 5th resistance (R5) and the second amplifier (VC1C) outfan connects, the other end of described 7th resistance (RG) respectively with one end, the 3rd amplifier of the 6th resistance (R6) (VC1D) inverting input connects, and the other end of described 6th resistance (R6) and the outfan of the 3rd amplifier (VC1D) connect, One end of the outfan of described second amplifier (VC1C) and the first resistance (R1) connects, the other end of the first resistance (R1) respectively with One end of second resistance (R2), the in-phase input end of the first amplifier (VC1A) connect, the other end and first of the second resistance (R2) The outfan of amplifier (VC1A) connects, and the outfan of described first amplifier (VC1A) is connected with channel acquisition circuit, and the described 3rd The in-phase input end of amplifier (VC1D) is used for being connected with the secondary signal outfan of field apparatus, the output of the 3rd amplifier (VC1D) End is connected with one end of the 3rd resistance (R3), the other end of the 3rd resistance (R3) respectively with one end of the 4th resistance (R4), first The inverting input of amplifier (VC1A) connects, the other end ground connection of the 4th resistance (R4).

Analog input device the most according to claim 2, it is characterised in that: described first amplifier (VC1A), the second fortune Put (VC1C), the 3rd amplifier (VC1D) uses model to be the integrated transporting discharging of LM324A.

Analog input device the most according to claim 1, it is characterised in that: described channel acquisition circuit also includes filtering Circuit and sample circuit, described filter circuit and sample circuit be arranged between common mode rejection circuit and CPU module, described common mode The input of suppression circuit is used for receiving on-site signal, and the outfan of described common mode rejection circuit connects with the input of filter circuit Connecing, the outfan of described filter circuit is connected with the input of sample circuit, and the outfan of described sample circuit is with CPU module even Connect.

5. according to the analog input device described in claim 1 or 4, it is characterised in that: described CPU module and channel acquisition electricity The first isolation circuit it is provided with between road.

Analog input device the most according to claim 1, it is characterised in that: between described CPU module and telecommunication circuit It is provided with the second isolation circuit.