CN205388524U - A signal sample protection circuit for pressure transmitter - Google Patents

Abstract

The utility model belongs to the technical field of diesel engine monitoring and discloses a signal sampling protection circuit for a pressure transmitter. The signal sampling circuit Part_B of the pressure transmitter with flow protection function; the signal sampling circuit Part_B of the pressure transmitter is composed of a field effect transistor Q4 connected to an operational amplifier U2 through a voltage dividing resistor. The measurement circuit combined with the power supply protection circuit of the pressure transmitter by the utility model is suitable for the measurement of pressure signals of diesel engine cooling water, lubricating oil, air intake and other media, and realizes the protection and signal protection of the power supply of the pressure transmitter. Sampling protection reduces the risk of measurement circuit damage caused by wrong wiring and transmitter damage, and improves the safety and reliability of the diesel engine monitoring system.

Description

A signal sampling protection circuit for pressure transmitter

technical field

The utility model belongs to the technical field of diesel engine monitoring, and mainly relates to a signal sampling protection circuit for a pressure transmitter used for measuring pressure signals of diesel engine cooling water, lubricating oil, intake air and other media, and can also be popularized and applied to other In the monitoring system of power equipment.

Background technique

Pressure signal measurement is a commonly used measurement technique in industrial automation control. Depending on factors such as application occasions, measurement range, accuracy requirements, and application costs, the types of sensors selected are different. At present, the pressure sensors commonly used in diesel engine monitoring are mostly in the form of pressure rheostat and pressure transmitter. The pressure rheostat outputs linear resistance signal with the change of pressure. This kind of sensor is cheap and widely used, but the line resistance increases with the extension of the measurement line. In turn, the measurement error will increase; the pressure transmitter outputs a 4-20mA linear current signal with the change of the pressure value, which can eliminate the signal error caused by the resistance of the transmission line. With the improvement of the process and the reduction of the cost, this kind of sensor is more and more widely used. . The pressure transmitter measurement circuit includes two parts: power supply and signal acquisition. The reliability of the circuit will directly affect the correctness of signal acquisition, which in turn will affect the safety and reliability of diesel engine operation.

Utility model content

In order to solve the above technical problems, the purpose of this utility model is to propose a signal sampling protection circuit for a pressure transmitter.

The utility model adopts following technical scheme for finishing its utility model task:

A signal sampling protection circuit for a pressure transmitter, which is a signal sampling circuit Part_B of a pressure transmitter with the functions of converting, amplifying and sampling the pressure transmitter signal and overcurrent protection for a single sensor; One end of the signal sampling circuit Part_B of the pressure transmitter is connected to the signal output end of the external pressure transmitter of the system through the terminal P-, and the other end is connected to the processor MCU; the signal sampling circuit Part_B of the pressure transmitter is controlled by the field The effect transistor Q4 is formed by connecting the operational amplifier U2 through a voltage dividing resistor.

A signal sampling protection circuit for a pressure transmitter, the sampling end of the sampling resistor connected to the field effect transistor Q4 is the D terminal.

A signal sampling protection circuit for a pressure transmitter, the model of the operational amplifier U2 is AD8608, and the output terminal of the operational amplifier U2 is an F terminal.

A signal sampling protection circuit for a pressure transmitter, the type of the field effect transistor Q4 is 2N7002.

Due to the adoption of the above-mentioned technical scheme, the utility model has the following advantages:

A measurement circuit composed of a signal sampling protection circuit for pressure transmitters and a pressure transmitter power supply circuit Part_A with power supply control and total current overcurrent protection functions, which realizes basic measurement functions and increases pressure Transmitter power supply protection and signal sampling protection reduce the risk of measurement circuit damage caused by wrong wiring and transmitter damage, and improve the safety and reliability of the diesel engine monitoring system.

Description of drawings

Figure 1 is a measurement circuit diagram for a pressure transmitter.

Fig. 2 is an enlarged diagram of the signal sampling circuit Part_B of the pressure transmitter in Fig. 1 .

detailed description

The utility model is described in conjunction with accompanying drawing and specific embodiment:

As shown in Figures 1 and 2, a signal sampling protection circuit for pressure transmitters is a pressure transmitter with the functions of converting, amplifying and sampling pressure transmitter signals and overcurrent protection for single-channel sensors. The signal sampling circuit Part_B of the pressure transmitter; one end of the signal sampling circuit Part_B of the pressure transmitter is connected to the signal output terminal of the external pressure transmitter of the system through the terminal P-, and the other end is connected to the processor MCU; the pressure transmitter The signal sampling circuit Part_B of the device is composed of a field effect transistor Q4 connected to an operational amplifier U2 through a sampling resistor. The sampling end of the sampling resistor connected to the FET Q4 is the D terminal, and the output terminal of the operational amplifier AD8608 is the F terminal; the model of the FET Q4 is 2N7002.

The signal sampling circuit Part_B of the pressure transmitter is combined with the power supply circuit Part_A of the pressure transmitter with power supply control and total current overcurrent protection functions to form the measurement circuit of the pressure transmitter;

One end of the power supply circuit Part_A of the pressure transmitter is connected to the power supply end of the external pressure transmitter of the system through the terminal P+, and the other end is connected to the DC power supply 24V; the power supply circuit Part_A of the pressure transmitter is connected by the diode D1 through the transistor Q1 and The field effect transistor Q2 is connected, the transistor Q1 is connected with the field effect transistor Q2, and the B terminal is connected to the processor MCU through the transistor Q3; the transistor Q1 is connected with the field effect transistor Q2, and the B terminal is connected with the comparator LM2901; the field effect transistor Q2 is FQD17P06.

Combined with the power supply circuit Part_A of the pressure transmitter with the function of power supply control and total current overcurrent protection, the measurement method of the pressure transmitter measurement circuit is formed, and the signal of the pressure transmitter is completed while supplying power to the pressure transmitter. Convert, amplify and sample, and have a hierarchical over-current protection function, that is, there are corresponding over-current protections for the total current of the measurement circuit and the partial current of each acquisition channel;

1) Transmit the electrical signal collected by the 4-20mA measurement circuit to the fourth input terminal of the processor MCU, where the pressure transmitter is connected to the circuit in series;

2) The power supply circuit Part_A of the pressure transmitter of the 4-20mA measurement circuit has power supply control and total current overcurrent protection functions;

The on-off control of the power supply to the 4-20mA measurement circuit is realized through the control signal MCU-PW-CRT. The relationship between the power supply control signal MCU-PW-CRT and the power supply state:

When the control signal MCU-PW-CRT is logic 1, the voltage UE is close to 5V, the transistor Q3 is saturated and turned on, and the voltage UB is about 12V under the voltage division of the resistor R2 and the resistor R3, and the field effect transistor Q2 is a P-channel MOS tube, its gate-source threshold voltage V _{GS (th)} = 4V, the actual gate-source voltage V _GS of Q2 ≈ 24V-UB = 12V > V _{GS (th),} so Q2 is turned on, and the 24V power supply is connected to the measurement circuit;

When the control signal MCU-PW-CRT is logic 0, the corresponding input voltage UE is close to 0V, the transistor Q3 is cut off, the voltage UB is about 24V, and the gate-source voltage V _GS of the transistor Q2 ≈24V-UB=0V<V _{GS(th )} Therefore, the transistor Q2 is turned off, and the 24V power supply is disconnected;

The total current overcurrent protection function of the local circuit Part_A means that when the total working current of the 4-20mA measurement circuit exceeds the set rated current value, the circuit will automatically disconnect the 24V power supply to achieve the purpose of circuit protection;

Take the 12-way pressure sensor to provide power as an example to illustrate the protection principle. Considering that the maximum operating current of each pressure sensor is 25mA, the maximum current value after the 12-way pressure sensor is connected to the circuit is about 300mA, so the 4-20mA measurement circuit is rated The current value is set to 350mA to ensure the normal operation of the circuit and prevent damage to the measurement circuit caused by the wrong inflow of excessive current.

3) The signal sampling circuit of the pressure transmitter adopts the sensor channel acquisition circuit Part_B, which can convert, amplify and sample the pressure transmitter signal, and has the overcurrent protection function for the single sensor; that is, the local circuit

The sensor channel acquisition circuit Part_B, each sensor channel acquisition circuit Part_B outputs the sampling signal Output-MCU-AD and sends it to the MCU for AD sampling;

At the same time, the MCU outputs 1 power supply control signal MCU-PW-CRT and 12 channel control signals MCU-CH-CRT. The former can realize the power supply control of the measurement circuit, and the latter can realize the individual control of each channel acquisition circuit;

The local circuit Part_B converts the 4-20mA signal input by the pressure transmitter into a voltage signal and amplifies it and sends it to the MCU. The MCU calculates the current value according to the voltage value, and calculates the actual pressure value according to the conversion formula between current and pressure; MCU Perform 12-bit AD conversion on the input voltage UF, with

(18)

The op amp U2 can amplify UD by 2 times, so (19)

According to the relationship between sensor pressure and current, taking the range of 0-1MPa as an example, the pressure value P to be measured is

(20)

According to the relationship between ID and point D voltage UD:

(twenty one)

Substituting formulas (18), (19), and (21) into (20) gives

(twenty two)

The MCU can calculate the pressure value to be measured according to the formula (22), the unit is MPa;

The range of the pressure transmitter signal is 4-20mA, and the corresponding input voltage UF range is 0.96-4.8V. When the MCU detects that the input voltage UF exceeds the upper limit of the range, it considers that the channel sensor needs to be over-current protected, so it is forced Set MCU-CH-CRT to logic 0; field effect transistor Q4 is an N-channel MOS transistor, and its gate-source threshold voltage V _{GS (th)} = 3V, when MCU-CH-CRT is logic 0, the field effect transistor The gate-source voltage V _GS of Q4 ≈0V<V _GS(th) , then Q4 is turned off and the sensor is disconnected, achieving the purpose of overcurrent protection for the channel sensor;

4) The specific implementation process of automatic power-off protection. When an overcurrent occurs during normal power supply, the MCU judges the power supply status of the circuit by reading the value of Output-MCU-PW. Once Output-MCU-PW is 0, Then the MCU thinks that the measurement circuit needs to be disconnected from the power supply, and sets the MCU-PW-CRT to 0; the state corresponding relationship is:

When the MCU-PW-CRT is logic 1 and the 24V power supply is connected to the measurement circuit, if the power supply is normal, UB is about 12V, and if UB<UC, the output terminal of the comparator U1 is in a high-impedance off state, Output-MCU-PW Pulled up to about 5V, the MCU reads it as a logic 1. At this time, the MCU thinks that the circuit is powered normally, and the MCU-PW-CRT remains 1;

When MCU-PW-CRT is logic 0, when the power supply is normally cut off, UB is about 24V, if UB>UC, the output terminal of comparator U1 is in a low-impedance conduction state, Output-MCU-PW is close to 0V, and MCU reads it as Logic 0, at this time the MCU thinks that the circuit power supply is cut off, and the MCU-PW-CRT remains 0;

When MCU-PW-CRT supplies logic 1 normally, if there is overcurrent in the circuit, IR1 is 350mA, then UR1 is 0.7V, so the triode Q1 is saturated and turned on, UB voltage is about 24V, UB>UC, the output terminal of comparator U1 It is a low-impedance conduction state, Output-MCU-PW is close to 0V, and MCU reads it as logic 0. At this time, MCU thinks that the total working current of the circuit is abnormal and needs to protect the measurement circuit, and MCU-PW-CRT is forced to be logic 0. The 24V power supply is disconnected.

Claims (4)

1., for a signal sampling protection circuit for pressure transmitter, it is characterized in that: be the signal sample circuit Part_B with pressure transmitter pressure transmitter signal changed, amplify and sampled and to the overcurrent protection function of single channel sensor；Signal sample circuit Part_B one end of described pressure transmitter is connected with its exterior pressure transmitter signal output part by terminals P-, and the other end connects processor MCU；The signal sample circuit Part_B of described pressure transmitter is connected to form with transport and placing device U2 by sample resistance by field effect transistor Q4.

2. a kind of signal sampling for pressure transmitter according to claim 1 protects circuit, it is characterized in that: the sample resistance sampling end being connected with field effect transistor Q4 is D end points.

3. a kind of signal sampling for pressure transmitter according to claim 1 protects circuit, it is characterized in that: described transport and placing device U2 model is AD8608, and transport and placing device U2 outfan is F end points.

4. a kind of signal sampling for pressure transmitter according to claim 1 protects circuit, it is characterized in that: described field effect transistor Q4 model is 2N7002.