TWI662789B - Pressure switch filter - Google Patents

Abstract

The invention provides a pressure switch filter. The pressure switch filter is used to filter an output signal of a pressure switch. The pressure switch filter includes: a pre-stage circuit, which is a timer. Circuit, the pre-stage circuit has an input end and an output end, the input end of the pre-stage circuit is coupled to a pressure switch output signal end, and the pre-stage circuit is connected in parallel with a first resistor and a first capacitor; A post-stage circuit, which is a comparator circuit, the post-stage circuit has a positive terminal, a negative terminal, and an output terminal, and the positive terminal of the post-stage circuit is coupled to the output terminal of the pre-stage circuit; A second resistor and a second capacitor are coupled between an output terminal of the front-stage circuit and a positive terminal of the subsequent-stage circuit, and a negative terminal of the subsequent-stage circuit is coupled with a third resistor and a fourth resistor.

Description

Pressure switch filter

The present invention relates to signal processing technology, and particularly to a pressure switch filter for removing noise from a pressure switch output signal.

The pressure switch is a component for judging the pressure condition. When the system pressure exceeds the set value, the internal telecommunication output signal state switches. Compared with the pressure sensor, its design principle is simple and low cost, so it is often used in hydraulic and pneumatic systems. It provides controllers or operators to know whether the working pressure meets the minimum requirements for sequential control.

A pressure switch is a component that senses pressure. When the pressure reaches a set value, it is reported back to the system as the basis for system research and judgment, so its reliability must be high. The main principle is that the piston is pushed by the pressure and the spring is moved. When the pressure reaches the set value, the micro switch at the rear end of the spring is touched, so that the switch that was originally an open circuit becomes a path, and the system pressure has been reached.

In order to accurately detect the oil pressure state, the pressure switch will be as close as possible to the power components of the oil pressure system. This component is usually a pump unit. It will be accompanied by vibration and transmitted to the pressure switch through mechanical and hydraulic channels during operation, causing noise from the micro switch output. The main console may misjudge the oil pressure state of the system because of receiving noise, so the output of the pressure switch will always be connected with a filtering device in order to reduce noise interference. And the filtering device must be able to adapt to the special requirements of the noise signal output by the pressure switch. A typical conventional filtering device is shown in Figure 1. It is a passive resistor-capacitor filter circuit. It averages the input value and outputs it. When the switching noise is not serious, the accurate low-level output can be maintained. Once the noise is serious, its output (average) When the value exceeds 0.8V, that is, when the duty cycle of the noise is greater than 1/5 of the signal, the TTL level console is easily misjudged as insufficient system pressure.

In order to solve the shortcomings of the prior art, the present invention provides a pressure switch filter, which can filter the inevitable surge noise generated during the operation of the pressure switch, eliminate the influence of the noise of the pressure switch and accurately reflect the oil pressure establishment of the hydraulic system The closed state reduces the occurrence of erroneous control operation situations where the system misjudges the oil pressure state.

The invention is a pressure switch filter. The pressure switch filter is used to filter the output signal of a pressure switch. The pressure switch filter includes: a pre-stage circuit, which is a timer. Circuit, the pre-stage circuit has an input end and an output end, the input end of the pre-stage circuit is coupled to a pressure switch output signal end, and the pre-stage circuit is connected in parallel with a first resistor and a first capacitor; A post-stage circuit, which is a comparator circuit, the post-stage circuit has a positive terminal, a negative terminal, and an output terminal, and the positive terminal of the post-stage circuit is coupled to the output terminal of the pre-stage circuit; A second resistor and a second capacitor are coupled between an output terminal of the front-stage circuit and a positive terminal of the subsequent-stage circuit, and a negative terminal of the subsequent-stage circuit is coupled with a third resistor and a fourth resistor.

In one embodiment of the present invention, the period of the timer circuit is 11 mS.

In one embodiment of the present invention, the high / low cycle ratio of the output terminal of the pre-stage circuit is greater than 5.

In an embodiment of the present invention, the negative terminal of the post-stage circuit has a TTL low upper limit reference voltage level of 0.8V.

The above summary and the following detailed description and drawings are all for further explaining the methods, means and effects adopted by the present invention to achieve the intended purpose. Other objects and advantages of the present invention will be described in the following description and drawings.

11‧‧‧Pressure Switch

12‧‧‧Previous circuit

a1, a2, a3‧‧‧‧Previous circuit input pin

b1‧‧‧Previous circuit output

13‧‧‧ post-stage circuit

13‧‧‧ post-stage circuit

R1‧‧‧first resistor

R2‧‧‧Second resistor

R3‧‧‧Third resistor

R4‧‧‧Fourth resistor

R5‧‧‧Fifth resistor

C1‧‧‧first capacitor

C2‧‧‧Second capacitor

N‧‧‧Noise

FIG. 1 is a schematic structural diagram of a conventional typical filtering device.

FIG. 2 is a schematic structural diagram of an embodiment of a pressure switch filter according to the present invention.

FIG. 3 is an input / output simulation trend diagram according to an embodiment of the present invention.

The following is a description of specific embodiments of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

FIG. 2 is a schematic structural diagram of an embodiment of a pressure switch filter according to the present invention. As shown in the figure, the embodiment includes: a pressure switch 11 which generates a pressure switch output signal; a front stage circuit 12, The preamp The circuit 12 is a timer circuit. The input end of the pre-stage circuit has three pins a1, a2, and a3, and is coupled to the output signal end of the pressure switch 11 to receive the output signal of the pressure switch. The circuit is connected in parallel with a first resistor R1 and a first capacitor C1. A post-stage circuit 13 is a comparator circuit. The post-stage circuit 13 has a positive terminal, a negative terminal and an output. Terminal, the positive terminal of the post-stage circuit 13 is coupled to the output terminal of the pre-stage circuit 12; the output terminal b1 of the pre-stage circuit 12 and the positive terminal of the post-stage circuit 13 are coupled to a second resistor R2 and A second capacitor C2, a negative terminal of the post-stage circuit 13 is coupled to a third resistor R3 and a fourth resistor R4; an output terminal of the post-stage circuit is coupled to a fifth resistor R5.

Please refer to FIG. 2 and FIG. 3 together with the input / output simulation trend diagrams of the embodiments of the present invention to describe the operation mode of the pressure switch filter of the present invention. The pressure switch filter of the present invention has two stages of circuits: a timer-based pre-stage circuit 12 and a comparator-based post-stage circuit 13 respectively. During the establishment of the oil pressure, the pressure switch generates noise due to mechanical disturbances. N, the noise of the pressure switch 11 is a surge, and the width is less than 2mS. By designing the resistance and capacitance of the first resistor R1 and the first capacitor, the period of the previous circuit (timer) is 11mS. When the a1 pin receives a low signal from the pressure switch 11, it starts the charging cycle of a2 pin, so that the front stage output terminal b1 outputs a high signal. Even if the a1 pin is triggered to receive a high noise signal during the period, the front stage The output of the circuit remains high until the end of the cycle. When starting the a2 pin is greater than 2 / 3Vcc (reference voltage), trigger a spike at the a1 pin, reset the a2 pin, the front output b1 briefly drops to the low position and returns to the high position with the end of the surge. The next charging cycle is also started to ensure that the high / low cycle ratio of the output of the previous stage is greater than 5. The negative terminal of the rear stage gives a low TTL upper limit reference voltage level of 0.8V (generated by the third resistor R3 and the fourth resistor R4), as long as the positive terminal voltage of the subsequent circuit is higher than 0.8V, a high signal is output by raising the resistor; and Add the resistance and capacitance (the second resistor R2 and the second capacitor C2) coupled to the output b1 of the front stage and the positive end of the rear stage to slowly reduce the voltage drop caused by the negative pulse that may occur in the circuit of the previous stage to ensure the subsequent stage. The level of the positive end of the circuit is higher than 2V, so that the output of the subsequent stage is not affected (the fifth resistor R5), and the high level is maintained to achieve the function of complete filtering. Conversely, when the pressure of the hydraulic system of the pressure switch is turned off, the high level of the output signal of the pressure switch 11 continues to exceed the timing period of the previous stage circuit. The low level signal of the front stage output b1 also attenuates the voltage of the positive stage of the rear stage. When the terminal reference voltage Vcc is reached, the output terminal of the post-stage circuit 13 is turned to a low position, which accurately reflects that the system oil pressure state of the pressure switch is off.

In one embodiment of the present invention, the pre-stage circuit is based on a timer, and a resistor (R1) and a capacitor (C1) are configured to obtain an appropriate charge and discharge cycle. The output remains high during the charge cycle and is not affected by the input voltage level. ; After the charging cycle is over, the high level of the input of the previous stage is quickly discharged, the low level of the output of the previous stage is first low, and then the high level is restored after the low of the input of the previous stage, and the next charging cycle begins.

In one embodiment of the present invention, the post-stage circuit is based on a comparator. The negative terminal of the post-stage circuit is given a TTL lower limit upper reference voltage level through a resistor (R3, R4), and the output of the pre-stage circuit passes a first order. After the resistance (R2) and capacitor (C2) are filtered, they are connected to the positive input of the subsequent stage circuit; if the output signal of the previous stage circuit is a surge of the pressure switch noise, it undergoes first-order filtering (R2, C2) to the subsequent stage circuit. The positive voltage of the circuit is still higher than the reference voltage level, and the output terminal of the subsequent stage is raised to a high level by the boost resistor (R5). On the contrary, if the output of the previous stage circuit is continuously high because the oil pressure of the pressure switch has been closed, the subsequent stage When the voltage of the positive terminal of the circuit drops below the reference voltage level, the output of the rear stage will fall to a low level.

Therefore, the present invention provides a pressure switch filter that can filter out the surge noise that is unavoidable during the operation of the pressure switch. The combination of a timer circuit and a comparator circuit in the present invention can definitely eliminate the noise effect of the pressure switch And it accurately reflects the hydraulic pressure establishment / shutdown state of the hydraulic system, reducing the occurrence of erroneous control operation situations where the system misjudges the hydraulic pressure state. The invention is suitable for pressure monitoring of all water pressure, oil pressure and air pressure control systems, and has high application flexibility.

The above-mentioned embodiments are merely illustrative for describing the features and effects of the present invention, and are not intended to limit the scope of the essential technical content of the present invention. Anyone skilled in the art can modify and change the above embodiments without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the rights of the present invention should be listed in the scope of patent application described later.

Claims (4)

A pressure switch filter is used to filter an output signal of a pressure switch. The pressure switch filter includes a pre-stage circuit, which is a timer circuit, and the pre-stage circuit The stage circuit has an input terminal and an output terminal. The input terminal of the preceding circuit is coupled to the pressure switch output signal terminal. The preceding circuit is connected in parallel with a first resistor and a first capacitor. The post-stage circuit is a comparator circuit. The post-stage circuit has a positive terminal, a negative terminal, and an output terminal. The positive terminal of the post-stage circuit is coupled to the output terminal of the pre-stage circuit. A second resistor and a second capacitor are coupled between the output terminal of the circuit and the positive terminal of the subsequent circuit. The negative terminal of the subsequent circuit is coupled with a third resistor and a fourth resistor. The pressure switch is activated. There will be surge noise during the process. The pressure switch filter eliminates the influence of the noise to accurately reflect the pressure on / off state of the pressure switch. The pressure switch filter according to claim 1, wherein the period of the timer circuit is 11 mS. The pressure switch filter according to claim 1, wherein the high / low cycle ratio of the output terminal of the preceding stage circuit is greater than 5. The pressure switch filter according to claim 1, wherein the negative terminal of the post-stage circuit has a TTL low upper limit reference voltage level of 0.8V.