4-20mA UV probe threshold LED indication circuit

Abstract

The invention discloses a circuit for realizing threshold LED indication of a 4‑20mA ultraviolet probe, and relates to the technical field of ultraviolet probe circuits. The input end of the 4‑20mA ultraviolet probe output 4‑20mA current signal circuit is connected to 24V direct current, and the output end is connected to a differential operational amplifier circuit. The output end of the 4‑20mA ultraviolet probe output 4‑20mA current signal circuit is also connected in series with a first sampling resistor to a 4‑20mA Out output end, and the output end of the differential operational amplifier circuit is connected to a comparator circuit, and the differential operational amplifier circuit and the comparator circuit form a current sampling comparison circuit, and the output end of the comparator circuit is connected to a first indicator light and a second indicator light through an LED driving circuit. The present invention realizes the transmission and power supply functions of a 4‑20mA current signal, as well as the indication function of being greater than or less than a specific threshold value, and judges the ultraviolet intensity through an LED threshold indicator light, and has broad application prospects.

Description

Technical Field

[0001] The invention relates to the technical field of ultraviolet probe circuits, in particular to a circuit for realizing threshold LED indication of a 4-20mA ultraviolet probe. Background Art

[0002] Currently, all UV probes on the market do not use the color of the LED to determine the UV intensity. The most widely used method in industry is to use analog 4-20mA current signals to transmit temperature, pressure, speed, irradiation values, etc., which has the advantages of long transmission distance and strong anti-interference ability. Technical difficulties of the 4-20mA UV probe to realize the threshold LED indication circuit:

[0003] ① The problem of sharing the power supply for the current sampling circuit and the LED driving circuit: As the changes in the detected UV value are reflected in the changes in the output current within the range of 4-20mA, the current sampling circuit and the LED driving circuit cannot obtain a stable operating voltage and work abnormally, and the resulting voltage drop may affect the signal acquisition on the device side.

[0004] ② Connect the current sampling circuit and the LED driving circuit in parallel between the two signal lines for power supply: When the current sampling circuit and the LED driving circuit are working, the power ground current generated is merged into the current signal output line, causing the output current signal to be significantly larger, seriously affecting the measurement accuracy.

[0005] In order to solve the above problems, it is particularly necessary to design a new 4-20mA UV probe circuit to realize threshold LED indication. Summary of the invention

[0006] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a circuit for a 4-20mA ultraviolet probe to realize threshold LED indication. The circuit principle is simple and the design is reasonable. It can realize the transmission and power supply functions of the 4-20mA current signal, as well as the LED indication function of being greater than or less than a specific threshold. The ultraviolet intensity is judged by the LED threshold indicator light. The circuit has strong practicality and is easy to promote and use.

[0007] In order to achieve the above-mentioned purpose, the present invention is realized by the following technical scheme: a circuit for realizing threshold LED indication by a 4-20mA ultraviolet probe, comprising a 4-20mA ultraviolet probe outputting a 4-20mA current signal circuit, a differential operational amplifier circuit, a comparator circuit and an LED driving circuit, wherein the input end of the 4-20mA ultraviolet probe outputting a 4-20mA current signal circuit is connected to a 24V direct current, the output end of the 4-20mA ultraviolet probe outputting a 4-20mA current signal circuit is connected to the differential operational amplifier circuit, the output end of the 4-20mA ultraviolet probe outputting a 4-20mA current signal circuit is also connected in series with a first sampling resistor to a 4-20mA Out output end, the output end of the differential operational amplifier circuit is connected to a comparator circuit, the differential operational amplifier circuit and the comparator circuit constitute a current sampling comparison circuit, and the output end of the comparator circuit is connected to a first indicator light and a second indicator light through an LED driving circuit.

[0008] Preferably, the differential operational amplifier circuit is composed of an operational amplifier, a second resistor to a fifth resistor, the comparator circuit is composed of a comparator, a sixth resistor, a seventh sampling resistor, and an eighth sampling resistor, the LED drive circuit includes a ninth resistor to a thirteenth resistor, a crystal switch tube, the first indicator light is composed of three parallel first LED lamps, a second LED lamp, and a third LED lamp, and the second indicator light is composed of three series-connected fourth LED lamps, a fifth LED lamp, and a sixth LED lamp; the output end of the 4-20mA ultraviolet probe output 4-20mA current signal circuit is connected to the second resistor to the positive input end of the operational amplifier, the positive input end of the operational amplifier is connected to the fourth resistor to the ground end, the output end of the 4-20mA ultraviolet probe output 4-20mA current signal circuit is connected in series with the first sampling resistor to the 4-20mA Out output end, and the 4-20mA The Out output terminal is connected to the third resistor to the negative input terminal of the operational amplifier, a fifth resistor is connected between the negative input terminal and the output terminal of the operational amplifier, the output terminal of the operational amplifier is connected to the sixth resistor to the positive input terminal of the comparator, the negative input terminal of the comparator is respectively connected to the seventh sampling resistor and the eighth sampling resistor to 24V DC and the ground terminal, the output terminal of the comparator is connected to the ninth resistor to the base of the crystal switch tube, the collector of the crystal switch tube is connected in sequence to the parallel circuit composed of the first LED lamp, the second LED lamp and the third LED lamp, and the parallel circuit composed of the tenth resistor, the eleventh resistor and the twelfth resistor to 24V DC, the node between the two parallel circuits is connected in series with the fourth LED lamp, the fifth LED lamp, the sixth LED lamp, and the thirteenth resistor to the emitter of the crystal switch tube, and the emitter of the crystal switch tube is grounded.

[0009] Preferably, the 4-20mA current signal output line of the 4-20mA current signal circuit of the 4-20mA UV probe is separated and independent from the power ground line of the current sampling comparison circuit and the LED drive circuit, so that the two circuit loops can work together without having a significant impact on each other.

[0010] Beneficial effects of the present invention: The circuit adopts a three-wire circuit structure to realize the transmission and power supply functions of 4-20mA current signals, as well as the LED indication function of being greater than or less than a specific threshold value. The LED threshold indicator light is used to judge the size of the ultraviolet intensity, and the application prospect is broad. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments;

[0012] Figure 1 It is a principle block diagram of the present invention;

[0013] Figure 2 It is a circuit diagram of the present invention. DETAILED DESCRIPTION

[0014] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0015] Reference Figure 1-2 The present specific implementation adopts the following technical scheme: a circuit for realizing threshold LED indication by a 4-20mA ultraviolet probe, comprising a 4-20mA ultraviolet probe outputting a 4-20mA current signal circuit UA, a differential operational amplifier circuit 1, a comparator circuit 2 and an LED driving circuit 3, wherein the input end of the 4-20mA ultraviolet probe outputting a 4-20mA current signal circuit UA is connected to a 24V direct current, the output end of the 4-20mA ultraviolet probe outputting a 4-20mA current signal circuit UA is connected to the differential operational amplifier circuit 1, the output end of the 4-20mA ultraviolet probe outputting a 4-20mA current signal circuit UA is also connected in series with a first sampling resistor R1 to a 4-20mA Out output end, the output end of the differential operational amplifier circuit 1 is connected to the comparator circuit 2, the differential operational amplifier circuit 1 and the comparator circuit 2 form a current sampling comparison circuit, and the output end of the comparator circuit 2 is connected to a first indicator light LED1 and a second indicator light LED2 through an LED driving circuit 3.

[0016] It is worth noting that the differential operational amplifier circuit 1 is composed of an operational amplifier OPA, a second resistor R2-a fifth resistor R5, the comparator circuit 2 is composed of a comparator COM, a sixth resistor R6, a seventh sampling resistor R7, and an eighth sampling resistor R8, the LED drive circuit 3 includes a ninth resistor R9-a thirteenth resistor R13, a crystal switch tube Q1, the first indicator light LED1 is composed of three parallel first LED lights DB1, a second LED light DB2, and a third LED light DB3, and the second indicator light LED2 is composed of three series-connected fourth LED lights DR1, a fifth LED light DR2, and a sixth LED light DR3.

[0017] The output end of the 4-20mA ultraviolet probe output 4-20mA current signal circuit UA is connected to the second resistor R2 to the positive input end of the operational amplifier OPA, the positive input end of the operational amplifier OPA is connected to the fourth resistor R4 to the ground end, the output end of the 4-20mA ultraviolet probe output 4-20mA current signal circuit UA is connected in series with the first sampling resistor R1 to the 4-20mA Out output end, and the 4-20mA The output terminal Out is connected to the third resistor R3 to the negative input terminal of the operational amplifier OPA, and a fifth resistor R5 is connected between the negative input terminal and the output terminal of the operational amplifier OPA. The output terminal of the operational amplifier OPA is connected to the sixth resistor R6 to the positive input terminal of the comparator COM. The negative input terminal of the comparator COM is respectively connected to the seventh sampling resistor R7 and the eighth sampling resistor R8 to 24V DC and the ground terminal. The output terminal of the comparator COM is connected to the ninth resistor R9 to the base of the crystal switch tube Q1. The collector of the crystal switch tube Q1 is connected in sequence to the parallel circuit composed of the first LED lamp DB1, the second LED lamp DB2 and the third LED lamp DB3, and the parallel circuit composed of the tenth resistor R10, the eleventh resistor R11 and the twelfth resistor R12 to 24V DC. The node between the two parallel circuits is connected in series with the fourth LED lamp DR1, the fifth LED lamp DR2, the sixth LED lamp DR3, and the thirteenth resistor R13 to the emitter of the crystal switch tube Q1, and the emitter of the crystal switch tube Q1 is grounded.

[0018] The working principle of this specific implementation is: the first sampling resistor R1 is connected in series between the 4-20mA ultraviolet probe output 4-20mA current signal circuit UA and the 4-20mA Out output terminal, and voltages U1 and U2 are generated at both ends of the first sampling resistor R1 respectively, and sent to the differential operational amplifier circuit 1, and the amplified voltage Uo=(R2+R5)×R4×U2 / [(R3+R5)×R2]-R5×U1 / R2. Uo is sent to the comparator circuit 2, and the compared voltage Uc=VCC / (R7+R8)×R8, and the comparator circuit 2 compares Uc with Uo:

[0019] ① When the measured ultraviolet radiation value is large, the 4-20mA current signal output by the 4-20mA ultraviolet probe output 4-20mA current signal circuit UA is large. At this time, the output voltage value Uo of the differential operational amplifier circuit 1 is greater than the compared voltage value Uc, and Ur outputs a high level to the LED drive circuit 3. At this time, the crystal switch tube Q1 is turned on. Since the first LED lamp DB1, the second LED lamp DB2, and the third LED lamp DB3 are connected in parallel, the conduction voltage is VF; the fourth LED lamp DR1, the fifth LED lamp DR2, and the sixth LED lamp DR3 are connected in series, and the conduction voltage is 3VF, so the first LED lamp DB1, the second LED lamp DB2, and the third LED lamp DB3 are lit, and the fourth LED lamp DR1, the fifth LED lamp DR2, and the sixth LED lamp DR3 are off, indicating that the ultraviolet radiation value is greater than the threshold.

[0020] ② When the measured ultraviolet radiation value is small, the 4-20mA current signal output by the 4-20mA ultraviolet probe output 4-20mA current signal circuit UA is small. At this time, the output voltage value Uo of the differential operational amplifier circuit 1 is less than the compared voltage value Uc, and Ur outputs a low level to the LED drive circuit 3. At this time, the crystal switch tube Q1 is cut off. At this time, the first LED lamp DB1, the second LED lamp DB2, and the third LED lamp DB3 are off, and the fourth LED lamp DR1, the fifth LED lamp DR2, and the sixth LED lamp DR3 are lit, indicating that the ultraviolet radiation value is less than the threshold.

[0021] This specific implementation method adds a current sampling comparison circuit and an LED drive circuit on the basis of a traditional two-wire ultraviolet probe circuit that outputs a 4-20mA current signal, and sets a separate power ground line to separate the 4-20mA current signal output line from the power ground lines of the current sampling comparison circuit and the LED drive circuit, so that the two circuit loops can work together without having a significant impact on each other; VCC and 4-20mA Out provide power for the ultraviolet probe circuit and form a 4-20mA current signal loop, and VCC and GND provide a power supply loop for the current sampling comparison circuit and the LED drive circuit, so that the current sampling comparison circuit and the LED drive circuit can obtain a stable power supply and work normally, and also greatly reduce the loop current of the current sampling comparison circuit and the LED drive circuit flowing into the 4-20mA current signal loop, avoiding affecting the 4-20mA current output signal. This circuit uses the three wires of the 4-20mA UV probe to simultaneously realize the transmission and power supply functions of the 4-20mA current signal, as well as the indication function of being greater than or less than a specific threshold. Whether it is greater than or less than the specific threshold can be judged by the color of the LED, and the size of the UV intensity can be judged by the LED threshold indicator. It is practical and reliable, and has broad application prospects.

[0022] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. 4-20mA UV probe to achieve threshold LED indication circuit, characterized in that: The invention comprises a 4-20mA ultraviolet probe output 4-20mA current signal circuit, a differential operational amplifier circuit (1), a comparator circuit (2) and an LED drive circuit (3). The input end of the 4-20mA ultraviolet probe output 4-20mA current signal circuit is connected to a 24V direct current, the output end of the 4-20mA ultraviolet probe output 4-20mA current signal circuit is connected to the differential operational amplifier circuit (1), the output end of the 4-20mA ultraviolet probe output 4-20mA current signal circuit is also connected in series with a first sampling resistor to a 4-20mA Out output end, the output end of the differential operational amplifier circuit (1) is connected to the comparator circuit (2), the differential operational amplifier circuit (1) and the comparator circuit (2) form a current sampling comparison circuit, and the output end of the comparator circuit (2) is connected to a first indicator light and a second indicator light through an LED drive circuit (3); The differential operational amplifier circuit (1) is composed of an operational amplifier, a second resistor to a fifth resistor, the comparator circuit (2) is composed of a comparator, a sixth resistor, a seventh sampling resistor, and an eighth sampling resistor, the LED drive circuit (3) includes a ninth resistor to a thirteenth resistor, and a crystal switch tube, the first indicator light is composed of three parallel-connected first LED lamps, a second LED lamp, and a third LED lamp, and the second indicator light is composed of three series-connected fourth LED lamps, a fifth LED lamp, and a sixth LED lamp; The output end of the 4-20mA UV probe output 4-20mA current signal circuit is connected to the second resistor to the positive input end of the operational amplifier, the positive input end of the operational amplifier is connected to the fourth resistor to the ground end, the output end of the 4-20mA UV probe output 4-20mA current signal circuit is connected in series with the first sampling resistor to the 4-20mA Out output end, and the 4-20mA The output terminal Out is connected to the third resistor to the negative input terminal of the operational amplifier, a fifth resistor is connected between the negative input terminal and the output terminal of the operational amplifier, the output terminal of the operational amplifier is connected to the sixth resistor to the positive input terminal of the comparator, the negative input terminal of the comparator is respectively connected to the seventh sampling resistor and the eighth sampling resistor to the 24V DC and the ground terminal, the output terminal of the comparator is connected to the ninth resistor to the base of the crystal switch tube, the collector of the crystal switch tube is sequentially connected to the parallel circuit composed of the first LED lamp, the second LED lamp and the third LED lamp, and the parallel circuit composed of the tenth resistor, the eleventh resistor and the twelfth resistor to the 24V DC, the node between the two parallel circuits is sequentially connected in series to the fourth LED lamp, the fifth LED lamp, the sixth LED lamp, the thirteenth resistor to the emitter of the crystal switch tube, and the emitter of the crystal switch tube is grounded; The comparator circuit (2) compares the compared voltage Uc with the output voltage value Uo of the differential operational amplifier circuit (1). When the measured ultraviolet radiation value is larger, the 4-20mA current signal output by the 4-20mA ultraviolet probe output 4-20mA current signal circuit is larger. At this time, the output voltage value Uo of the differential operational amplifier circuit (1) is larger than the compared voltage value Uc, and Ur outputs a high level to the LED drive circuit (3). The crystal switch tube is turned on, the first LED lamp, the second LED lamp, and the third LED lamp are lit, and the fourth LED lamp, the fifth LED lamp, and the sixth LED lamp are turned off, indicating that the ultraviolet radiation value is greater than the threshold value. The comparator circuit (2) compares the compared voltage Uc with the output voltage value Uo of the differential operational amplifier circuit (1). When the measured ultraviolet radiation value is small, the 4-20mA current signal output by the 4-20mA ultraviolet probe output 4-20mA current signal circuit is small. At this time, the output voltage value Uo of the differential operational amplifier circuit (1) is smaller than the compared voltage value Uc, and Ur outputs a low level to the LED drive circuit (3), the crystal switch tube is cut off, the first LED lamp, the second LED lamp, and the third LED lamp are turned off, and the fourth LED lamp, the fifth LED lamp, and the sixth LED lamp are turned on, indicating that the ultraviolet radiation value is less than the threshold value.

2. The circuit for realizing threshold LED indication of the 4-20mA ultraviolet probe according to claim 1, characterized in that: The 4-20mA current signal output line of the 4-20mA ultraviolet probe output 4-20mA current signal circuit is independent and separate from the power ground line of the current sampling comparison circuit and the LED drive circuit (3), so that the two circuit loops can work together without affecting each other.

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