CN114390748A - Circuit for realizing threshold LED indication by 4-20mA ultraviolet probe - Google Patents

Abstract

The invention discloses a circuit for realizing threshold LED indication by a 4-20mA ultraviolet probe, and relates to the technical field of ultraviolet probe circuits. The input end of a circuit for outputting a 4-20mA current signal by the 4-20mA ultraviolet probe is connected with 24V direct current, the output end of the circuit is connected with a differential operational amplification circuit, the output end of the circuit for outputting the 4-20mA current signal by the 4-20mA ultraviolet probe is also connected with a first sampling resistor in series to an output end of a 4-20mA Out, the output end of the differential operational amplification circuit is connected with a comparator circuit, the differential operational amplification circuit and the comparator circuit form a current sampling comparison circuit, and the output end of the comparator circuit is connected with a first path of indicator lamp and a second path of indicator lamp through an LED driving circuit. The invention realizes the functions of transmitting and supplying 4-20mA current signals and indicating the function of being more than or less than a specific threshold value, judges the ultraviolet intensity by the LED threshold value indicating lamp and has wide application prospect.

Description

4-20mA UV probe realizes threshold LED indication circuit

technical field

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

Background technique

At present, all the UV probes on the market do not judge the UV intensity by the color of the LED, and the most widely used in the industry is to use the analog 4-20mA current signal to transmit the temperature, pressure, speed, irradiation value, etc. It has the advantages of long transmission distance and strong anti-interference ability. The technical difficulties of 4-20mA UV probe to realize the circuit of threshold LED indication:

① The problem of sharing the power supply of the current sampling circuit and the LED drive circuit: as the change of the detected ultraviolet value reflects the change of the output current in the range of 4-20mA, the current sampling circuit and the LED drive circuit cannot obtain a stable working voltage and work abnormal, and the resulting voltage drop may affect the device-side signal acquisition.

② Connect the current sampling circuit and the LED drive circuit in parallel between the two signal lines to supply power: the current of the power supply ground wire generated when the current sampling circuit and the LED drive circuit are working will flow into the current signal output line, causing the output current signal to be significantly larger, which is a serious problem. affect the measurement accuracy.

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

SUMMARY OF THE INVENTION

In view of the deficiencies in the prior art, the purpose of the present invention is to provide a 4-20mA ultraviolet probe to realize the threshold LED indication circuit, the circuit principle is simple, the design is reasonable, the transmission and power supply functions of the 4-20mA current signal are realized, and the realization of The LED indication function that is greater than or less than a specific threshold value is used to judge the size of the ultraviolet intensity through the LED threshold value indicator light, which is practical and easy to promote and use.

In order to achieve the above purpose, the present invention is achieved through the following technical solutions: a circuit for realizing threshold LED indication by a 4-20mA UV probe, including a 4-20mA UV probe outputting a 4-20mA current signal circuit, a differential operational amplifier circuit, and a comparator circuit And LED drive circuit, the input end of 4-20mA UV probe output 4-20mA current signal circuit is connected to 24V DC, the output end of 4-20mA UV probe output 4-20mA current signal circuit is connected to differential operational amplifier circuit, 4-20mA UV The output end of the probe output 4-20mA current signal circuit is also connected in series with the first sampling resistor to the 4-20mA Out output end, the output end of the differential operational amplifier circuit is connected to the comparator circuit, and the differential operational amplifier circuit and the comparator circuit form a current Sampling and comparison circuit, the output end of the comparator circuit is connected with the first indicator light and the second indicator light through the LED driving circuit.

Preferably, the differential operational amplifier circuit is composed of an operational amplifier, a second resistor-fifth resistor, and the comparator circuit is composed of a comparator, a sixth resistor, a seventh sampling resistor, and an eighth sampling resistor. The LED driving circuit includes a ninth resistor-thirteenth resistor and a transistor switch, the first indicator light is composed of three parallel first LED lights, second LED lights, and third LED lights, and the second LED lights are connected in parallel. The road indicator is composed of three series-connected fourth LED lights, fifth LED lights, and sixth LED lights; the output end of the 4-20mA UV probe outputting 4-20mA current signal circuit is connected to the second resistor to the positive input end of the operational amplifier , the positive input terminal of the operational amplifier is connected to the fourth resistor to the ground terminal, the output terminal 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 terminal, and the 4-20mA Out output terminal Connect 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, and the negative input terminal of the comparator is connected The terminals are respectively connected to the seventh sampling resistor and the eighth sampling resistor to 24V direct current and the ground terminal, the output end of the comparator is connected to the ninth resistor to the base of the transistor switch, and the collector of the transistor switch is connected to the first LED lamp and the first LED in turn. The parallel circuit composed of the second LED lamp and the third LED lamp, the parallel circuit of the tenth resistor, the eleventh resistor and the twelfth resistor is connected to 24V DC, and the nodes between the two parallel circuits are connected in series with the fourth LED lamp, the fifth The LED lamp, the sixth LED lamp, and the thirteenth resistor are connected to the emitter of the transistor switch, and the emitter of the transistor switch is grounded.

Preferably, the 4-20mA current signal output wire of the 4-20mA UV probe outputting the 4-20mA current signal circuit is separated from the current sampling and comparison circuit and the power ground wire of the LED drive circuit, so that the two circuit loops can cooperate with each other. work, and will not have a greater impact on each other.

Beneficial effects of the invention: the circuit adopts the circuit structure of three wires, realizes the transmission and power supply functions of 4-20mA current signal, and realizes the LED indication function greater than or less than a specific threshold, and judges the magnitude of the ultraviolet intensity through the LED threshold indicator , the application prospect is broad.

Description of drawings

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments;

Fig. 1 is the principle block diagram of the present invention;

FIG. 2 is a circuit diagram of the present invention.

Detailed ways

In order to make the technical means, creative features, achievement goals and effects realized by the present invention easy to understand, the present invention will be further described below with reference to the specific embodiments.

1-2, this specific embodiment adopts the following technical solutions: a 4-20mA UV probe realizes a circuit for threshold LED indication, including a 4-20mA UV probe outputting a 4-20mA current signal circuit UA, a differential operational amplifier circuit 1, and a comparator Circuit 2 and LED drive circuit 3, 4-20mA UV probe outputs 4-20mA current signal The input end of circuit UA is connected to 24V DC, 4-20mA UV probe outputs 4-20mA current signal The output end of circuit UA is connected to differential operational amplifier circuit 1 Connected, the output end of the 4-20mA UV probe outputting 4-20mA current signal circuit UA is also connected in series with the first sampling resistor R1 to the 4-20mA Out output end, the output end of the differential operational amplifier circuit 1 is connected to the comparator circuit 2, and the differential The operational amplifier circuit 1 and the comparator circuit 2 form a current sampling and comparison circuit. The output end of the comparator circuit 2 is connected to the first indicator LED1 and the second indicator LED2 through the LED driving circuit 3 .

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

4-20mA UV probe output 4-20mA current signal The output end of the 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 4-20mA UV The output terminal of the probe output 4-20mA current signal circuit UA is connected in series with the first sampling resistor R1 to the 4-20mA Out output terminal, and the 4-20mA Out output terminal is connected with the third resistor R3 to the negative input terminal of the operational amplifier OPA, and the operational amplifier OPA A fifth resistor R5 is connected between the negative input end and the output end of the operational amplifier OPA, the output end of the operational amplifier OPA is connected to the sixth resistor R6 to the positive input end of the comparator COM, and the negative input end of the comparator COM is respectively connected to the seventh sampling resistor R7, The eighth sampling resistor R8 is connected to the 24V DC and ground terminals, and the output terminal of the comparator COM is connected to the ninth resistor R9 to the base of the transistor switch Q1, and the collector of the transistor Q1 is connected to the first LED lamp DB1 and the second LED in turn The parallel circuit composed of the lamp DB2 and the third LED lamp DB3, the parallel circuit of the tenth resistor R10, the eleventh resistor R11 and the twelfth resistor R12 is connected to 24V DC, and 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 are connected to the emitter of the transistor Q1, and the emitter of the transistor Q1 is grounded.

The working principle of this specific embodiment is: the first sampling resistor R1 is connected in series between the 4-20mA UV probe output 4-20mA current signal circuit UA and the 4-20mA Out output terminal, and the two ends of the first sampling resistor R1 generate The voltages U1 and U2 are 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 comparator circuit 2, the compared voltage Uc=VCC/(R7+R8)×R8, comparator circuit 2 compares Uc with Uo:

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

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

This specific embodiment adds a current sampling and comparison circuit and an LED driving circuit on the basis of the traditional two-wire UV probe circuit that outputs a 4-20 mA current signal, and sets a separate power ground wire to connect the 4-20 mA current signal output line to the current sampling circuit. The power and ground wires of the comparison circuit and the LED drive circuit are separated, so that the two circuit loops can work together without having a great influence on each other; VCC and 4-20mA Out provide power for the UV probe circuit and form 4 -20mA current signal loop, VCC and GND provide the power loop for the current sampling and comparison circuit and the LED driving circuit, which can not only make the current sampling and comparison circuit and the LED driving circuit obtain a stable power supply and work normally, but also greatly reduce the current The loop current of the sampling comparison circuit and the LED drive circuit flows into the 4-20mA current signal loop to avoid affecting the 4-20mA current output signal. The 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 greater or less than a specific threshold, which can be judged by the color of the LED if it is greater or less than a specific threshold. It is practical and reliable to judge the magnitude of the ultraviolet intensity through the LED threshold indicator light, and has broad application prospects.

The basic principles and main features of the present invention and the advantages of the present invention have been shown and described above. Those skilled in the art should understand that the present invention is not limited by the above-mentioned embodiments, and the descriptions in the above-mentioned embodiments and the description are only to illustrate the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have Various changes and modifications fall within the scope of the claimed invention. The claimed scope of the present invention is defined by the appended claims and their equivalents.

Claims (2)

1. The circuit for realizing threshold LED indication by the 1.4-20mA ultraviolet probe is characterized by comprising a 4-20mA ultraviolet probe output 4-20mA current signal circuit (UA), a differential operation amplification circuit (1), a comparator circuit (2) and an LED drive circuit (3), wherein the input end of the 4-20mA current signal circuit (UA) output by the 4-20mA ultraviolet probe is connected with 24V direct current, the output end of the 4-20mA current signal circuit (UA) output by the 4-20mA ultraviolet probe is connected with the differential operation amplification circuit (1), the output end of the 4-20mA current signal circuit (UA) output by the 4-20mA ultraviolet probe is also connected with a first sampling resistor (R1) to a 4-20mA Out output end in series, the output end of the differential operation amplification circuit (1) is connected with the comparator circuit (2), and the differential operation amplification circuit (1) and the comparator circuit (2) form a current sampling comparison circuit, the output end of the comparator circuit (2) is connected with the first indicator light (LED1) and the second indicator light (LED2) through the LED driving circuit (3).
2. 2. The 4-20mA ultraviolet probe of claim 1 implementing threshold LED indication circuitry, characterized in 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) consists of a Comparator (COM), a sixth resistor (R6), a seventh sampling resistor (R7) and an eighth sampling resistor (R8), the LED driving circuit (3) comprises a ninth resistor (R9) -a thirteenth resistor (R13) and a transistor switching tube (Q1), the first road indicator lamp (LED1) consists of three first LED lamps (DB1), a second LED lamp (DB2) and a third LED lamp (DB3) which are connected in parallel, and the second road indicator lamp (LED2) consists of three fourth LED lamps (DR1), a fifth LED lamp (DR2) and a sixth LED lamp (DR3) which are connected in series;

   the output end of the 4-20mA ultraviolet probe output 4-20mA current signal circuit (UA) is connected with a second resistor (R2) to the positive input end of an operational amplifier (OPA), the positive input end of the operational amplifier (OPA) is connected with a 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 with a first sampling resistor (R1) to a 4-20mA Out output end in series, the 4-20mA Out output end is connected with a third resistor (R3) to the negative input end of the operational amplifier (OPA), a fifth resistor (R5) is connected between the negative input end and the output end of the operational amplifier (OPA), the output end of the operational amplifier (OPA) is connected with a sixth resistor (R6) to the positive input end of a Comparator (COM), and the negative input end of the Comparator (COM) is respectively connected with a seventh sampling resistor (R7), An eighth sampling resistor (R8) is connected with a 24V direct current, the output end of the Comparator (COM) is connected with a base electrode of a ninth resistor (R9) to a transistor switch tube (Q1), a collector electrode of the transistor switch tube (Q1) is sequentially connected with a parallel circuit consisting of a first LED lamp (DB1), a second LED lamp (DB2) and a third LED lamp (DB3), a parallel circuit consisting of a tenth resistor (R10), an eleventh resistor (R11) and a twelfth resistor (R12) is connected with the 24V direct current, a node between the two parallel circuits is sequentially connected with an emitter electrode of the fourth LED lamp (1), the fifth LED lamp (DR2), the sixth LED lamp (DR3), a thirteenth resistor (R13) to the transistor switch tube (Q1), and an emitter electrode of the transistor switch tube (Q1) is grounded.

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