CN204439817U - A digitally controlled resistance box - Google Patents

Abstract

The utility model discloses a numerical control resistance box, including an at least temperature automatic control circuit, temperature automatic control circuit includes temperature detect circuit, electronic switch, fan and DC power supply, and electronic switch and fan motor concatenate between DC power supply's positive negative pole, and temperature detect circuit's output termination electronic switch's control end. The utility model discloses a temperature automatic control circuit drive fan heat dissipation makes numerical control resistance box remain throughout to work under the suitable temperature, and the resistance of resistance is stable accurate, and the precision height, the resistance box components and parts that detect can not damage long service life because of overheated.

Description

A digitally controlled resistance box

[technical field]

The utility model relates to resistance testing, in particular to a numerically controlled resistance box.

[Background technique]

The application of the resistance box is generally used in the fields of impedance switching, resistance load and so on. For impedance switching, the combination switch resistance box for teaching is common, and the resistance setting is completed by switching multiple switches. The resistance box with multi-stage switch combination has problems such as complicated switching, difficult reading, and low resistance power. However, electronic loads have higher requirements in the use of voltage, power and other environments, and are not suitable for alternating current. The resistance box for verification generally realizes switching between different resistance values by manually adjusting the rotary switch, and at the same time reads the resistance value according to the indication of the rotary switch. At the same time, because the switching of the resistance value is to be completed manually, and the manual completion takes a long time, the response time of the tested instrument cannot be measured.

The invention application with the application number CN201310497771.1 discloses a digital resistance box for verification. This kind of digital resistance box for verification can input the required resistance value through the keyboard [3], and the processing unit [2] controls the resistance selection after the input is completed. [1] The circuit automatically adjusts the resistance value and displays the resistance value to the LCD screen [4]. Among them, the selection of the resistance is realized by controlling the switching of different relays by the processing unit [2]. At the same time, this kind of digital resistance box for verification can increase or decrease the output resistance value within a certain range within a certain period of time, and the switching time of different resistance values can also be adjusted, which can realize automatic operation in the verification, and can also be used for measuring The sampling time of the testing instrument. The invention can facilitate staff to adjust and read the resistance value, avoids the troublesome disadvantages of using a rotary switch to adjust the resistance and read the resistance value, and improves the work efficiency of the test personnel.

The digital resistance box will generate heat during the working process. For high-precision digital resistance boxes, high temperature will affect the resistance value of the resistors, thereby affecting the accuracy of detection; too high temperature will also damage the electrical components of the resistance box.

[Content of the invention]

The technical problem to be solved by the utility model is to provide a numerically controlled resistance box with high detection accuracy and not easily damaged by high temperature.

In order to solve the above-mentioned technical problems, the technical solution adopted by the utility model is that a numerically controlled resistance box includes at least one automatic temperature control circuit, and the automatic temperature control circuit includes a temperature detection circuit, an electronic switch, a fan and a DC power supply, an electronic switch and a fan The motor is connected in series between the positive and negative poles of the DC power supply, and the output terminal of the temperature detection circuit is connected to the control terminal of the electronic switch.

In the numerical control resistance box described above, the temperature detection circuit includes a first voltage divider circuit, a second voltage divider circuit, a first comparator, and a second comparator; the first voltage divider circuit includes a first resistor and a thermistor, and a first voltage divider circuit The first terminal of the resistor is connected to the positive pole of the DC power supply, the second terminal is connected to the first terminal of the thermistor, and the second terminal of the thermistor is connected to the negative pole of the DC power supply; the second voltage dividing circuit includes a second resistor and a third resistor; The first terminal of the second resistor is connected to the positive pole of the DC power supply, the second terminal is connected to the first terminal of the third resistor, and the second terminal of the third resistor is connected to the negative pole of the DC power supply; the non-inverting input terminal of the first comparator is connected to the thermistor the first terminal of the first comparator, the inverting input terminal is connected to the first terminal of the third resistor; the non-inverting input terminal of the second comparator is connected to the inverting input terminal of the first comparator, and the inverting input terminal is connected to the output terminal of the first comparator, The output terminal of the second comparator is used as the output terminal of the temperature detection circuit and connected to the control terminal of the electronic switch.

In the numerical control resistance box described above, the thermistor is a negative temperature coefficient thermistor.

In the numerical control resistance box described above, the temperature detection circuit includes a sixth resistor, one end of the sixth resistor is connected to the first end of the third resistor, and the other end is connected to the output end of the second comparator.

In the numerical control resistance box described above, the temperature detection circuit includes a fourth resistor and a second capacitor, one end of the fourth resistor is connected to the positive pole of the DC power supply, and the other end is connected to the output end of the first comparator; one end of the second capacitor is connected to the first The non-inverting input terminal of the comparator, and the other terminal is connected to the negative pole of the DC power supply.

The digitally controlled resistance box described above includes a fifth resistor and a seventh resistor, the fifth resistor is connected between the output terminal of the second comparator and the positive pole of the DC power supply, and the seventh resistor is connected between the output terminal of the second comparator and the positive pole of the DC power supply. between the negative poles of the DC power supply.

In the numerical control resistance box described above, the electronic switch is a MOS tube, the gate of the MOS tube is connected to the output end of the temperature detection circuit, the source is connected to the negative pole of the DC power supply, and the drain is connected to the first end of the fan motor. The second terminal is connected to the positive pole of the DC power supply.

The numerically controlled resistance box described above includes an indicator light, and the indicator light is connected in parallel with the fan motor.

In the numerical control resistance box described above, the DC power supply includes a DC 24V power supply, a diode, a first capacitor and a third capacitor, the anode of the diode is connected to the positive pole of the DC 24V power supply, the cathode of the diode is the positive pole of the DC power supply, and the negative pole of the DC 24V power supply is The negative pole of the DC power supply; the first capacitor and the third capacitor are respectively connected between the positive and negative poles of the DC power supply, and the third capacitor is an electrolytic capacitor.

In the numerically controlled resistance box mentioned above, the resistances of the numerically controlled resistance box are respectively installed in a plurality of areas according to the resistance value, and each area includes an automatic temperature control circuit.

The numerical control resistance box of the utility model drives the fan to dissipate heat through the temperature automatic control circuit, so that the numerical control resistance box always works at a suitable temperature, the resistance value of the resistance is stable and accurate, the detection accuracy is high, and the components of the resistance box will not be damaged due to overheating. damage, long life.

[Description of drawings]

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

Fig. 1 is the structural diagram of the numerical control resistance box of the embodiment of the utility model.

Fig. 2 is a schematic diagram of the automatic temperature control circuit of the numerically controlled resistance box of the embodiment of the utility model.

[Detailed ways]

The structure of the numerical control resistance box of the utility model embodiment is shown in Figure 1, and the resistance of 6 groups of decimal numbers is respectively installed in 6 areas according to the resistance value, and each area includes an automatic temperature control circuit.

The temperature automatic control circuit is shown in Figure 2, including a temperature detection circuit, an electronic switch Q1, a DC power supply, an input connector CN1 and an output connector CN3. The input connector CN1 is connected to an external DC 24V power supply, and the two pins of the output connector CN3 are connected to an external fan motor.

The anode of the diode D1 is connected to the positive pole of the DC 24V power supply through the pin 1 of the input connector CN1, the cathode of the diode D1 is used as the positive pole of the DC power supply, the pin 1 of the input connector CN1 is used as the negative pole of the DC power supply, and the negative pole of the DC 24V power supply is connected externally, and the capacitor C1 and the capacitor C2 are respectively connected between the positive and negative poles of the DC power supply, wherein the capacitor C3 is an electrolytic capacitor.

In this embodiment, the electronic switch Q1 is a power MOS transistor SSG4402N.

The temperature detection circuit includes a first voltage divider circuit, a second voltage divider circuit and LM393. LM393 is a dual-voltage comparator, including comparator U1A and comparator U1B. When the voltage at the positive input terminal is higher than the voltage at the inverting input terminal, it outputs a high level, and when the voltage at the positive input terminal is lower than the voltage at the inverting input terminal, it outputs a low level.

The first voltage divider circuit includes a resistor R1 and a negative temperature coefficient thermistor NTC R1. The first end of the resistor R1 is connected to the positive pole of the DC power supply, and the second end is connected to the first end of the negative temperature coefficient thermistor NTC R1. The negative temperature coefficient The second end of the thermistor NTC R1 is connected to the negative pole of the DC power supply. The second voltage dividing circuit includes a resistor R2 and a resistor R3. The first terminal of the resistor R2 is connected to the positive pole of the DC power supply, the second terminal is connected to the first terminal of the resistor R3, and the second terminal of the resistor R3 is connected to the negative pole of the DC power supply. The non-inverting input terminal of the comparator U1B is connected to the first terminal of the negative temperature coefficient thermistor NTC R1, and the inverting input terminal is connected to the first terminal of the resistor R3. The non-inverting input terminal of the comparator U1A is connected to the inverting input terminal of the comparator U1B, the inverting input terminal is connected to the output terminal of the comparator U1B, and the output terminal of the comparator U1A is used as the output terminal of the temperature detection circuit to connect to the gate of the power MOS transistor SSG4402N .

One end of the resistor R6 is connected to the first end of the resistor R3, and the other end is connected to the output end of the comparator U1A. One end of the resistor R4 is connected to the positive pole of the DC power supply, and the other end is connected to the output end of the comparator U1B. One end of the capacitor C2 is connected to the non-inverting input end of the comparator U1B, and the other end is connected to the negative pole of the DC power supply. The resistor R5 is connected between the output terminal of the comparator U1A and the positive pole of the DC power supply, and the resistor R7 is connected between the output terminal of the comparator U1A and the negative pole of the DC power supply.

The source of the MOS transistor SSG4402N is connected to the negative pole of the DC power supply, the drain is connected to the pin 2 of the output connector CN3, and the pin 1 of the output connector CN3 is connected to the positive pole of the DC power supply.

Both ends of the LED indicator light D2 are respectively connected to pin 1 and pin 2 of the output connector CN3.

When the temperature automatic control circuit in any area detects that the temperature reaches above 50°C, the resistance of the negative temperature coefficient thermistor NTCR1 is reduced from 100K to 22K, and the voltage at the non-inverting input terminal of U1B of the comparator LM393 will be smaller than the voltage at the inverting input terminal (reference voltage), comparator U1B output is low level, U1A non-inverting input terminal voltage is equal to U1B inverting input terminal voltage, then U1A non-inverting input terminal voltage is greater than inverting input terminal voltage, U1A output is high level, power MOS tube The SSG4402N will turn on, causing the LED signal light to glow and the fan to turn, increasing convection and reducing the temperature of the CNC resistance box. At this time, the high level output by U1A is fed back to the inverting input terminal of U1B through the resistor R6, which will further increase the reference potential of the inverting input terminal of U1B, and the output of U1B will remain low, so that the output of U1A will continue to be high. Guarantee the continuous operation of fans and LED signal lights.

Claims (10)

1. A numerically controlled resistance box, characterized in that it comprises at least one automatic temperature control circuit, the automatic temperature control circuit comprises a temperature detection circuit, an electronic switch, a fan and a DC power supply, and the electronic switch and the fan motor are connected in series at the positive and negative terminals of the DC power supply. Between the poles, the output terminal of the temperature detection circuit is connected to the control terminal of the electronic switch. 2. The numerically controlled resistance box according to claim 1, wherein the temperature detection circuit comprises a first voltage divider circuit, a second voltage divider circuit, a first comparator, and a second comparator; the first voltage divider circuit comprises a first voltage divider circuit A resistor and a thermistor, the first end of the first resistor is connected to the positive pole of the DC power supply, the second end is connected to the first end of the thermistor, and the second end of the thermistor is connected to the negative pole of the DC power supply; the second voltage divider circuit Including the second resistor and the third resistor; the first terminal of the second resistor is connected to the positive pole of the DC power supply, the second terminal is connected to the first terminal of the third resistor, and the second terminal of the third resistor is connected to the negative pole of the DC power supply; the first comparison The non-inverting input terminal of the comparator is connected to the first terminal of the thermistor, and the inverting input terminal is connected to the first terminal of the third resistor; the non-inverting input terminal of the second comparator is connected to the inverting input terminal of the first comparator, and the inverting input terminal The output end of the first comparator is connected, and the output end of the second comparator is used as the output end of the temperature detection circuit to be connected to the control end of the electronic switch. 3. The numerically controlled resistance box according to claim 2, wherein the thermistor is a negative temperature coefficient thermistor. 4. The digitally controlled resistance box according to claim 2, wherein the temperature detection circuit includes a sixth resistor, one end of the sixth resistor is connected to the first end of the third resistor, and the other end is connected to the output end of the second comparator. 5. The digitally controlled resistance box according to claim 2, wherein the temperature detection circuit includes a fourth resistor and a second capacitor, one end of the fourth resistor is connected to the positive pole of the DC power supply, and the other end is connected to the output terminal of the first comparator ; One end of the second capacitor is connected to the non-inverting input end of the first comparator, and the other end is connected to the negative pole of the DC power supply. 6. The numerically controlled resistance box according to claim 2, characterized in that, comprises the fifth resistor and the seventh resistor, the fifth resistor is connected between the output terminal of the second comparator and the positive pole of the DC power supply, and the seventh resistor is connected Between the output terminal of the second comparator and the negative pole of the DC power supply. 7. The numerical control resistance box according to claim 1, characterized in that, the electronic switch is a MOS tube, the gate of the MOS tube is connected to the output end of the temperature detection circuit, the source is connected to the negative pole of the DC power supply, and the drain is connected to the negative pole of the DC power supply. The first end of the fan motor and the second end of the fan motor are connected to the positive pole of the DC power supply. 8. The numerically controlled resistance box according to claim 1, characterized in that it includes an indicator light, which is connected in parallel with the fan motor. 9. The numerically controlled resistance box according to claim 1, wherein the DC power supply comprises a DC 24V power supply, a diode, a first capacitor and a third capacitor, the anode of the diode is connected to the positive pole of the DC 24V power supply, and the cathode of the diode is a DC power supply The positive pole of the DC 24V power supply is the negative pole of the DC power supply; the first capacitor and the third capacitor are respectively connected between the positive and negative poles of the DC power supply, and the third capacitor is an electrolytic capacitor. 10. The numerically controlled resistance box according to claim 1, characterized in that the resistance of the numerically controlled resistance box is respectively installed in a plurality of areas according to the resistance value, and each area includes an automatic temperature control circuit.