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LM324 Based Temperature Setting Controller Design [Video]

  • Contents

Temperature setting controller is widely used in high and low voltage power distribution cabinets, terminal boxes, substations, used for real-time detection of environmental temperature and humidity changes, and the protection of power electronics devices. It is also commonly used in places requiring temperature and humidity detection and comprehensive control, such as vegetable greenhouses, granaries, etc.

 

This paper designs a temperature setting controller which used temperature sensor AD592, lon sensor HDP 07 as a detecting component, with four channels of integrated op-amp LM324 as a core control element, it automatically measures and detect the environment temperature, control output, and gives an alarm and protect condensation, etc... It overcomes the shortcomings of existing thermocoagulation controllers that require high software knowledge for design, debugging, and maintenance personnel, complex circuit structure and large temperature response deviation, and simplifies the circuit structure.

LM324Catalog

I.Control Principle of Temperature Setting Controller

II.Circuit Design

  2.1 DC Voltage Regulation

  2.2 Partly Design of Temperature Setting Control

III. The text

 3.1 Adjustment and Testing of Temperature Control

 3.2 Adjustment and Testing of Condensation Control

IV. Conclusion

FAQ

Ordering & Quantity

 

I.Control Principle of Temperature Setting Controller

The LM324 voltage comparator is used as the main control chip of the temperature condensation controller. The temperature sensor is used to convert the temperature change into the current change, and the condensation sensor is used to convert the humidity change into the resistance change. The LM324 voltage comparator controls the temperature condensation Controller to achieve alarm display and output. The principle block diagram of the temperature condensation controller based on the LM324 voltage comparator is shown in Figure 1.

block diagram of LM324 voltage comparator

Figure 1: Block Diagram of LM324 Based Temperature Condensation Controller

II.Circuit Design

The circuit design of the temperature condensation controller based on LM324 voltage comparison mainly includes the design of two parts, the DC stabilized power supply and the temperature condensation control,  The main components of the controller include temperature and humidity sensors, which are connected to the control circuit board through the base through four wires of red, blue, black and yellow, and the dial connected to the control circuit board, and finally packaged by the shell.

 

2.1 DC Voltage Regulation

The power supply part of the temperature coagulation controller circuit designed in this paper is composed of a DC stabilized power supply module, a sensor input module, an alarm display module, a voltage comparison module, etc.

 Basically, all electronic products are powered by a DC power supply, and the daily grid voltage is AC 220V, so the AC power must first be converted into DC power to provide a stable DC power supply for the circuit. This thermocoagulation controller needs to provide 8V for the voltage comparison module It also provides 12V DC for the output relay module. After voltage regulation by the transformer, it is rectified by a bridge rectifier circuit composed of four diodes, filtered by a capacitor, and output by a three-terminal integrated voltage regulator.

 

2.2 Partly Design of Temperature Setting Control

The temperature condensation control part design adopts an LM324 voltage comparator as the main control chip of the whole temperature condensation control circuit. LM324 is a four-channel integrated operational amplifier with a true differential input. It is composed of four groups of completely independent operational amplifiers. Its main function in the circuit is to compare the input voltage and the reference voltage, change the output voltage according to the level of the two-channel voltage, and perform the corresponding control output.

This thermocoagulation controller uses AD592  as the temperature sensor. AD592  is an integrated temperature sensor. It is a high-performance current sensor launched by American  Analog Devices, which converts temperature changes into the current. It has the advantages of small error, low cost, temperature change, and current change into linearity. Its output current is based on absolute zero (-273°C). For every 1°C increase or decrease in the ambient temperature, it will increase the output current by 1 microampere.

 The temperature sensor converts the temperature change into a voltage change through a voltage follower and then inputs it to the inverting input terminal of the voltage comparator. The wire-wound potentiometer is connected to the dial to provide a reference voltage and provide it to the non-inverting input terminal of the voltage comparator. If the input voltage of the LM324 voltage comparator is lower than the reference voltage, it means that the ambient temperature is lower than the setting temperature of the dial, and the voltage comparator outputs a high level. At this time, the diode displays an alarm and controls the output. Increase the temperature until the ambient temperature is higher than the settting temperature, the voltage comparator outputs a low level, and the entire temperature control process is a closed-loop system, which can quickly and sensitively control the action of the temperature condensation controller. Figure 2 is the circuit schematic diagram of the temperature control module.

Schematic Diagram of Temperature Control Module

Figure 2: Schematic Diagram of the Temperature Control Module

This temperature condensation controller selects HDP-07 as the condensation sensor. HDP-07 is a new type of condensation sensor that measures or predicts the occurrence of air condensation through changes in its resistance. Its structure is to make a tree-like current on a ceramic substrate and then coat it with resin and conductive particles to form a resistive film. It has the characteristics of a typical switch-type sensor, which is extremely sensitive to high humidity and presents a high resistance state; in a low humidity environment, it reflects a low resistance state. It has the advantages of small size, short measurement period, quick response, high precision, etc. It overcomes the shortcomings of a complex structure, large volume, complex operation, and low precision of the chilled mirror condensation sensor made of traditional optical principles. It is widely used on occasions that need to control high humidity and condensation. Figure 3 is a schematic diagram of the humidity control module.

schematic diagram of humidity control module

Figure 3:Schematic Diagram of the Humidity Control Module

When the relative humidity in the ambient temperature reaches 100%, the water vapour in the air will liquefy and condense into dew, and the equipment will malfunction due to humidity and reduce the service life. Therefore, the temperature condensation controller designed in this paper (using the HDP-07 condensation sensor) is used to detect the occurrence of condensation and eliminate it in time. The condensation sensor and the comparator constitute a zero-crossing comparator. Usually, in a low humidity environment, the resistance of the condensation sensor is very small. The sensor reflects the character of switch closure, and the comparator outputs a low level; when the ambient humidity reaches 83% at the critical value, the condensation sensor presents a high-impedance state, and the comparator outputs a high level, to control the electronic switch triode to turn on and display the alarm and control the output to reduce humidity. The temperature condensation based on the LM324 voltage comparator is used as the main control chip compared with the circuit based on software control, the control circuit has a simpler circuit structure, more convenient debugging and assembly use, and lower cost.

 

III.The Text

3.1 Adjustment and Testing of Temperature Control

(1) Benchmark

Turn the dial scale to 0 degrees, clamp the red test pen of the multimeter to the middle tap of the wire-wound potentiometer, ground the black test pen, turn the multimeter to the DC voltage range, adjust the potentiometer W2, and make the voltmeter read 2.73V.

 

(2) Linear adjustment accuracy

First, adjust the dial scale to -30 degrees, adjust the potentiometer W2, so that the voltage reading is 2.43V; the second step, adjust the dial scale to 40 degrees, write down the value of the multimeter, if the value is greater than 3.13V, it indicates the slope is too large, then adjust the dial scale to 30 degrees, adjust the potentiometer W1 and re-adjust W2, the voltage reading is 2.43, and then adjust the dial scale to 40 degrees, observe whether the voltmeter reading is 3.13V, if not, repeat step two until the voltage reading is 2.43V.

 

(3) Adjust the accuracy of the temperature sensor

Adjust the dial scale to room temperature, adjust the potentiometer WS, so that the temperature alarm indicator diode is on, and adjust the potentiometer back and forth at this critical value, and the temperature indicator will change between on and off in a short time.

 

(4) Test

Adjust the dial scale to be lower than room temperature, the temperature condensing controller does not work; adjust the dial scale to higher than room temperature, the temperature alarm indicator of the temperature condensing controller is on, the relay is closed, and the output 220V alternating current indicates that the temperature control part is working normally.

 

3.2 Adjustment and Testing of Condensation Control

When the condensation controller detects, it can add water vapour or breathe on the condensation sensor with the mouth for about 5 seconds. The humidity alarm indicator on the controller is on, the relay is closed, and the output is 220V AC, indicating that the condensation control part can work normally.

 

IV. Conclusion

This article summarizes the design and production of the temperature condensation controller based on the LM324 voltage comparator. The temperature coagulation controller has successfully realized temperature control and condensation generation control through the test. It has the advantages of good stability, strong anti-interference ability, wide adjustment range, high precision, and rapid response. It solves the complex circuit structure of the temperature coagulation controller. , The response accuracy is not high. Only the LM324 voltage comparator is used as the main control chip of the control circuit, which is convenient for assembly and debugging low cost, and does not need to use software control, those are the characteristics of the thermocoagulation controller. It’s suitable for technological innovation and promotion.


FAQ

  • What is widely used in high and low voltage power distribution cabinets?

Temperature setting controller

  • What is used to convert the temperature change into the current change?

Temperature sensor

  • What is lm324?

LM324 is a Quad op-amp IC integrated with four op-amps powered by a common power supply. The differential input voltage range can be equal to that of the power supply voltage. Generally, op-amps can perform mathematical operations.

  • Which is the difference between lm324 and lm339?

The LM324 has a complementary output while the LM339 is open collector. In the complementary output, current can flow in either direction as required (either source or sink) while the open collector output can only sink current.

  • What is op-amp used for?

Operational amplifiers are linear devices that have all the properties required for nearly ideal DC amplification and are therefore used extensively in signal conditioning, filtering or to perform mathematical operations such as add, subtract, integration and differentiation.

  • How does an op-amp work?

  • What is lm324 used for?

LM324 IC Applications

The applications of IC LM324 include the following. By using this IC, conventional op-amp applications can be implemented very simply. This IC can be used as oscillators, rectifiers, amplifiers, comparators etc.

  • What is the function of a temperature controller?

A Temperature Controller is a device that is used to control a heater or other equipment by comparing a sensor signal with a set point and performing calculations according to the deviation between those values.


 

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