Biochemical incubator uses potentiometer to set temperature

Shanghai Xinzhuang Instrument Co., Ltd. has developed the LNB brand biochemical incubator, which is energy-efficient, environmentally friendly, and at the forefront of domestic technology. This incubator features a dual-temperature control system for both heating and cooling, making it ideal for use in scientific research institutions, universities, production units, and laboratories in fields such as biology, genetic engineering, medicine, health, epidemic prevention, environmental protection, agriculture, forestry, and animal husbandry. It is widely used for low-temperature constant temperature testing, culture experiments, and environmental testing. The controller circuit of the biochemical incubator consists of a temperature sensor, a voltage comparator, and a control execution circuit.

The circuit uses a new integrated temperature sensor ICl. The voltage comparator is made up of resistors R1-R7, temperature-setting potentiometers RP1 and RP2, and voltage comparator IC2 (N1, N2). The control execution circuit includes transistors V1, V2, relays K1, K2, and diodes VD1, VD2. The biochemical incubator can be upgraded from an old single or double-door refrigerator by using the refrigerator's cooling function, installing a heating device (such as an electric heating wire or a 150W iodine tungsten lamp), and adding an exhaust fan inside to ensure even temperature distribution within the box.

Potentiometer RP1 sets the upper temperature limit, while RP2 sets the lower limit. Relay K1 controls the heating device via an intermediate relay, and relay K2 controls the refrigerator’s refrigeration system through another intermediate relay. Pins 5 and 2 of IC2 are connected to the center taps of RP1 and RP2, respectively. Pins 6 and 3 of IC2 are connected to the output of ICl through resistor R3. When the voltage at pin 2 of IC2 minus the voltage at pin 5 is approximately 0.01V, the corresponding temperature is 1°C. If the temperature remains within the set range, the voltage at pin 2 is higher than that at pin 5, and the voltages at pins 3 and 6 match or are lower than pin 2. In this case, pins 1 and 7 output a low level, turning off V1 and V2, and relays K1 and K2 remain inactive, so neither the cooling nor heating circuits operate.

If the internal temperature exceeds the upper limit, the voltage at pins 3 and 6 of IC2 becomes higher than that at pins 2 and 5, causing pin 1 of IC2 to switch from low to high. This turns on V2, activates relay K2, closes its normally open contact, and starts the refrigeration system. Conversely, if the temperature drops below the lower limit, the voltage at pins 3 and 6 of IC2 falls below that at pins 2 and 5, triggering pin 7 of IC2 to switch to high. This turns on V1, activates relay K1, closes its normally open contact, and powers the heating system.

Components like R1-R5 are selected as 1/4W metal film resistors with 1% accuracy, while R6-R9 can be 1/4W carbon film resistors. Both RP1 and RP2 are wire-wound potentiometers for higher precision. Capacitors C are monolithic capacitors. Diodes VD1 and VD2 are 1N4148 silicon switching diodes. Transistors V1 and V2 are S9013 or C8050 NPN silicon transistors. The temperature sensor ICl is LM35DZ, LM36, or TMP36, and IC2 is LM393 operational amplifier. Relays K1 and K2 are 12V DC relays.

Shanghai Xinzhuang Instrument Co., Ltd. has also developed low-temperature constant temperature instruments, ultrasonic devices, box-type instruments, microbial equipment, ice-making refrigeration tools, and laboratory support instruments. The company has gradually established a product pattern featuring various scientific instrument technology reserves. They offer free nationwide delivery, competitive pricing, quality guarantees, and lifetime maintenance services.

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