What is a thermostatic bath?Incubation bath, as its name implies, canprovideconstanttemperatureOfgroovebody。It can be divided into constant temperature air (usually calledIncubator）Thermostatic liquid (usually referred to as thermostatic bath).Due to the different temperature ranges of constant temperature liquid, it can be divided into low-temperature constant temperature bath (generally - 40 ℃~100 ℃)super thermostatic bath (Generally, room temperature~300 ℃).It is also called oil tank because the liquid medium above 100 ℃ cannot use water.There are many homonyms of thermostatic bath, such as thermostatic water oil bathConstant temperature water bath、Thermostatic water tank、Thermostatic circulatorElectric heatingConstant temperature water bathThey are usually heated by resistance wire, cooled by compressor, and assisted byPID controller, keep a relatively standard temperature, so as to achieve the experimental purpose.
Heating temperature control technology
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The constant temperature bath requires accurate temperature control of the liquid temperature in the bath (the temperature control accuracy is 0.1 ℃ or even 0.01 ℃).The most common method is to use resistance wire heating and compressor refrigeration, supplemented by PID microcomputer self-tuning precise temperature control mode, to stabilize the temperature of the incubation bath at the required set temperature.
Incubation bath is generally equipped with highly stablertd PRT or othersTemperature sensorTo realize the temperature control and automatic protection functions of the thermostatic bath.The controller uses a special noise suppression circuit, so it can detect the small resistance change required by the thermostatic bath with high stability.AC bridge is used inside the instrument to measure temperature to reduce heatpotential。Customized, highaccuracy, Lowtemperature coefficientThe short and long term stability of the temperature set point is guaranteed by the resistance of.
Advanced filtering technology overcomes power noiseinterfereandstrayOfelectromagnetic interference andradio interference。useProportional integral controlFunction to control the power supplied to the thermostatic bath heater. Precise factory debugging almost eliminates the impact of overshoot, so that the thermostatic bath can quickly reach its highesttemperature stability 。A key factor in the excellent performance of incubation bath is our hot port technology.The refrigeration spiral tube and heater are installed on the side of the stainless steel cylinder of the thermostatic bath in a sandwich shape, and the bottom of the steel cylinder becomesheat exchangePort, through which most of the heat enters and exits the incubation bath.Good insulation design around the steel cylinder minimizes heat leakage.[1]
Safety protection measures
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The general safety protection measure is to adopt the dual protection function of over temperature and over pressure.Once the limit temperature or power supply voltage is exceeded, the automatic power-off protection will be started to ensure its long-term uninterrupted and reliable operation.
Scope of application
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Various thermostatic baths are widely used in fine chemicals, bioengineering, medicine and food, metallurgy, petroleum, agriculture and other fields.It provides users with high-precision constant temperature field source, and is an ideal constant temperature equipment for research institutes, colleges and universities, industrial and mining enterprise laboratories, and quality inspection departments.
Product features
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At present, the thermostatic bath produced in China has reliable technology and constant performance.It can meet the different needs of most users.
1. Unique large screen backlightliquid crystalDisplay, set temperature, actual temperature, heating power, working status and other information are clear;
2. High performance monolithic microcomputer control, self-tuning PID regulation, importedrtd Temperature measurement, high temperature control precision, small fluctuation;
4. Stainless steel platen and liner can effectively avoidcorrosion、rustPhenomenon;
5. It has the functions of couple break protection and overtemperature alarm, and provides multiple security measures;
6. The instrument is stable and reliable, easy and safe to operate.[1]
Constant temperature medium
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At present, the mediums used in thermostatic bath are alcohol, water, antifreeze, edible oil, silicone oil, cylinder oil, etc.Water is the cheapest medium, and its working range is generally 5~95 ℃, but it can not cover the most commonly used 0 ℃. Most thermostatic baths use antifreeze instead of water.According to relevant research, the performance of the frozen liquid mixed with water at a ratio of 1:1 is still normal at - 30 ℃.The surface temperature field of the tank is related to room temperature and medium evaporation.According to Reference 3, the surface tension of pure antifreeze under normal pressure is 4649 mN/m (while the surface tension of pure water is 0728 mN/m (20 ℃), antifreeze and hydration will greatly increase the surface tension of water, resulting in increased molecular cohesion, which makes the evaporation less than pure water, so its vertical temperature field is better than pure water.This performance is especially obvious for the constant temperature bath with jet structure.The author carried out relevant experiments, using 15 mK and 32 mK vertical temperature fields of pure water and antifreeze (mixed according to water and antifreeze 1:1) respectively.When the evaporation of constant temperature medium is large, the tank surface needs to be covered to improve the vertical temperature field.The author has carried out relevant experiments on a constant temperature bath with jet structure (98 ℃). The results show that when there is a covering field on the surface of the bath, the vertical uniformity is 12 mK, and the fluctuation is 8 mK;When there is no cover, the vertical uniformity is 28 mK, and the fluctuation is 12 mK.
It can be seen that the impact of no covering is considerable.This should be noted in some cases where the groove surface cannot be covered for inspection.
At high temperature, the working medium with small evaporation capacity can reduce such influence, and low viscosity silicone oil is a choice.The author used low viscosity silicone oil as the medium for the constant temperature bath of a manufacturer. The results showed that at - 30 ℃, the vertical uniformity was 4 mK, and the fluctuation was 12 mK;At 100 ℃, the vertical uniformity is 2 mK, and the fluctuation is 5 mK.
Edible oil is also a cheap heat conduction medium, which is widely used in the working range of 100~200 ℃.However, the temperature of the heating wire is very high after it is electrified, and the cooking oil is very easy to carbonize, forming particles with large viscosity, which are wound on the heating wire, making its thermal conductivity worse and reducing the stability of the bath temperature.More importantly, it reduces the insulation resistance between the heating wires, leading to insecurity.Therefore, it is recommended to use silicone oil within the working range of 100~300 ℃ and replace it periodically.[2]
auxiliary equipment
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A variety of auxiliary equipment is required in the process of testing with thermostatic bath.For example, liquid level lifter, thermostatic bath support, etc.These accessories can help you improve the efficiency of the laboratory and facilitate the test operation.
