In microbiological experiments, many experimental projects require the use of electrothermic incubators to detect samples of microorganisms. These microorganisms are sensitive to temperature during the culture process. For example, the total number of bacterial colonies needs to be cultured at a constant temperature of 36C for 24 to 48 hours. ; Common E. coli needs 36C, 24 hours; fecal E. coli needs 44C, 24 hours; Vibrio cholerae needs 36C, 24 hours and so on. These experiments must have a reliable electric heating incubator to ensure that it will directly affect the results of microbiological testing.
At present, most of the electrothermal constant temperature incubators used in laboratories use bimetallic spiral tube type temperature control devices, which have the advantages of simple structure, low cost, and high temperature control accuracy. However, it is a contact type device, and after a long time of use The surface of the contact surface becomes rough due to frequent ignition, which increases the damping when the contact points move together. In severe cases, the surfaces of the two contacts can not be detached due to igniting and melting, resulting in the appearance of an electrothermal incubator at work. Poor temperature control and out of control temperature.
After repeated research and comparison, the author used a solid state relay with a 20A/220V addition, which is a module integrating the control signal processing circuit and the thyristor to replace the function of the original temperature-controlled contact. The principle is: the use of the original temperature control contacts to control the signal added to the solid state relay, because the control signal in the range of 3 ~ 32VDC, solid state relays can be fully turned on, the signal current does not exceed 5mA, so the original temperature after conversion The control contact will not cause the ignition during the control signal of the solid state relay, thus ensuring the temperature control reliability of the electrothermal incubator.
The modified temperature control circuit is shown in Figure 1.
In the figure, K1, Lamp 1, Lamp 2, and R2 are the power switch, heating indicator, power indicator, and heating element of the original thermostat; K2 is the contact of the original thermostatic chamber temperature control device; BJ is 9V/220V, 10W The transformer; ZL is 015A/50V rectifier element; C is 220L/50V filter capacitor; R1 is 1008, 1/8W current limiting resistor; RCT is 20A/220V solid state relay. BT, ZL, and C generate a control signal source of about 13 VDC, which is applied to the control terminals 3 and 4 of the RCT via R1 and K2. When the temperature in the thermostatic chamber is lower than the set temperature, K2 is turned on and the RCT is controlled beyond 3 VCD. Signal, RCT 1, 2 pin conduction, constant temperature incubator heat up; When the set temperature, K2 disconnected, RCT 3, 4 foot voltage is 0V, RCT 1, 2 feet cut, incubator stop heating Therefore, the original temperature control not only achieves the purpose of temperature control, but also avoids the shortcomings of the contact ignition.
Using the method, seven sets of electric thermostatic incubators and five sets of electric constant temperature water baths have been modified. The temperature control precision is up to 5C. It has been used normally for more than three years. So far, no temperature control failures and malfunctions have been found in retrofitted thermostatic devices. According to the modification principle, this device is also suitable for the temperature control system of electric constant temperature water bath and electric constant temperature drying oven.
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