1, working principle

The working principle is that the ambient temperature is automatically sampled and monitored by the temperature sensor. When the ambient temperature is higher than the control set value, the control circuit is started, and the control hysteresis can be set. If the temperature is still rising, when the temperature rises to the set over-limit alarm temperature point, the over-limit alarm function is activated. When the controlled temperature cannot be effectively controlled, in order to prevent the destruction of the device, the function of the trip can be used to stop the device from continuing to operate. Mainly used in various high and low voltage switchgears, dry transformers, box substations and other related temperature applications used in the power sector.

  1. Precautions for purchasing a thermostat

(1) Selection of thermostat input and output voltage

First of all, we must ensure that the input voltage is in line with the actual situation. There is not much demand for AC power supply. The main reason is that when the DC power supply is used, the positive and negative poles must be wired correctly. The line cannot be reversed, otherwise the temperature controller will be burnt out. Therefore, we recommend the use of AC powered thermostats. It is also worth noting that some thermostats do not support the on/off of DC power, or the DC voltage that can be turned on and off is small. This must be consulted with the merchant when purchasing the thermostat, so as to avoid unnecessary trouble. .

(2) Thermostat output control power

The output control power of the thermostat is the first problem to be considered when selecting the thermostat. This is related to the safety and stability of the use. If it is not properly selected, it may cause a fire. The output control voltage and current are marked on the thermostat, and the output control voltage can be obtained by multiplying the output control voltage and current. The operating power of the controlled device must be less than the output control power of the thermostat. Otherwise, there is a possibility of a safety hazard.

For example, if the temperature controller is marked with 220V and 10A, the output control power of the thermostat is 2200W. Under normal circumstances, the power of the controlled device should not be greater than 2000W.

Warm reminder: the power of the general controlled equipment should not be greater than 90% of the output control power of the thermostat, leaving a 10% margin to ensure the stable operation of the thermostat.

  1. How to check the quality of a thermostat

(1) Look at the output control core selected by the thermostat – relay. The relay is the core component of the output control, and the stability of its performance determines the quality of the thermostat. The selection of the relay brand largely affects the manufacturing cost of the thermostat, so the general manufacturers use mainly domestic relays, such as Songle and Hongfa. A better manufacturer chooses Taiwan relays, such as Matsukawa. Good manufacturers use imported famous brand relays, such as Omron and Panasonic. The quality of relays of different grades is very different, and the price is also very different. Therefore, only good manufacturers will use Omron, Panasonic and other big brands of relays to ensure the quality of their products.

quality. Customers can use this as a reference factor when choosing a thermostat.

(2) The CPU of the thermostat is the brain of the thermostat, and its quality affects the accuracy and stability of the thermostat. There are two main types of data acquisition cores on the market: one is the acquisition core combined with the microcontroller and ADC chip, and the other is a powerful CPU integrated with the acquisition core of the ADC. Generally speaking

The core stability of the integration is better, because there are many links that are prone to problems. At present, some merchants have appeared in the market to attract customers, and the microcontroller and ADC are said to be “dual-core” because they are similar in appearance. This is purely a flickering customer, please be sure to pay attention to this point. At present, the temperature controller used in the market mainly uses 10 bits and 12 bits, and the high-end uses 14 or 16 bits. The higher the number of bits, the smaller the temperature change that can be resolved, that is, the higher the accuracy. Therefore, the temperature controller should be purchased as much as possible.

(3) The software programming method of the manufacturer is also an aspect that affects the accuracy of the thermostat. The temperature sensor used in general thermostats is the temperature sensor of NTC. The curve of its resistance value with temperature is not linear. The slope of the curve is different in different temperature ranges. Therefore, when programming, the manufacturer should divide the program into multiple segments according to this feature so that the display temperature is closer to the actual temperature. However, the program is something that the customer can’t see, and the general merchant will not tell the customer actively, so it is more difficult to pay attention to this.

(4) Look at the power supply mode of the thermostat. There are two main types of thermostat power supply methods on the market: switching power supply and transformer power supply. Since the switching power supply is a high-frequency power supply, the requirements on the power supply part are high, and it is easy to generate EMI interference, which affects the stability of the temperature controller. The average customer does not know the quality of the power supply of the thermostat. Therefore, it is recommended to use a thermostat powered by a transformer. There are two types of transformers, one is the more common open type transformer, and the other is a potted transformer, that is, a plastic case. The potting transformer has better moisture resistance and the effect of electrical isolation is better. Therefore, it is recommended to use a thermostat powered by a potting transformer.

(5) Try to buy a digital thermostat. There are two main types of thermostats on the market: mechanical and electronic. The electronic thermostat has the characteristics of user-friendly operation interface and intuitive operation. Therefore, the temperature controller should be electronically selected as much as possible.

4, the requirements of the accuracy of the thermostat

The temperature controller must also be considered for the accuracy of the thermostat. For example, we need to control the temperature accuracy of 0.1 degrees, and some thermostats have an accuracy of 1 degree, which does not meet the practical requirements.

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