Forehead Thermometer Working Principle According to the difference of the purpose of use, a variety of thermometers have been designed and manufactured. Its design is based on: the use of the phenomenon of thermal expansion and contraction of solids, liquids, and gases under the influence of temperature; under the condition of constant volume, the pressure of gas (or vapor) changes due to the difference of temperature; the role of thermoelectric effect; The transformation of temperature; the influence of thermal radiation, etc. 1. Gas thermometer: use hydrogen or helium as the temperature measurement material, because the liquefaction temperature of hydrogen and helium is very low, close to absolute zero, so its temperature measurement range is very wide. This thermometer has high accuracy and is mostly used for precise measurements.     2. Resistance thermometer: It is divided into metal resistance thermometer and semiconductor resistance thermometer, which are made according to the characteristic of resistance value changing with temperature. Metal thermometers are mainly made of pure metals such as platinum, gold, copper, and nickel, as well as rhodium-iron and phosphor bronze alloys; semiconductor thermometers are mainly made of carbon, germanium, etc. Resistance thermometers are easy to use and reliable, and have been widely used. It has a measurement range of around -260°C to 600°C. 3. Thermocouple thermometer: It is a temperature measuring instrument widely used in industry. Made by thermoelectric phenomenon. Two different metal wires are welded together to form the working end, and the other ends are connected to the measuring instrument to form a circuit. When the working end is placed at the temperature to be measured, when the temperature of the working end and the free end are different, an electromotive force will appear, so a current flows through the loop. Through the measurement of electrical quantities, using the temperature at a known location, the temperature at another location can be determined. It is suitable for two substances with a large temperature difference, and is mostly used for high temperature and low turbidity measurement. Some thermocouples can measure high temperatures up to 3000°C, and some can measure low temperatures close to absolute zero.   4. Pointer thermometer: It is a thermometer shaped like a dashboard, also known as a cold and summer watch. It is used to measure the room temperature and is made of the principle of thermal expansion and contraction of metal. It uses a bimetallic sheet as a temperature sensing element to control the pointer. The bimetallic sheet is usually riveted with copper sheet and iron sheet, and the copper sheet is on the left and the iron sheet is on the right. Because the thermal expansion and contraction effect of copper is more obvious than that of iron, when the temperature rises, the copper sheet pulls the iron sheet to bend to the right, and the pointer is deflected to the right (pointing to high temperature) driven by the bimetallic sheet; otherwise , the temperature becomes lower, and the pointer is deflected to the left (pointing to low temperature) driven by the bimetallic sheet. 5. Glass tube thermometer: The glass tube thermometer uses the principle of thermal expansion and contraction to achieve temperature measurement. Because the expansion coefficient of the temperature measurement medium is different from the boiling point and freezing point, our common glass tube thermometers mainly include: kerosene thermometer, mercury thermometer, and red pen water thermometer. Its advantages are simple structure, convenient use, relatively high measurement accuracy and low price. The disadvantage is that the upper and lower limits and accuracy of the measurement are limited by the quality of the glass and the properties of the temperature-measuring medium. And can not be transmitted far, fragile. 6. Pressure thermometer: The pressure thermometer uses the liquid, gas or saturated vapor in a closed container to generate volume expansion or pressure change as a measurement signal. Its basic structure is composed of three parts: temperature bulb, capillary tube and indicating table. The advantages of pressure thermometers are: simple structure, high mechanical strength, not afraid of vibration. Inexpensive and requires no external energy. The disadvantage is: the temperature measurement range is limited, generally -80~400℃; the heat loss is large and the response time is slow. 7. Mercury thermometer is a kind of expansion thermometer. The freezing point of mercury is -38.87°C and the boiling point is 356.7°C. It is used to measure the temperature within the range of 0--150°C or 500°C. It can only be used as an instrument for on-site supervision. Using it to measure temperature is not only simple and intuitive, but also avoids the errors of external remote thermometers.

Safe Digital Oral Thermometer for Adults: Soft silicone tip with stainless steel probe is reliable. A medical thermometer that can be used orally rectal or underarm use. Convenient and safe for you and your family Accurate and Fast Reading: About 10 seconds read time. This digital thermometer is used latest advance sensory probe and the temperature reading is clinically tested and accurately detect the fever, help you determine whether you need a rest or medical care LCD Screen Display: This oral thermometer is easy to read with clear display, beeper alarm, memory display, auto shut off, easily switch the units between ℉ and ℃ Easy to Use and Clean: Waterproof tip allows you to clean the fever thermometer in an easy and hygienic way. Please use wipe with water and clean with medical alcohol after or before each use. Lightweight and portable, with a free storage case, you can carry it to anywhere and use it anytime Note: Please read the product manual carefully before using. Start measuring when you see “Lo℉”. To ensure an accurate result, do not touch the probe with your hands or other objects with high temperature before taking your temperature  

【Two measurement modes】The infrared Non-Contact Thermometer is a thermometer that measures the temperature of human body and object surface by using the principle of receiving infrared. When using under body mode, it is only required to detect with forehead to measure the body temperature quickly and accurately within 0.5 seconds. The thermometer can also be used to measure the object temperature. 【High-definition Display】The thermometer features the LCD large-size liquid crystal display, high brightness with backlight, clear and soft display, thus making reading clear.Press and hold the set button for 3 seconds, then press the "+" button or the "-" button to switch between ℃ and ℉. 【High Quality】In order to provide reliable results and ensure excellent performance, we apply updated high-precision sensor probes and the latest smart chips to the thermometer. So the thermometer is faster, more reliable, and more secure to use. 【32 readings memory storages】Our thermometer can memory 32 readings to continusly track your family member's tempreature. Which can handle it in advance if your family members' temperature is slightly high. 【Durable Design】The thermometer can adjusted within the range of 3-5CM/1.18-1.97in(about) which requires no a fixed measurement distance. And the thermometer features the excellent durability.