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Types of thermometers: A brief introduction to the following types of thermometers: 1. Liquid crystal thermometers: Liquid crystals made from different formulations have varying phase transition temperatures; when these phases change, their optical properties also change, causing the liquid crystals to appear in a different color. If liquid crystals with different phase transition temperatures are applied to a piece of paper, the temperature can be determined from the change in the color of the liquid crystals. The advantage of this thermometer is that its readings are easy to read, while its disadvantage is its lack of precision; it is commonly used in aquariums for ornamental purposes to indicate water temperature. 2. Resistance thermometer: The resistance of a metal increases as the temperature rises. When the temperature changes only slightly, its resistance is approximately linearly related to the temperature; over larger temperature ranges, it can usually be represented by a simple quadratic polynomial. By measuring the resistance of a metal, it is possible to determine the temperature. Such thermometers are usually made of platinum wire and can achieve precision of 10–3 degrees, making them suitable for accurate measurements. Due to its high melting point, platinum allows for a wider measurable temperature range, approximately from -250 degrees Celsius to 1200 degrees Celsius. 3. Gas thermometer: At constant pressure, for gases with low density, there is a linear relationship between volume and temperature. A thermometer made using this relationship is called a constant-pressure gas thermometer. At a constant volume, for gases with low density, pressure and temperature are linearly related. A thermometer made using this relationship is called a constant-volume gas thermometer. 4. Rotating thermometer: A rotating thermometer is made of a coiled bimetallic strip. One end of the bimetallic strip is fixed, while the other end is connected to the pointer. Due to the different degrees of expansion of the two metal sheets, they curl to different extents at various temperatures; accordingly, the pointer points to different positions on the dial. The temperature can be determined by reading the value on the dial. 5. Semiconductor thermometers: The resistance of semiconductors changes in a way that is different from that of metals; as the temperature rises, their resistance decreases, and the degree of this change is relatively large. Therefore, even small temperature changes can cause significant variations in resistance, resulting in thermometers with high precision; they are often referred to as temperature sensors. 6. Thermocouple thermometer: A thermocouple thermometer consists of two different metals connected to a sensitive voltmeter. At different temperatures, metal contacts create different potential differences at the two ends of the metal. The potential difference is very small, so a sensitive voltmeter is required to measure it. The voltage meter reading can tell us why the temperature is what it is. 7. Optical pyrometer: When an object’s temperature is high enough to emit a large amount of visible light, its temperature can be determined by measuring the amount of thermal radiation it emits; such a thermometer is known as an optical pyrometer. This thermometer is mainly composed of a telescope equipped with a red filter, along with a circuit that includes a small light bulb, an ammeter, and a variable resistor. Before use, establish the relationship between the temperature corresponding to different filament brightness levels and the readings on the ammeter. When in use, align the telescope with the object to be measured, adjust the resistor so that the brightness of the bulb matches that of the object, and then the temperature of the object can be read from the ammeter. Basic Facts about Ear Thermometers 1. The Principle of Ear Thermometers Ear thermometers use sensors to detect the thermal radiation emitted by an object, thereby measuring the temperature of that object. Any object whose temperature is above absolute zero (–273.15 °C) emits thermal radiation, with wavelengths ranging from 3 μm to 30 μm, which falls within the infrared light range; hence it is also known as infrared light or infrared thermal radiation. 2. Proper use of an ear thermometer: An ear thermometer measures the temperature of the eardrum, and it must be aligned with the eardrum during measurement. The temperature of the eardrum is higher than that of the surrounding areas of the ear canal. For this reason, some ear thermometers display the highest value measured, or the user takes multiple readings and uses the highest value as the recorded ear temperature. That’s how it works. 3. Precautions for using an ear thermometer: In a new environment, it must wait for 30 minutes before it can be used. Newborns have fairly uniform body temperatures, so there is no need to insert the probe too deeply. For infants under 1 year old, the outer ear needs to be pulled back when taking measurements. For those over 1 year old and adults, the ears need to be pulled upward and toward the back of the ear to straighten the ear canal. Gently insert the ear thermometer probe to an appropriate depth of about 1–2 centimeters, aiming it at the eardrum. There’s no need to overemphasize it. Gently press the measurement button to read the temperature value. After waiting for an appropriate amount of time, measure again. After multiple measurements, the highest value is taken as the ear temperature reading. 4. Factors affecting ear thermometers: Ear cuffs. It is generally recommended to replace the ear cuffs regularly; after being used multiple times, they can cause the temperature reading to decrease by 0.1°C to 0.3°C. It must be kept clean at all times, especially avoiding contact with hands, as the oils on the hands can cause the measured temperature to be lower. Alcohol: Gently wiping the ear cups with a thin layer of alcohol can lower the temperature by 0.1 ℃ to 0.2 ℃; they can be used after 2 to 3 minutes. Cleaning with a large amount of alcohol will lower the temperature reading by 1 ℃ to 2 ℃, or even to such a level that the ear thermometer can no longer detect a temperature; it will take more than 15 minutes before it can be used again. Wait time: When taking repeated measurements, it is necessary to wait for more than 15 seconds so that the ear thermometer can dissipate the heat remaining from the previous measurement, thereby preventing heat accumulation. Otherwise, multiple measurements taken over a short period of time will result in higher reading values, with an impact of approximately 0.1 °C to 0.3 °C. Insertion time: Experiments have shown that when a digital thermometer is left in the ear for 15 seconds, it can even cause the measured temperature to rise by 0.6 °C, an effect that is quite significant; therefore, it is not recommended to keep the thermometer probe in the ear for too long. 5. Advantages and disadvantages of ear thermometers. Advantage: The biggest advantage of ear thermometers is their ability to measure body temperature quickly. Disadvantage: They require quite a few specific conditions regarding people, situations, and objects. The requirements for people include the subjects being tested and the testers, those for tasks involve time and timing, and those for equipment include accessories related to ear thermometers as well as cleanliness; all of these can affect the accuracy of the measurements. This is also one of the main reasons why, despite being a high-tech product, it has not been able to replace traditional thermometers over the years. Taking the aforementioned advantages and disadvantages into account, an ear thermometer is a good choice for preliminary measurement and monitoring of body temperature, or as a tool for initial screening of potential infected individuals during outbreaks such as SARS. However, for further confirmation, given the current state of development, a traditional thermometer is still the better choice. Frequently Asked Question Q1: Does the temperature measured by an ear thermometer vary from person to person? ? Experiments in Japan have found that there can be a difference of up to 0.5 °C in body temperature measurements between skilled and unskilled individuals (while the accuracy of traditional thermometers is ±0.1 °C). Since using an ear thermometer requires some practice and its accuracy is not as good as that of traditional thermometers, people outside the country do not consider ear thermometers suitable for use by the general public. According to ASTM (American Society for Testing and Materials) standards: the ear temperature should be within the range of 36 °C to 39 °C, with an accuracy of ±0.2 °C; outside this range, the accuracy is ±0.3 °C. Q2: Can plastic wrap replace ear thermometers? ? Plastic wrap has good transmittance in the visible light range, but it causes attenuation of infrared rays in that spectrum; the extent of this attenuation depends on the material of the plastic wrap. PE plastic wrap offers the best transmittance, yet it still results in a decrease in the readings from ear thermometers by 0.1°C to 0.4°C. PVDC plastic wrap has the greatest impact, causing a reduction in ear thermometer readings by 1°C to 2°C – an effect that many find surprising. Q3: Will the temperatures of the left and right ears be the same? ? The ear temperature in the left and right ears is not necessarily the same. Based on our experimental results, the average temperature of the left ear is 0.1 °C higher than that of the right ear. There are many factors that can cause an increase in ear temperature readings, such as sleeping on one side and pressing on the ear. Q4: Does an ear thermometer use infrared radiation for sensing? ? The sensors of ear thermometers passively convert the received thermal radiation signals into temperature values. Some forehead thermometers emit red light; its purpose is merely to inform the user of the area being measured by the thermometer, and it is not used to detect skin temperature through that red light, which often leads to misunderstandings among users.