- Celsius scale: In this scale, the distance is divided into one hundred equal sections, and one of these sections is the unit of temperature in this scale. It is denoted by the symbol Co, and in this scale, the zero degree Celsius ((T=0Co) is the freezing point of water, and the degree of one hundred (T=100Co) is the boiling point of water.
- Fahrenheit scale: In this scale, the distance is divided into 180 equal sections, and one of these sections represents the unit of temperature measurement. It is denoted Fo and in this scale the freezing point is (T=32F) and the boiling point is (T=212Fo).
Types of medical thermometers:
The theory of action of the mercury thermometer is based on the volumetric expansion of mercury. Mercury thermometers consist of a mercury storage repository connected to a graduated glass capillary tube and when the temperature rises, the mercury begins to expand volumetric and rises along the graduated tube according to the patient's temperature. Medical mercury thermometers are characterized by a narrowing of the capillary tube to prevent mercury from returning to the mercury warehouse immediately after taking the reading so that the doctor can know the patient's temperature and when needed to take another reading, the doctor towers the scale until the mercury returns to the warehouse.
- Mercury thermometers:
2. Electronic thermometers:
This type is also used to measure the patient's temperature while giving him general anesthesia, and to treat patients with rapid change in body temperature and is also used to measure body temperature externally through the skin or internally to measure the temperature of internal organs in the body such as the larynx and stomach through special sensors for this purpose.
Electronic thermometers are accurate, compact and sensitive to body temperature changes. The idea of a scale is based on converting thermal energy into an electrical quantity that can be recorded, processed and thus easily read.
Thermal energy is converted into electrical quantity using transducers used in the medical field, and the most important transformers are:
- Metal Thermal Resistor (RTD):
The metal thermal resistor consists of platinum or nickel metal and platinum is often used because the relationship between heat and platinum resistance is linear.
It is also characterized by its small size and this feature enables it to be used in the medical field by placing it at the end of a needle implanted under the skin. One of the advantages of the thermal resistor is that it has a low heat capacity in addition to the speed of the thermal resistor affected by temperature change.
It consists of a semiconductor material and its theory is based on the fact that the electrical resistance of semiconductors decreases when the temperature rises, that is, it has a negative thermal coefficient (NTC).
- Thermistor thermal resistor:
The relationship between temperature and resistance to the thermistor is generally nonlinear, but in the short term of a medical thermometer of 35 to 42 degrees Celsius it is considered linear. The thermistor also has a small heat capacity and a rapid impact of changes in temperature and small size.
A thermocouple is composed of two conductors of two different materials bonded together at a single point.
Since the thermal conductivity of each material is different from the other, when their point of contact is heated, an electromotive force is created between the other parties. The value of this electromotive force depends on the type of material the conductors are made of and the temperature of the object. The higher the body temperature, the higher the electromotive force.
The thermocouple has a very small contact point, small heat capacity and rapid impact on temperature changes.
The instantaneous temperature measuring device for the patient used in clinics is either the form of a continuous temperature measuring device and is used in the continuous monitoring room and close monitoring.