Body temperature is an important index to know the state of life, which reflects the metabolic results of the organism, and is one of the conditions for normal functional activity. NTC thermistor are widely used in body temperature measurement, and medical monitoring instrument are one of the instruments that includes NTC thermistor.
Medical monitoring instrument is a device that measures and controls the physiological parameters of patients, and can be compared with a known set value, it would give a alarm if there is excessive value. Medical monitoring instrument is different with monitoring diagnostic instrument, it must monitor patients’ physiological parameters 24 hours continuously, detect variational trend, point out the emergency situation, as the basic of doctors’ emergency treatment and cure, minimize the complications, reach the purpose of alleviating and eliminating the diseases. The six standard parameters of the medical monitoring instrument are ECG, respiration, noninvasive blood pressure, blood oxygen saturation, pulse, body temperature. In addition, optional parameters include: invasive blood pressure, end-tidal carbon dioxide, respiratory mechanics, anaesthetic gas, cardiac output (invasive and non-invasive), bi-spectral index and so on.
NTC thermistor is located in the body temperature probe of the medical monitoring instrument. The body temperature probe is generally divided into two types: skin-surface probe and body-cavity probe. As an important accessory of medical monitoring instrument, it must monitor patients’ physiological parameters 24 hours continuously, ensure the patients’ comfort during their use, therefrom, as the core temperature measurement component of body temperature probe -- NTC thermistor, it must have the following characteristics:
1. High reliability, high stability, high accuracy
2. Small size, high sensitivity, fast response
3. Good thermal cycle endurance
4. good interchangeability, good consistency
Now the common NTC thermistor specifications of domestic and foreign body temperature probe are 25℃@2.252KΩ B25/50=3935K, 25℃@10KΩ B25/50=3935K, also use 25℃@30KΩ B25/50=3935K, 25℃@6KΩ B25/50= 3935K, etc., at present domestic and foreign parameter standard is generally reference YSI standard. The standards to measure the stability and reliability of NTC thermistor are mainly shown in three aspects:
1. Change rate of resistance after resistance solder-ability test
2. Change rate of resistance after hot and cold shock
3. Change rate of resistance after high temperature aging
Therefore, the selection of NTC thermistor for the temperature probe of the medical monitoring instrument should proceed from the following aspects:
1. Resistance, B value of the specifications and accuracy comply with the design requirements
2. Stability of NTC thermistor ( change resistance is small after solder-ability test/aging test)
3. Volume size of NTC thermistor (good for encapsulation)
In recent years, EXSENSE Electronic Technology Co., Ltd. is committed to the research and development for hign reliable, high stable NTC thermistor chip, and achieved significant achievements. The MT series NTC thermistor produced by our company, its change rate of resistance ≤0.3% after resistance solder-ability test, the resistance change rate ≤0.3% after high temperature aging for 1,000 hours, accuracy can up to 0.02 ℃. Adapted to the developmental needs of the NTC thermistor "small and fine" on medical equipment. Now it’s widely used in the medical monitoring instrument, temperature probe of infant incubator, etc..