Thermistors

956 Words2 Pages

Ange Liu
Dr. Prasad
BMEN 3130.002
17 January 2014
Lab 1 Literature Report: Temperature Sensor Lab
Temperature is a vital sign of the human body and is one of the first signs of a patient’s health. Temperature sensors are among one of the most basic types of medical devices and the purpose of this lab is to understand the basics of such a device. There are many ways to measure temperature using electronic circuits, this lab will focus on thermistors (Chandrahas).
“Thermistors are thermally sensitive resistors whose prime function is to exhibit a large, predictable and precise change in electrical resistance when subjected to a corresponding change in body temperature” (What). There are many types of thermistors; first they are divided into subcategories of negative or positive temperature coefficient of resistance (NTCs, PTCs, respectively). There are two types of NTC thermistors: beaded and thermistors with metalized surface contacts. The normal range for the NTC thermistor to sense is from -50°C to +150°C. The vernier sensor used in the lab has a range from -25 to 125°C with a maximum temperature tolerance of 150°C without damage. Bead type thermistors are used in this lab. “Commercial bead type resistors have a platinum lead with diameters ranging from 0.018 mm to 0.1 mm”. They generally offer high stability and reliability, quick response, and operate at high temperatures. In a thermistor, voltage changes with temperature. Resistance and temperature have an inverse relationship (Chandrahas).

Normal body temperature differs between person to person from 97.6°F to 99.6°F. Many factors cause variations of body temperature throughout the day such as activity, time of day, and hormones. The most common abnormalit...

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...digital thermometers. They are placed on the temporal artery of the forehand and reads infrared heat. Plastic “fever” strip thermometers measures temperature from the forehead, but are very inaccurate. Pacifier thermometer is intended for babies to suck on in their mouth. It is inaccurate because it depends on stability in the mouth and that is very difficult for babies. Glass and mercury thermometers is probably the oldest and most common thermometer around the world. It was very popular until it is realized that they create the risk of exposure to mercury (Types). Rate of respiration can be measured by counting the number of breathes in a certain amount of time. Anything done ‘free handed’ is not as accurate as it should be; thought it is convenient and easily accessible. To obtain an average of results, for each part of the lab there shall be 3 trials per person.

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