Thermometers

Electronic thermometers are the most used piece of equipment in a hospital. They get the most abuse from being carried in pockets and henceforth banged against door jambs or laid on a table only to be knocked to the floor a few minutes later. All in all they are fairly sturdy little instruments. There are many different brands available such as Welch Allyn, Tyco, Philips, and others. The one thing they all have in common is a removable probe that fits in the patient’s mouth or rectum. I was once told by a doctor that the way you can tell the difference in probes is by the taste. Moving right along then!

Seriously though 99% of all thermometer complaints we get in our shop is probe related. These probes are very delicate especially at the tip. Inside the tip of a thermometer probe is an electronic component called a thermistor. A thermistor is a variable resistor. It’s resistance is varied in proportion to the amount of heat placed on it. As it heats up and the resistance changes it causes the monitoring circuitry attached to it to display the temperature on a digital readout. This thermistor is very tiny and doesn’t take shock very well. Bouncing it off the floor or swinging it against a wall will severely shorten its lifespan.

Another type of thermometer is called a tympanic thermometer. Tympanic thermometers use infrared technology to measure heat. Tympanic thermometers, or ear thermometers, use a different type of sensor. They typically use what is called a thermopile sensor. This sensor is made of several thermocouples that are placed in series. Each thermocouple is made of 2 different types of metal. A voltage is produced when there is a difference in temperature across the junction of the two metals. Since the eardrum gives off heat in the form of Infrared Radiation this heat is picked up by the thermocouple and the resulting temperature is measured against ambient air, (room temperature), and displayed on an LCD screen. Because the reaction of the metal is very quick a temperature reading can be made in less than a second. This makes the tympanic thermometer the choice of most pediatric departments where small children seldom sit still long enough to have a probe in their mouth or anywhere else for that matter.