Electrical Codes, Standards, Recommended Practices and Regulations

generators. Electrically operated temperature detectors consist of resistance thermometer

device (RTD) elements, light detectors, pressure-gage thermometers, and thermocouple

devices. RTD elements consist of a coil of platinum wire wrapped around a mica frame and

enclosed in a glass tube. The device is connected to a thermometer bridge for measuring coil

resistance. Light detectors determine high temperatures by sensing the wavelength of the

radiation being emitted by a heat source. Pressure-gage detectors utilize a metal bulb

connected to a pressure gage through a capillary tube. The vapor pressure of the fluid in the

bulb is proportional to the