Loss of physical and mental efficiency occurs under definable degrees of heat stress. Severe heat stress can lead to fatigue, exhaustion and possibly even disability or death. The Wet-Bulb Globe Temperature (WBGT) index combines the effects of temperature, humidity, radiant heat, and wind into one single index employed to express environmental heat stress.
Heat stress can be reduced by decreasing the lengths of exposure and decreasing the workload of individuals under heat stress. Factors such as the type of clothing worn, the type of work performed, the psychological effects of stress, and availability of fluids can affect the assessment of heat stress, but these factors are not easily quantified. Environmental factors such as temperature, humidity, and wind are more easily measured to assess heat stress.
To calculate the WBGT index, the measurement of the black globe (radiant heat), wet bulb (evaporative heat), and ambient air (dry bulb) temperatures are required. The wet-bulb temperature can be calculated using air temperature and relative humidity if a wet-bulb thermometer is not available.
A custom cable length will need to be specified when the BlackGlobe is ordered. The maximum suggested cable length is 304 meters (1,000 feet).
The BlackGlobe requires an analog measurement. One single-ended and one excitation channel are required.
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Heat stress refers to the human body’s inability to maintain a normal temperature because of conditions such as high temperature and humidity. Certain jobs or activities require people to be subjected to these conditions, which may put their bodies at risk of heat-related illnesses and possibly result in death. Heat-related illnesses include heat cramps, heat exhaustion, and heat stroke.
Typical temperature measurements require an aspirated shield to prevent direct solar radiation from skewing the measurements. In contrast, direct solar radiation is required as a component to measure environmental heat stress.
For both of these services, calibration can be made at different values if it is requested by the purchaser at the time of purchase. In addition, both of these calibration services can be requested after sensor purchase using a returned material authorization (RMA) number. To request an RMA number, refer to the Repair and Calibration page.
Note the difference between calibration and a field check. Calibration cannot be done in the field, as it requires an experienced technician and specialized equipment.
Field checks of measurements can be done to determine if the data make sense with the real-world conditions. Follow these steps to field check a sensor: