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Tri-sensor Calculation and Remote Cable
Wet Bulb Globe Temperature
7
Measurements
The QUESTemp° 34 & 36 data logging area heat stress monitor directly senses the
four parameters: ambient or dry bulb temperature (DB), natural wet bulb temperature
(WB), globe temperature (G), and relative humidity (RH).
The QT° 34/ 36 compute the Wet Bulb Globe Temperature (WBGT), stay times for
three possible indices (QT° 36 only), and the Heat Index (HI) or the Canadian
Humidex. Using inputs on the side of the instrument, two additional sensor arrays can
monitor up to three locations simultaneously.
On the QUESTempº 36 model, you can measure air flow, in meters per second, by
plugging an optional hot wire anemometer sensor into a side jack on the unit.
Using Detection Management Software (DMS), you can determine the thermal comfort
indices, Predicted Mean Vote (PMV) and Predicted Percent Dissatisfied (PPD) (with
the QUESTempº 36 model only).
Wet Bulb Globe Temperature
The WBGT is a weighted average of the three temperature sensors, a globe
thermometer, a wet bulb thermometer, and a dry-bulb thermometer, using the
equations listed below.
The resulting WBGT values can then be compared to indices of work-rest regimens
(stay times) based upon work loads.
Stay Times/Rest Times (QTº36 only)
Stay times represent how long a worker should be able to safely work under heat
stress conditions (available on QUESTempº 36 only). Select one of the three
indices for displaying and printing from the unit: ACGIH Stay Times, NAVY PHEL’s,
or EPRI Action Limits. (For setup, please refer to “Setup” on pages 9 -10. For
detailed rest times please refer to charts in Appendix B.)
Measurements
WBGT (indoor) = 0.7WB + 0.3G (denoted as “WBGTi” on the display)
WBGT (outdoor) = 0.7WB + 0.2G + 0.1DB (denoted as “WBGTo” on the display)