USER GUIDE Heat Index Psychrometer Model RH25
Introduction Thank you for selecting the Extech Instruments Model RH25 Heat Index Psychrometer. The RH25 measures Temperature and Relative Humidity (using precision capacitance RH sensor). The RH25 also calculates and displays Heat Index, Dew Point, Wet Bulb, and Wet Bulb Globe temperatures. The High Temperature Alarm feature alerts the user when Heat Index or Wet Bulb Globe levels exceed user‐preset limits. Data Hold and MIN/MAX/AVG memory utilities make it easier to recall important data.
Operation Keypad POWER: Switch the meter ON or OFF; also used to enter the MAX/MIN/AVG memory mode. HOLD: Press to enter Data Hold (reading freezes on display). Press again to exit Data Hold. MODE: Press to step through the measurement modes: TEMP (Temperature), RH (Relative Humidity), HI (Heat Index), DP (Dew Point), (WB (Wet Bulb), and HI/WB (Wet Bulb Globe). Powering the meter Press POWER to switch meter ON.
Selecting oC/oF units of measure With the meter OFF, press and hold the POWER and MODE buttons simultaneously until the unit of measure appears on the lower right corner of the LCD. Use the MODE button to select the o o desired unit of measure ( C or F). Press POWER twice to step past the alarm settings until the normal measurement mode is displayed. High Alarm for Heat Index and Wet Bulb Globe temperature 1.
Appendices Appendix A – Heat Index based on Temperature (oF) vs. Relative Humidity (%) Note: Italic values are Heat Index based on the Temperature (left column) and Relative Humidity (top row). o F 90% 80% 70% 60% 50% 40% o 85 84 82 81 80 79 o 101 96 92 90 86 84 o 121 113 105 99 94 90 133 122 113 105 98 142 129 118 109 148 133 121 80 F 85 F 90 F o 95 F o 100 F o 105 F o 110 F 135 Appendix B – Heat Index based on Temperature (oF) vs.
Battery Replacement When the low battery icon (BAT) appears on the LCD, the CR‐2032 lithium button battery must be replaced. The battery compartment is located on the rear of the meter. 1. Use a coin to turn the battery compartment cover counter‐clockwise to open. 2. Note the position, orientation, and polarity of the existing battery installation. 3. Replace the CR‐2032 Lithium battery following the same position, orientation, and polarity. 4.
