The Amprobe THWD-1 digital psychrometer functions both as a psychrometer to measure relative humidity, and as a thermometer. The device is designed to calibrate and check the efficiency of heating and air conditioning systems. Although the newer models have replaced THWD-1, some older units remain in use as of this writing.
1 Gently push down on the sides of the sensor cover, and pull it from the top of the psychrometer.
2 Turn on the device by pressing the “On / Off” button in the upper left corner of the six-button control panel.
3 Press the “C / F” button in the upper right corner of the control panel to choose between the Celsius and Fahrenheit temperature scales.
4 Consider the temperature and humidity readings. They will appear on the display screen as soon as you can choose your temperature scale.
The minimum and maximum readings
5 Obtain and store the minimum humidity and temperature reading for the area you are looking at by pressing and holding the “Mn / Mx” button in the lower right corner of the control panel, and releasing it when the display shows “Min.”
6 Obtain and save the maximum humidity and the reading of the temperature by pressing the “Mn / Mx” button until the display shows “Max.”
7 Clear the maximum and minimum readings and store them, if necessary, by pressing the “RST” button in the lower-left corner of the control panel until the entire screen flashes.
Dew point and damp bulb Readings
8 Press and hold the “TD / WBT” button until “TD” appears on the left side of the display screen. This will indicate the temperature at which the atmospheric water vapor will begin to condense in its test area.
9 Release the “TD / WBT” button, and note the reading of the dew point temperature that appears on the screen.
10 Press and hold the “TD / WBT” button again until “Wb” appears on the left side of the display screen.
11 Release the “TD / WBT” button. Note the reading as soon as the screen stops blinking. (If the screen is flashing, it means that the unit is adjusting the wet-bulb temperature due to changing conditions in the test area.)
Data retention function
12 Take the standard dew point or wet bulb readings, as indicated above.
13 Press the “Hold” button as soon as you have read it. Press and hold until the word “Hold” appears on the screen.
14 Record your reading as necessary. For example, it is possible to use the “wait” function if you need to send your reading to a technician or enter a computer outside the test area.
15 Release the unit from the “standby” mode by pressing the “RST” button.
Tips and warnings
- To cancel the 20-minute automatic hibernation timer, press the “On / Off” and “Min / Max” buttons at the same time. Release the “On / Off” button until “n” appears on the screen, and then release the “Min / Max” button.