Extech Instruments RH300 User manual
USER MANUAL
Digital Psychrometer
Models RH300 and RH305 (kit)
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RH300-en-GB_v1.7 9/16
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Introduction
Congratulations on your purchase of the Extech RH300 Digital Psychrometer. This device measures
Humidity, Air Temperature, Dew Point temperature and Wet Bulb temperature. Advanced features
include External Temperature Measurement (with optional probe), Data Hold, selectable Auto Power
Off, and MAX/MIN/Average reading. Careful use of this meter will provide years of reliable service.
Meter Description
1. Humidity Sensor & Air Temperature Sensor
2. Triple LCD Display
3. ON/OFF button
4. T1-T2/Dew Point/T1 button
5. °F/°C select
6. MIN/MAX/RESET button
7. T2-DP/Wet Bulb/T2 button
8. HOLD button
9. T2 Probe Jack
Note: The battery compartment is located
on the rear of the instrument
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Display Description
1. Relative Humidity %
2. T1 (Air Temp)
3. T1-T2
4. Dew Point
5. Wet Bulb
6. T2-Dew Point
7. °C/°F
8. T2 (Type K probe)
9. Maximum
10. Minimum
11. Low Battery/Hold
Operation
Open the Protective Sensor Cap
Twist the protective sensor cap, located at the top of the
meter, counter-clockwise a quarter of a turn to expose
the sensor
Turn Power ON or OFF
Press the ON/OFF button to turn power on or off. The meter will perform a short self-test
when turned on.
Taking Air Temperature and Humidity Measurements
1. Hold the probe in the area to be tested.
2. Allow adequate time for readings to stabilize.
3. The Relative Humidity measurement appears in the top
display.
4. Pressing the T/DP/T1 button toggles the lower left
display between T1 (Air Temperature) and DP
(Dew point) measurements.
5. The lower right display will read WB (Wet Bulb) temperature.
Note: If the external Type K probe is not connected, T1-T2, T2-DP, and T2
measurements will not be displayed.
CLOSE OPEN
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Taking External (Type K probe) Measurements
Plug in the optional external Type K temperature probe.
1. Pressing the T/DP/T1 button toggles the lower left display between T1 (Air
temperature), T1-T2 (∆T), and DP (Dew point) measurements.
2. Pressing the ∆/WB/T2 button toggles the lower right display between T2 (Type K),
T2-DP (Type K temperature-Dew Point), and WB (Wet Bulb).
Selecting temperature units of measure (C/F)
Press and hold the oC/oF button momentarily to toggle the temperature units.
Minimum (MIN) Maximum (MAX) Function
The MIN/MAX mode allows the user to view only the lowest (MIN) or highest (MAX)
readings. Press the MnMx/Reset button once and MIN appears on the display. The
display is now showing the lowest humidity and temperature reading in memory. Press
the MnMx/Reset button again and MAX appears on the display. The display is now
showing the maximum humidity and temperature readings in memory. To exit the
MIN/MAX mode, press the MnMx/Reset button again and the MIN and MAX icons
disappear. To clear the current min/max readings in memory, press and hold the
MnMx/Reset button for more than two seconds.
Data Hold
Press the HOLD button momentarily to freeze the displayed reading. The 'HLD' icon will
appear on the upper right-hand side of the display. Press the HOLD button again to
return to normal operation.
Automatic Power OFF
The meter automatically shuts off after a programmed period of time. The default time is
10 minutes. To program the time period, press down the HOLD button while turning the
meter on. Continue to hold down both buttons and the meter will cycle through the
selectable power-off times: n, 2, 5, 10, 20, 40 or 60 minutes. “n” disables the auto power
off function. When the desired power-off time appears in the display, release both
buttons to select the time and return to normal operation.
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Calibration
The following verification and calibration procedures require the 33% and 75% RH reference bottles
which are supplied with the Model RH305 kit.
Accuracy Verification
Checking the 33% or 75% RH Calibration:
1. Insert meter’s sensor into the 33% or 75% salt reference bottle.
2. Check the reading after 10 minutes.
3. Verify that the reading is within the accuracy specification.
Relative Humidity Calibration (33% and 75%)
Calibration Preparation
Ensure that fresh batteries are installed in the meter.
Move the protective vent cap to the Open position.
Power the meter ON and set it to display dew point (DP) and wet bulb (Wb) in the lower display
area.
Calibration Procedure
1. Follow the Preparation steps above before continuing.
2. Power the meter OFF.
3. Insert the meter into a 33% salt bottle.
4. Leave the meter OFF for one hour (to stabilize).
5. After the meter has stabilized for one hour:
Press and hold the °C/°F button while powering the unit ON.
The unit enters calibration mode (32.8% flashes on the display).
The DP and Wb display areas show DP ---- Wb ----°C.
6. Once the 33% calibration is complete, the display stops flashing and a constant 32.8% is
displayed.
7. Allow the meter to remain ON and move it to the 75% salt bottle.
8. Allow the meter to remain for one hour in the 75% salt bottle to stabilize.
Important: Do NOT power the meter OFF while in the Calibration mode! Note that
AUTO POWER OFF is disabled while in the Calibration mode.
9. After one hour, press and hold the MN/MX button until 75.3% begins flashing on the meter
display. The meter has now entered the 75.0% calibration stage.
10. After 30 minutes have elapsed, the meter will automatically exit the calibration mode and
return to the normal operating mode.
11. The Calibration is complete, turn power OFF.
Note: To exit from the calibration procedure before completion, press the ON/OFF button.
Note: If the salt at the bottom of the calibration bottles appears dry, the bottles should be replaced.
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Maintenance
Cleaning and storage
1. The meter should be cleaned with a damp cloth and mild detergent when necessary. Do not use
solvents or abrasives.
2. Store the meter in an area with moderate temperature and humidity (refer to the operating and
storage range in the specifications chart earlier in this manual).
Battery Replacement
When the battery power falls low, the symbol will appear on the LCD. Replace the two (2) 1.5
‘AAA’ batteries by removing the rear battery compartment cover and accessing the battery
compartment. Observe correct polarity when placing the batteries in the compartment. Ensure that
the compartment cover is securely fastened when finished.
Never dispose of used batteries or rechargeable batteries in household waste.
As consumers, users are legally required to take used batteries to appropriate collection
sites, the retail store where the batteries were purchased, or wherever batteries are sold.
Disposal: Do not dispose of this instrument in household waste. The user is obligated to take end-of-
life devices to a designated collection point for the disposal of electrical and electronic equipment.
Other Battery Safety Reminders
oNever dispose of batteries in a fire. Batteries may explode or leak.
oNever mix battery types. Always install new batteries of the same type.
Error Messages
An error message will appear on the display if the meter fails an internal diagnostic test.
1. ER1: Relative Humidity failure. Repair/replacement is necessary.
2. ER2: Internal temperature failure. Repair/replacement necessary.
3. ER3: Reference resistance failure. Repair/replacement necessary.
4. ER4: Internal temperature is out of range.
5. ER5: External temperature is out of range.
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Specifications
Range and Resolution Accuracy
Humidity 0.0 to 100.0% RH ±3% RH (10 to 90%) @ 23oC
Temperature (internal) -20 to 50oC (-4.0 to 122.0oF) ±1oC (±1.8oF)
Temperature (external) -20 to 70oC (-4.0 to 158.0oF) ±1oC (±1.8oF)
Display Triple LCD
Sensor Type Humidity: Precision capacitance sensor
Temperature: Thermistor
Response Time 60 seconds typical
Dew Point -90.4 to 122.0oF (-68 to 50oC) (calculated from RH and Air temperature
measurements)
Wet Bulb -6.88 to 122.0oF (-21.6 to 50oC) (calculated from RH and Air
temperature measurements)
Operating Conditions -20 to 50oC (-4 to 122oF); < 99% RH non-condensing
Storage Conditions -40 to 85oC (-40 to 185oF); <99% RH non-condensing
Power Supply 2 x 1.5V ‘AAA’ batteries
Battery Life Approx. 80 hours
Dimensions / Weight 178.5 x 48.8 x 25.2mm (7 x 1.9 x 1”); 140g (4.9 oz.)
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