Extech Instruments RH300 User manual

USER MANUAL

Digital Psychrometer

Models RH300 and RH305 (kit)

www. .com information@itm.com1.800.561.8187

RH300-en-GB_v1.7 9/16

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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RH300-en-GB_v1.7 9/16

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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RH300-en-GB_v1.7 9/16

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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RH300-en-GB_v1.7 9/16

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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RH300-en-GB_v1.7 9/16

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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