# Extech RH300 Digital Psychrometer

# Extech RH300 Digital Psychrometer

## Key Features At A Glance

-   Simultaneously displays %RH, air temperature, and dew point or wet bulb (or external probe temperature)
-   Takes wet bulb measurements without slinging
-   Calculates T1-T2 differential (air minus external probe temp) and T2-minus-dew-point using the optional TP890 probe
-   Unique sensor cap twists to a closed position to protect the sensor during storage
-   Data Hold freezes the current reading, with Max/Min capture and Auto Power Off
-   Humidity range 10 to 90%RH at +/-3%RH; dew point down to -68.0 degrees C and wet bulb to -21.6 degrees C
-   Compact 7 x 1.9 x 1 in housing at 3.3 oz; ships complete with two AAA batteries

The RH300 is a compact digital psychrometer that simultaneously displays relative humidity, air temperature, and either dew point, wet bulb, or external probe temperature on a single screen. Its compact form makes it well-suited for field applications, and a unique sensor cap twists to a closed position to protect the sensor during storage.

A psychrometer characterizes the moisture state of air by relating humidity, temperature, and the derived dew point and wet bulb values. The RH300 performs wet bulb measurements without slinging, and using the optional TP890 thermistor temperature probe it calculates a T1-T2 differential (air temperature minus external probe temperature) as well as a T2-minus-dew-point value. Data Hold, Max/Min readings, and Auto Power Off round out the operating feature set.

ValueTronics stocks and holds its own inventory in a 20,000 sq ft secure warehouse at 1675 Cambridge Drive in Elgin, Illinois.

## Brand Heritage

The Extech brand operates as part of FLIR Systems, Inc., which holds the copyright on this product line. The two names reflect a single corporate relationship rather than separate manufacturers.

## Accessories Supplied

-   2 AAA batteries

## Product Core & Specifications

Parameter

Range

Max Resolution

Basic Accuracy

Humidity

10 to 90%RH

0.1%RH

±3%RH

Temperature (internal)

\-4 to 122°F (-20 to 50°C)

0.1°

±1.8°F or ±1°C

Temperature (external)

\-4 to 158°F (-20 to 70°C)

0.1°

±1.8°F or ±1°C

Dew Point

\-90.4 to 122°F (-68.0 to 49.9°C)

0.1°

—

Wet Bulb

\-6.9 to 122°F (-21.6 to 49.9°C)

0.1°

—

Dimensions / Weight

Dimensions

7 x 1.9 x 1" (178.5 x 48.4 x 24.7 mm)

—

—

Weight

3.3 oz (95 g)

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—

> **Important:** The external temperature probe (TP890) is optional and is not included with the base unit; it is required to measure external temperature and to calculate the T1-T2 differential (air temperature minus external probe temperature) and T2-dew point.

> **Important:** This product is available with optional calibration traceable to NIST — order with -NIST after the part number.

> Recommended pairing: use the optional Extech TP890 Thermistor Temperature Probe to enable external temperature measurement and the T1-T2 differential calculation.

ValueTronics supplies both new and used test and measurement equipment. New units ship factory-sealed, exactly as received from the manufacturer; every used unit is inspected and functionally verified in-house at our 20,000 sq ft secure facility in Elgin, Illinois before it ships. Our Test Architects can help you select the condition, calibration, and configuration that fit your application.

**Please review the Manufacturer's Data Sheet to verify published specifications. Feedback on this webpage is always welcome — please reach out to your Test Architect at any time for questions or concerns. Thank you, we truly appreciate you being our customer.**

## Details

- **Price:** 114.0 USD
- **Vendor:** Extech
- **Type:** Data Log
- **Tags:** Extech, Factory New, FLIR Systems, Inc., Manufacturers, Meters & DAQ, Model 300, product_manual_group_2, Product_new, Psychrometer, RH300, Thermometer

## Variants

| Variant | Price | Available |
|---------|-------|-----------|
| Default Title | 114.00 USD | In stock |

## Images

- Extech RH300 Digital Psychrometer

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> Source: [ValueTronics](https://valuetronics.com/products/rh300-extech-thermometer-new)
> Updated: 2026-06-03