Delta-t AT2, RHT2NL, RHT2V, RHT2 DATA SHEET

Delta-T Devices Data Sheet

Relative Humidity & Air Temperature Sensors

Types RHT2nl, RHT2v & AT2

The RHT2 and AT2 sensors are designed
for weather station measurements of relative
humidity and air temperature.

They are lower cost replacements for the
former Delta-T RHA1 and AT1 sensors, with
superior specifications and reduced
maintenance cost for the RH sensor.

• High RH accuracy and stability

• Plug-in replacement sensor

modules

• Avoids the need to return
sensor for recalibration

• Simple 0-1V linear outputs for
easy interfacing

• High temperature accuracy
with thermistor sensors, if
required

• Thermistor output easily
logged as temperature with
Delta-T loggers

• Low transducer power
requirement

Solar Radiation Shield

The common feature of the RHT2 and AT2 sensors is
the solar radiation shield type SRS2 that protects the
sensors from solar radiation and rain when they are
mounted outdoors.

The features include:

• 13-plate naturally aspirated shield

• UV stabilised thermoplastic plates

• Good solar radiation shielding

• Protection from long wave ground thermal

radiation

• Simple mounting bracket for vertical or horizontal
masts or poles up to 50 mm diameter

Shielded RH and Temperature Sensors

The RHT2 comprises an RH and air temperature
transducer housed in the solar radiation shield. The
transducer requires power and provides two output
signals for the RH and air temperature.

The RH and air temperature sensing elements are
contained in a plug-in module. The module is
interchangeable and can be replaced at routine
maintenance intervals.

The modules come in two versions depending on the
precision of temperature measurement required:

• The RHT2nl gives highest temperature precision
of ±0.1 °C with non-linear thermistor output

• The RHT2v is lower cost, with a broader
tolerance of ±0.5 °C, and a linear 0-1V output
derived from a PRT temperature element

Shielded Air Temperature Sensor

The AT2 is a high accuracy, shielded, air temperature
probe for weather station measurements.

• High accuracy thermistor sensor.

• Stainless steel sheathed probe (125 mm long x

4.8 mm diameter).

• Thermistor output easily logged as temperature
with Delta-T loggers.

• No sensor power requirement.

RHT2-DS-3a.doc 23/07/03

Plug-in Replacement Modules

Routine checking at least once every year is the minimum
for RH sensing elements, since the RH element may show
some ageing with time. This is a common feature of all
capacitative polymer type sensors.

The general recommendation for the replacement interval
is every two or three years, in clean atmospheric
conditions. If atmospheric pollutants are present, or if the
atmosphere is acidic then the replacement must be made
every year.

Plug-in Replacement Modules minimise the cost and delay
of maintenance. They are interchangeable and can be

fitted and used without any further calibration

.

RHT2nl, RHT2v & AT2 Technical Specifications

specifications are subject to change without notice

Relative Humidity Sensor [RHT2nl & RHT2v models]

RH Output range 0 to 100%RH
Sensitivity 10 mV per %RH; 0 to 1 V
Ageing characteristic Typical: ~-1.5 to -2% first year; ~-1% second year; ~-0.5% third year.
Accuracy at 23°C ± 2% RH (5 to 95% RH)

± 2.5% RH (RH<5% and >95%) (hysteresis and non linearity included)
Humidity linearisation 7 points, 6 segments, memorised in the module EEPROM
Operating conditions 0 to100% RH, -20 to +80°C
Storage conditions -40 to +85°C
Response time t <10 s (90% of a step from 11% to 75% RH).
Load impedance
Voltage supply
Size and Weight
Enclosure rating IP65

> 10 kΩ

5 to 32 VDC, ≤2 mA RHT2nl, ≤4 mA RHT2v

length 96 mm, ∅ 18 mm, 80 g

Air Temperature Sensor [ RHT2nl and AT2 models only ]

Output range -50 to +150°C
Thermistor resistance 2K ohm at 25°C, non-linear
Accuracy ± 0.1°C over 0 to 70°C
AT2 probe dimensions 125 mm x 4.8 mm dia

(thermistor only)

Air Temperature Sensor [ RHT2v model only ]

Output range -20 to +80°C
Sensitivity 10 mV per °C; 0 to 1 V
Accuracy ± 0.5% (± 0.5°C)

Solar Radiation Shield type SRS2

Overall height / Diameter 22 cm / 12 cm

Plate spacing

3 x Top Plates; 10 x Lower Plates

Material UV stabilised thermoplastic

Radiation temperature error
at 1 kW.m-2 irradiance level:

11 mm

0.4°C @ 3 m.s-1

0.65°C @ 2 m.s-1

1.4°C @ 1 m.s-1 or slower

Ordering Information

type reference item description

RHT2nl-02

RHT2v-02

RHT2nl-chp
RHT2v-chp
SRS2
AT2-02

RH Sensor and Precision Air Temperature sensor type RHT2nl (2m cable) both mounted in same solar radiation
shield. RH accuracy 2%; Precision Thermistor Temp sensor (± 0.1°C, 0 to 70°C) with non-linear output.

RH Sensor and Linearised Air Temperature sensor type RHT2v (2m cable) both mounted in same solar
radiation shield. RH accuracy 2%; Temp sensor with linearised voltage output (± 0.5°C, -20 to 80°C).

Replacement plug-in RH & Temperature module for RHT2nl sensor

Replacement plug-in RH & Temperature module for RHT2v sensor

RH/Air Temp Solar radiation shield type SRS2 - suitable for RHT2nl, RHT2v and AT2 units

Air Temperature Sensor type AT2 (2m cable) mounted in own solar radiation shield (± 0.1°C, 0 to 70°C)

Delta-T Devices Ltd

Tel: [phone], Fax: [phone], E-mail: [e-mail]

128 Low Road, Burwell, Cambridge,CB5 0EJ, UK

, Web: www.delta-t.co.uk

RHT2-DS-3a.doc
23/07/03