Meteorological Thermometers are used to measure the
temperature of the air. To measure the temperature of the
air accurately, it is important that the thermometer is
shielded from direct sunlight but is still exposed to a good
airflow. Therefore, thermometers are usually put in the
stevenson screen at the Meteorological Garden so that to
shield from direct heat radiation which could influenced a
higher reading of temperature.
HMP45A & HMP45D Humidity and
Temperature Probes
The HMP45A and HMP45D probes are
designed for the measurement of
relative humidity and temperature.
Humidity measurement is based on the
capacitive thin film polymer sensor
HUMICAP 180. Temperature measurement
is based on resistive platinum
sensors (Pt 100 and Pt 1000).
Both the humidity and temperature
sensors are located at the tip of
the probe and in standard version
protected by a membrane filter.
The HMP45A and HMP45D have a similar
humidity output, but the temperature
output is active in HMP45A (voltage
output 0-1V)
and passive in HMP45D (resistive
output Pt 100).
There are four (4) types of Mercury-in glass thermometer in a stevenson screen:
1. Maximum Thermometer
2. Minimum Thermometer
3. Wet-bulb Thermometer
4. Dry-bulb Thermometer
Pressure Recording Instruments
Vaisala PTB220B Barometric Pressure Sensor
Fully compensated digital barometers designed to cover a wide range of environmental pressure and temperature. They can be used successfully both in accurate pressure measurement applications at room temperature and in demanding automatic weather station applications.The PTB220 series digital barometers use the BAROCAP silicon capacitive absolute sensor developed by Vaisala for barometric pressure measurement applications.
The measurement principle of the PTB220 series digital barometers is based on an advanced RC oscillator and three reference capacitors against which the capacitive pressure sensor and the capacitive temperature compensation sensor are continuously measured. The microprocessor of the barometer performs compensation for pressure linearity and temperature dependence.
The pressure and temperature adjustment in the PTB220 consists of seven temperature levels over the operating temperature range of the barometer and of six to eleven pressure levels over the operating pressure range of the barometer at each temperature level. The calculated individual basic pressure and temperature adjustment coefficients are stored in the EEPROM of each pressure transducer. The user cannot change these basic factory adjustments.
The multipoint fine adjustment for pressure and the final pressure calibration of the PTB220 Class A barometers is done using a manual Ruska 2465 dead-weight tester. The multipoint fine adjustment and calibration of the Class B barometers is done automatically using electronic working standards.
The PTB220 digital barometers use the BAROCAP silicon capacitive absolute pressure sensor developed by Vaisala for barometric pressure measurement applications. The BAROCAP sensor has excellent hysteresis and repeatability characteristics, low temperature dependence and a very good long-term stability. The ruggedness of the BAROCAP sensor is outstanding and the sensor is resistant to mechanical and thermal shocks.
Wind Instruments
Wind Observer II Ultrasonic Wind Sensor
Wind Speed
-Range: 0-126 knots (0-233 km/h)