QUESTION: Can Vaisala Humicap HMP155 with an additional PT100 temperature probe fit inside the MeteoShield Pro?

ANSWER: YES, since the standard MeteoShield Pro sensor clamp fits sensors up to Ø20 mm, the Vaisala HUMICAP HMP155 fits just fine as it is clamped where its body has a 20 mm diameter (see photos). Additionally, as shown in the accompanying photos, we manufacture a dual-clamp mount for the HMP155 with an additional temperature probe.

While the MeteoShield Pro is the highest precision solar radiation shield for meteorology in the marketplace, the Vaisala HMP-155 temperature and humidity probe is arguably the most accurate sensor for stable long term measurement in the industry. The Vaisala HMP155 HUMICAP® humidity sensor with an additional temperature probe provides one of the most reliable humidity and temperature measurements since its sensor head is warmed continuously. This allows the capacitive humidity sensor to remain in relative humidity which is lower than the error prone 90% RH and above. The drawback is that an additional external temperature sensor is required to recalculate (convert) the measured relative humidity readings into real readings. This is the reason why the additional PT100 temperature probe is required.

IMPORTANT INSTALLATION NOTES

• It is recommended that the additional temperature probe be housed in its own solar radiation shield as to avoid temperature errors from the heated HMP155 humidity sensor and its electronics.

• If the additional temperature probe requires installation inside the same solar screen as the heated HMP155, we highly recommend that the PT100 be located at least 1 cm above the top the HMP155 to allow for sufficient airflow and to limit the heat transfer from the heater and the HMP155 electronics.

• We manufacture a special mount for the MeteoShield Pro, which is designed to hold the additional air temperature sensor of the HMP155 sensor from Vaisala. No additional modifications are required.

TOTAL SENSOR SHIELD ACCURACY

Since the precise Vaisala temperature and humidity sensor can only accurately measure air conditions that exist inside a radiation shield, the solar radiation shield dictates the total accuracy of the sensor shield combination because:

• During sunshine hours, the solar shield minimizes errors from solar heating and reflected and radiated light and heat from the ground.

• During rain, the solar shield minimizes errors by protecting the sensor from the direct impact of dispersed rain droplets and water spray due to the wind. This is essential to minimize evaporative cooling errors and latent heat effects of wet sensors.