T/RV Sensor | What is it and how do you use it?

In a T/RH sensor, the temperature (T) and relative humidity (RH) come together. Both the air temperature in degrees Celsius (°C) and the RH in percentage of water vapor in the air at this temperature are measured.

 

Installation of the T/RV-sensor

The installation of the sensor itself is very easy: attach the sensor with a tie-wrap or string to a tripod and place it among the plants. The sensor transfers the data on the temperature and relative humidity of the environment where it is placed. There are many microclimates present in a greenhouse. Therefore, the installation and positioning of the sensor are very important:

 

• • When only one sensor is available, the best place to position it is in the center of a greenhouse or section. (Lee et al., 2019).

 

• • When using multiple sensors, more distribution is possible to get a better overall picture of the temperature and humidity in the greenhouse. (Bhujel et al., 2020).

 

Do’s en Don’ts for installing a sensor

 

• • Place the sensor between the lower and upper leaves, depending on what needs to be measured.

 

• • Install the sensor in a location that is representative of most plants, such as not along an aisle.

 

• • Use a radius of one meter of plants around the sensors. This helps minimize the edge effect.

     

 

• • Do not place a sensor near a metal structure. Metal can radiate or absorb heat into the air, which could create a microclimate that is not representative of the plants.

 

• • Do not place the sensor in direct sunlight. This can cause the sensor to heat up, leading to an overestimation of the temperature and an underestimation of the humidity, as warmer air can hold more water vapor.

 

Analyze data from the T/RH sensor.

Every five minutes, the T/RH sensor sends the temperature and RH values to MyLedgnd. Here you have a direct overview of the progression of these values throughout the day. At the same time, you can analyze multiple sensors simultaneously to highlight differences in values between different sections of the greenhouse (see images 1 and 2).

 

Image 1: Temperature progression with a too high and a too low peak.

 

Image 2: Progression of relative humidity with a too low peak.

 

What conclusions can be drawn from the measured data?

The temperature and relative humidity are interesting to compare with:

 

• • Soil temperature: A too high/too low soil temperature compared to the air temperature can cause plant stress or non-optimal water and nutrient supply. Therefore, it is useful to compare the soil temperature with the air temperature.

 

• • Dew point temperature: By comparing the air temperature with the dew point temperature, you can determine if there have been moments when condensation was present in the greenhouse or even on the plant. Condensation encourages fungi and other diseases, making it easier for them to infect a plant. Naturally, this is something you want to avoid. A more accurate comparison is made by comparing the leaf temperature with the dew point temperature.

 

• • Fotosynthetic active radiation (PAR):
    

    By comparing PAR (Photosynthetically Active Radiation) with the temperature in the greenhouse, you can gain insight into the effect of radiation on heating the greenhouse. By comparing the fluctuating PAR and temperatures with each other, you can better adjust shading in the future. This way, you will experience fewer temperature fluctuations in your crop.

     

 

• • Absolute humidity (AH): Absolute humidity shows the total water vapor in g/m³ in the air and is calculated using the air temperature and relative humidity. This makes it easy to observe over time whether the total water vapor per cubic meter of air remains constant or fluctuates, for example, by opening windows.

 

Advice from Ledgnd

The T/RH sensor is the foundation for quickly gaining insight into the climate for plants and in the greenhouse. For even more specificity, we recommend using a PAR sensor, leaf temperature sensor, and soil sensor to make the above comparisons possible.

Ultimately, this will provide insight into the balance of air and soil temperature, condensation in the greenhouse, the effect of radiation on air temperature, and the trend of absolute humidity in the greenhouse.

 

References

Bhujel, A., Basak, J. K., Khan, F., Arulmozhi, E., Jaihuni, M., Sihalath, T., … & Kim, H. T. (2020). Sensor Systems for Greenhouse Microclimate Monitoring and Control: A Review. Journal of Biosystems Engineering, 45(4), 341-361.

Lee, S. Y., Lee, I. B., Yeo, U. H., Kim, R. W., & Kim, J. G. (2019). Optimal sensor placement for monitoring and controlling greenhouse internal environments. Biosystems Engineering, 188, 190-206.