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• How does one apply the oxygen probe of the oxygen sensor to the substrate mat?
• Where to stick the oxygen probe of the oxygen sensor into the substrate mat?
• How many sensors are required?
• How to determine the interval times?
• How to process the gathered data?

If you choose an invasive optochemical oxygen sensor, then it is important that you correctly put this into the mat. This is done as follows:

1. Put the substrate probe support into the mat.
2. Make a hole using the substrate predrill.
3. Stick the oxygen probe through the substrate probe support into its position.

The special substrate pre-drill and substrate support are included with the oxygen sensor. This enables you to make a hole in the substrate mat, without too much disruption of the mat’s structure. Then you stick the sensor through the support, into the mat. This ensures the probe not to shift, as a result of which you will receive a correct measurement. Video below show how this is done.

  

Basically, you can stick the sensor anywhere in the mat, but it is best to stick the sensor as deep into the mat as possible, and placing it as closely to the cutting block as possible. Depending on the height of the substrate you should stick the sensor 10 – 15 cm deep into the mat. The tip of the sensor must at any rate end up at the roots in the bottom of the mat. Rockwool substrate mats are usually most wet at the bottom, due to which the greatest concentration of roots is situated in the bottom of the mat. The consequence of this is that the oxygen need in the bottom of the mat is highest, which makes it the best spot to monitor the oxygen. 

It is also recommendable to place the sensor in a watertight box. Although the sensor is splash-proof, it is not water resistant.  

The number of sensors required, depends on the size of the greenhouse. In order to get a good overview of the oxygen consumption, three to four sensors per hectare should suffice.

The interval time to be set depends on how accurately you want to measure. In general, an interval of five minutes will suffice to get a good view on the oxygen consumption in the root environment. However, maybe you want to administer more water during the summer and then you might want to shorten the interval time. 

Take into account that you need to charge the optochemical oxygen sensor more often as the interval time is shorter. At one measurement per five minutes, the sensor can operate in the field at least two weeks without charging; In case of shorter interval times, this is obviously less.

Stored data can be imported from the sensor by connecting the sensor to a laptop or PC. With Microsoft Excel you can subsequently process the data. The data can be sued to assess whether the water administering strategy is optimal for the type of crop. The oxygen demand of the root environment varies during the cultivation season, so it is essential to administer the correct quantities of water. Too wet a substrate could lead to uncontrolled fungus development; too dry a substrate causes you to miss out production.

Depending on the use, the lifespan of the coating is 6 months or 400,000 measurements. When this number is reached, you should replace the coating. This is done as follows:

1. Slow unscrew the tip on the sensor. The tip is mounted watertight on the probe, by use of an o-ring sealing. Unscrewing it slowly is the easiest wat to remove the tip.
2. Replace the rubber O-ring (2 pieces) by new ones. These are included with the new tip. 
3. Slowly screw the new tip onto the sensor. This allows the overpressure in the sensor to escape. 
4. Make sure that the tip is properly tightened, otherwise water could end up in the sensor, causing a poorer signal and/or more interference.

In principle an optochemical oxygen sensor does not require any maintenance with the exception of the replacement of the oxygen probe tip after every six months or after 400,000 measurements. It is important though that after replacing the oxygen probe tip you always carry out a calibration. You can choose between 1-point or 2-point calibration. The manual states how this should be done. 

If you notice that the sensor shows unusual oxygen values, then you might want to perform another calibration, which is recommended. Multiple use may constitute measuring errors in the sensor.

Optochemical oxygen sensors are also available in a non-invasive variant that is suitable for the measuring of oxygen on directly visible measuring points. For this type of measuring, you require the read-out probe in combination with oxygen sensor stickers. The sticker is place on locations that are directly visible for the read-out probe. Hold the read-out probe in front of an applied sticker to perform a measurement. The monitoring of oxygen in, for example transparent Phalaenopsis pots or in Eb-Vloed systems is now possible. The advantage is that the sticker is always in balance with its surroundings and that you measure in the exact same location.

Placing the oxygen sensor sticker is rather simple. Detach your sticker from the strip and attach it to the inside of a pot. It is important that the pot is colorless, otherwise you will not be able to measure from the outside of the pot. You can only measure at locations that are visible to the read-out probe of the sensor. Please note: the oxygen sensor sticker is disposable and will last about six months. 

  

Apart from the hand-meter there is also an Oxygen sensor available, that can be linked to a climate computer. Oxygen Analogue Sensor Kit. This makes continuous measurements possible, to get more insight in the effects of water administering. The effect of each dripping session and night session can be measured this way and, in combination with additional data from the climate computer, lead to new insights. 

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