Calibrating the Dissolved Oxygen Sensor Probe

Is your Nutrient Controller Dashboard showing DO Data at 0.0%? These steps will help solve the issue.

There are three types of Dissolved Oxygen probes available on the market; Galvanic, Polarographic and Optical. Growlink uses a Galvanic style probe with your Nutrient Controller so that's what will be discussed in this article. Galvanic probes have no warm up time and are naturally polarized so they report correct data immediately as opposed to other styles that need anywhere from 15 minutes to 6 hours before they start to work properly. However, the downside of this style is that the membrane needs to be replaced every 2 months to maintain accurate measurement. 

Here is a brief description of how Galvanic probes operate. When submerged in water, oxygen molecules pass through the permeable membrane at the tip of the probe. These O2 molecules undergo a chemical reduction reaction with the Lead or Zinc Anode (spiral metal wire shown in photo below) with help of the DO solution (electrolyte) contained in the cartridge tip of the prob. Lead and Zinc readily give off electrons while the Silver cathode (metal wire at very tip of probe) remains inert but receives electrons. The more O2 present in the water, the more rapidly the reaction occurs and the more electrons given off.

Since the amount of electrons is proportional to the concentration of oxygen in the water, your controller reads this minimal electrical charge and interprets it into a percentage which is then displayed on the dashboard. 

 

galvanic_dissolved_oxygen_sensor

So why is my probe reading 0.0%? 

If the electrolyte solution in the cartridge is empty, or low enough that the anode and cathode are not both submerged, the reaction cannot happen and no voltage is generated. This will result in a 0% reading. 

To fix this follow these simple steps.

1. Remove the DO probe from your system. Be sure to depressurize or drain the system before loosening the fitting holding the probe. 

2. Unscrew the cartridge at the tip of the probe as shown below.

IMG_1130

3. Use the bottle of DO Solution provided with the probe to refill the cartridge. This will only take 1 mL or less. If you fill the cartridge too much it will overflow when you reinsert the probe tip. If this happens and the solution gets on your skin don't worry it's nontoxic. Be sure to wash your hands afterwards. 

4. Reinsert the tip of the probe in to the cartridge and screw back on tightly.

5. Reinstall the probe in to your system and pressurize or refill the system once again. 

You should now see DO data start to post on your dashboard. Keep in mind that like any other probe you must have good flow across the sensor surface to achieve accurate readings. Galvanic probes consume oxygen from the surrounding water. If fresh water is not constantly flowing over the membrane the probe will use up the O2 molecules in the water close to it and readings will drop to 0% because the reaction can no longer occur. 

If you're still seeing low or 0% readings make sure your probe is placed in a part of the system where there is constant flow.