The Optical Oxygen Sensor

Optical dissolved oxygen sensors rely upon a removable cap as part of their measurement principle. Over time this cap will degrade with continued exposure to sterilization cycles, strong chemicals, abrasion, and other process related factors. Cap quality can be tracked with the quality indicator in ArcAir Software. When the quality indicator reaches 60% ArcAir will provide a warning message "DO Replace Sensor Cap". Eventually when the quality indicator reaches 35% then the sensor will cease to function. At this point a cap change is necessary for on-going measurement.


Types of Caps for the Oxygen Sensor

Hamilton offers multiple types of caps for optical dissolved oxygen sensors. The H0 and H2 caps listed below work for the majority of our products including the VisiFerm, VisiPro and VisiWater. The H3 and H4 caps are specific for the VisiFerm mA product line. The VisiTrace sensor offers a specific cap called the L0. The replacement procedure for the L0 is a similar process.

H0 Cap (Ref 243515), H3 Cap (Ref 10068400) – Our most common general purpose replacement caps provides the fastest response time and is compatible with most fermentation and cell culture media. Both products are steam sterilizable, autoclavable and CIP compatible. The H0 cap directly replaces our older P0 cap (Ref 242427) and is suitable for use on all VisiFerm, VisiPro, and VisiWater sensors. The H3 cap works with our VisiFerm mA sensors.

H2 Cap (Ref 243505), H4 Cap (Ref 10078261) – H2 and H4 caps are specifically designed for increased chemical resistance. They are recommended for processes containing lipophilic compounds, oil-like substances, and aggressive chemicals that may attack silicone coatings. Both caps are steam sterilizable, autoclavable and CIP compatible. The H2 cap replaces our older H1 and P1 cap (Ref 243500 and 243510) in non-abrasive applications. It is suitable for use on VisiFerm, VisiPro, and VisiWater sensors. The H4 cap is a new product for use with our VisiFerm mA products.

Replacing the Sensor Cap

Removing the cap is easy – it can be unscrewed from the end of the oxygen probe. This will reveal the threading and o-ring underneath. Whenever you change the cap a visual inspection of the o-ring should be performed. If the o-ring does not look to be in good shape or exhibits wear or degradation it should be changed. Finger tighten the replacement cap and perform zero and air calibration.

If you replace the sensor cap with the same type as you removed, you will need to do a simple calibration using the ArcAir software or mobile app. No change in settings is required. If you change from one sensor cap type to another (e.g. from H0 to H2) you will need to change the sensor cap type in the settings of the probe. This is done through the ArcAir software or mobile app.

Working with ArcAir Software

ArcAir Software is the primary confirmation and calibration tool for Hamilton sensors. ArcAir for PC is available as a free download from the Hamilton website. Mobile and App versions are also available. ArcAir offers both wired and wireless communication with the sensors. For more information about connection options see this Knowledgebase article.

Procedure to identify a different cap

Open ArcAir. Identify the optical DO sensor with the new cap and click on it.

If the cap has been changed from H0 to H2 or vice versa then go to SETTINGS>MEASUREMENT SETTING to identify the new cap. Type in the new cap part number at the variable <ODO CAP REF>.

ArcAir mobile app example


ArcAir PC Example


Procedure to perform a calibration

Open ArcAir. Identify the optical DO sensor with the new cap and click on it.

Select the tab labeled <CALIBRATION>. Select <IN AIR> and follow the procedure to perform an Air calibration.

Once air calibration is complete select <ZERO POINT> and repeat the procedure in pure nitrogen (99.999% N2). It is highly recommended that the sensor is mounted into a flowcell or the Calibration Station (Ref 243575) to avoid excess oxygen contaminating the zero calibration. Flow rate for nitrogen should be kept at 0.5 l/min for several minutes prior to calibration. The outlet flow of nitrogen should vent to atmosphere to avoid any back pressure.

ArcAir Mobile App Example


ArcAir PC Example

Once the Air and zero calibration are complete exit from the sensor and use as needed in your application.