Vaisala PEROXCAP® Technology

Children´s hospital in Helsinki, Finland - Vaisala

Our innovative technology for sensing vaporized hydrogen peroxide is called PEROXCAP®, designed for bio-decontamination applications. 

This unique technology enables accurate and repeatable measurement of the bio-decontamination cycle with a single unit. Vaisala’s PEROXCAP® probe for vaporized hydrogen peroxide, relative saturation, relative humidity, and more…

The PEROXCAP® sensor technology works using measurements from two capacitive thin-film polymer HUMICAP® sensors. Vaisala HUMICAP sensors guarantee quality and reliability, with their reputation for high accuracy, excellent long-term stability, and negligible hysteresis even in the most demanding high-concentration H2O2 applications in atmospheric pressure.

The HUMICAP sensor is a thin-film polymer sensor consisting of a substrate on which a thin polymer film is deposited between two electrodes. The polymer film absorbs or releases vapor according to humidity changes in the environment. As the humidity changes, the dielectric properties of the polymer film change, and so does the capacitance of the sensor. The instrument’s electronics measure the capacitance of the sensor and convert it into a humidity reading.

The upper electrode is made of corrosion resistant conductive material and functions as one of the two electrodes in the capacitor. It protects the active material of the sensor from dust, dirt and conductive particles. The thin film polymer is sandwiched between the two electrodes. This conductive layer still lets through water and H2O2 vapor.

The advanced upper electrode is one of the secrets behind a cutting-edge humidity sensor. The thin-film polymer absorbs water and H2O2 vapor. The amount is proportional to the ambient relative humidity (sensor with catalytic layer) or relative saturation (sensor without catalytic layer) depending on the sensor in question (A or B). It amplifies the amount of water and H2O2 in the air. We synthesize our own polymers in order to optimize its performance. The lower electrode is made of corrosion resistant conductive material and functions as one of the two electrodes in the capacitor.
Intelligent PEROXCAP® measurement technology

PEROXCAP® measurement uses two HUMICAP sensors: one HUMICAP sensor with a catalytic layer and the other one without the catalytic layer. The catalytic layer catalyzes hydrogen peroxide from the vapor mixture. Therefore, the HUMICAP sensor with the catalytic layer only senses water vapor, providing a measurement of partial water pressure, i.e. relative humidity (RH). The other HUMICAP sensor without the catalytic layer senses the air mixture with both hydrogen peroxide vapor and water vapor. The difference between the readings from these two sensors indicates the vapor concentration of H2O2.

Operating principle of PEROXCAP


Repeatable measurement even in high humidity environments

The PEROXCAP® sensor has several unique features to ensure reliable measurements. First, the probe heats up at intervals to maintain measurement performance and lengthen the sensors’ lifespan. The automatic chemical purge function helps maintain measurement accuracy between calibration intervals in challenging vaporized hydrogen peroxide processes. The purging process involves rapid heating of the sensor to remove possible impurities.  

Finally, the HPP270 series probes, based on PEROXCAP® sensors, have a built-in ability to evaluate sensor performance through its “Sensor Vitality” value. This value is like a health check for the sensor. Accessed with Vaisala Insight software, sensor vitality is displayed as a percentage, and we recommend replacing HPP270 series probes when the value reaches ≤ 40%. 

Multiple measurements for comprehensive bio-decontamination monitoring

Combining the PEROXCAP® sensor with an additional temperature sensor allows up to three measurement parameters: hydrogen peroxide vapor concentration, temperature, and humidity, referring to both relative humidity and relative saturation. The HPP271 probe measures only H2O2 vapor concentration and temperature dew point.

Learn more about Relative Saturation in this on-demand webinar. 

The advanced HPP272 probe measures all relevant parameters during bio-decontamination processes, including: hydrogen peroxide vapor, temperature, and humidity as relative saturation and relative humidity, dew point, and vapor pressure.

In vH2O2, it’s crucial to understand that water and hydrogen peroxide have a very similar molecular structure, and they both affect the humidity of the air in which they are present.

  • Relative saturation is a parameter that indicates the humidity of the air caused by both H2O2 vapor and water vapor. When relative saturation reaches 100 %RS, the vapor mixture starts to condense.
  • Relative humidity is a parameter that indicates the humidity of the air caused only by water vapor.
Relative Saturation and Relative Humidity

Traceable H2O2 factory calibration

Every PEROXCAP® sensor is manufactured in Vaisala's own cleanroom and individually calibrated at the Vaisala factory. Both H2O2 and RH calibrations are traceable to international SI units which ensures that the measured values represent the real environment.

H202 graph

As an example, at 20 °C and 500 ppm hydrogen peroxide, the humidity level 25%RH is equivalent to 60%RS. When this gas mixture starts to condense (relative saturation being 100%), relative humidity is 45%.