Fluorescent Oxygen Sensor Gains A Completive Edge

Electrochemical sensors are extremely sensitive to changes in the gas pressure, even when the O2 concentration remains constant. LuminOx from SST Sensing (UK) is available in two versions: LOX-01 (without built-in pressure compensation) and LOX-02 (which contains a barometric pressure sensor).

LOX-01 measures oxygen partial pressure between 0 and 300mbar. If the total gas pressure changes, then the ppO2 changes and LuminOx reports this.

LOX-02 reports both oxygen pressure (ppO2 in mbar) and O2 concentration (vol. % O2), the latter being calculated from the total gas pressure and the ppO2. This means that LuminOx will continue to read the correct oxygen concentration, even during rapid pressure changes. As for the temperature measurement, LuminOx is able to transmit the total gas pressure to the host via the two-wire communications interface.

The three sensors were supplied with 21% O2 and the gas temperature was held at 20 degrees C. A pump was used to introduce a brief pulse of positive pressure of around 250mbar. The blue line in the graph below is the pressure measured inside the test enclosure. The pressure is read on the axis to the right of the graph. The O2% reported by the three sensors is measured on the left axis.

A similar test was performed with smaller (20mbar) positive and negative pulses.

LuminOx is affected slightly but only briefly during the pressure event. The electrochemical sensors are affected significantly (the O2% error is as large as 34%) and the disturbance in the output lasts for a long time.