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Sensor customizations

Below you will find a list of explanations of the different options for oxygen sensor customizations. Please note that most of these options will be a trade-off with other sensor characteristics (see below). Also, most options will add extra cost to the price.

Fast response
The normal response time of the smallest microsensors is around 1-3 seconds. But for some experiments, e.g. photosynthesis measurements, it may be an advantage to have an even faster response time. Unisense makes sensors with response times down to 0.2-0.3 seconds.

Low stirring sensitivity
The standard stirring sensitivity of our sensors is 2%, but in some delicate systems, you may require the sensor to be even less sensitive than that. Unisense produces sensors with stirring sensitivities down to 0.5%.

High signal
The maximum signal is different for each sensor and will depend on several parameters. If you require a high sensitivity (high resolution) of the signal, sensors can be customized with a high maximum signal.

Shaft length
For some set-ups, an extended shaft length of the sensor is an advantage. This may be to allow room for more sensors or more auxiliary equipment.

Tip length
Some systems are tiny so that even the standard tip length, i.e. the length of the thin part of the microsensor, is too short. This problem can be solved using customized sensors with a more slender design.

Tip diameter < 10µm
Our smallest standard sensor is 10µm but Unisense can make oxygen sensors down to 2-3µm for specific measurements.

High temperature tolerance
Adding organic electrolyte in some sensors will increase the temperature tolerance up to around 100oC.

O2sensor-tip-ox500

Theory on response time, stirring sensitivity, and signal-to-noise ratio of oxygen sensors

There is a relationship between response time, stirring sensitivity and signal to noise ratio of an oxygen sensor.

Modelling shows that for an ideal sensor the stirring sensitivity can be approximated by R/4L, where R = radius of the hole in the sensor tip and L = distance from the tip to the cathode.
The response time is proportional to L squared (L2). Thus a fast responding sensor has a very small L.
In order to reduce the relative noise (= low noise to signal ratio, high signal to noise ratio) a large signal is an advantage. A large signal also offers better resolution of the measurement. The signal is proportional (rough calculation) to R2/L (R squared divided with L). Thus sensors with a large R and a small L give the highest signal to noise ratio.

Examples:
1) A sensor with a fast response and a low stirring sensitivity must have a small signal.
2) A sensor with a fast response and a large signal will must have a higher stirring sensitivity.

For general use we can make sensors with a stirring sensitivity of <2% and a response time of <3 s, which is a good compromise for most users.

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