|SGX electrochemical sensors detect gases by producing a chemical reaction between the gas and oxygen contained in the sensor. This reaction produces a small current, which is proportional to the concentration of the gas present. The sensor is, in effect, a type of fuel cell, hence all electrochemical oxygen sensors are of the self-powered, diffusion limited, metal-air battery type, comprising an anode, a semi-solid electrolyte paste and an air cathode. The cell comprises an enclosure containing two electrodes, a flat PTFE tape with an active catalyst, the cathode and a block of lead (anode). The enclosure is sealed apart from a small capillary that controls the rate at which oxygen can enter the cell.
As the electrochemical reaction results in the oxidation of the lead anode, the electrical/chemical properties of the cell change, requiring periodic calibration. The oxidation of the lead anode also means the oxygen analyzer sensors have a limited life. Once all the available lead has been oxidized the cell will no longer produce an output and must be replaced. But what happens if the lead is removed and another material is used?
SGX Sensortech, a division of Amphenol UK, has such a part, the RoHs certified, EC410. This device does not use lead in the manufacturing process and has the added benefits:
- Increased life compared with other oxygen sensors. This is because the EC410 does not contain reagents that can be consumed (such as lead). The sensor lifetime will be more consistent since the lead-based sensors can suffer from inconsistent packing and wetting of the lead anode.
- The volume of liquids within the EC410 sensor is much smaller than that of other oxygen sensors and almost totally contained within the water-absorbing layer. This means that the chances of the EC410 sensor leaking are significantly less than other oxygen sensors.
- The internal pressure inside the EC410 sensor does not change with time. The pressure in lead-based oxygen sensors rises with time, increasing the chances of leakage both internally (causing premature sensor death) or externally (causing loss of sensor life and damage to associated circuitry).
- The EC410 Sensor is much lighter than lead-based oxygen sensors. The effect of dropping the sensor is reduced since there is no lead mass to move around which can cause output spikes.
- The EC410 sensor does not contain any toxic metals and is therefore RoHS compliant.
- The sensor response to pressure is as good if not better than other oxygen sensors.
- The size of the EC410 sensor is consistent with other oxygen sensors.
Absorption of acidic gases from the sample is reduced due to the low pH of the electrolyte within the sensor.
In additional to the EC410, SGX also offer the SGX-4OX (and the SGX-7OX) which do contain lead for customers not concerned with RoHs requirements. Finally, test the EC410 sensor out, SGX offers the ECVQ-EK3 evaluation boards.