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Description of SEC-Sensor by way of example H2-SEC-Sensor

Hydrogen Sensor SECS

1. Description of Technology

The SolidsenSe Hydrogen Sensor is based on the electrochemical gas detection principles. This technology can used to detect chemicals or gases that can be oxidized or reduced in chemical reactions.

Hydrogen:

The following reaction takes place when Hydrogen diffuses into the sensor.

  • H2 diffuses into the working electrode which holds free places for Hydrogen Molecules.
  • At the point where Hydrogen and Electrolyte mix, H2 will break up into 2H+ and 2 electrons.

The amount of electrons (Current) is directly proportional to the concentration of Hydrogen. Protons (H+) move through the electrolyte to the Counter Electrode where H+ and Oxygen form Water.

The Reference Electrode is isolated and maintains the base potential to stabilize the Sensor output, even when the sensor is exposed to high concentrations of Hydrogen. 3 Electrode Sensors have a wider detection range with good direct linearity.

Oxygen is not needed for the chemical reaction. But this does not mean that the sensor can work in environments without oxygen. The atmosphere without oxygen will cause the free Oxygen inside the Electrolyte to disappear slowly. This process absorbs only the Hydrogen. Since the H2 is the fuel for the reaction the life expectancy of the sensor is beyond five years.

2. Design

Dimensions:

8mm wide x 10mm high x 1mm thick Contact separation: 2.5mm between pads Contact size: 2mm x 1mm. The material is gold and can be soldered or bonded

Operation:

Gas enters through a diffusion and protection filter from the back side. This filter protects the sensor from dust and water allowing the gas to flow through. It is nearly impossible to keep gas from entering into the sensor unless the filter is completely blocked.

Composition:

The electrode on the left is the Reference Electrode (R) The electrode in the middle is the Measurement Electrode (M) The electrode on the right is the Counter Electrode (C).

The final layers are the electrolyte and the protection skin.

A single sensor is part of a wafer which contains 48 Sensors. This type of wafer is readily available and can be purchased immediately. Every wafer is gas tested prior to shipment.

The sensors are separated through pre-manufactured break lines as shown on the illustration below. The separation process is very easy if you follow the Order: It is important to break the sensors away from the wafer using the following Order.

1. Break the wafer at the RED lines first. It is not important which one is used first.
2. Break the wafer at the GREEN lines next.

The Difference to the Standard Electrochemical Sensors:

Acid Electrolyte, e.g. H2SO4 is replaced by a solid Electrolyte

I. What happens with the old system?

  1. Standard sensors require a sealed housing to protect surrounding from the aggressive acidic electrolyte.
  2. As acid takes in and releases water a risk for leakage exists in humid atmosphere or a dry out effect in dry atmosphere. Therefore, the biggest part of such a sensor is a reservoir for the acid electrolyte.
  3. Because of the need for a large electrolyte reservoir acid based sensors are big.
  4. There is potential damage to electronic circuits in case of leaks from the sensor.
  5. Production of acid based sensors is complicated
  6. Acid is dangerous

II. What is the difference with solid Electrolyte?

  1. The solid electrolyte is not dangerous and much easier to handle.
  2. No housing is needed.
  3. No reservoir is needed.
  4. The reading is very fast and promptly reacts to gas leaks in the environment. Adjustment to humidity or temperature variations is immediate.

Plastic Housings not required. The sensor is built on a ceramic wafer.

I. What does it mean for the old system?

  1. Plastic housings need to be sealed. Acid and change of temperature damages plastic with time.
  2. Sensor construction with contacts and pins connected via wires to the Electrodes through the housing is complex. The process is risky and can reduce sensor life and quality.

II. What are the open ceramic sensor advantages?

  1. Sensors can be produced in parallel in one production step.
  2. Ceramic Electrodes and Electrolyte can be built up in layers.
  3. Production is fully automated, increases quality and stability.

Connection differences:

I. What happens with the old system?

  1. Electrodes are produced separately
  2. The connection is made with platinum wire
  3. The platinum wire needs to be connected to contact pins.
  4. Contact pins must be protected from the acid electrolyte.

II. The new system

  1. The wire and the electrode are printed on layers.
  2. The last layer is gold and can be soldered to directly.

3. Temperature Dependence

Temperature dependence differs from the common Electrochemical Sensor. Normally temperature changes also cause changes in the relative humidity in ambient air. Solid electrolyte sensors adjust immediately to humidity changes. The sensor adapts to the new temperature in minutes as it is so small.

All materials used for the H2 Sensors are suitable for use in temperatures up to 80C and down to -20C. However 80C and very dry air reduce the humidity inside the Electrolyte and may result in less sensitivity. The curve below shows this reactions at 60C.

Humidity dependence

The standard humidity range for the solid electrolyte sensor is between 15%rh and 90%rh non-condensing. Water drops cannot block the diffusion opening but may cause a momentary change with the behaviour of the sensor. The chart below shows no change to the sensor output when the humidity changes from 15%rh to 90%rh in Minute 30. The spike results from a high gas concentration during mass-flow adjustments from dry air to wet air.

The Gas concentration was 1300ppm H2. As you can see there is a drop of signal during the first 10min which is a kind of stabilization to the dry air. The switch to 90%rh shows no change. This test was done at room temperature of 23C.

The red line at 1A was an old style sensor used as a reference device. These types of Sensors will normally not show a big change due to different humidity due to the reservoir of acid internally. They will dry out very slowly but consistently. If they dry out completely the sensors will no longer react to gas.

Our Solid Electrolyte sensor may change behaviour but will quickly adapt to the changed environment. The sensor will not show further dry out problems.

4. Life Time of the Hydrogen Sensor

The Sensor is made of materials that do not have limited life times.

  • No poisoning from silicon materials.
  • No consumable material.

Because of the long lasting materials used for the construction of the sensor aging is not a factor. However, the oldest sensor in use today was manufactured in January 2008. During the past year the manufacturing process and materials used have been optimized.

The sensor life warranty is 2 years. As soon as our life time test reaches the second year we plan to expand warranty accordingly.

5. Sensitivity and Response Time from the latest Sensor Generation

The latest revision has a much bigger dynamic range and performs faster than the prior generation. The chart below was made using sensors from the production standard run from Dec. 08. This revision level can be identified the gold contacts and the hole on the counter electrode.

Sensitivity and Response Time

Remark: The red sensor with no. 999 at 3A is the reference Sensor. The first 6 sensors where sealed and protected sensors

Download Pricelist 2009.pdf

 

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