Electrochemical gas sensor system with improved accuracy and speed
An electrochemical cell for sensing gas has added mechanical support for the working electrode to prevent flexure of the working electrode due to pressure differentials. The added mechanical support includes: 1) affixing a larger area of the working electrode to the body of the cell; 2) a gas vent to a cavity of the body to equalize pressures; 3) a rigid electrolyte layer abutting a back surface of the working electrode; 4) infusing an adhesive deep into sides of the porous working electrode to enhance rigidity; 5) supporting opposing surfaces of the working electrode with the rigid package body; and 6) other techniques to make the working electrode more rigid. A bias circuit is also described that uses a controllable current source, an integrator of the varying current, and a feedback circuit for supplying a voltage to the counter electrode and a bias voltage to the reference electrode.
1. An electrochemical gas sensor comprising:
a body containing a cavity;
an electrolyte contained within the cavity;
a plurality of electrodes on the inside of the cavity, the electrodes being in contact with the electrolyte, the electrodes including a porous first electrode, such that a gas and the electrolyte enter the first electrode;
a gas opening in the body for allowing the gas to enter the first electrode to cause a chemical reaction to occur,
the first electrode being supported within the cavity;
a first conductor electrically connected between the first electrode and a first metal pad on an outside surface of the body; and
an electrically conductive adhesive that directly contacts the porous first electrode, affixes the first electrode to the body, forms an electrical connector between the first electrode and the first conductor, and also forms a gas seal around at least a portion of the first electrode, wherein the adhesive defines a gas cavity around the gas opening such that a surface of the porous first electrode extends along an entire surface of the gas cavity opposing the gas opening.
2. The sensor of claim 1 wherein the conductive adhesive substantially covers an entire first surface of the first electrode except for a gas inlet area for rigidly affixing the first electrode to the body.
3. The sensor of claim 1 further comprising a gas passageway that allows the gas that enters the first electrode via a front surface of the first electrode to also enter the cavity and provide a gas pressure to an opposing back surface of the first electrode to substantially equalize gas pressures applied to the front surface and the back surface.
4. The sensor of claim 3 wherein the conductive adhesive is patterned to provide the gas passageway into the cavity.
5. The sensor of claim 3 wherein the first electrode is configured to allow the gas to diffuse out of a side of the first electrode and into the cavity.
6. The sensor of claim 1 wherein the gas enters a front surface of the first electrode, the sensor further comprising a substantially rigid electrolyte layer contacting a back surface of the first electrode for mechanically supporting the first electrode.
7. The sensor of claim 1 wherein side surfaces of the first electrode are sealed to prevent the gas from exiting the side surfaces of the first electrode.
8. The sensor of claim 1 further comprising a porous second electrode within the cavity, side surfaces of the second electrode being sealed to prevent the gas from entering the side surfaces of the second electrode.
9. The sensor of claim 8 wherein the first electrode is a working electrode and the second electrode is a counter electrode.
10. The sensor of claim 1 wherein a first adhesive is infused through sides of the first electrode to add mechanical stability to the first electrode.
11. The sensor of claim 1 wherein the first electrode is positioned with respect to the gas opening to receive the gas into a front surface of the first electrode, and the electrolyte forms an electrolyte layer in contact with a back surface of the first electrode, the electrolyte layer having a back surface, the sensor further comprising:
a mechanical support portion, the electrolyte layer being between the first electrode and the mechanical support portion, the mechanical support portion contacting the back surface of the electrolyte layer to, in turn, mechanically support the first electrode.
12. The sensor of claim 1 wherein the first conductor is embedded within the body.
13. The sensor of claim 12 further comprising a metal shield layer between at least a portion of the first conductor and an outer surface of the body, the metal shield layer being embedded within the body.
14. The sensor of claim 1 wherein side surfaces of the first electrode are sealed by a polymer.
15. The sensor of claim 1 further comprising:
a metal shield layer encased within the walls of the body, the metal shield layer being located between the conductors and at least one outer wall of the body.