pH sensor with internal solution ground

• US 20030132755A1
• Filed: 12/13/2002
• Published: 07/17/2003
• Est. Priority Date: 12/14/2001
• Status: Active Grant

• Current Assignee: Rosemount Analytical, Inc. (Emerson Electric Company)
• Original Assignee: Rosemount Analytical, Inc. (Emerson Electric Company)
• Inventors: Feng, Chang-Dong, Baril, Richard N., Koluvek, Roland H., Covey, Joe N., Covey, Beth Meinhard
• Granted Patent: US 6,894,502 B2
• Time in Patent Office: Days
• US Class Current: 324/438
• CPC Class Codes: G01N 27/401 Salt-bridge leaks; Liquid junctions
• CPC Class Codes: G01N 27/4035 Combination of a single ion-sensing electrode and a single reference electrode G01N27/406 and G01N27/413 take precedence

Abstract

The invention relates to an internal solution ground for primary use with a pH sensor, and preferably with a multi-sensing instrument monitoring a pH sensor and one or more additional secondary sensors having non-isolated circuits. In one aspect, a pH sensor assembly includes a pH electrode, a reference electrode, and an internal solution ground wire. The internal solution ground wire shares a liquid junction with the reference electrode but is protected by the reference fill solution. In one embodiment, the internal solution ground can be electrically isolated through a capacitor or, alternately, a capacitor and resistor in parallel.

Claims

1. A pH sensor assembly comprising:

a pH electrode;

a reference electrode assembly comprising a container containing an electrolyte solution in contact with a liquid junction extending to an outside surface of the container and a reference electrode disposed in the container and in contact with the electrolyte solution; and

an internal solution ground comprising a conductor disposed within the container, in contact with the electrolyte solution, and electrically connected to the circuit common.

2. The pH sensor assembly of claim 1 further comprising circuitry having a first terminal electrically connected to the reference electrode and a second terminal electrically connected to the pH electrode.

3. The pH sensor assembly of claim 2 further comprising a capacitor electrically connected to the conductor and electrically connected to a common of the circuitry.

4. The pH sensor of claim 3 further comprising a resister electrically connected in parallel across the capacitor.

5. A multi-sensing instrument having a circuit common, the multi-sensing instrument comprising:

a pH sensor assembly comprising;

a pH electrode;

a reference electrode assembly comprising a container containing an electrolytic reference solution in contact with a liquid junction extending to an outside surface of the container, the container adapted to be placed in a liquid to be sensed, and a first reference electrode disposed in the container and in contact with the reference solution; and

a pH sensing circuit having a first terminal connected to the reference electrode and a second terminal electrically connected to pH electrode;

a second sensor assembly comprising;

a second reference electrode adapted to be operably coupled to the liquid to be sensed;

a second sensing circuit having a terminal electrically connected to the second reference electrode, the first and second sensing circuitry electrically connected to the circuit common; and

a capacitor electrically connected between the circuit common and one of the first and second reference electrodes.

6. The multi-sensing instrument of claim 5 wherein the second sensing circuit is a pH sensing circuit.

7. The multi-sensing instrument of claim 5 wherein the second sensing circuit is a conductivity circuit.

8. The multi-sensing instrument of claim 5 wherein the second sensing circuit is an amperometric sensing circuit.

9. The multi-sensing instrument of claim 5 further comprising a resistor electrically connected in parallel across the capacitor.

10. The multi-sensing instrument of claim 5 further comprising:

at least one additional secondary sensor assembly comprising a third reference electrode adapted to be operably coupled to the liquid to be sensed and a third sensing circuit having a terminal electrically connected to the third reference electrode, the third sensing circuitry electrically connected to the circuit common; and

a second capacitor electrically connected between the circuit common and the third reference electrode.