Potentiostatic apparatus and methods

• US 5,198,771 A
• Filed: 09/03/1991
• Issued: 03/30/1993
• Est. Priority Date: 09/03/1991
• Status: Expired due to Fees

• Current Assignee: Transducer Research, Inc. (TSI Incorporated)
• Original Assignee: Transducer Research, Inc. (TSI Incorporated)
• Inventors: Penrose, William R., Fidler, John C., Bobis, James P., Stetter, Joseph R.
• Primary Examiner(s): Wieder, Kenneth A.
• Assistant Examiner(s): Solis, Jose M.
• Application Number:
  US07/753,835
• Time in Patent Office: 574 Days
• Field of Search: 204/406, 204/407, 204/153.10, 324/438, 324/444
• US Class Current: 324/438
• CPC Class Codes: G01N 27/49 Systems involving the determination of the current at a single specific value, or small range of values, of applied voltage for producing selective measurement of one or more particular ionic species
• CPC Class Codes: G05F 1/561 Voltage to current converters amplifiers H03F

Abstract

A potentiostat for an amperometric sensor uses a voltage-controlled current source (VCCS), which may be either unidirectional or, preferably, bidirectional. An error amplifier compares the potential of the sensor'"'"'s reference or counter electrode, relative to ground potential, to a set-point potential. The error voltage serves as an input to the VCCS. The output of the VCCS--a current proportional to the error voltage--is supplied to the sensor'"'"'s auxiliary electrode. In a steady state, the error voltage is just large enough to supply current that is equal to the current through the sensor'"'"'s working and auxiliary (or counter) electrodes. The error voltage can either serve directly as an output voltage or it can be amplified without introducing a feed-back loop disturbance. The VCCS permits direct grounding of the sensor'"'"'s working electrode and operation of the error amplifier at a low or moderate gain, so as to increase the circuit'"'"'s frequency response and reduce the probability of oscillation. Also, in conjunction with an adjustable low-pass filter, the VCCS permits optimization of the system'"'"'s frequency response so as to yield improved stability.

Claims

1. A potentiostat circuit for controlling and maintaining a stable potential difference between the working electrode and the reference or counter electrode of an amperometric sensor and for generating an output signal that is substantially proportional to the current flowing through said working electrode, said circuit comprising a voltage-controlled current source whose input is an error voltage generated by an error amplifier and whose output is a current that is proportional to the error voltage, wherein said error amplifier compares the potential of the reference or counter electrode, measured relative to ground potential, to a set-point potential, and wherein the error voltage gives rise to a current that is equal to the current passing through said working electrode when the current flow in said circuit is in a steady state, and wherein the voltage-controlled current source is a variant of the Howland current pump.

2. The circuit of claim 1, wherein said current pump comprises two operational amplifiers, one of which acts as the main amplifier for the voltage-controlled current source whereas the other amplifier is a high-impedance unity-gain follower.

3. The circuit of claim 2, comprising two resistors that provide a positive feedback which maintains a stable output current for varying load resistances.