Pstat.SetIruptMode()

Type: INSTANCE FUNCTION

Purpose: SetIruptMode() controls current-interrupt IR-compensation.

Using this function you can control:

  1. Current-interrupt timing
  2. Voltage-error calculation mode
  3. Feedback mode

The current-interrupt feature of the potentiostat uses a three-sample algorithm to estimate the IR-free voltage. It first samples V at the given current level, then it interrupts the current path and waits a time period, τ. At that point it samples V again. It waits τ seconds again, and samples V for the third time. It then turns on the current.

The sample time, τ, is increased as the current decreases. The Time parameter used in the call to SetIruptMode is used directly as τ on the least-sensitive current ranges. On the more-sensitive current ranges, τ is longer, but remains proportional to the Time parameter. τ is constrained to be between 10 µs and 32 768 µs. Values outside this range are clipped to the nearest point within the range.

There are two different ways of calculating the IR-voltage error. In calculation Mode 1, the three voltages, Vi, Voc1, and Voc2 are used to calculate an IR-error voltage VIR via an extrapolation. In Mode 2, an average is used.

VIR = Vi – 2 × Voc1 + Voc2 (Calculation Mode 1)

VIR = Vi – 1/2 (Voc1 + Voc2) (Calculation Mode 2)

A third "calculation mode", Mode 0, is used to turn off the interrupt. In Mode 0, all of the other function parameters are ignored.

After the IR error is calculated, it can be used in several different ways, most of which involve feedback of the error signal.

In Galvanostat mode, there is never any IR-compensation feedback. The feedback mode setting is therefore ignored in the Galvanostat mode. The measured error is used to correct potential measurements stored in the data curve.

In Potentiostat mode, there are three different feedback modes.

  1. No feedback.
  2. Normal feedback. The measured error voltage is added to the voltage applied for the next point.
  3. Control loop with fixed gain.

Usage: Pstat.SetIruptMode(FbMode, CalcMode, Timer, Eoc, Gain)

 

       
  FbMode INDEX

Feedback mode. Can use a predefined constant:

IruptOff = 0 (no feedback)

IruptNorm = 1 (normal feedback)

IruptClfg = 2 (control-loop fixed gain)

  CalcMode INDEX

IR-error calculation mode. Use predefined constants:

EuNone = 0 (no interrupt measurement)

EuExtrap = 1 (extrapolation)

EuAverage = 2 (average)

  Timer REAL

Nominal τ value (units are seconds). This is the shorted time. Can be longer at low currents. Predefined constant:

IruptTime = 50 × 10–6

  Eoc REAL Open-circuit E. Used only in control-loop modes.
  Gain REAL Cell gain. Used only in fixed-gain control loop.

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