Additional Information and Specification for Gill 8 and Gill 12

The standard Gill 8 or Gill 12 (described here as Gill 12) is supplied with the following items:

Unless fitted with extensive options the Gill 12 is housed in a robust fully screened metallic case with an internally screened mains supply. The instruments have one double-sided circuit board for improved reliability with a minimum of wire links. Both the mains input mains earth and the RS232 / COM link are all electrically isolated to prevent troublesome earth loops. Every Gill 12 has an internal Potentiostat; Zero Resistance Ammeter; Frequency Response Analyser and a Galvanostat

The programs shown below are just those that are supplied with the Gill 12 as standard. Optional software packages available for this instrument to increase performance are included under options. ACM’s version 4 software will operate in all Microsoft Windows operating systems excluding Windows 3.1. 

Sequencer 

The Sequencer is the host program for all the other Version 4 software techniques. It enables series of tests to be performed in a logical sequence. It has a few features of its own including:

Core Running

The Core running program actually controls the instrument using the test Sequence pre-set via the Sequencer. Individual channels can be switched on or off in the Core Running. Real time data for each channel can be observed using typical Windows features such as Full Screen Cascade and Tile. 

Long Term

Tests that obtain and present data from an electrochemical cell or probe with respect to time including: 
Linear Polarisation Resistance; Potentiostatic; Galvanic and Potential monitoring.

Measurements.
Data is presented in real time for instant visual analysis. Typically this technique is used to monitor the corrosion rate in relation to time by using a series of Linear Polarisation Resistance tests. For multiple channel instruments individual windows simultaneously present the data from each respective channel. These techniques represent the basic tools of long term corrosion testing. 

Linear polarisation tests can be controlled in a variety of ways. The two main types are Step and Sweep. Step polarisations can be either of the square wave variety or a modified square wave where the cell is left isolated between Anodic and Cathodic polarisations. Sweep options include sweep from rest potential to start potential and initial delays at start potential. 

Cyclic Sweeps

This type of test is presented on V/ I or V/ Log I graphs typically referred to as Evans Diagrams. Other terms frequently used are Cyclic Voltammetery Potentiodynamic Sweeps and Polarography. A custom sweep facility enables complex Voltage/ Time graphs to be constructed that are later used to polarise the cell. A range of typical tools are available to analyse the data including positioning and measurement of Tafel Slopes and Linear Polarisation Resistance measurements. The corrosion rate may be measured using either the Stearn and Geary or the Current Intercept method. The technique is often used as a traditional way to detect resistance to pitting. To facilitate this a current limit may be used.

C&V Noise

Electrochemical Current and Voltage Noise and Potentiostatic measurements at a rate of 50 or 60 measurements per second whilst rejecting mains interference. Typical measurement accuracy is from a few pA upwards. 

AC Impedance

AC Impedance uses a scan of test frequencies normally from a high to a low frequency to analyse Resistive and Capacitive characteristics of a corrosion cell. Data is presented in either Nyquist Bode Phase or Bode Impedance formats. Curve fitting software is inclusive to calculate the Solution Resistance Double Layer Capacitance and the Polarisation Resistance. The technique is frequently used in systems with a significant solution resistance or as a method to analyse the performance of a coating. For very high impedance cells greater than 10 MOhms the technique is normally used in conjunction with the optional Paint Buffer. 

Galvanodynamic Sweeps & Galvanostatic

These tests use the current to polarise and control an Electrochemical cell. In many ways it is similar to Cyclic Sweeps and Long Term LPR / Potentiostatic except that current is used to control the cell rather than voltage.

Harmonic Analysis

This technique relies on the non linear nature of electrochemistry. The technique applies an AC signal typically of about 0.1Hz to the cell and a measurement is made of the 1st 2nd and 3rd Harmonic of the current response. Using these results the polarisation resistance and Tafel slopes are mathematically calculated. The technique can be used as part of a Long Term test.

IR Compensation

A technique which is used to compensate a potentiodynamic or potentiostatic test in real time for the depolarising effects of solution resistance. The solution resistance is first measured using an AC signal. The value of this resistance is used together with the polarisation current to adjust the polarisation potential via Ohms Law. To take a simple case where the polarisation resistance and the solution resistance are identical the polarisation potential imposed by the Potentiostat is effectively doubled.

Analysis

Screen shots:

ACM instruments supplies analysis software with its products. This offers the user a number of standard tools which are typically used by electrochemists and corrosion scientists. However for user specific analysis we recommend the user to transfer data to a typical commercial package such as Excel. Version 4 analysis software offers the following features:-

Data Management Tools:-

- Browsing data files as thumb nail graphs.
- Selecting data from multiple files into data banks for comparison.
- Exporting individual or batched data files to text or ASCII format suitable for spread sheets.
- Exporting graphs as bitmaps and metafiles for including in reports.
- Storing data in a HTML format suitable for viewing with a web browser or uploading to a web page.

Common Data Manipulation Tools:-

- Cut and paste ability enables graphs to be inserted into text documents with ease.
- Re-definable axis where an axis type and units can be set.
- Editing of data points and joining any gaps created.
- Zero plot enabling data vs. time graphs with different start times to be referenced to zero on the time axis.
- Inclusion of labels to highlight specific points / areas of the graph.
- Printing the graph to include any labels and rulers displayed.
- Zooming where the graph can be rescaled manually automatically or by using the mouse.
- Cursors which can be moved along the data line giving the X and Y co-ordinates as well as data specific information such as average trend and frequency.
- Smoothing of data by averaging adjacent points can be performed on the data either between cursors the selected data bank or all of the displayed data.
- Saving data enables modified graphical data to be stored for later retrieval.
- Corrosion rate calculation in mm or mils per year.

Data Specific Features:-

- Circle fit for Nyquist graphs.
- Isotropic Scaling of Nyquist graphs.
- Tafel rulers for calculation of bA bC and intercepts on V vs LogI graphs.
- Least squares fit and manual line fitting for the calculation of the Linear Polarisation Resistance of a Voltage vs Current graph.
- Fast Fourier Transform graphs created from Current and Voltage data.
- Point to Point graphs created from Current and Voltage data.
- Graphs area calculated from the base line on Current and Voltage graphs.
- Peak counter on Current and Voltage data.
- Load test at cursor on long term LPR step and sweep graphs. This gives the ability to load the sweep or step data relating to the data point at the cursor.
- Ability to analyse data files containing hundreds of thousands of points.

Manual Instrument Control

The Field machine is supplied with Manual Instrument Control. This is a stand alone single page program which tries to recreate the nostalgia of the Manual Potentiostat Sweep Generator and twin channel chart recorder of yesteryear. Rate of movement of the mouse is directly proportional to the rate of change of cell potential. Such tactile feel of an electrochemical cell is typically missing with modern automated systems. It is recommended as an educational or investigative tool. Data is shown in graphical form in real time and stored in an ASCII format for analysis with a typical commercial package such as Excel.

Specifications