Additional Information and Specification for Gill AC

The standard Gill AC is supplied with the following items:

Unless fitted with extensive options the Gill AC 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 AC 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 AC 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.
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.

 

Options for Gill AC

The Gill AC can be fitted with an extensive range of options that can significantly alter both the appearance and the performance of the instrument. These are listed below followed by a more detailed description for each option.

Gill AC with standard options
Extra channels and power
	Additional Gill AC's
	4 Way COM Card
	8 Way COM Card
	Sequential Channel's
	2A Power output
	5A Power output
	Up to 100A or more available on request
Quick fit software options
	Galvanodynamic Sweeps
	Harmonic Analysis
	IR Compensation
	Linear Polarisation Resistance Noise
	Gill AC Solo
	Gill AC Duo
	Gill AC Trio
	Bubble Test Software
		BTS option
	Customised Software Automated Emailing and Internet Storage of Data
	Instrument Control DLL
Hardware modifications
	Voltage Input
	Thermocouple Input
	Paint Buffer
	DC Weld Test Option
	AC Weld Test Option (with DC WTO)
	AC Weld Test Option (without DC WTO)
	Offsetting Ability for Weld option
	Electrical Resistance
	Critical Pitting Temperature test
	Optional Heater / Stirrer for CPT test
	Limited Distance Modem Base Station
	Limited Distance Modem
	Five Year Warranty

Additional Gill AC

Up to 32 Gill ACs can be operated from the same PC with independent and simultaneous operation. Software does not need to be purchased again for each extra instrument. One option from running several instruments at the same time is the ability to synchronise the start of tests on all channels thus overcoming the usually unavoidable test time error associated with Sequential or Multiplexed instruments.

4 and 8 way COM cards

Each additional instrument requires a communication port in order to operate it. For example a 24 instrument system will require three 8 way COM cards. We can supply four or eight way communication ports. Both cards require a half size PCI slot. To capitalise on our experience it is often more convenient to ask ACM to supply a fully working PC to do the job.

Sequential Channel

Each Gill AC can be fitted with up to 128 sequential channels. Each channel can be treated as if it is independent from the other sequential channels. The Core Running program provided with the instrument will sort out the timing for the tests on each channel. The user must be aware that this is a switched system and with only one Potentiostat only a single test can be done at any one time. Sometimes a mixture of additional Gill ACs and sequential channels can offer an economical solution.

Additional Software for incorporation in the Sequencer program.

Galvanodynamic Sweeps

This program enables the instrument to be controlled as a Galvanostat rather than a Potentiostat. The program enables both single and multiple cycle Sweeps to be performed as well as long term tests including Linear Polarisation Resistance and Galvanostatic tests.

Harmonic Analysis

A novel and little used technique for measuring the non linear response to a sine wave polarisation. It is unique in that in one simple measurement values for Polarisation Resistance and Tafel slopes bA & bC are obtained. The technique can be used as a long term test in order to monitor corrosion rates with respect to time. The technique typically uses a polarisation of about 0.1Hz or less and measures the 1st 2nd and 3rd Harmonic Current response. The Sequencer program allows the operator to use this technique in series with other perhaps more trusted techniques such as LPR in order to compare results.

IR Compensation

IR Compensation 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. Unlike interrupt methods that effectively apply high frequency spikes to the system and have the potential for instability this method maintains control of the cell at all times without any unwanted high frequency polarisations.

Linear Polarisation Resistance Noise (Patent applied for)

A new corrosion monitoring technique that employs the virtues of LPR and Noise. The method is good for multi phase environments such as those experienced in splash zones and multi phase flow. The technique may also be of assistance when used with Rotating Disc Electrode systems. In multiple phase environments such as splash zones or in multiple phase oil / brine solutions the technique gives two results: the average monitored corrosion rate and the corrosivity of the conductive phase. In many cases it is the corrosivity of the conductive phase that is most important. Especially as in the case of an oil/brine mixture the more corrosive brine has a chance of separating out and causing enhanced corrosion rates at a place where a probe does not exist. Note that as far as I am aware no other technique including Electrochemical Noise and Electrical Resistance can do this. Further details on the technique are available under application notes.

Gill AC Solo / Duo / Trio variants

In this case we supply the same instrument as the Gill AC except with reduced software ability in order to reduce the capital cost of the instrumentation. All instruments include Sequencer and Core Running programs plus Solo Duo or Trio of the following programs normally included with the Gill AC: Cyclic Sweeps; Long Term; Current & Voltage Noise and AC Impedance. The missing programs can be purchased at a later date at a 30% supplement.

Advanced Options for Gill AC

Voltage Input

Voltage inputs can be used to monitor other parameters that have a voltage output such as temperature pressure or velocity. Each voltage input can be selected as a test within the Sequencer program enabling a voltage measurement to be taken at the start or end of any electrochemical test. These inputs can be configured and scaled for display with the correct units together with the long term electrochemical data. Up to four voltage inputs per Gill AC are available on board. Additional voltage inputs are available on request. If requested voltage Inputs can be configured at 0 or 4 to 20mA inputs at no additional charge. A small additional charge is made for direct measurement of a thermocouple.

Paint Buffer

The Paint Buffer is fitted with ultra high impedance components and switches that can handle low currents of the order of 10pA with a good level of resolution below that. It is recommended for use with high impedance cells such as those that are coated or for miniature electrodes. It is housed in a small die-cast box and connects via a cable to the rear panel of appropriately fitted Gill AC’s.

DC Weld Test option

This option enables the host instrument to test multiple electrode couples with up to five elements such as encountered with welds or mixed metal systems. Each element in the couple is attached to its own Zero Resistance Ammeter complete with automated current ranges. Thus the individual current response from each element is monitored in both the galvanic and polarisation mode. Versions of the following programs are supplied with this option: Long Term; Cyclic Sweeps and C&V Noise.  These programs are operated through the sequencer program in the normal way. The maximum read rate for C&V Noise is reduced to one reading per second whilst using this option. The specification of the additional ZRAs is as follows:-

- Current Range 10pA to 500mA
- Seven Current Ranges per ZRA.
- Seven Counter Resistors 10 100 1K 10K 100K 1M 10M Ohms
- Input Offset Voltage 10µV

AC Weld Test option

This option enables AC Impedance tests to be applied to the multiple electrode couple. The individual current response to a polarising AC signal is obtained from each of the test electrodes whilst it remains galvanically coupled to the other test electrodes in the cell. It includes the same hardware as with the DC weld test option. 

Offsetting Ability for Weld Test option

This technique enables more than one electrode to be tested in the same cell at the same time. Each test is performed around each electrode's rest potential as if it were isolated from the other electrodes in the couple. A typical use for this technique may be to test 100 painted sample simultaneously during an accelerated exposure test thus reducing the immersion time and also ensuring the test time occurs at the same time for all samples being tested. Letting our minds run free and with quite a bit more complexity the technique enables each of the electrodes in the multiple electrode system to be running completely different tests at the same time whilst still using a single Auxiliary and Reference Electrode. We would like to do a product like this trouble is finding a customer who wants one!

Instrument Control DLL

The Instrument Control DLL is a library of commands that enables operators to control the instrument using their own software. It can be used in Microsoft’s or Borlands C type programming languages. A version that can be controlled from other languages can be supplied at an additional charge.

Electrical Resistance

This option enables the instrument to measure an Electrical Resistance Probe with high resolution. A lot has been made of high accuracy ER measurements in recent times and indeed the electronics is perfectly capable of giving very high resolution measurements and corrosion rates.  However to obtain high accuracy it is important to have very stable temperatures with no variations. In our opinion even temperature fluctuations between the corroding and check elements of a 1/1 000 °C will lead to significant errors when trying to calculate the corrosion rate over a short period of time especially when the corrosion rates are low. Operators can reduce external temperature variations by insulating the probe with waterproof material to reduce the chance of cooling by evaporation. Other than that it comes down to probe design. For higher accuracy try to select a probe that endeavours to reduce any heat difference between the corroding and check elements. ACM can get an indication of the accuracy of the measurement by measuring the resistance of the check element. If this resistance remains constant throughout the test period there is a good likelihood that the corrosion measurements obtained are satisfactory. By measuring the check elements resistance at a set temperature the temperature of the probe whilst in use can be calculated provided the materials thermal coefficient of resistance is known. Our software will include a list of materials with such coefficients.

GPS Tracking System 

This technique enables the location of the corrosion measurement to be recorded with the data for later cross referencing. It does not include the GPS device itself which will interface with the PC. ACM can provide this part with the system if required. The option gives the ability to pre-program the instrument with sequences of electrochemical tests for specific probe locations such that as the operator goes from probe to probe the instrument knows the location of the probe and which tests it is programmed to perform. The data will automatically be added to previous data for that probe.

Bubble Test Software

The Bubble Test program is designed for the repetitive testing of corrosion inhibitors. Unlike our standard Sequencer based software which gives great flexibility the Bubble Test program appears to already know what is required of it. Once its initial parameters are set it is ready to perform tests on inhibitors day after day with minimum operator intervention. Tests are typically done in triplicate to gain a level of confidence in the results. Results are presented in a report-ready graphical form that can be printed out at the end of a test including:-

- LPR graph showing LPR; corrosion current or corrosion rate vs time. 
- As above but with markers and labels showing the corrosion rate immediately before the inhibitor was added and the corrosion rate and % inhibition after 1 2 5 10 and 15 hours.
- As above but with operator set titles above and below the graph. 
- Corrosion rate bar graph displaying the corrosion rate on each channel immediately before the inhibitor was added 2 hours after and 16 hours after. Parameters can be changed.
- % inhibition bar graph displaying the % inhibition on each channel at 2 hours and 16 hours after the inhibitor was added. Parameters can be changed.
- Result table displaying the results from the above two bar graphs in a table format with titles and extra information above and below the table. 
- Cyclic Sweep or Tafel type graph showing the results of a Cyclic Sweep done at the end of the Bubble Test. Titles can be added both above and below the Tafel graph.

Such customisation is normal at ACM Instruments hence the depth of options. Just ask for what you want and we will be pleased to supply it.

Replacement Electrode Cables

Replacement cables can be provided to any length required or with any type of termination. It is quite common for operators to specify a complete set of straight through cables for connection directly to a specific probe.