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Chapter 2 — The pH/mV Amp

11

Select
filter

Drag labels and tick
marks to adjust axis

e-corder

input

channel number

Pause/Resume buttons

Select input
channel

Invert signal

Gain range
(sensitivity)

Preview signal

Average signal
amplitude

Select filter

e-corder

input

channel number

Pause/Resume button

Preview signal

Invert
signal

Gain range
(sensitivity)

Select input
channel

Average signal amplitude

Figure 2–7

The pH/mV Amp pH
dialog box, for
previewing a signal
(Chart software on a
Windows Computer)

Figure 2–8

The pH/mV Amp pH
dialog box, for
previewing a signal
(Chart software on a
Macintosh Computer)

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Summary of Contents for EA168

Page 1: ...e corder www eDAQ com eDAQ Amp User Manual Quad pH mV Amp E E E E E 2 E 2 E 2 E 2 Ref Ref Ref Ref Channel 1 Channel 2 Channel 3 Channel 4 168 On line On line On line On line isolated ...

Page 2: ...Ltd Chart and Scope are trademarks of ADInstruments Pty Ltd and are used under license by eDAQ EChem is a trademark of eDAQ Pty Ltd Other Trademarks Mac OS and Macintosh are registered trademarks of Apple Computer Inc Windows 98 Windows Me Windows 2000 and Windows XP are trademarks of Microsoft Corporation PostScript and Acrobat are registered trademarks of Adobe Systems Incorporated All other tra...

Page 3: ...g the Signal 10 3 Electrode Calibration 15 Signal Calibration 16 Temperature Compensation 21 Manual Temperature Compensation 21 Automatic Temperature Compensation 22 Isopotential Point 24 Viewing Electrode Response 24 Manual Compensation Response 25 Removing the Calibration 26 A Technical Aspects 27 Quad pH mV Amp Operation 27 Technical Description 27 B Troubleshooting 29 C Specifications 31 D Ele...

Page 4: ...iv Quad pH mV Amp ...

Page 5: ...recording signals from pH electrodes either combination or half cell electrodes potentiometric ion selective electrodes ISEs redox or ORP oxidation reduction potentiometric electrodes other high impedance sources up to 2 V requiring electrometer input Signals from up to four electrodes can be recorded simultaneously ...

Page 6: ...mage that may have occurred during transit Contact your eDAQ distributor if you encounter a problem You should also become familiar with the basic features of your e corder system which are discussed in the e corder Manual on the Installer CD eDAQ Amps The Quad pH mV Amp is part of a family of preamplifiers known as eDAQ Amps The Quad pH mV Amp is designed for recording signals from up to four pH ...

Page 7: ...le for use with carbon fibre and other microelectrodes Current gain ranges of 10 pA to 100 nA in 1 2 5 steps QuadStat a four channel three electrode potentiostat suitable for use with amperometric biosensors Current gain ranges of 2 nA to1 mA channel in 1 2 5 steps Bridge Amp suitable for sensors requiring a low drift high gain differential amplifier Also provides DC excitation GP Amp suitable for...

Page 8: ...4 Quad pH mV Amp ...

Page 9: ...is chapter describes how to connect and use your eDAQ Quad pH mV Amp IMPORTANT Always make sure that the e corder is turned off before you connect or disconnect the Quad pH mV Amp Failure to do this may result in damage to the e corder and or the pH mV Amp ...

Page 10: ...th a separate reference electrode Half cell electrodes should be connected to the BNC input connector marked E 2 The separate reference electrode is connected to the 4 mm socket marked Ref The On line Indicators When lit these indicate that the software such as Chart or Scope has located and initialized the pH mV Amp If the light does not go on when the software is run check that the pH mV Amp is ...

Page 11: ...s inside Refer servicing to qualified service personnel Input Output I C Bus I C 2 Channel 4 Channel 3 Channel 2 Channel 1 1 5 9 6 Digital Ground Regulated 17 V DC Regulated 8 V DC Regulated 17 V DC Power lines SCL DSC SDA DSD INT I2C control signals 1 5 9 6 Digital Ground Regulated 17 V DC Regulated 8 V DC Regulated 17 V DC SCL DSC SDA DSD INT I2C control signals Input Output pH mV signals BNC co...

Page 12: ... end and four cables with BNC connectors at either end Output Made in Australia by eDAQ Pty Ltd No user serviceable parts inside Refer servicing to qualified service personnel Input Channel 4 Channel 3 Channel 2 Channel 1 Made in Australia by eDAQ Pty Ltd No user serviceable parts inside 2 I C Bus Rated Voltage 90 250 V AC Refer servicing to qualified service personnel 50 60 Hz 25 VA Output Input ...

Page 13: ...e connected as shown in Figure 2 4 The remainder are linked via I2 C cables connecting the I2 C output of one eDAQ Amp to the I2 C input of the next as in Figure 2 5 The signal outputs of each eDAQ Amp are connected to an input channel of the e corder The pH mV Amp Self Test After you have installed the software connected the e corder to a computer as described in your e corder Manual and connecte...

Page 14: ...n Choosing the pH Amp menu command or clicking the button will access the pH Amp dialog box which replaces the Input Amplifier dialog box for that e corder channel your Chart and Scope Software Manuals have details on the Input Amplifier dialog box Previewing the Signal The pH Amplifier dialog box allows you to preview a signal so that you can select the amplification and filter settings The dialo...

Page 15: ...ew signal Average signal amplitude Select filter e corder input channel number Pause Resume button Preview signal Invert signal Gain range sensitivity Select input channel Average signal amplitude Figure 2 7 The pH mV Amp pH dialog box for previewing a signal Chart software on a Windows Computer Figure 2 8 The pH mV Amp pH dialog box for previewing a signal Chart software on a Macintosh Computer ...

Page 16: ...put Amplifier dialog in the Chart Software Manual for further details Changes made here update settings in the main window of the program Setting the Range Use the Range pop up menu to select the input range sensitivity of the channel At 25 C a change of one pH unit corresponds to a 59 mV change This relationship is used in Table 2 1 which shows the pH ranges corresponding to various pH mV Amp ran...

Page 17: ...ications it is recommended to have the Mains Filter on Inverting the Signal Ticking the Invert checkbox reverses signal polarity that is positive and negative signal values are reversed Units Calibration Clicking the button access the Units Conversion dialog box For more information about Units Conversion see the Chart Software Manual or Scope Software Manual However when using Chart software for ...

Page 18: ...14 Quad pH mV Amp ...

Page 19: ... compensation MTC adjustment or enables automatic temperature compensation ATC if temperature readings are collected on a second channel The resulting calibration information is used to convert the raw voltage signal from the electrode into appropriate units pH pF pNa etc which will then be displayed in the Chart window Multiple point i e more than two points linear or non linear calibration can b...

Page 20: ...signal values can be entered directly by typing them in it is more usual for the electrode to be immersed in a standard buffer solution of known pH or ion concentration and the signal recorded for a minute or so until it has stabilized If two point calibration is required then the electrode is immersed in a second standard buffer solution of a different pH or ion concentration After recording the ...

Page 21: ...menu Raw signal values Select region of signal for raw value Calibration temperature Decimal places selection Electrode response dialog button Calibration report Temperature compensation Select region of signal for raw value Choose the pH Calibration command from the channel menu Choose the pH command from the channel menu Figure 3 2 The Electrode Calibration dialog box of the pH Calibration Exten...

Page 22: ...and two markers and indicate the maximum and minimum data points in the selection Figure 3 4 Usually a region of steady signal is selected Figure 3 4 and then clicking the Value button enters the raw signal value the Figure 3 3 Selection of raw mV data from two buffer solutions for use in electrode calibration Figure 3 4 Selecting different regions of the electrode signal ...

Page 23: ...u cans also define new units or delete unwanted ones Unit names are stored in a preferences file and become available to other files Choose Define Unit from the Units pop up menu to access the Define Unit dialog box Figure 3 7 to enter a new unit name Results of double point calibration Results of single point calibration Click on arrow to enter average signal value Enter buffer pH Select region o...

Page 24: ... and return to the Chart window click the button To abandon the changes click the button Ionic Charge Use the pop up menu Figure 3 7 to select the value for the number of electrons transferred at the electrode This usually corresponds to the charge of the ion and thus for pH sodium or potassium measurements n 1 for magnesium or calcium n 2 while for halides or nitrate n 1 The value of n is used to...

Page 25: ...sis for compensation of the readings The pH extension offers two types of temperature compensation manual temperature compensation MTC Used where the measurements are made at a constant temperature but where Tm Tc Automatic temperature compensation ATC Used where temperature fluctuations are expected to occur during the experiment that is when Tm is not constant In these cases temperature should b...

Page 26: ...tic option is chosen the pH extension will use temperature data from one of the Chart channels to correct the pH channel for variations in temperature To choose the automatic temperature compensation option click in the radio button next to the Automatic option The channel selection pop up menu can select the channel on which temperature was recorded Recording Temperature To use a temperature chan...

Page 27: ... 10 Select Temperature from the channel menu Select suitable range 5 V up to 100 C 2 V up to 40 C Access Units Conversion for temperature signal Preview of temperature signal 0 V 0 C and 5 V 100 C are the factory default settings for the RTD probe Figure 3 9 Uncalibrated temperature channel warning alert Figure 3 10 Previewing the temperature signal and setting up units for the temperature channel...

Page 28: ...o Appendix D for more information on how to determine the isopotential point Viewing Electrode Response The pH extension plots the voltage response of the electrode versus pH or other ion giving a calibration graph of the electrode Click the button in the pH dialog box Figure 3 1 and Figure 3 2 Typical electrode responses are shown in Figure 3 11 The isopotential point will be set to zero unless t...

Page 29: ...bration temperature and a second plot showing the response at the specified temperature The calibration response can be identified as the line with one or two calibration points on it These are represented as dots The information displayed on the right of the dialog shows the calibration points and the values used for the Nernst equation Calibration point Calibration points Single point calibratio...

Page 30: ...ort Removing the Calibration The calibration can be turned off at any time by choosing the command from the channel pop up menu Figure 3 1 and Figure 3 2 This displays the raw electrode signal in millivolts or volts again Response at 65 C Isopotential point Response at 25 C Figure 3 12 Electrode Response dialog box when using manual temperature compensation ...

Page 31: ...vely an extension of the e corder s analog input channels It provides very high impedance electrically isolated inputs suitable for direct connection to pH or other ion selective electrodes software controlled filtering of the signal reference electrode input software selectable gain ranges Technical Description As with other eDAQ Amps all internal functions of the Quad pH mV Amp are controlled fr...

Page 32: ... be connected to the Ref socket The output of the electrometer amplifier is fed to a 3 pole 10 Hz low pass filter The E 2 signal is protected with a actively driven shield If you use a half cell electrode with a coaxial cable then the shield will be extended to the electrode This will minimize signal leakage and allow the use of longer cable runs typically several metres than would otherwise be th...

Page 33: ...able is firmly connected to the BNC connector on the back panel of the pH mV Amp and to a BNC input on the front panel of the e corder All or some of on line indicators fail to light when the Chart software is opened and the pH mV Amp controls are not accessible If all the lights are off then the I2 C cable from the pH mV Amp to the e corder may not be properly connected Check to see that the I2 C...

Page 34: ...30 Quad pH mV Amp ...

Page 35: ...dary ranges 1000 500 200 100 50 20 10 5 2 mV supplied by e corder Input resolution 16 bits 0 0015 of range Input impedance 1013 Ω typical Amplifier noise 1µV rms 4 µV p p DC 10 Hz Maximum Input 10 V Input Connection type Insulated BNC E and E 2 4 mm socket Ref Bandwidth Low pass filter 3 dB 10 Hz 3 pole Bessel Secondary filters 5 2 1 Hz digital filters of e corder ...

Page 36: ...tors Provides control and power Power requirements 17 V DC 8 V DC 3 W Physical Configuration Dimensions h w d 60 150 200 mm 2 4 5 9 7 9 inches Weight 1 5 kg 3 3 lb Operating conditions 0 35 C 0 90 humidity non condensing eDAQ reserves the right to alter these specifications at any time ...

Page 37: ...is the gas constant 8 314 J K 1 mol 1 T is the temperature in Kelvin F is the Faraday constant 96487 C mol 1 n is the number of electrons transferred at the electrode usually the charge of the ion pY log10 Y where Y is the activity of the ionic species Note that if pY is plotted against E then the Nernst equation predicts that a straight line should be obtained of intercept E0 and a slope of RT nF...

Page 38: ...l remains constant as temperature changes Most pH electrodes are constructed so that the isopotential is about 0 mV which for most pH electrodes also corresponds to pH 7 However it is not uncommon to find that even in new pH electrodes this value may be anywhere between 50 mV and that the value also changes as the electrode ages Ion selective electrodes may have an isopotential completely outside ...

Page 39: ... Calibration Both single and two point calibration assume that the electrode has a linear response to ion activity Experimentally there will always be some deviation from linearity in the response This is most noticeable at very high or low concentrations In these instances a non linear calibration technique must be used for accurate work Also if you need to calibrate an electrode directly in term...

Page 40: ...36 Quad pH mV Amp In either case the Chart Multipoint calibration extension can be used for non linear electrode calibration See our web site at www eDAQ com for more information ...

Page 41: ...s Bridge Amp 3 GP Amp 3 Picostat 3 Potentiostat 3 Quad pH mV Amp 2 3 QuadStat 3 electrode calibration 15 ATC 22 MTC 25 non linear 35 report 26 undoing 26 electrode connectors 6 electrode isopotential point 24 electrode response 24 26 determination 34 electrode response dialog axis scaling 24 printing or copying 26 F filtering 13 front panel 6 G GP Amp 3 I I2C connector 8 Ionic Charge menu 20 ISE e...

Page 42: ...H calibration extension 15 26 pH electrode isopotential point 24 pH range settings 12 Picostat 3 Potentiostat 3 preferences file 19 problems 29 Q Quad pH mV Amp 2 3 QuadStat 3 R reference electrode connector 6 T technical specifications 31 32 Temperature Amp dialog box 11 12 temperature compensation 21 24 automatic 22 manual 21 22 troubleshooting 29 U Units pop up menu 19 user modification 27 V Vi...

Page 43: ...thorization number You must ship the defective product at your expense We will pay return shipping The product should be packed safely preferably in its original packaging and have the RAN on the shipping label Returns sent without a RAN may be refused delivery This warranty does not cover hardware that has been modified by the user in any way been subjected to unusual physical electrical or envir...

Page 44: ...being used for example Windows XP or Macintosh OS 10 2 the software version you are using for example Chart v5 1 2 We endeavor to answer all your questions but in some cases for example where the problem relates to the other equipment that you are using a nominal fee may be charged Jurisdiction eDAQ Pty Ltd is bound by the laws of New South Wales in Australia and any proceedings shall be heard by ...

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