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Page 22

10.1.3 Temperature Compensation

The slope of a pH sensor (section 10.1.2) is affected by temperature. This
effect is compensated for either by using an Automatic Temperature
Compensation (ATC) sensor or by entering the sample temperature
manually. Figure 10-3 shows the slope of a pH sensor at various
temperatures.

-600

-400

-200

0

200

400

600

0

7

14

Electrode
Potential (mV) at
0 oC (54mV/pH)

Electrode
Potential (mV) at
50 oC (64mV/pH)

Electrode
Potential (mV) at
100 oC (74mV/pH)

pH Electrode Response, as a Function of Temperature

Electrode Response (mV)

pH

Figure 10-3

Summary of Contents for Aqua-pH

Page 1: ... The introduction has a diagram and explanation of the display and controls of the Aqua pH It also contains a full listing of all of the items that you should have received with your Aqua pH Please take the time to read this section as it explains some of items that are mentioned in subsequent sections 3 Main Section The main section of the handbook provides complete details of the Aqua pH includi...

Page 2: ...ion Notes 13 5 3 Calibration Messages 13 5 4 Manual Temperature Setting 13 6 Selecting Buffers for Auto Buffer Recognition 14 7 Battery Saver Function 15 8 Initialising the Aqua pH 16 9 Troubleshooting 17 9 1 General Error Messages 17 9 2 pH and mV Troubleshooting 18 9 3 Temperature Troubleshooting 19 10 Appendices 20 10 1 pH Sensor Fundamentals 20 10 2 Checking the reference junction of a pH sens...

Page 3: ...Page 2 1 Introduction 1 1 Aqua pH Display and Controls ...

Page 4: ...calibrate all parameters See sections 3 and 5 Also used to select buffers for automatic buffer recognition See section 6 Used to select pH mV or Temperature modes See section 2 Switches the Aqua pH on and off Hold this key for 3 seconds to invoke Battery Saver mode See section 7 and These keys toggle the Aqua pH between Large Display mode and Dual Display mode See section 2 NOTE The digits in Larg...

Page 5: ... 1 Aqua pH pH mV Temperature Instrument 121112 2 pH Sensor Porous Teflon Double Junction 1m 121207 3 Temperature Sensor Stainless Steel 1m 121247 4 pH6 88 Buffer 200mL 121306 5 pH4 00 Buffer 200mL 121381 6 9V Battery 130026 7 Aqua pH Handbook 130050 Options that may have been ordered with your Aqua pH 1 Hard Plastic Carry Case 130057 ...

Page 6: ... to 105 0 Auto pH Buffer Recognition pH4 00 pH6 88 pH7 00 pH9 23 pH10 06 Additional Temperature Specifications Temperature Sensor Offset Range 10 0o C to 10 0o C General Specifications Display 24 Character alphanumeric LCD with full text prompts and error messages Power 9V Alkaline Battery for 100 hours operation Battery Saver On Auto switch off after 5 minutes Off Continuous use Dimensions 157 x ...

Page 7: ...he top line and Temperature data is shown on the bottom line No Temperature data is shown if the Temperature sensor is unplugged as manual Temperature compensation is not applicable to mV Calibration is not available in this mode Press or to toggle between dual readout or large digit readout Temperature Mode 25 0o c Temperature data only is shown on the top line Select this mode to calibrate Tempe...

Page 8: ...e sensor is not connected then the Aqua pH will use manual temperature compensation 4 Ensure that temperature has already been calibrated or manually set see sections 5 1 and 5 4 NOTE If the decimal point in the temperature reading is replaced by a then the temperature readout is not calibrated 5 Remove the wetting cap from the pH sensor 6 Rinse the pH and Temperature sensors in distilled water an...

Page 9: ...both sensors into a small sample of pH4 00 pH9 23 or pH10 00 Buffer so that the bulb and reference junction are both covered as per the diagram in step 8 DO NOT place the sensors directly into the buffer bottle Discard the used buffer after use pH9 23 and pH10 00 buffers are highly unstable Avoid using these buffers if possible Discard immediately after use 12 When the reading has stabilised press...

Page 10: ... A full 2 point calibration should be performed at least monthly Of course more frequent calibration will result in greater confidence in results 3 All calibration information is retained in memory when the Aqua pH is switched off even when the battery is removed 4 The Aqua pH displays the value of the pH buffer that it has attempted to recognise at calibration Ensure that the buffer value display...

Page 11: ...If a 1 point calibration has failed the Aqua pH will display the following message then the failed asymmetry value of the sensor 1 point 6 88 Cal Failed then Asym 1 50pH 3 If a 2 point calibration has been successfully performed the Aqua pH will display the following message and then the asymmetry and slope of the sensor 2 point 4 00 Cal OK then Asym 0 10pH Slope 99 5 4 If a 2 point calibration ha...

Page 12: ...Page 11 4 Millivolt Calibration The mV section is factory calibrated There is no user calibration facility for this mode ...

Page 13: ...er to section 5 4 for details on setting manual temperature compensation values 4 Place the sensor into a beaker of room temperature water alongside a good quality mercury thermometer Stir the sensor and the thermometer gently to ensure an even temperature throughout the beaker 5 When the reading has stabilised press and hold the key for 2 seconds 6 The reading from the sensor is now displayed on ...

Page 14: ...If a temperature calibration has failed the Aqua pH will display the failed offset value of the sensor Cal Failed Offset 10 5o c 5 4 Manual Temperature Setting 1 Switch the Aqua pH on 2 Select Temperature mode see section 2 3 Manual temperature setting is only available if the Temperature sensor is not connected 4 Press and hold the key for 2 seconds The current Manual Temperature Setting is now d...

Page 15: ...he or keys to alternate between pH6 88 and pH7 00 buffers 6 Press the key to save the primary buffer 7 After the message Buffer 2 Select the display will now show the currently selected secondary pH buffers for example 4 00 9 23pH Select or 4 00 10 0pH Select 8 Use the or keys to alternate between pH9 23 and pH10 00 buffers the display shows pH10 0 for the latter but this buffer is stored as pH10 ...

Page 16: ...menu is now displayed For example ON 9 00V 4 In this mode use the or keys to toggle the battery saver function on or off ON enables the battery saver function The unit will turn itself off after 5 minutes OFF disables the battery saver function The unit will not switch itself off NOTE The display also shows the battery volts This gives the operator an idea of how much battery life is remaining The...

Page 17: ...s action may be required if a sensor is replaced To initialise the Aqua pH 1 Switch the Aqua pH off 2 Press AND HOLD the key while switching the Aqua pH on 3 The following messages are now displayed Memory Cal Reset You MUST Re Calibrate TPS AQUA P V1 0 S1234 4 The meter then displays pH and Temperature Note that the decimal points have been replaced with a to indicate that the unit requires re ca...

Page 18: ...al User calibration settings have been lost or corrupted Re calibrate the instrument A 2 point calibration is required for pH section 3 and a 1 point calibration for temperature section 5 Meter displays the word OFF and switches off Battery is below 6 00 volts Replace the battery Meter will not turn on Battery is exhausted Replace the battery Flashing symbol Battery is below 7 50 volts Replace the...

Page 19: ... per instructions supplied with the sensor Flush with distilled water and replace electrolyte 2 Point calibration fails Slope is less than 85 0 1 Incorrect primary buffer 2 Glass bulb not clean 3 Sensor is aged 4 Connector is damp 5 Buffers are inaccurate Ensure that you are using the buffers which the Aqua pH has been set to automatically recognise See section 6 Clean glass bulb as per instructio...

Page 20: ...Replace electrolyte Inaccurate readings even when calibration is successful Reference junction blocked Clean reference junction as per instructions supplied with the sensor Displays 7 00 for all solutions Electrical short in connector 1 Check connector Replace if necessary 2 Replace sensor Displays 4 5 pH for all solutions Glass bulb or internal stem cracked Replace sensor 9 3 Temperature Troubles...

Page 21: ...ence junction A saturated solution of KCl is used to make contact with the sample It is vital that the KCl solution has an adequate flow rate in order to obtain stable accurate pH measurements 10 1 1 Asymmetry of a pH Sensor An ideal pH sensor produces 0 mV output at 7 00 pH In practice pH sensors generally produce 0 mV output at slightly above or below 7 00 pH The amount of variance from 7 00 pH ...

Page 22: ...practice pH sensors usually produce slightly less than this The output of a pH sensor is expressed as a percentage of an ideal sensor For example an ideal sensor that produces 59mV pH unit has 100 Slope An sensor that produces 50 15mV pH unit has 85 Slope see Figure 10 2 600 400 200 0 200 400 600 0 7 14 85 Slope at 25 oC 50 15mV pH 100 Slope at 25 oC 59mV pH Response of pH Electrode as a Function ...

Page 23: ... Compensation ATC sensor or by entering the sample temperature manually Figure 10 3 shows the slope of a pH sensor at various temperatures 600 400 200 0 200 400 600 0 7 14 Electrode Potential mV at 0 oC 54mV pH Electrode Potential mV at 50 oC 64mV pH Electrode Potential mV at 100 oC 74mV pH pH Electrode Response as a Function of Temperature Electrode Response mV pH Figure 10 3 ...

Page 24: ... faulty The following test can be performed to help determine if the Aqua pH or the pH sensor is faulty 1 Initialise the Aqua pH see section 8 2 Disconnect the pH sensor 3 Connect the centre pin of the BNC socket with the outside frame of the socket using a short piece of wire or a paper clip etc 4 The meter should read approximately 7 00 If you press the key for 2 seconds the Aqua pH will calibra...

Page 25: ...your Aqua pH firmware may of benefit to us Please obtain the version number before phoning or faxing The version number is displayed on the bottom left of the display when the Aqua pH is switched on For example TPS AQUA P V1 0 S1234 V1 0 in this example is the firmware version number S1234 in this example is the instrument s serial number ...

Page 26: ... the equipment Shipping damage is not covered by this warranty Please note A guarantee card is packed with the instrument or sensor This card must be completed at the time of purchase and the registration section returned to TPS Pty Ltd within 7 days No claims will be recognised without the original guarantee card or other proof of purchase This warranty becomes invalid if modifications or repairs...

Page 27: ...ime phone number Your company name ORDER number and return street address A description of the fault Please be specific Note Please Repair does NOT describe a fault Your equipment will be repaired and returned to you by air express where possible For out of warranty units a repair cost will be calculated from parts and labour costs If payment is not received for the additional charges within 30 da...

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