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19

109118-1 Rev. A,10/96

3.4

Problem Solving (cont)

3.4.3

Electrode Problem Solving (cont)

2.

The junction is designed to allow the fill solution to leak
out of the tip of the electrode at a slow controlled rate. To
test for proper flow, rinse the tip of the electrode, blot dry
and let the electrode hang in the open air for 15 minutes. If
it is flowing properly, salt crystals of the fill solution will
form on the junction. If they do not, refer to the
manufacturer's instructions for junction cleaning or
replacement.

Slow response or unstable readings in samples can be caused by
a number of things. Those listed below assume that everything
was fine in the calibration buffers.

1.

Low ionic strength samples will tend to be very drifty. You
are trying to take an electrical measurement in a solution
that is a very poor conductor. Try adding a drop of KCl fill
solution to about 5 mL of the sample. In most cases it will
not change the pH but will give the sample enough ionic
strength for the electrode to finish the reading.

2.

Non aqueous samples (organics) do not follow the normal
pH scale and can cause some measuring problems. These
solutions are usually low in ionic strength, may dehydrate
the pH membrane and often cause the junction to plug due
to incompatibility with the electrode fill solution. The most
reliable way to pH organics is to dilute them with water
until stable readings can be generated.

3.

Concentrated samples can cause pH measuring errors.
This is caused by problems with the pH sensing glass and
its ability to distinguish the Hydrogen ion activity over the
mass of other ions in the sample. The creation of new
junction potentials due to KCl dissociation problems can
also cause instability. The best solution is to dilute the
samples into measurable ranges.

For more information refer to the Corning Guide to pH
Measurement.

3

Summary of Contents for 440 pH Meter

Page 1: ...ded for use by persons knowledgeable in safe laboratory practices If the 440 is not used in accordance with these instructions for use the protection provided by the equipment may be impaired The 440...

Page 2: ...asurements 9 2 6 Temperature Measurements 10 2 7 Changing the Resolution 11 2 8 Chart Recorder 11 2 9 Interfacing via the RS232 Output 12 3 Support Information 3 1 Basic Theory 13 3 2 Operating Hints...

Page 3: ...ories packing sheet for a list of the additional components 3 To attach the electrode arm to the pH meter a The electrode arm can be attached to the left or right hand side Using the screwdriver suppl...

Page 4: ...r lead to the ATC socket 2 If you are using a separate ATC probe connect it to the ATC socket 3 Connect the power supply unit to the DC socket 1 3 Display and Controls DC power supply unit socket ATC...

Page 5: ...value used when setting calibration buffers Also changes display resolution Selects calibration buffers Selects automatic endpoint detection Turns the display off and places the meter in standby mode...

Page 6: ...play and Controls cont 440 Display temperature or slope value automatic or manual temperature compensation slope value displayed calibration buffer indicator auto endpoint is selected main display mod...

Page 7: ...corrected for temperature see Section 2 6 If you are not using an ATC in the system the Model 440 assumes a temperature of 25 C 2 point calibration Place the tip of the electrode in the second buffer...

Page 8: ...hecks the electrode output for stability and automatically freezes the display when the reading appears stable It can be used during calibration and routine measurements Turn auto endpoint on by press...

Page 9: ...cannot be set closer than 2 pH units from each other You also cannot move one buffer value past another For changes on the low end change buffer 1 first and for changes on the high end change buffer 3...

Page 10: ...will show ATC If not the display will show MTC and 25 C Buffer Temperature Correction Table If you use standard buffers listed below the 440 automatically corrects for temperature using the values sh...

Page 11: ...y The REC socket 2 5 mm phone jack provides a voltage proportional to the displayed reading in pH and mV modes The polarity of the output is the same as the polarity of the input signal Approximate Re...

Page 12: ...computers is part number 477758 and can be ordered from your distributor The pin configuration of that connector and Model 440 output protocols are as follows Pin Signal 1 device enable link to pin 5...

Page 13: ...mple The Model 440 measures and converts the resulting minute electrode voltages into a pH reading The response of a pH electrode or its slope is defined by the Nernst equation Electrode response E0 2...

Page 14: ...urate You should be calibrating and measuring at room temperature 5 When transferring from one sample to another always rinse the electrode with distilled water and blot dry Handle the electrode caref...

Page 15: ...warm water Leave the tip of the electrode in an inch 25 mm of pH 7 0 or 4 0 buffer when it is not being used Do not leave it in distilled water For long term storage follow the electrode manufacturer...

Page 16: ...ble 3 4 Problem Solving Most problems are caused by electrode faults rather than by the Model 440 but power fluctuations can corrupt calibration values being held in the meter memory 3 4 1 Meter Test...

Page 17: ...er fails the above test call the number on the back of this manual for warranty and service information 3 4 2 Meter Error Codes Error codes are designed to give the user information on electrode perfo...

Page 18: ...nd reconditioning electrodes Although slope is useful in generally determining when it is time to do maintenance on an electrode response time is by far the critical factor effecting accuracy of measu...

Page 19: ...r Try adding a drop of KCl fill solution to about 5 mL of the sample In most cases it will not change the pH but will give the sample enough ionic strength for the electrode to finish the reading 2 No...

Page 20: ...rating ATC Display LCD display Outputs RS232 Recorder Input Conditions Impedance greater than 1012 ohms Operating Conditions Operating temperature 5 to 40 C Operating humidity max 80 at 35 C non conde...

Page 21: ...tandards UL1262 CSA151 IEC1010 The 440 also complies with the European EMC Directives and therefore carries the CE mark Environmental Compliance The casework components of the 440 are marked with the...

Page 22: ...3 pH Electrode Rinse Sachets 30 packs 471226 Power Supply 100 120V 50 60Hz 1 471228 Power Supply 230V 50Hz 1 477758 RS232C Cable 1 470109 Shorting Test Clip 3 470493 Dot Matrix Printer with Cables 1 W...

Page 23: ...1992 All rights reserved Corning Incorporated Science Products Division Corning New York 14831 USA Telephone 1 800 222 7740 US and Canada 1 607 974 0353 Outside US Fax 1 607 974 0345 430 Rev A 6 96...

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