Jenway 3520 Instruction Manual

Model 3520

pH/mV/Temperature Meter

Operating Manual

352 050/REV A/03-03

Safety

Please read this information carefully prior to installing or using this equipment.

1. The unit described in this manual is designed to be operated only by trained personnel. Any adjustments, maintenance and repair must be carried out as defined in this manual, by a person qualified to be aware of the hazards involved.

2. It is essential that both operating and service personnel employ a safe system of work, in addition to the detailed instructions specified in this manual.

3. References should always be made to the Health & Safety data supplied with any chemicals used. Generally accepted laboratory procedures for safe handling of chemicals should be employed.

4. If it is suspected that safety protection has been impaired in any way, the unit must be made inoperative and secured against any intended operation. The fault condition should immediately be reported to the appropriate servicing authority.

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Model 3520 pH/mV/Temperature Meter

Operating Manual

Contents Section 1 Introduction

Instrument Description 1.1 Instrument Specification 1.2

Section 2 Installation

Unpacking 2.1 Installation 2.2

Displays/Controls 2.3 Inputs/Outputs 2.4

Section 3 Operation

Theory of pH measurement 3.1 pH Measurement 3.2 Preparation of Buffer Solution 3.3

Solution Temperature Values 3.4 Good Practice Guidelines 3.5 Set-Up Parameters 3.6 pH Calibration 3.7 Error Codes 3.8 mV Mode 3.9 Performing Measurements 3.10 Status Page 3.11 Results Storage and Display 3.12 GLP Functions 3.13

Section 4 Maintenance

General 4.1 Cleaning/Re-conditioning of Glass Electrodes 4.2

Section 5 Optional Accessories

Optional Accessories 5.1 Spares 5.2

Section 6 Interfacing

Analogue 6.1 RS232 6.2 Keypad Emulation 6.3 Printing 6.4

Section 7 Troubleshooting

Troubleshooting 7.1 Functional Checks 7.2 Reset Procedure 7.3

EC Declaration of Conformity

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Section 1

Introduction

1.1 Instrument Description

The Model 3520 is a fully specified laboratory pH/mV/Temperature meter that includes full support for good laboratory practices (GLP). The meter supports 1, 2 or 3 point pH calibration on either manually entered pH buffers or automatically temperature compensated buffers to DIN, JIS and NIST standards. Powerful data logging capabilities are included with the ability to store up to 500 readings either manually, at timed intervals or on alarm events.

1.2 Instrument Specification pH (1, 2 or 3 point cal)

Range: -2.000 to 20.000pH Resolution: 0.001 / 0.01 / 0.1pH Accuracy: ±0.003pH

mV (Absolute or Relative)

Range: -1999 to +1999mV Resolution: 0.1mV Accuracy: ±0.2mV Input Impedance: >1012ohms

Temperature Measuring

Ranges: -10 to +105°C / 14 to 221°F Resolution: 0.1°C / 1°F Accuracy: ±0.5°C / ±1°F

ATC Range: 0 to 100°C / 32 to 212°F Manual Temp. Compensation: 0 to 100°C / 32 to 212°F Auto Buffer Selection: Jenway (2.00, 4.00, 7.00, 9.20 and 10.00)

DIN (3.06, 4.65, 6.79, 9.23, 12.75) NIST (1.68, 4.01, 6.87, 9.18, 12.45) JIS (1.68, 4.01, 6.87, 9.18, 12.45) or manually entered buffers

Calibration: User selectable 1, 2 or 3 point Outputs: Analogue 1mV per 0.01pH

RS232 serial and IrDA printer interface Alarm - open collector

Clock: 24 hours, hrs/min/sec or day of month/month/year, leap year

corrected (European and American formats)

GLP: Calibration reminder interval (1-999 hours)

Alarm outputs (open collector and audible) Security code protected user data

Display: Back lit 1/8 VGA monochrome LCD Languages: English, French, German, Italian, Spanish, Portuguese Power: Power Supply 9Vac Size: 275(l)x240(w)x150(d)mm Weight: 850g

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Section 2

Installation

2.1 Unpacking

Remove the Model 3520 from the packaging and ensure the following items are included:

1. Model 3520 pH/mV/Temperature Meter

2. Glass bodied combination pH electrode (924 005)

3. ATC probe (027 500)

4. Electrode holder

5. 4, 7 and 10pH buffer sachets

6. BNC shorting plug (009 146)

7. Power Supply (as specified at time of ordering the product)

8. Condensed operating instructions (352 051)

9. Operating Manual (352 050) Any shortages or damage should be reported immediately to the manufacturer or your local

distributor.

2.2 Installation

The Model 3520 is supplied ready to use. Connect the ATC (if required) and the pH electrode to the rear panel Temp and pH sockets.

The electrode stand requires minimal assembly (refer to the diagram below).

Fig. 2.2.1 Electrode Holder Assembly

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2.3 Display

Fig. 2.3.1 – Display

1. Primary display – 4½ digit. Provides direct readout in pH and millivolts of samples and standards.

2. Mode annunciators – shows selected measurement mode; pH, mV (Absolute and Relative).

3. Secondary display – 3½ digit display. Provides direct readout of automatic or manual temperature.

4. Mode annunciators – indicates temperature in °C or °F and whether the measurements are manually temperature compensated (MAN symbol).

5. Endpoint symbol – this symbol is displayed when an endpoint has been detected.

6. Mode tags – Each mode tag is highlighted when selected; SETUP, MODE (pH or mV), STATUS or RESULTS. If a double headed arrow symbol is present this indicates that the mode can be changed to an alternative option (pH/mV).

7. Real time clock - will display either date or time.

8. The following symbols will appear along the display: Padlock - Set up parameters security locked

Notepad symbol - data logging to internal memory IrDA status Alarm indication - an Up arrow refers to Hi alarm / a Down arrow refers to Low alarm

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2.4 Keypad

2.4.1 Keypad

1. ESC used to switch the instrument on and to place into standby mode (only if power supply lead remains connected to the instrument). Also used to escape/exit a mode.

2. CAL / CLR used to select and perform a calibration sequence. This key is also used to clear readings from Memory. Used to select Abs/Rel mV in mV mode.

3. Print key used to initiate a print.

4. Up Arrow used for adjustment during set up, to scroll results and to toggle between mV and pH modes.

Down Arrow used for adjustment during set up, to scroll results and to toggle between mV and

pH modes.

Left Arrow used for adjustment during set up and to move between mode tags. Right Arrow used for adjustment during set up and to move between mode tags. STO used to accept an entered value in set-up mode and to instigate a stored reading.

This key can also be used as a CAL key during calibration.

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2.5 Inputs/Outputs Fig. 2.5.1 – Rear panel layout

1. Ref Socket 2mm pin socket. Connection socket for separate reference electrode. When performing measurements with some pH and ion selective electrodes a separate reference electrode is needed.

2. pH Socket BNC type socket which allows combination pH or redox electrodes to be used.

3. Temp Socket 8 pin mini-DIN socket. This allows the optional Automatic Temperature Compensation (ATC) probe to be connected.

4. Alarm Output 2 x 4mm sockets. Open collector alarm outputs. Red for Hi / Black for Low.

5. Printer Socket 9 way socket for RS232 and IrDA connection.

5. Power In AC 9V I/P socket. 2.1 x 5.5mm socket allowing the power supply to be connected to the instrument.

7. Analog Out 2x4mm sockets. Analogue output (buffered electrode potential).

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Section 3

Operation

3.1 Theory of pH Measurement

pH is a unit of measurement which defines the degree of acidity or alkalinity of a solution. It is measured on a scale of 0 to 14. The pH value quantifies the degree of hydrogen ion activity of an acid or a base.

The internationally accepted symbol, pH, is derived from “p”, the mathematical symbol of the negative logarithm and “H”, the chemical symbol for Hydrogen. The pH value is the negative logarithm of Hydrogen ion activity as shown in the mathematical relationship pH= -log[H+].

The pH value of a substance is directly related to the ratio of the Hydrogen ion [H+] and the Hydroxyl ion [OH-] concentrations. If the concentration of H+ is greater than OH-, the material is acidic and has a pH value of less than 7. Conversely, if the concentration of OH- is greater than H+ the material is basic, with a pH value greater than 7. If the concentrations of H+ and OH- are equal the material is neutral with a pH value of 7.

It can, therefore, be seen that pH is a measurement of both acidity and alkalinity, even though by definition it is a selective measurement of hydrogen ion activity. The logarithmic relationship between hydrogen ion concentration and the pH unit means that a change of one pH unit represents a ten-fold change in hydrogen ion concentration.

3.2 pH Measurement

pH can be measured by using either pH papers/indicators or a pH meter, dependent on the level of accuracy required. pH papers or indicators change colour as the pH level varies. These can be used as a guide to the pH level, but can be limited in accuracy and difficult to interpret correctly in murky or coloured samples. For greater accuracy the use of a high impedance pH meter is recommended, together with a pH measuring electrode and reference electrode.

Each component part of the measurement system can be described as follows: a) the pH meter – is a high impedance amplifier used to accurately measure the minute electrode

voltages produced. The pH meter will display the results directly in pH units on either an analogue or digital display. Voltages can also be read for special applications, ORP (Oxidation-Reduction Potential) measurements or with Ion Selective Electrodes.

b) the pH electrode – is a hydrogen ion sensitive glass bulb, with a millivolt output that varies with the changes in the relative hydrogen ion concentration inside and outside of the bulb. The pH electrode has very high internal resistance, making the voltage change with pH difficult to measure. The input impedance of the pH meter and leakage resistances are therefore important factors.

c) the reference electrode – these cells consist of an internal element, usually a silver/silver chloride wire, electrolyte (KCl) and a liquid junction. The liquid junction provides a leak path for the internal electrolyte to “weep” into the sample chamber and provide an electrical contact with the liquid to be measured. If the liquid junction is inefficient then measurement will be inaccurate. It is common for the reference electrode to be incorporated into the pH electrode. It is then called a combination electrode. The Model 3520 is supplied with a combination electrode.

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The voltage developed by each individual pH electrode in the presence of a known hydrogen ion concentration is theoretically predictable, but in practise deviations from the theoretical value can be expected. These deviations will change slowly during the life of an electrode. It is therefore essential to routinely calibrate the system using solutions with a known and constant pH value. These solutions are called buffers.

3.3 Preparation of Buffer Solutions

Care must be taken in the preparation of all buffer solutions. The correct quantity of distilled or deionised water should be used when preparing the solutions. For accurate and repeatable results it is essential to follow the manufacturers instructions carefully.

3.4 Solution Temperature Values

The value of all buffer solutions varies with solution temperature. For accurate calibration of electrodes using buffer solutions, it is necessary to measure the temperature of the buffer solution being used. The unit should then be calibrated to the corrected pH value. Manufacturers of buffer powders and solutions will provide a table of values at varying temperatures for their buffers.

Note: Buffer solutions will contaminate with exposure to air and should be stored in airtight containers when not in use. Used solution should be discarded and not returned to the container as this will cause contamination. For best results fresh solutions should be prepared prior to calibration.

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3.5 Good Practice Guidelines

The types of electrodes are many and various. For the majority of tests carried out on aqueous solutions, with a reasonable ionic strength; at ambient temperatures and with limited use in strongly acidic or alkaline solutions, the standard glass or epoxy bodied combination electrode is ideal. For other applications a more suitable pH/reference electrode pair may be required; details or advice supplied on request.

The following general guidelines indicate the care and maintenance required for the three main groups of electrodes (Combination, Reference and pH). For more detailed advice on specific electrodes contact the electrode manufacturer.

1) After use Rinse thoroughly with deionised water

Short term storage Immerse in pH 4 buffer (all types) Long term storage Fit wetting cap filled with 3M KCl adjusted to pH 4.

2) Electrodes should be stored a) away from direct sunlight b) in a vertical position c) within their specified temperature range

3) Always ensure the electrode is used within its specified temperature range. Degradation of

electrodes used above their specified temperature is rapid and irreversible.

4) Ensure the level of fill solution is above the internal elements in the electrode and that this

level remains above the sample in use.

5) DO NOT touch the sensitive glass pH membrane or reference junction during use. Excess

droplets of solution may be removed by gently blotting with filter paper or tissue. DO NOT rub the electrode as this may induce an electrostatic charge.

6) Ensure no air bubbles are trapped at the bottom of the electrode. Removal of air bubbles is

possible by holding the electrode vertically and gently tapping the electrode body. Larger bubbles may be removed by shaking the electrode in a downward direction.

7) During use ensure the electrode is rinsed in deionised water between each measurement to

eliminate risk of contamination of solutions.

8) Ensure that the side port/inlet if present is uncovered, especially during a long run of tests.

9) For samples such as blood, serum or any measurements of Tris buffer solutions the junction

may become badly clogged. For these measurements it is recommended that the Tris buffer electrode is used (924 030).

10) For applications associated with the measurement of food extracts, it is recommended that

the Food electrode is used (924 051). This will reduce the risk of blockage from fat proteins, will be easy to clean and is perfect for measurements in agar media. This electrode is also recommended for measurements where deposits on the electrodes are likely. The flat surface is easy to clean and robust.

11) For low ionic strength applications the Environmental electrode (924 050) is recommended.

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