Hanna Instruments pH 210 User manual

Instruction Manual
pH 210 pH 211
pH 212 pH 213
Microprocessor-based
Bench pH/mV/°C Meters
Manufacturers since 1978 These Instruments are in
Compliance with the CE Directives
http://www.hannainst.com
HANNA LITERATUREHANNA LITERATURE
HANNA LITERATUREHANNA LITERATURE
HANNA LITERATURE
MANPH213R2 02/00
Hanna publishes a wide range of catalogs and
handbooks for an equally wide range of applications.
The reference literature currently covers areas such
as:
• Water Treatment
• Process
• Swimming Pools
• Agriculture
• Food
• Laboratory
• Thermometry
and many others. New reference material is constantly
being added to the library.
For these and other catalogs, handbooks and leaflets,
contact your dealer or the Hanna Customer Service
Center nearest to you. To find the Hanna Office in
your vicinity, check our home page at
www.hannainst.com.

2
Dear Customer,
Thank you for choosing a Hanna Product. Please read this instruction
manual carefully before using the instrument.
This manual will provide you with the necessary information for a
correct use of the instrument, as well as a precise idea of its versatil-
ity.
If you need more technical information, do not hesitate to e-mail us
at [email protected].
These instruments are in compliance with directives.
TABLE OF CONTENTSTABLE OF CONTENTS
TABLE OF CONTENTSTABLE OF CONTENTS
TABLE OF CONTENTS
PRELIMINARY EXAMINATION ...................................................... 3
GENERAL DESCRIPTION ............................................................. 3
FUNCTIONAL DESCRIPTION pH 210 AND pH 211 ....................... 4
SPECIFICATIONS pH 210 AND pH 211 ...................................... 5
FUNCTIONAL DESCRIPTION pH 212 AND pH 213 ....................... 6
SPECIFICATIONS pH 212 AND pH 213 ...................................... 7
OPERATIONAL GUIDE ................................................................ 8
pH CALIBRATION ................................................................... 11
TEMPERATURE CALIBRATION (pH 212 AND pH 213 ONLY) ........ 14
mV CALIBRATION (pH 213 ONLY) ........................................... 15
INTERFACE WITH PC (pH 212 AND pH 213 ONLY) .................... 16
pH VALUES AT VARIOUS TEMPERATURES ................................. 18
ELECTRODE CONDITIONING & MAINTENANCE ............................. 19
TEMPERATURE CORRELATION FOR pH SENSITIVE GLASS ..........22
TROUBLESHOOTING GUIDE ..................................................... 23
ACCESSORIES ......................................................................... 24
WARRANTY ............................................................................ 30
CE DECLARATION OF CONFORMITY ........................................... 31
31
CE DECLARATION OF CONFORMITY
Recommendations for Users
Before using this product, make sure that it is entirely suitable for the environment in which it is
used.
Operation of this instrument in residential areas could cause unacceptable interferences to radio and
TV equipment, requiring the operator to take all necessary steps to correct interferences.
The glass bulb at the end of the pH electrode is sensitive to electrostatic discharges. Avoid touching
this glass bulb at all times.
During operation, ESD wrist straps should be worn to avoid possible damage to the electrode by
electrostatic discharges.
Any variation introduced by the user to the supplied equipment may degrade the instrument's EMC
performance.
To avoid electrical shock, do not use this instrument when voltages at the measurement surface
exceed 24VAC or 60VDC.
To avoid damages or burns, do not perform any measurement in microwave ovens.

3
PRELIMINARY EXAMINATIONPRELIMINARY EXAMINATION
PRELIMINARY EXAMINATIONPRELIMINARY EXAMINATION
PRELIMINARY EXAMINATION
The Hanna pH 210, pH 211, pH 212 and pH 213 are micropro-
cessor-based bench meters for pH and temperature measurements.
pH 211 and pH 213 can also measure ion concentration (ISE) and
ORP (Oxidation Reduction Potential) in the mV range.
The pH measurements are compensated for temperature effect manu-
ally or automatically with the HI 7669/2W temperature probe.
The meter comes equipped with a large easy-to-read LCD which shows
the pH (or mV) and temperature simultaneously together with graphic
symbols.
The calibration process is guided step by step through clear indications
on the LCD. A stability indicator make the calibration procedure error-
free.
Through the RS 232C serial port you can transfer the data to a PC
(pH 212 and pH 213 only).
GENERAL DESCRIPTIONGENERAL DESCRIPTION
GENERAL DESCRIPTIONGENERAL DESCRIPTION
GENERAL DESCRIPTION
Remove the instrument from the packing material and examine it
carefully to make sure that no damage has occurred during shipping.
If there is any damage, notify your Dealer or the nearest Hanna
Custumer Service Center.
Each meter comes supplied complete with:
•HI 1131B glass-body combination pH Electrode with 1 m
(3.3') cable
•HI 7669/2W Temperature Probe
•HI 76404 Electrode Holder
• pH 4.01 & 7.01 Buffer Solutions (20mL each)
•HI 7071S Electrolyte Solution
• 12VDC Power Adapter
• Instruction Manual
Note: Save all packing material until you are sure that the
instrument functions correctly. All defective item must be
returned in the original packing with the supplied accessories.
30
WARRANTYWARRANTY
WARRANTYWARRANTY
WARRANTY
All Hanna Instruments meters are guaranteed for two years against
defects in workmanship and materials when used for their intended
purpose and maintained according to instructions. The electrodes
and the probes are guaranteed for a period of six months. This
warranty is limited to repair or replacement free of charge.
Damage due to accident, misuse, tampering or lack of prescribed
maintenance are not covered.
If service is required, contact the dealer from whom you purchased the
instrument. If under warranty, report the model number, date of
purchase, serial number and the nature of the failure. If the repair is
not covered by the warranty, you will be notified of the charges
incurred. If the instrument is to be returned to Hanna Instruments, first
obtain a Returned Goods Authorization number from the Customer
Service department and then send it with shipping costs prepaid.
When shipping any instrument, make sure it is properly packaged for
complete protection.
To validate your warranty, fill out and return the enclosed warranty
card within 14 days from the date of purchase.
All rights are reserved. Reproduction in whole or in part is prohibited
without the written consent of the copyright owner,
Hanna Instruments Inc., 584 Park East Drive, Woonsocket, Rhode
Island, 02895 , USA.
Hanna Instruments reserves the right to modify the design, con-
struction and appearance of its products without advance notice.

4
FUNCTIONAL DESCRIPTIONFUNCTIONAL DESCRIPTION
FUNCTIONAL DESCRIPTIONFUNCTIONAL DESCRIPTION
FUNCTIONAL DESCRIPTION
pp
pp
pHH
HH
H 210 AND210 AND
210 AND210 AND
210 AND pp
pp
pHH
HH
H 211211
211211
211
1) Liquid Crystal Display (LCD)
2) CFM key, to confirm calibration values
3) CAL key, to enter or exit calibration mode
4) WC key, to manually decrease temperature or select pH buffer
5) VC key, to manually increase temperature or select pH buffer
6) MR key, to recall the stored value
7) MEM key, to store a value in memory
8) RANGE key, to select measurement range (pH 211 only)
9) ON/OFF switch
10) Power adapter socket
11) BNC electrode connector
12) Electrode reference socket
13) Temperature probe socket
14) RESET button
29
Extension cables for screw-type electrodes (screw to BNC
adapter)
HI 7855/1 Extension cable 1m (3.3') long
HI 7855/3 Extension cable 3m (9.9') long
OO
OO
OTHER ACCESSORIESTHER ACCESSORIES
THER ACCESSORIESTHER ACCESSORIES
THER ACCESSORIES
HI 710005 Voltage adapter from 115 VAC to 12 VDC (USA plug)
HI 710006 Voltage adapter from 230 VAC to 12 VDC (European
plug)
HI 710012 Voltage adapter from 240 VAC to 12 VDC (UK plug)
HI 710013 Voltage adapter from 230 VAC to 12 VDC (South
Africa plug)
HI 710014 Voltage adapter from 230 VAC to 12 VDC (Australia
plug)
ChecktempC Pocket-size thermometer (range -50.0 to 150.0C)
HI 76405 Electrode holder
HI 8427 pH and ORP electrode simulator with 1 m (3.3')
coaxial cable ending in female BNC connectors
HI 931001 pH and ORP electrode simulator with LCD and 1 m
(3.3') coaxial cable ending in female BNC connectors
HI 7669/2W Temp. probe with 1 m (3.3') cable
HI 92000 Windows®compatible software
HI 920010 9 to 9-pin RS232 cable
CONNECT TO
SCREW TYPE
ELECTRODES
CONNECT TO THE
BNC SOCKET
OF THE METER
HI 7855 SERIES CABLE CONNECTORS
CONNECTOR AND 3.0 mm (0.12") CABLE WITH BNC
Windows®is registered Trademark of "Microsoft Co."

5
SPECIFICATIONSSPECIFICATIONS
SPECIFICATIONSSPECIFICATIONS
SPECIFICATIONS
pp
pp
pH 210 ANDH 210 AND
H 210 ANDH 210 AND
H 210 AND pp
pp
pH 211H 211
H 211H 211
H 211
Range pH 0.00 to 14.00
mV ±399.9 (ISE, pH 211 only)
mV ±1999 (ORP, pH 211 only)
°C 0.0 to 100.0
Resolution pH 0.01
mV 0.1 (ISE, pH 211 only)
mV 1 (ORP, pH 211 only)
°C 0.1
Accuracy pH ±0.01
(@20°C/68°F) mV ±0.2 mV (ISE, pH 211 only)
mV ±1mV (ORP, pH 211 only)
°C ±0.5
Typical EMC pH ±0.03
Deviation mV ±2 mV (pH 211 only)
°C ±0.3
pH Calibration Automatic 1 or 2 points with 5 memorized buffers
(4.01, 6.86, 7.01, 9.18, 10.01)
Temperature Automatic or manual
Compensation from 0 to 100C (32 to 212F)
Electrode HI 1131B glass-body combination
refillable pH electrode (included)
Temperature probe HI 7669/2W (included)
Input impedance 1012 Ω
Power supply 12 VDC adapter (included)
Environment 0 to 50C (32 to 122F)
max. 95% RH non-condensing
Dimensions 240x182x74 mm (9.4x7.1x2.9")
Weight 1.1 kg (2.5 lb.); kit with holder: 2.5 kg (5.5 lb.)
28
Kynar®is registered Trademark of "Pennwalt Corp."
Ultem®is registered Trademark of "General Electrics Co."
HI 1413B
Glass-body, single junction, flat tip, Viscolene, non-refillable, combina-
tion pH electrode. Use: surface measurement.
ORP ELECTRODES
HI 3131B
Glass-body, refillable, combination platinum ORP electrode.
Use: titration.
HI 3230B
Plastic-body (Ultem®), gel-filled, combination platinum ORP elec-
trode. Use: general purpose.
HI 4430B
Plastic-body (Ultem®), gel-filled, combination gold ORP electrode.
Use: general purpose.
Consult the Hanna General Catalog for more electrodes with screw-
type or BNC connectors.
110 mm
4.3"
12 mm
0.5"
HI 1413
150 mm
5.9"
12 mm
0.5"
"S" VERSION
HI 3131
120 mm
4.7"
12 mm
0.5"
HI 3230
"S" VERSION
120 mm
4.7"
12 mm
0.5"
HI 4430
"S" VERSION

6
FUNCTIONAL DESCRIPTIONFUNCTIONAL DESCRIPTION
FUNCTIONAL DESCRIPTIONFUNCTIONAL DESCRIPTION
FUNCTIONAL DESCRIPTION
pp
pp
pHH
HH
H 212 AND212 AND
212 AND212 AND
212 AND pp
pp
pHH
HH
H 213213
213213
213
1) Liquid Crystal Display (LCD)
2) CFM key, to confirm calibration values
3) CAL key, to enter or exit calibration mode
4) WC key, to manually decrease temperature or select pH buffer
5) VC key, to manually increase temperature or select pH buffer
6) MR key, to recall the stored value
7) MEM key, to store a value in memory
8) COMM key, to set baud rate
9) RANGE key, to select measurement range
10) ON/OFF switch
11) Power adapter socket
12) BNC electrode connector
13) Electrode reference socket
14) Temperature probe socket
15) RESET button
16) RS232C socket
27
FC 100B
Plastic-body (Kynar®), double junction, refillable, combination pH
electrode. Use: general purpose for food industry.
FC 200B
Plastic-body (Kynar®), open junction, conic, Viscolene, non-refillable,
combination pH electrode. Use: meat & cheese.
FC 210B
Glass-body, double junction, conic, Viscolene, non-refillable, combina-
tion pH electrode. Use: milk, yogurt.
FC 220B
Glass-body, triple-ceramic, single junction, refillable, combination pH
electrode. Use: food processing.
FC 911B
Plastic-body (Kynar®), double junction, refillable with built-in ampli-
fier, combination pH electrode. Use: very high humidity.
120 mm
4.7"
12 mm
0.5"
FC 100
75 mm
2.95"
6 mm
0.25"
FC 200
120 mm
4.7"
12 mm
0.5"
FC 210
120 mm
4.7"
12 mm
0.5"
9.5mm DIA
0.37"
FC 220
110 mm
4.3"
12 mm
0.5"
FC 911

7
Range pH -2.00 to 16.00 / -2.000 to 16.000
mV ±999.9 (ISE and ORP, pH 213 only)
°C 0.0 to 100.0
Resolution pH 0.01 / 0.001
mV 0.1 (ISE and ORP, pH 213 only)
°C 0.1
Accuracy pH ±0.002 & ±0.01
(@20°C/68°F) mV ±0.05% f.s. (ISE and ORP, pH 213 only)
°C ±0.5
Typical EMC pH ±0.01
Deviation mV ±0.6 (pH 213 only)
°C ±0.5
pH Calibration Automatic 1 or 2 points with 5 memorized buffers
(4.01, 6.86, 7.01, 9.18, 10.01)
Temperature From 0 to 100C (32 to 212F) manual or
Compensation automatic with HI 7669/2W probe (included)
Electrode HI 1131B glass-body combination
refillable pH electrode (included)
Temperature probe HI 7669/2W (included)
Input impedance 1012 Ω
Computer Interface Opto-isolated RS232C
Power supply 12 VDC adapter (included)
Environment 0 to 50C (32 to 122F)
max. 95% RH non-condensing
Dimensions 240x182x74 mm (9.4x7.1x2.9")
Weight 1.1 kg (2.5 lb.); kit with holder: 3.0 kg (6.5 lb.)
SPECIFICATIONSSPECIFICATIONS
SPECIFICATIONSSPECIFICATIONS
SPECIFICATIONS
pp
pp
pHH
HH
H 212 AND212 AND
212 AND212 AND
212 AND pp
pp
pHH
HH
H 213213
213213
213
26
HI 1330B
Glass-body, semimicro, single junction, refillable, combination pH
electrode. Use: laboratory, vials.
HI 1331B
Glass-body, semimicro, single junction, refillable, combination pH
electrode. Use: flasks.
HI 1230B
Plastic-body (Ultem®), double junction, gel-filled, combination pH
electrode. Use: general, field.
HI 2031B
Glass-body, semimicro, conic, refillable, combination pH electrode.
Use: semisolid products.
HI 1332B
Plastic-body (Ultem®), double junction, refillable, combination pH
electrode. Use: general purpose.
120 mm
4.7"
5mm
0.2"
5mm DIA
0.2"
"S" VERSION
HI 1330
120 mm
4.7"
12 mm
0.5"
"
S
"
VERSION
HI 1230
75 mm
2.
95
"
6 mm
0.25"
"
S
"
VERSION
HI 2031
120 mm
4.7"
12 mm
0.5"
"S" VERSION
HI 1332
210 mm
8.25"
8 mm
0.3" 7.5mm DIA
0.29"
"S" VERSION
HI 1331

8
OPERATIONAL GUIDEOPERATIONAL GUIDE
OPERATIONAL GUIDEOPERATIONAL GUIDE
OPERATIONAL GUIDE
Power connection
Plug the 12VDC adapter into the power supply socket (#10 on page
4; #11 on page 6).
Note: pH 212 and pH 213 use an EEPROM to retain the pH, mV
and temperature calibrations as well as the serial communica-
tion setting. The instrument will retain the data after a
calibration or serial communication setting, even when it is
unplugged.
Note:Note:
Note:Note:
Note: Make sure the main line is protected by a fuse.
Electrode and Probe connections
For combination pH or ORP electrodes (with internal reference)
connect the electrode's BNC to the socket on the back of the meter
(#11 on page 4; #12 on page 6).
For electrodes with a separate reference, connect the single cell
electrode's BNC to the BNC socket (#11 on page 4; #12 on page 6)
and the reference electrode plug to the reference socket (#12 on
page 4; #13 on page 6).
For temperature measurements and automatic temperature compen-
sation connect the temperature probe to the appropriate socket
(#13 on page 4; #14 on page 6).
Note: to prevent damage to the electrode, remove the pH electrode
from the solution before turning the meter off.
If the meter is OFF, detach the electrode from the meter before
immersing the electrode in the storage solution.
pH MEASUREMENTS
Make sure that the instrument has been calibrated before taking pH
measurements.
• Switch the instrument on by pressing the ON/OFF
switch.The meter automatically defaults to the pH mea-
surement mode.
• Submerge the tip (4cm/1½") of the elec-
trode and the temperature probe into the
sample to be tested. Allow time for the
electrode to stabilize.
4 cm
(1½")
25
ORP PRETREATMENT SOLUTIONS
HI 7091L Reducing Pretreatment Solution, 460 mL
HI 7092L Oxidizing Pretreatment Solution, 460 mL
pH ELECTRODES
All electrodes part numbers ending in B are supplied with a BNC
connector and 1 m (3.3') cable, as shown below :
HI 1043B
Glass-body, double junction, refillable, combination pH electrode. Use:
strong acid/alkali.
HI 1053B
Glass-body, triple ceramic, conic shape, refillable, combination pH
electrode. Use: emulsions.
HI 1083B
Glass-body, micro, Viscolene, non-refillable, combination pH electrode.
Use: biotechnology, micro titration.
HI 1131B
Glass-body, single junction, refillable, combination pH electrode.
Use: general purpose.
120 mm
4.7"
12 mm
0.5"
9.5mm DIA
0.37"
"S" VERSION
HI 1043
120 mm
4.7"
12 mm
0.5"
"S" VERSION
HI 1053
120 mm
4.7
"
12 mm
0.5" 5 mm
0.2" 3 mm
0.12" 3.0 mm DIA
0.12"
HI 1083
120 mm
4.7"
12 mm
0.5"
9.5mm DIA
0.37"
"S" VERSION
HI 1131

9
• pH is displayed on the primary display and temperature on the
secondary one.
• With pH 211 and pH 213 it is also possible to view the mV
reading by pressing the "RANGE" key.
If measurements are taken successively in different samples, it is
recommended to rinse the electrode thoroughly with deionized water
or, if not available, tap water first and then with some of the next
sample to condition the electrode before immersing it in the sample.
The pH reading is affected by temperature. In order for the meter to
measure the pH accurately, temperature must be taken into consid-
eration. To use the Automatic Temperature Compensation feature,
connect and submerge the HI 7669/2W temperature probe into the
sample as close to the electrode as possible and wait for a couple of
minutes.
If the temperature of the sample is known or tests are always
performed at the same temperature you can simply manually
compensate for it. For this purpose the temperature
probe must be disconnected.
The display will then show the default temperature
of 25C or the last recorded temperature reading
with the "C" symbol blinking.
Note the temperature of the sample using a
ChecktempC or an accurate reference thermometer.
The temperature can now be adjusted with the VC and WC keys.
24
ACCESSORIESACCESSORIES
ACCESSORIESACCESSORIES
ACCESSORIES
pH CALIBRATION SOLUTIONS
HI 70004P pH 4.01 Buffer Sachets, 20mL, 25 pcs
HI 70007P pH 7.01 Buffer Sachets, 20mL, 25 pcs
HI 70010P pH 10.01 Buffer Sachets, 20mL, 25 pcs
HI 7004L pH 4.01 Buffer Solution, 460 mL
HI 7006L pH 6.86 Buffer Solution, 460 mL
HI 7007L pH 7.01 Buffer Solution, 460 mL
HI 7009L pH 9.18 Buffer Solution, 460 mL
HI 7010L pH 10.01 Buffer Sol., 460 mL
HI 8004L pH 4.01 Buffer Solution in FDA approved bottle, 460 mL
HI 8006L pH 6.86 Buffer Solution in FDA approved bottle, 460 mL
HI 8007L pH 7.01 Buffer Solution in FDA approved bottle, 460 mL
HI 8009L pH 9.18 Buffer Solution in FDA approved bottle, 460 mL
HI 8010L pH 10.01 Buffer Solution in FDA approved bottle, 460 mL
ELECTRODE STORAGE SOLUTIONS
HI 70300L Storage Solution, 460 mL
HI 80300L Storage Solution in FDA approved bottle, 460 mL
ELECTRODE CLEANING SOLUTIONS
HI 70000P Electrode Rinse Sachets, 20 mL, 25 pcs
HI 7061L General Cleaning Sol., 460 mL
HI 7073L Protein Cleaning Sol., 460mL
HI 7074L Inorganic Cleaning Sol., 460mL
HI 7077L Oil & Fat Cleaning Sol.,460 mL
HI 8061L General Cleaning Solution in FDA approved bottle, 460 mL
HI 8073L Protein Cleaning Solution in FDA approved bottle, 230 mL
HI 8077L Oil & Fat Cleaning Solution in FDA approved bottle,460mL
REFILL ELECTROLYTE SOLUTIONS
HI 7071 3.5M KCl + AgCl Electrolyte, 4x50mL, for single junc-
tion electrodes
HI 7072 1M KNO3Electrolyte, 4x50 mL
HI 7082 3.5M KCl Electrolyte, 4x50 mL, for double junction elec-
trodes
HI 8071 3.5M KCl + AgCl Electrolyte in FDA approved bottle,
4x50mL, for single junction electrodes
HI 8072 1M KNO3Electrolyte in FDA approved bottle, 4x50 mL
HI 8082 3.5M KCl Electrolyte in FDA approved bottle, 4x50 mL, for
double junction electrodes

10
ORP MEASUREMENTS (pH211 and pH213 only)
An optional ORP electrode must be used to perform ORP measurements
(see accessories).
Oxidation-reduction potential (REDOX) measurements provide the quan-
tification of the oxidizing or reducing power of the sample tested.
To correctly perform a redox measurement, the surface of the ORP
electrode must be clean and smooth.
• Switch the meter on and press the "RANGE" key to
enter the mV mode.
• Submerge the ORP electrode tip (4cm/1½") into
the sample. Allow a few minutes for the reading
to stabilize.
• The meter displays the mV reading on the primary display.
• If readings are out of range, "---" will appear on the LCD.
TAKING TEMPERATURE MEASUREMENTS
Taking a temperature measurement is very easy.
Connect the HI 7669/2W temperature probe and
turn the instrument on. Dip the temperature probe
in the sample and allow the reading on the second-
ary display to stabilize.
HOLD FUNCTION
Press and hold MEM. The last reading will be frozen on the display
until MEM is released. During this operation, the MEM indicator is also
shown on the LCD.
Press MR and the previously memorized reading will be
displayed with the MEM indicator on the LCD.
4 cm
(1½")
23
TROUBLESHOOTING GUIDETROUBLESHOOTING GUIDE
TROUBLESHOOTING GUIDETROUBLESHOOTING GUIDE
TROUBLESHOOTING GUIDE
Symptoms Problem Solution
The meter is slow in
responding or gives
faulty readings
The meter does not ac-
cept the 2nd buffer
solution for calibration
The reading drifts
Display shows:
Display shows:
Display shows:
Display shows:
"WRONG 1 "
and
"WRONG "
Display shows:
"WRONG 2
"
and
"WRONG "
The meter does not
work with the tempera-
ture probe
The meter fails to cali-
brate or gives faulty
readings
The electrode is not work-
ing or the reference
junction is clogged
Out of order pH electrode
Defective pH electrode
Out of range pH scale
Out of range tempera-
ture scale
Out of range mV scale
Erroneous buffer solution
used for offset calibra-
tion
Defective electrode
Erroneous buffer solution
used for slope calibration
Defective electrode
Out of order temperature
probe
Out of order pH electrode
Leave the electrode in a stor-
age solution after cleaning
the junction. If problem per-
sists, replace the electrode
Follow the cleaning proce-
dure. If this doesn't work
replace the electrode
Replace the electrode
a) Recalibrate
b) Make sure the pH sample
is in the specified range
c) Check the electrolyte level
and the general state of
the pH electrode
Make sure the temperature
is in the 0 to 100C range
and the temperature probe is
plugged in
Electrode not connected
Make sure the buffer setting
is correct and the solution is
fresh. Replace the buffer if
necessary
Replace the electrode
Make sure the buffer setting
is correct and the solution is
fresh. Replace the buffer if
necessary
Replace the electrode
Replace the probe
Replace the electrode