Omega PHB21 User manual

PHB21
Portable pH/mV Meter

Instruction Manual
Portable pHmeter
PHB21
Index
Specifications...............................................................2
PHMeasurement.............................................................3
MVMeasurement............................................................7
PartsDescription .............................................................8
EquipmentOperation.........................................................9
EquipmentOperationpH-SetUp...............................................12
EquipmentOperationpH-Calibrate ............................................14
EquipmentOperationpH-Read ...............................................15
EquipmentOperationpH-Check ..............................................16
EquipmentOperationpH-Register .............................................17
EquipmentOperationmV-SetUp..............................................19
EquipmentOperationmV-Calibrate............................................21
EquipmentOperationmV-Read...............................................22
EquipmentOperationmV-Check..............................................23
EquipmentOperationmV-Register.............................................24
EquipmentOperationºC-SetUp...............................................26
EquipmentOperationºC-Read ...............................................29
EquipmentOperationTurningOff...............................................30
ElectrodeTypepH...........................................................31
Maintenance ..............................................................32
CommunicationCables......................................................34

2. Specifications
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pH / ORP / Temperature
Automatic Resolution Selection
Electrode automatic Check
Continuous or Hold Readings
Non-Volatile Memory, even when turned off
sustains the set up programmed
Automatic Calibration for all parameters
Manual or Automatic Temperature
Compensation
Maximum and Minimum Sound Alarm
Recognizes Buffer
Battery Charge Automatic Monitored
99 points Datalogging
110/220Vac Capability (AC Adapter)
Supplied with Glass Electrode, Buffers and
Carrying Case
Simple 3 keys operation
pH
Range -2,00 to 20,00 pH
Resolution 0.1 / 0.01 pH
Relative Precision 0.01 % (full scale)
mV
Range ± 1999 mV
Resolution 1 mV
Relative Precision 0.05 % (full scale)
Temperature
Range 20 to 120 ºC
Resolution 0.1 ºC
Relative Precision 0.08% (full scale)
General
Input Impedance 1013 Ù
Isopotential Adjust ± 50%
Sensibility Adjust 80 to 120 %
Temp. Compens. Auto / Manual -20 to 120 ºC
Display Alphanumeric 2 lines x 16 characters
Datalogging Up to 99 Readings
Alarms maximum and minimum
Dimensions L x H x D (mm) 100x75x180
Weight 0.45 kg
Enclosure IP-67
Power 9Vcc Battery
Battery Life 60 hours
Accessories
Glass pH Combined Electrode PHE-21R
Buffer Solutions 4.01 pH and 7.00 pH
Alkaline Battery 9 V
Instruction Manual CD
Optional
Thermocompensator PHE-22R
Redox Electrode ORE-22R
Depth Probe PHE-221
AC Adapter CDH-30PW (110/220Vac 50/60Hz)
2

++ -
MA M A
+
K = aM * aA- / aMA (EQ-1)
+ + -
HCl H Cl
+ + -
CH COOH H CH COO
33
NaOH Na OH
+ + -
+ + -
NH OH NH OH
44
+ + -
HOH H OH
3. PH Measurement
3
Stable chemical compounds, are electrically neutral when mixed with water.
In order to form a water solution, dismember in positive or negative charged particles.
These charged particles are called "i ”. When we apply differential potential in two electrodes immersed in a
++
solution, it is possible to verify that positive ions (H , Na and more) will migrate to the negative terminal, that is
--
why we call them cations. The reverse happens with negative ions (OH , Cl and more) that will migrate to the
“ “
positive terminal and we call them anions. The ions freedom to migrate thru a solution is measured with
the solution ". Chemical compounds that produce conductive solutions are called
" ". Those that totally dissociate (strong acids, strong bases and salt) are called "
".
The others whose dissociation is not big (acids and weak bases) are called " ". For an
hypotetical chemical compound "MA" that dissociates in cations and anions , the reaction can be written as:
ons
“Electrical Conductivity
lectrolytes Strong
Electrolytes
Weak Electrolytes
E
+-
MA
+and -
The arrow indicates that exists a balance between MAnot dissociated and the ions M andA dissociated.
The extension that this reaction moves to the right or left, varies from one compound to the other and with the solution
Temperature.
For a specific temperature, there is a relation between the ions activity and the non dissociated molecules, that can vary
between 0 up to 100%. This relation is called K Dissociation and it is expressed by the equation:
Where: K =
aM+ =
aA- =
aMA =
"K" .
CTE dissociation.
ions activity M+.
ions activityA-.
dissociated molecules activity MA.
For Chloridric acid, the is practically infinity, caused by the complete dissociation for ions and So it is a strong acid:
+-
HCl
On the other hand,Acetic acid has a low . Reacts as the following way:"K"
Few hydrogen ions result at the solution, so the acetic acid is an weak acid when the most present ion is the OH-, the
solution is alkaline.
The sodium hydroxide is totally dissociated, this is the reason for being a On the other hand theAmmonia
Hydroxide do not dissociate too much, this the reason for being a .
STRONG BASE.
WEAK BASE(NH OH)
4
As we can see, for both acids and bases the strength of a solution depends on the H+ or OH- ion numbers available that
depends not only on the compound concentration at the water, but also on the " " Pure water dissociates for
Ions H+ and OH-, but it is very weak.
K dissociation.
The water molecules number dissociated is low, in comparison with the non dissociated, so we can consider as an
activity of HOH equal to 100%.

600 -
-100 -
500 -
-200 -
0
400 -
-300 -
300 -
-400 -
200 -
-500 -
100 -
-600 -
3. PH Measurement (cont.)
4
At 25°C the of water has a value of 10 where we can take that is the activity product (aH+) by
(aOH-) is equal to ion OH-, the solution is neutral and activities of H+ and OH- must be both of 10 mols / L.
If a strong acid, such as HCl, is added to water, many ions H+ are added; this should reduce the number of ions OH-. For
example: if added HCl until the OH+ activity turns 10-2 the OH- activity must turn 10-12. The hydrogen potential scale is
Established by a definition merely operational, the acid degree or activity of ions H+ will be expressed by therm "pH”
(Hydrogenionic potential).
The pH will be defined as:
"K" dissociation (EQ-1)
pH=-log |aH+|
If the activities of ion H+ is 10-x so pH is "x".For example, at pure water @ 25°C, the hydrogen ion activity is 10-7, so the pH
Is 7 @ 25°C.An acid solution has more ions H+ then OH-.So the ions H+ activities will be bigger than 10-7, being, 10-6, 10-5
and more. The pHof an acid solution by definition, must be lower than 7, will be 6, 5, 4...
If the OH- number exceed the number of ions H+ the H+ activity must be lower than 10-7, being, 10-8, 10-9 and more... The
pHwill be bigger then 7, will be 8, 9, 10...
To avoid solution ionic concentration modification being measured it is necessary that the current that goes thru the circuitry
composed by the galvanic cell (pH electrode) be minimum (I < 1pA), such as the voltage drop caused by the internal
resistance of the same electrochemistry cell being null, not to cause measuring errors. Such condition restrict the choice to
Choose the instrument to a "HIGH IMPEDANCE VOLTMETER”. The instrument will have a scale graduated in pH,
calibrated by glass electrode and a reference electrode based on the relation between the pH and the electromagnetic force
Of the cell.
Above equation, define the equation of a line, whose decline is and whose origin ordenate is . The electrode must
have a zero volts point (isopotential), that can be achieve performing a correspondence to 7 to zero volts, to any
temperature, using a internal BUFFER at the glass electrode, whose pH variation with the temperature compensates to the
temperature variation at the electrode.
The approximate decline of the line mV / pH involves the factor adjustment of factor KT @ 59.16 mV decade of pH, @ 25°C
by controlling the equipment “ that does the decline around the isopotential. The temperature compensator is
applied to correct the decline based on real sample temperature, varying the definition of the instrument, relating to a
1pHunit, from54.20 mV @ 0°C up to 66.10 mV @ 60°C.
-KT E
SENSIBILITY"
E = E0 - KT (pH)

3. PH Measurement (cont.)
Electrode Description
Electrode Usage Instruction
5
1 - - rugged construction, in order to avoid ease breakage.
2 - - chemically inert.
3 - .
4 - - ease operation for electrolyte solution filling.
5 - - assuring stable readings..
6 - - chemically aggressively resistant.
7 - - avoid contamination with solutions that contain Silver, Mercury, Sulfite, etc.
Avoid AgCl preciptations. Provides quick readings on temperature variations.
8 - - contains reference electrolyte solution for transportation or storage.
9 - (on refillable electrodes only).
10 -
pH sensing Bulb
Glass Body
Punctual Ceramic
Seal
Low Noise Cable
Polypropylene Cap
Ionic Barrier
Transportation Cap
Electrolyte Fill Hole
Argental Reference.
1 - Before using the electrode, verify it’s body for possible mechanical defects or cracks
and in case it occur, replace it immediately.
2 - Take off the transportation cap and rinse the electrode with distilled water, remove
eventual crystallization at the diaphragm (3). The transportation cap must always be
used when transporting the electrode, avoiding dehydration of the bulb (1).
3 - Remove the seal (4) in order to establish Atmospheric Pressure (only applicable for
refillable electrodes) and close it again.
4 - Eliminate possible air bubbles that may occur internally at the bulb (1), by shacking
the electrode vertically.
5 - On Refillable electrodes, the electrolyte level must be at a maximum of 10 mm
below the hole (9).
6 - Always refill, when necessary, the electrolyte level with 3 MKCl thru the hole (9). On
Bridge Electrolytic Electrodes, with the proper bridge (see table 1) thru the hole (9).
7 - When the Electrode is not in use, always immerse into electrolyte reference.
8 - To measure, just immerse the electrode into the sample, covering the diaphragm (3).
9 - Switching from one solution to other, always wash electrode with distilled water.
BULB (1)
DIAPHRAGM
(3)
REFILL HOLE
(9)
SEAL
(4)
TRANSPORT CAP (8)

3.
These are solutions that resist the ph variations, by effect of adding acids or bases and/or by dilution, all happening like if they
had an acid reserve and/or alkaline. Selected solutions are used as standard for calibration of ph meters based on operational
definition. They are fixed points that define the pH scale. Composed, usually, by a weak acid mixed with its own strong base salt.
The KCl is a neutral salt, so does not interfere at the pH value. It can be used to raise the conductivity at the sample, in case we
Are measuring a weak electrolyte.
Supplied in 475ml Bottles (other volumes upon request)
OMEGA offers the following Buffer Solutions:
PHA-4 4.01pH
PHA-7 7.00pH
PHA-10 10.01pH
6
PH Measurement (cont.)
Buffer Soutions

7
4. MV Measurement
In order to measure potential redox it is used metallic electrodes, generally Platinum or Silver. This type of
electrode refers to chemical reactions in solutions that operate only by electrons transference. Such reactions
occur with composed elements presenting two or more oxidizing stages. Ex.: Fe2+ / Fe3+. The redox
measurement applications in a determined process, complies with previous knowledge of certain factors:
presence of infectants capable of competing with the main redox reaction, approximate values of the ions activity
coefficients entering the final equation of the potential differential, approximate speed of the reaction to be
controlled, necessary or not to control the pH.At Oxide reduction systems where the ions H+ take part at the
reaction, the redox potential depends on the pH. In order to obtain a complete description of such systems it is
necessary to indicate, besides the reference electrode, the pH value. The temperature has two effects over the
redox potential. First it enters as a factor over the logarithem of equation. This means that a determined
reason of the ionic activity, the electrode will develop a different potential. Second, the temperature influence the
Ionic activity on each ion of the solution.
NERNST
Oxide Redox Potential Measurement

5. Parts Description
4
8
6
7
5
3
1
2
1 -Display:Alphanumeric 2 Lines x 16 characters
2 -Membrane Keyboard
3 - Battery Lid cover
4 - Serial Output RS-232
5 - Protection lids for field protection usage
6 -AC Adapter output
7 - BNC Connector: pH Electrode Inlet
8 -BNC Connector: Thermocompensator Inlet
Items Description
8