Milwaukee Instruments MA916B-3, MA917B-1, MA916B-1, MA918B-1 User Manual
pH electrodes are constructed from a special composition
glass which senses the hydrogen ion concentration. This
glass is typically composed of alkali metal ions. The alkali
metal ions of the glass and the hydrogen ions in solution
undergo an ion exchange reaction, generating a potential
difference. In a combination pH electrode, the most widely
used variety, there are actually two electrodes in one body.
One portion is called the measuring electrode, the other the
reference electrode. The potential generated at the junction
site of the measuring portion is due to the free hydrogen
ions present in solution.
The potential of the reference portion is produced by the
internal element in contact with the reference fill solution.
This potential is always constant. In summary, the measuring electrode delivers a varying voltage and the reference
electrode delivers a constant voltage to the meter. The voltage signal produced by the pH electrode is a very small,
high impedance signal. The input impedance requires that it
be interfaced only with equipment with high impedance circuits.
pH Electrode
basics
pH Electrodes
6
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Milwaukee has a wide assortment of pH and ORP electrodes to meet all your specific requirements. Finding
the right electrode for a specific application is a very
important task and in order to solve this selection problem it is important to consider the following:
• Glass body electrode versus Epoxy (plastic)
body electrode: Glass body electrodes stand
higher temperatures (typically 100°C against 80°C
for plastic) and are more resistant to corrosive
chemicals and solvents. They are easier to clean
and are available in different shapes depending on
the application. On the other hand plastic body
electrodes are more rugged and the glass bulb is
better protected.
• Gel filled electrodes versus refillable electrodes:
refillable electrodes last longer since electrolyte
can be changed for repeated usage. The
response is faster due to a greater outflow of electrolyte into the sample and therefore less likely to
clog. Gel filled electrodes require less maintenance and resist to higher pressure.
• Double reference junction versus Single junction reference: Double junction reference elec-
trodes have a longer live and protects the sample
measured from silver contamination from the electrolyte. The Silver wire is more protected and
therefore gets less contaminated. The single junction electrodes normally costs less and are ideal
for general purpose applications
• Conic shaped versus Sphere shaped: The
conic-shaped electrode is easier to clean and to
maintain (ideal for applications such as dairy). Has
a more rugged tip and therefore ideal for penetration. The sphere-shaped has a faster response
time due to the larger surface area on the bulb.
Model
MA919B/1 MA924B/1
Measuring Range 0 to 13 pH ±2000 mV
Temperature Range -5 to 80 °C -5 to 80 °C
Shaft material glass glass
Reference Electrolyte KCL 3.5M KCL 3.5M
Reference Type double Ag/AgCl double Ag/AgCl
Reference Junction open open
Shape of membrane spheric Platinum ring
Max. Pressure 0,1 bar 0,1 bar
Connector type BNC BNC
Cable length coaxial 1 meter coaxial 1 meter
Shaft length 120 mm 120 mm
Diameter 8 mm 8 mm
Application food laboratory food laboratory
8 mm
M
A
9
2
4
B
/1 =1 m
M
A
9
1
9
B
/1 =1 m
8 mm
120 mm
120 mm
The pH electrode, due to the nature of its construction,
needs to be kept moist at all times. In order to operate properly, glass needs to be hydrated. Hydration is required for
the ion exchange process to occur. If an electrode should
become dry, it is best to place it in some tap water for a half
hour to condition the glass.
pH electrodes are like batteries; they run down with time and
use. As an electrode ages, its glass changes resistance.
This resistance change alters the electrode potential. For
this reason, electrodes need to be calibrated on a regular
basis. Calibration in pH buffer solution corrects for this
change. Calibration of any pH equipment should always
begin with buffer 7.0 as this is the "zero point." The pH scale
has an equivalent mV scale. The mV scale ranges from
+420 to -420 mV. At a pH of 7.0 the mV value is 0. Each pH
change corresponds to a change of approx. ±60 mV. As pH
values become more acidic the mV values become greater.
pH electrodes have junctions which allow the internal electrolyte solution of the measuring electrode to leak out into
the solution being measured.
pH Electrode
basics
pH Electrodes
7
www.milwaukeeinst.com
Model MA916B/1 - MA916B/3 MA917B/1 MA918B/1
Measuring Range 0 to 13 pH 0 to 14 pH 0 to 12 pH
Temperature Range -5 to 100°C (23 to 212°F) 0 to 100°C (32 to 212°F) -5 to 100°C (23 to 212°F)
Shaft Material glass glass glass
Reference Electrolyte KCl 3.5M + AgCl KCl 3.5M KCl 3.5M + AgCl
Reference Junction ceramic, single ceramic, single ceramic, triple
Reference Type single, Ag/AgCl double, Ag/AgCl single, Ag/AgCl
Shape of membrane spheric spheric conic
Max pressure 0.1 bar 0.1 bar 0.1 bar
Connector Type BNC BNC BNC
Cable length coaxial, 1 or 3 m coaxial, 1 m coaxial, 1 m
Shaft length 120 mm 120 mm 120 mm
Diameter 12 mm 12 mm 12 mm
Application laboratory applications laboratory applications laboratory applications
Glass Conic Tip Sensor
Glass Spheric Sensor
Epoxy Electrode
M
A
9
1
8
B
/1 =1 m
M
A
9
1
7
B
/1 =1 m
M
A
9
1
6
B
/1 =1 m
/3 =3 m
12 mm
120 mm
12 mm
120 mm
12 mm
120 mm
MA916B/1 (will be
replaced by SE100)
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