Alpha 2000 Uživatelský manuál stáhnout pdf (Strana 7)

Thermo Scientific / Alpha Process Products / 2000 Series Controllers / www.thermo.com/process 7

Measurement

of pH in

wastewater

poses several

challenges,

one of which

is fouling of

the reference

electrode system

The Conventional

Combination Electrode:

The conventional combination

electrode consists of two parts:

the glass electrode and the

reference

(Figure 1).

The glass electrode contains a

silver wire immersed in conductive

solution. During measurement, the

glass bulb and stem are the only

parts which come in contact with the

sample. Hence, contamination of the

silver wire and conductive solution

does not occur.

The reference electrode, on the

other hand, is constructed simply

with a porous junction and a silver

wire. This porous junction allows

the reference electrolyte to flow

from its chamber to the sample,

establishing a connection between

the two. However, the porosity also

allows contaminants to flow into the

reference chamber, reacting with the

electrolyte and/or silver wire.

The reference electrode is also

susceptible to clogs. In the case

of conventional combination

electrodes, the entire electrode

must be replaced due to a clogged

reference electrode.

About Differential

pH Measurement:

When contamination and clogging

occurs, performance of the entire

electrode is compromised.

The Differential Electrode:

The differential electrode replaces

the exposed silver wire with a

design built on the benefits of

a pH glass electrode

(Figure 2).

Quadraple junction salt bridges and

an electrolyte-filled chamber act as

barriers to prevent contaminants

from entering the inner chamber,

while at the same time, allowing

connection between the reference

electrolyte and the sample.

In the event of clogs, the salt

bridges and electrolyte are easily

replaceable, reducing downtime and

cost of maintenance.

An individual liquid ground is also

built into the electrode, effectively

eliminating noises from ground loops

potential

(Figure 3):

(E1 – E3) – (E2 – E3) = E1 – E3

With these design improvements,

the differential electrodes enjoy a

longer lifespan in harsh wastewater

environments as compared to

conventional electrodes.

Figure 1: The conventional combination

electrode is made up of a glass

electrode and a reference electrode

pH

Reference

Electrode

(E2)

pH

Glass

Electrode

(E1)

Figure 2: Differential electrode

replaces porous reference electrode

with a glass electrode

Pre-Amplifier

Figure 3: Individual liquid ground

loop eliminates noises from ground

loop potentials

Process

Electrode

(E1)

Solution

Ground

(E3)

Reference

Electrode

(E2)

1 2 3 4 5 6 7 8 9 10 11 12 ... 23 24

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