Application Areas For Sensor Type 8201; Measuring Principle - Burkert 8201 Manuel Utilisateur

2.2 Application areas for sensor Type 8201

2.3 Measuring principle

The 8201 pH sensor works as a single-rod measuring cell. The measuring electrode and reference
electrode are combined in one element. An enamelled steel tube is used as the basic carrier.
This is turned into a measuring electrode by additionally applying an ion-selective enamel layer (yel-
low) with metallic voltage conductor. The voltage conductor is housed in the non-conductive blue
enamel carrier layer. An ion exchange of positive hydrogen ions (H+) and negative alkali ions (K-)
takes place on the surface (source layer) of this enamel layer.
The AgAgCI reference electrode is located in the interior of the enamel pipe filled with electrolyte.
A ground ceramic diaphragm is pressed onto the lower end of the pipe. Voltage transfer takes place
when the electrolyte makes contact with the medium via the annular gap of the diaphragm.
3-molar KCI is used as the electrolyte, and is stored in a separate pressure container and
permanently connected with the electrode via a hose. The pressure of the pressure container is
maintained slightly above the process pressure via an attached pressure controller. For non-
pressurised processes the static overpressure of the pressure container mounted approx. 0.5 m above
the electrode is generally sufficient (50mbar). Thanks to the self-adjusting, extremely low permanent elec-
trolyte flow through the very small annular gap, contamination of the reference electrode is practically
excluded.
Accidental operation without electrolyte is prevented by optional level monitoring of the pressure con-
tainer.
When a minimum level has been reached the electrolyte supply bottle in the pressure container simply
needs to be changed.
This procedure is extremely easy to handle.
A Pt1000 for temperature compensation is also integrated in the sensor.
Transmitters with isotherm option and high-ohm inputs are suitable for analysing the low-energy
measurements. The maximum length of transfer between electrode and transmitter should not exceed
5 m.
Diagram 1:
Dependency of the pH measuring range on
Temperature
Diagram 2:
Sensor corrosion resistance depending on
temperature and pH value
Note
A corrosive attack of under 0.1 mm/year is
deemed resistant
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