Type 8201

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5.2. pH/temperature diagram

pH value

0

2

4

6

8

10

12

20

40

60

80

100

120

140

160

Operational area

at a measuring deviation

of < ± 0.1 pH at 0.1 mol/l (0.1 N) Na+

6.

Product installation

6.1. Installation notes

Intended performance is limited to proper installation of the fitting (by weld), integrating the probe into the process using the ap-

propriate adaptation kit, proper mounting of the electrolyte vessel (electrolyte attachment perpendicularly downwards) close to the

measuring point and connecting the pH sensor and electrolyte vessel using the hose connection supplied. The electrolyte supply

bottle is inserted into the electrolyte vessel and the pH sensor filled with electrolyte by opening the ventilation screw.

The assembly position of the pH sensor can be chosen freely. During operation care must be taken that the active surface (length ap-

prox. 45 mm from probes lower edge) is completely surrounded by medium. The flow velocity should not exceed 3…4 m/s. Dry-stor-

age of the pH sensor is unrestricted.

The probe is connected to the transmitter by means of the attachment cable. Inductive level switch is attached to a suitable analysing

device.

7.

Product operation

7.1. Measuring principle

The pH sensor works as a single-rod measuring cell. The measuring electrode and reference electrode are combined in one element.

An enamelled steel pipe is used as the basic carrier. The measuring electrode is created by additionally attaching an ion-sensitive

enamel layer (yellow) with metallic voltage conductor (positioned in the non-conductive blue enamel carrier layer). An ion exchange

of H+ions and alkali ions takes place on the surface (gel layer) of this enamel layer. The Ag/AgCI reference electrode is located in the

interior of the enamel pipe filled with electrolyte. A ceramic machined diaphragm is pressed into the lower end of the pipe. Electro-

lytic conduction takes place through the contact of the electrolyte via the annular gap of the diaphragm to the measuring solution. A

Pt1000 for temperature compensation is also integrated in the sensor. The electrolyte (conform to FDA) used is 3-molar KCI, stored in

a separate electrolyte vessel and permanently connected to the probe via a hose.

The pressure of the electrolyte vessel must be maintained above the process pressure by means of a Bürkert Type TPM001 pres-

sure controller (not supplied, see data sheet Type TPM001  for more information) or another one available on the market. We

recommend a pressure difference of at least 0.5 bar. Under these conditions, the electrolyte flow rate is about 0.01 ml/h (actual flow

rate specified in the test report delivered with the device). For non-pressurised processes the static overpressure of the pressure

vessel mounted approx. 0.5 m above the probe is generally sufficient (50 mbar). Due to the extremely low permanent electrolyte flow

through the very small annular gap, contamination of the reference electrode is practically excluded. Accidental operation without

electrolyte is prevented by optional inductive level monitoring of the pressure container. When a minimum level has been reached, the

electrolyte supply bottle in the pressure container is simply changed.

Bürkert Transmitter/Controller Type 8619 provides the analysis of the measured value. The maximum length of cable (5 m) between

probe and converter (transmitter) has to be respected. pH probe Type 8201 is supplied without adaptation. The appropriate set is se-

lected according to the fitting/armature chosen. Different hygienic variations of Type 8201 are available. Various standard armatures

Type 8200 can be used as well.