AUX E&H Series Instruções de Operação descarregar pdf (Página 37)

5.5.2 Check

The function group CHECK is only accessible for instruments equipped with the Plus packet.

Two different monitoring functions can be selected for the measurement in the function group

CHECK:

SCS electrode monitoring

The sensor check system monitors the pH and reference electrode for inaccurate measurement

and total failure.

The SCS detects:

– Breakage of electrode glass

– Fine short circuits in the pH measuring

circuit, e.g. moisture or dirtbridges in

clamping points

– Soiling or blocking of reference electrode

– Leakage current on IsFET sensor

Three methods are used:

– Monitoring of pH electrode for high

resistance (an alarm is signalled when the

impendance drops below a minimum value

of 500 kΩ). This function cannot be

selected when using an antimony or IsFET

electrode (A4).

– Monitoring of reference electrode

impedance (an alarm is signalled when the

defined threshold is exceeded). This

function can only be selected with a

symmetrical connection.

– Monitoring of leakage current with IsFET

sonsors (pre-alert E168 at I

Leak

>200 nA,

error E008 at I

Leak

>400 nA).

Caution:

• Do not remove the electrode from

the process without Hold. Since

the SCS is measured against

PMC, no contact between the

inner conductor and PMC would

trigger an alarm.

PCS alarm (Process Check System)

Function AC is used to examine the measuring signal for deviations. If the measuring signal is

constant for a specific period of time (several measured values), an alarm is issued. This type

of behaviour may be caused by soiling, blocking, etc.

Function CC monitors the relay activity. Due to freely selectable monitoring periods for the limit

functions, a relay failure will be recognised and an alarm will be triggered.

Note:

• Reference electrode monitoring is

only possible in conjunction with

the symmetrical connection (with

PMC).

• A current PCS alarm is auto-

matically deleted as soon as the

sensor signal changes.

• Due to its semiconductor

component, the IsFET sensor is

light-sensitive and reacts with

measured value fluctuations. For

this reason, avoid direct solar

radiation during calibration and

operation. Normal ambient light

does not affect the measurement.

22 mA

SCS.CDR

Fig. 5.8 SCS alarm

Constant measuring signal

= alarm is triggered

LIVE.CDR

Fig. 5.9 PCS alarm (live-check)

PM253E5A.CHP

Liquisys M CPM 223 / 253 Instrument configuration

Endress+Hauser 35

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