User Manual

<4. COMMISSIONING OF pH/ORP>
4-8
IM 12A01A02-01E 5th Edition : Oct. 31, 2013-00
4.2.5 Impedance settings
This screen is used to set the impedance relating to an input impedance check.
Input 1 impedance represents the “glass membrane impedance” of a pH sensor. In case of an
ORP sensor, it represents “metal electrode impedance.” Input 2 impedance stands for “reference
impedance.”
If you select “Input impedance: Low,” the display moves to the Input impedance screen, enabling
you to set the high and low limits.
The FLXA21 has an impedance check, which is capable of monitoring the impedance of various
sensorsystems.Inorderto“netune”thisdiagnostictool,itisnecessarytosetituptomatchthe
sensors used.
The system can be set to measure the impedances of glass (input 1 impedance: high) and
reference (input 2 impedance: low) electrodes. In applications that tend to leave deposits on the
electrodesortoclogthereferencesensorjunction,theimpedancecheck(seterrorconguration)
on the reference sensor can be used to initiate an alarm, or to initiate the wash cleaning process,
ifoneofthelimitsisexceeded.Sensorswithaliquidearthusethisliquidearthinimpedance
measurement.SensorswithaliquidearththatYokogawacanprovideincludePH8EFP,PH8ERP,
PH8EHP, OR8ERG, OR8EFG, etc. In pure water measurement using PH8EHP, the impedance
ofthesolutiontobemeasuredishigh;settingsontheErrorcongurationscreenshouldbesetto
Off so that the “Impedance 2 too high” error is not generated.
Asensorwithoutaliquidearthcannotmeasureimpedance.AllsettingsontheErrorconguration
screen should be set to Off so that no “Impedance 1 too high” or “Impedance 2 too high” error is
generated.
SensorsnotequippedwithaliquidearththatYokogawacanprovideincludeHA405,HA406,
DPA406,DPA405,DPAS405,HF405,HA485,DPA485,etc.
Thisliquidearthreferstoametalpolebuiltintoasensororconnectedexternallythatcontactsthe
solution to be measured and transmits the potential of this solution to the converter.
4.2.6 Concentration
Generally pH values are not converted into concentrations. Following linear conversion is not
suitable for a lot of measurements.
The FLXA21 is capable of converting a measured pH value into concentration for display.
Parametersrequiredforconcentrationcalculationcanbearbitrarilysetbytheuser.Those
parameters are as follows:
Unit: Thedefaultvalueis%.Theunitcanbeselectedfromamongmg/L,g/L,and
ppm.
pH: The default values are 0 and 14 pH (0 to 14). They are the pH zero and span
requiredforconversiontoconcentration.
Concentration: The default value are 0 and 100%. Concentration for each pH can be set.
Concentration can be assigned to the pH value zero and span individually.