User Manual

<15. OPERATION OF SENCOM pH/ORP>
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IM 12A01A02-01E 5th Edition : Oct. 31, 2013-00
n PH (ORP)’s zero, slope, and sensor, and Impedance
l Zero
=calibratedsensoroffsetinmV.Theoretically,thesensorreads0mVinabuffersolutionofpH
7. The ZERO value indicates the condition of the sensor. The trend of ZERO drift of the sensor is
used to predict the lifetime of the sensor.
ZERO can also be displayed in pH units and then it represents the pH value where the sensor
outputis0mVat25ºC.SettingcanbemadeinCommissioning→Measurementsetup→
Calibrationsettings→ZeroandSlopeunits.
SettingofthezerovaluecanbemadeinCommissioning→Measurementsetup→Calibration
settings→Zero/Slope/ITP.For details, see section 16.2.4.
l Slope
=calibratedefciencyofthesensorunitasapercentageofthetheoreticalslopeofthesensor
unit.ThetheoreticalslopefollowstheNERNSTequationandis59.16mV/pH(at25ºC).The
SLOPE can be calibrated only after a two-point calibration in buffer solutions with a different pH
value. A low slope indicates that the sensor is not clean or is faulty.
TheSLOPEcanalsobedisplayedasamV/pHvalueat25ºCiftheuserhasdenedthisvariable
asmV/pHinCommissioning→Measurementsetup→Calibrationsettings→ZeroandSlope
units.
SettingoftheslopevaluecanbemadeinCommissioning→Measurementsetup→Calibration
settings→Zero/Slope/ITP.Fordetails,seesection16.2.4.
pH14
pH0
pH7, 0mV
Theoretical value
+mV
-mV
Calibration curve (slope)
Zero
F0410.ai
Figure 15.6 Zero/slope
l Sensor
Represents the electromotive force of the sensor.
l Impedance 1
For a PH sensor, “Impedance” shows electrical resistance of the glass membrane electrode. The
FLXA21 checks the impedance to know damage of the electrode.
For an ORP sensor,”Impedance” shows electrical resistance of metal electrode.
The FLXA21 checks the impedance to know the surface condition of smudge and the snapping
of sensor wires. In case of “Input Impedance setting” is “High” and the measured input-1
impedancevalueishigherthan100kΩ,thedisplayshows“MΩRANGE”.Themeasuredinput-1
impedancevalueislowerthan100kΩ,displayshows“BAD”.
If both impedance measurements are disabled (Error setting: Off), the display shows “- - - - (bar)”.
If either impedance measurement 1 or 2 is enabled, the display shows both the impedance
values.
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SENCOM