Yokogawa EXA PH202 2-Wire pH/ORP Analyzer - Manual (Page 108)

IM 12B07D02-01E
Appendix 11-11
(6) After the display reading has stabilized, read and note it. Measure the temperature of the test
solution, and check the ORP of the test solution at that temperature using Fig. 11-3.
If the ORP reading is within the tolerance shown in Fig. 11-3 then the sensor is normal.
Note: If the measurement value is only slightly out of tolerance, you should check whether the test
solution was fresh and whether it was mixed in the correct amounts (see mixing instructions
above).
0 10 20 30 40 50
0
100
200
300
400
500
600
(mV)
Quinhydrone solution
ORP
Temperature C
Tolerance
Tolerance
Ferrous & Ferric solution
F6.1E.eps
Fig. 11-3 ORP of Test Solution
(7) Replace the sensor in its holder.
Be careful to make sulfuric acid solution.
11-5-2. Manual Calibration
The procedure for calibration is described in 11-5-5 (1).
Calibration is performed by using a solution of known ORP value, and adjusting the PH202 to read
the same value. Alternatively you may calibrate the PH202 to read the same as another 'standard'
instrument in a given solution. The electrode check described in 11-5-1 above is performed if the
measured value appears to be well out of tolerance. Calibration of the ORP value is performed by
zero-shift one-point calibration.
11-5-3. Calibration with Sample
The procedure is described in 11-5-5 (2).
Calibration with a sample enables measuring a representative sample (e.g. by laboratory analysis)
while the ORP sensor is on line and measuring the same sample solution, saving the measured data
in the memory of the PH202, and then adjusting the PH202 to read the same value (as obtained
e.g. by laboratory analysis). So normal on-line control or pH measurement is not affected. The ORP
measurement is calibrated by zero-shift one-point calibration.
11-5-4. Data Entry
If the above methods of calibration present problems, another alternative is the direct entry of
calibration data using the Service Code Menu (refer to Chapter 5). For example, the sensor may
be calibrated in a test laboratory and then transported to its location in the field and the sensor
parameters entered into the associated PH202.
Service Code 23 allows you to access and enter ITP, Asymmetry Potential (or Zero Point) and Slope
parameters.
WARNING