Rev: 01
P/N: 95343
Page | 14
1.
Remove the reference cap by unscrewing it from the reference sleeve using a coin edge and discard the
old reference electrolyte.
2.
Fill the sleeve completely with fresh pH reference electrolyte (KCl saturated with silver chloride). Tap
the body of the MP25 sonde a few times to dislodge any bubbles.
3.
Screw the reference cap back on to the sleeve. As you screw the sleeve into place, air and excess
electrolyte is forced out of the sleeve through the reference electrode junction (the white, porous circle
at the end of the sleeve). This not only purges bubbles from the electrolyte, but also displaces any
lodged particles or biological growth out of the junction.
Oxidation-Reduction Potential (ORP)
ORP is measured as the voltage drop across the platinum
membrane of an ORP electrode. The ORP sensor on the MP25
system is the 1 mm silver-colored dot you can see when looking
down at the pH sensor. The pH/ORP reference electrode is
used to complete the voltage-measuring circuit.
ORP electrode maintenance is also minimal, only occasional cleaning the platinum surface with a soft cloth
or soft cotton swab and soapy water. If the platinum is discolored, you can polish the ORP electrode with
very light abrasive, like 900-grit wet-and-dry sandpaper or a pencil eraser. You must be careful not to scratch
or polish the pH glass bulb.
ORP uses a one-point calibration as follows:
1.
Rinse your sensors at least twice with the ORP standard you’ll use for calibration.
2.
Fill the calibration cup with enough ORP standard solution to cover both the ORP and reference
electrodes.
3.
Follow the MP25 calibration instructions in the prompts after selecting ORP_mV to calibrate.
