- How to determine if a pH probe is defective or at
the end of it's life:
- First, immerse the electrode in a pH 7.01 buffer
and use the mV (range key) to change the meter display to milli-volts.
- Next compare the reading to +/- 30.00mV. If the reading exceeds this
value, the electrode should be cleaned or replaced as it will be unstable.
An electrode in this condition will not be able to be reliably calibrated.
- How to "calibrate" an ORP probe:
- NO Calibration of the instrument
should be attempted
- Instead the ORP probe
should be checked for usability
immerse the electrode in an ORP standard such as 230mV or 470mV.
observe the ORP reading. If the reading is within 50mV of the standard,
it is a usable electrode.
- If the reading is outside those
limits, the probe should be replaced or cleaned
- Trying to calibrate the controller
without a milli-volt simulator is a bad idea. ORP is very different from pH.
- We do sell pH/ORP "calibrators".
These essentially are milli-volt simulators with displays showing pH or ORP
units directly. A knob control allows the user to output any value to
the BNC connected instrument.
- Decrease in slope of pH electrode:
- Usually caused by problems associated
with the glass. Oil, dirt, or salts which have built up on the surface
need to be cleaned. A "Cal-Check" Meter or controller will indicate this
condition. A value of 58.16mV is equal to a slope of 100%. Slopes
above 90% are normally considered acceptable.
- Increase in offset of the pH electrode:
- Typically caused by a clogged reference
junction or aging of the electrode.
- Cleaning of the electrode can partially
restore the electrode's offset closer to zero.
- Eventually, if the offset is too great,
the reading becomes unstable (see Tip #1)
- Reset of pH500 controller back to
factory default settings:
- Pressing the following key in sequence
will reset the controller. Remember to make note of how your controller
is setup prior to making this step.
- Press the four keys simultaneously (use
- CFM key, SETUP key, → and CAL DATA.
- The controller is now reset and ready to
be reprogrammed for your application. Use the notes of your
configuration to reprogram the unit.