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                           "pH meters, pH probes, pH controllers and much more"

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  • 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
    • First, immerse the electrode in an ORP standard such as 230mV or 470mV. 
    • Next 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 two hands):
    • 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.







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MBH Engineering Systems 2008
Last modified: 29-Oct-2008