Question
How often should a pH or conductivity probe be calibrated?
Summary
pH / conductivity probe calibration frequency
Answer
Hach does not publish any recommendations on how often a sensor needs to be calibrated. This is left up to the end users QA/QC to establish.
Typically, pH probes and many conductivity probes are calibrated at the start of each 8 hour shift, but this can vary depending on application.
In theory, a probe is calibrated (or at a minimum controlled with a calibration standard) prior to any measurement series. So, every time a measurement series is started, one would have to:
In practice, only certified labs are running such a procedure. For practical reasons, many labs will calibrate less frequently.
Calibration frequency depends on:
In all cases the calibration frequency is a customer experience based decision linked to the sample type measured and the measurement frequency. As a manufacturer, Hach can only give generic advise and recommendations for use which would be:
For pH sensors, please visit the Hach pH Buffer page for a complete listing of calibration buffers.
For conductivity sensors, please visit the Hach Conductivity Standards page for a complete listing of calibration standards.
Typically, pH probes and many conductivity probes are calibrated at the start of each 8 hour shift, but this can vary depending on application.
In theory, a probe is calibrated (or at a minimum controlled with a calibration standard) prior to any measurement series. So, every time a measurement series is started, one would have to:
- Calibrate the sensor
- Control the calibration with a standard different from the one(s) used for calibration (this process is also called running a Check Standard).
- Run the sample series (10 samples is typically considered the maximum, but it can vary)
- Run another check standard with the standard used in step 2.
- Repeat step 3.
In practice, only certified labs are running such a procedure. For practical reasons, many labs will calibrate less frequently.
Calibration frequency depends on:
- The environment factors and measuring conditions.
- The likelihood the sensor will change with time.
- The likelihood the sensor will be contaminated by the sample
- How the sensor is maintained by the operator between each measurement.
- The customer experience in regard to samples and application.
In all cases the calibration frequency is a customer experience based decision linked to the sample type measured and the measurement frequency. As a manufacturer, Hach can only give generic advise and recommendations for use which would be:
- Prior to using the sensor, use a check standard.
- If the reading of the check standard is outside of the accuracy acceptance limits, then recalibrate the sensor.
- If the calibration is outside of the acceptance limits, then clean/maintain the sensor according to manufacturer recommendations. If maintenance doesn't help, then replace the sensor.
- This process will give information on how frequently calibration/maintenance/replacement of the sensor needs to be done in regard to the frequency of use and the sample matrix.
For pH sensors, please visit the Hach pH Buffer page for a complete listing of calibration buffers.
For conductivity sensors, please visit the Hach Conductivity Standards page for a complete listing of calibration standards.