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The Calibration Worksheet assists record keeping for your YSI ProDSS Instrument. Note the calibration details are also logged locally on the instrument sensors. Please reach out to our team if you require calibration support.
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Common questions about sales, rental, servicing, calibration and support. Can't find your answer? Talk to an expert.
This is one of the most common questions we are asked, but there is no single calibration interval that is appropriate for every instrument or application. The appropriate interval depends on the instrument and sensor technology, how and where the equipment is used, and the accuracy and QA/QC requirements of your monitoring programme.
The principal factors to consider are discussed below.
Sensors and parameters
Multiparameter instruments use a range of measurement technologies, including thermistors, electrodes, ion-selective electrodes (ISEs) and optical sensors. Each has different characteristics in terms of stability, drift, maintenance and calibration requirements. A single calibration interval should therefore not necessarily be applied across all parameters or sensor technologies.
Equipment age and condition
Sensor condition can also influence calibration stability. Depending on the instrument, serviceable or consumable components may include electrodes, ISE modules, reference junctions, DO membranes and optical sensing caps. As sensors age or their condition deteriorates, more frequent calibration, verification or maintenance may be required.
Storage and transport
Correct storage and handling are important to maintaining sensor performance. For example, electrodes and ISEs may require specific storage conditions, while sensors that have been stored for extended periods may require conditioning before calibration and use.
Operating conditions
The environment in which an instrument is used can significantly affect calibration stability. Extremes of temperature or pH, high turbidity, biological fouling, contamination and other challenging conditions may affect measurement accuracy, stability or sensor response.
Required measurement accuracy
Calibration frequency should be appropriate to the accuracy required from the measurement. Regulatory, compliance and environmental research programmes may have defined accuracy, uncertainty or data-quality requirements which necessitate more frequent calibration and verification using recognised standards and documented procedures. Less demanding applications may allow longer intervals where instrument performance can be demonstrated to remain within an acceptable tolerance.
QA/QC requirements
Development of Quality Assurance and Quality Control (QA/QC) procedures specific to the organisation, project or monitoring programme is strongly recommended. These should define calibration and verification frequency, methods, standards, acceptance criteria and record keeping, helping to ensure measurements are produced consistently regardless of instrument or operator.
Ultimately, the monitoring organisation is responsible for defining the accuracy requirements, QA/QC procedures and calibration regime appropriate to its monitoring programme, taking account of manufacturer recommendations and any applicable regulatory, contractual or project-specific requirements.
Calibration and verification are related but distinct processes.
Calibration adjusts the instrument or sensor response against a known standard. Verification checks the response of an already calibrated instrument against an appropriate reference or certified standard to confirm that it remains within an acceptable tolerance.
Verification is generally quick, cost-effective and straightforward to perform and should form part of routine water quality monitoring procedures. Where permitted by the applicable QA/QC procedure and manufacturer guidance, satisfactory verification results can demonstrate that a sensor remains within the required acceptance criteria without unnecessary recalibration.
Recording verification results also provides valuable information on sensor stability and can help organisations develop evidence-based calibration intervals for their equipment and applications.
Don't automatically recalibrate a stable sensor simply because an arbitrary period has elapsed. Verify it against an appropriate standard and recalibrate when required by the manufacturer's procedure, your QA/QC programme, or when verification falls outside the acceptable tolerance.
Calibration and verification are only as reliable as the standards used. Standards should be appropriate for the instrument and expected measurement range, within their expiry date, correctly stored and protected from contamination.
Where required by the monitoring programme, standards with appropriate traceability or certification should be used. Please contact us for guidance on selecting suitable calibration standards for your instrument.
The following table is based on manufacturer guidance and Flux Enviro's experience of calibrating, servicing and maintaining water quality instrumentation.
Calibration requirements vary by sensor technology and application and should always be considered alongside the current manufacturer's operating manual and the requirements of your own QA/QC procedures. Consider this a starting point which can be refined using your own verification data.
Parameter | Routine Verification | Calibration | Practical Considerations |
|---|---|---|---|
Temperature | Check periodically against a known or traceable reference | Factory calibrated | Temperature sensors are generally very stable. Temperature accuracy is important as temperature is used in the compensation of several other parameters. |
Conductivity | Verify before each day of use | Calibrate if verification results fall outside manufacturer or organisation QA/QC thresholds | Conductivity sensors are generally stable and may retain calibration for several weeks. Use a fresh, appropriate conductivity standard and ensure the sensor is clean before verification or calibration. Where salinity compensation is applied to dissolved oxygen measurements, accurate conductivity data may also be important to the final DO result. |
pH | Verify before each day of use | Calibrate as required | A new or well-maintained pH sensor may retain calibration for several days. A 2-point calibration bracketing the expected sample pH is suitable for most applications; use 3 points where a wider measurement range is expected. Allow the buffer and sensor to temperature-equilibrate and ensure the correct temperature-dependent buffer value is being used. Record pH mV values and calibration slope where available, as these provide useful information on electrode condition and calibration quality. |
ORP | Verify before each day of use | Calibrate as required | Verify using an appropriate ORP reference solution such as RS250. Electrode condition and response time should be monitored. |
Dissolved Oxygen – Optical (ODO) | Verify before each day of use | Calibrate each day of use | A 1-point calibration in water-saturated air is recommended by YSI for most applications. Ensure the optical sensing cap is clean, undamaged and adequately hydrated. |
Dissolved Oxygen – Galvanic / Polarographic | Verify before each day of use | Calibrate each day of use | Membrane and electrolyte condition directly affect sensor performance. Recalibrate following membrane or electrolyte replacement and after sensor maintenance. |
Turbidity | Verify before each day of use | Calibrate if verification is outside the required acceptance criteria | Turbidity sensors are generally stable and may retain calibration for several weeks. Keep optical surfaces clean and use appropriate approved turbidity standards. |
Barometer | Check periodically against a known reference | Normally factory calibrated; user calibration available where required | Accurate barometric pressure is particularly important for dissolved oxygen calibration. |
Flux Enviro rental water quality meters are calibrated on the day of dispatch, or on the preceding working day, and supplied ready for use.
Appropriate calibration and/or verification standards are supplied with our rental instruments, enabling users to verify instrument performance on receipt and undertake additional verification or recalibration during the rental period where required by their own QA/QC procedures.
Calibration records are also provided with all instruments.
YSI ProQuatro Calibration Checklist
YSI EXO Calibration Checklist
Ultimately, an appropriate calibration frequency should be based on evidence rather than an arbitrary time interval. Manufacturer recommendations provide the starting point, while routine verification allows organisations to demonstrate instrument performance and refine calibration intervals to suit their equipment, operating conditions and data-quality requirements.
For further assistance regarding instrument calibration please reach out to our Servicing Team and we'll be happy to assist further.
Still have a question? Our Bangor-based team knows the equipment inside out and usually replies within one working day.
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