Last week we shared with you tip #4, always keep your firmware and software updated. This is very important, because your data is only as up to date as your software. Please be sure to regularly check out our website for all recent software/firmware updates to ensure you sonde is always working properly. Now we are ready for tip #5.
Tip #5: Properly Calibrate All Your Sensors Prior to Collecting Data
We always recommend that the first place you go to when you have questions regarding a calibration procedure for a certain sensor, is the manual. The manual covers most of the details but what we want to cover in this post are the details that may not be spelled out in your manual so directly and some precautions to be aware of regarding calibration.
First take a look at your temperature sensor. Is it giving you accurate readings? All water quality sensors depend on a working temperature sensor to provide reliable data. If your temperature sensor is bad, there’s no reason to proceed with calibrations. You’ll need to replace the temperature sensor before proceeding because there is no way to calibrate the temperature on most devices. In order to determine if your temperature is reading accurately, obtain a NIST traceable thermometer or other certified temperature sensor to check against your instruments temperature accuracy. Check your manual for your temperature sensor’s specifications and if it’s outside this range, you’ll need to either send the unit in for service or obtain a replacement. Also be sure to have your traceable thermometer returned for recertification on a regular interval. This is usually quarterly or yearly depending on the device.
Next, make sure you are always using fresh calibration standards or solutions. Check the manufacturer’s expiration date and note when the bottles were opened. The expiration date on the bottle is generally for an unopened bottle and can differ once the bottle has been opened. People contact the YSI technical support team sometimes and ask if they can use standards that are only expired by a month or two. It’s not recommended to use calibration standards that are expired. Generally the expiration date is there because the calibration standard degrades to a point that it will no longer be able to assist us in accurate calibrations.
Our technical support team also receives questions about using standards more than once for calibration purposes. Most S.O.P.’s recommend not reusing standards for calibration. Calibrations using expired or previously used standards may result in gathering questionable data. In both of these instances you are likely introducing error, and you would need to develop a way to quantify how much error is being introduced so your data can be corrected.
One thing you can definitely do with your standards is reuse them for RINSING. Feel free to collect your calibration standards from today in a bottle labeled as RINSE and use them to rinse between standards during your next calibration.
During calibration, take note of the sensors response times and make sure you allow the probes enough time to stabilize before proceeding. If the probe is having trouble stabilizing during calibration, you can expect similar issues when you are trying to collect data in the lab or out in the field. You may want to consider whether you need to perform some maintenance or replace a probe if the problem cannot be resolved.
After calibration, make note of indicators like the conductivity cell constant, the pH millivolt slope, the DO gain, or the QC score provided by our new EXO sondes. These diagnostic tools will assist you in determining the success of your calibration. On a related note, you don’t want to accept any calibrations that are out-of-range or giving warnings of questionable results. This indicates there is a problem and further investigation is needed to determine the cause of the problem. Forcing a bad calibration is never a good idea and it is likely you will be collecting questionable data if you bypass these warnings.
Finally, dispose of your calibration standards according to your regions requirements. This varies from region to region so contact your local water authorities like the EPA or the water department to determine disposal requirements for specific calibration standards.
Keep you a look out for the final 2 tips to getting you water quality sonde field ready coming out next week, or or feel free to watch the full webinar "Gearing Up For Sampling Season."
A special thanks to our technical support team for providing some of the information in this post.
Additional Blog Posts of Interest:
YSI Expert Tip #1: Always Inspect the Condition of Your Sensors.
YSI Expert Tip #2: Properly Maintain Your Instrument Sensor Connections.
YSI Expert Tip #3: Always Check Your Batteries and Power Supply.
YSI Expert Tip #4: Always Keep Firmware & Software Updated.
YSI Expert Tip #6: Finalize Your Sonde Settings Prior to Leaving for the Field.
YSI Expert Tip #7: When Going Into the Field, Always Bring a Field Survival Kit.