Multiprobe Use and Calibration
Why do we use multiprobes?
Multiprobes are used to measure multiple parameters such as temperature, dissolved oxygen, conductivity and pH (in addition, some units can measure turbidity, chlorophyll or nitrates). These measurements are often taken in conjunction with a chemistry sample collection.
Multiprobes provide excellent information by providing an immediate number; they are also relatively inexpensive and easy to maintain. However, these measurements only provide instantaneous data, unable to monitor and provide data illustrating temporal variability. To combat this, continuous monitors are left out for days or years to capture changes that occur throughout the day and between seasons. Continuous monitors require regular maintenance on a weekly or biweekly basis.
For more information about parameters measured with these probes (temperature, pH, dissolved oxygen, turbidity) check out What's In Your Water.
What do we use?
There are a number of different types of multi-probes available for use; all work under the same basic principles. Daily calibration ensure reliability and proper functioning. Probes contained on the multiprobe must all fall within the pass/fail range of their respective parameters as directed by the Standard Operating Procedures (SOPs). These SOPs can be found at the end of these instructions. With Utah Water Watch, we will generally be using the SmarTroll and Oakton PCSTestr. While the setup and controls of the probes will be different, the basic methods are the same.
All probes need to be calibrated within 24 hours prior to sampling. We recommend that you calibrate at home before you leave to monitor. All solutions should be within the expiration date.
Multiprobe, tablet or data logger, deionized water, calibration sheet, calibration standards (pH and conductivity), waste bottle, calibration cup and guard (should already be with your multiprobe), field data sheet, pen/pencil
General calibration and use best practices:
Find specific calibration instructions below for SmarTroll and Oakton PCSTestr (based on the Utah Division of Water Quality SOPs).
Calibrate within 24 hours prior to sampling, best done before going out in the field.
Calibrate for each probe you will be measuring (conductivity, pH and dissolved oxygen).
- Rinse with deionized (DI) water between each calibration
- Ensure probes are fully submerged in the buffer solutions
- Calibrate your conductivity (SpCond) and use a calibration solution that is closest to your expected measurement ( a common standard is 1413 or 500 uS/cm).
- pH – use 2 point calibration that buffers the expected measurement (i.e. your water measures generally around 8 pH, calibrate with a 7 and 10 pH).
- Dissolved oxygen, use saturated air to calibrate to 100% sat. Use a damp sponge or half inch of water in the calibration cup. If the cup screws on, be sure the cup is loose. Some probes may require knowing the barometric pressure.
- Temperature cannot be calibrated, but is good to do a check against a NIST certified thermometer to make sure the equipment is working properly.
Document all buffers and readings on the calibration sheet provided.
Perform a check after calibration by taking a reading in a different conductivity solution and pH solution and double check the dissolved oxygen in saturated air. The conductivity reading should be within ±10% of the expected value and the pH an dissolved oxygen readings should be within ±5% of the expected value.
Turn on the multiprobe and position the meter in the thalweg (main stream flow); or along a bank/edge in the flow if the waterbody is too deep or fast; or lower from a bridge. Ensure the measurements are upstream of other sampling activity, in well mixed water and avoid disturbing bottom sediments.
Wait 1-2 minutes for the values to settle and record them on the data sheet provided.
When finished sampling, make sure the meter is rinsed thoroughly and properly stored in the cap with a damp sponge or tap water.
Meter specific instructions:
For the Utah DWQ SOP: Calibration, Maintenance and Use of Hydrolab Multiprobe
See also, Manufacture Manuals: