Multi-parameter probes PROS –Collect multiple metrics of water quality at the same time –Internal data logger – can collect in unattended (log) mode CONS –Require calibration and maintenance –Expensive ($5-10K and up)
Calibration For every sensor (except temperature) Follow manual and fill out log (keeps track of sensor condition/status) Required before every deployment and should be tested again after retrieval Should test standards using a separate meter/test strip if possible Most calibrations are one-point, some 2- point
2 point calibration Data in this range (interpolated)
Sequence Change D.O. membrane day before!!! Check temperature against thermometer Conductivity first – 1 pt cal (typically 50mS) pH second – 2 pt cal (typically pH 7 and 10) should be about 180mV difference Turbidity and/or chlorophyll – 2 pt cal, see manual for correct protocol and standards. D.O. last, needs to equilibrate in H 2 O- saturated air. Most likely to drift over time.
Calibration tips ALWAYS RINSE between calibration standards with water and some old standard. AVOID contamination. Save $$$ by knowing your chemistry…BUT check self-made standards with a different instrument. pH sensors go bad – CHECK for a 180mV difference, if less than 165mV then replace.
D.O. issues Frequent membrane changes ensure good data! Become good at this procedure! No bubbles! No wrinkles! Membrane should be firm, but not Allow membrane to stabilize overnight for best results. Calibrate in water-saturated air, membrane must be dry.
D.O. tests Check D.O. sensor function by: –Disconnect power and wait 2 mins. Readings should start high and drop towards 100% saturation (see D.O. sat table for mg/L value at that temperature) –Sensor should read 100% in water-sat air, and drop to 30% or less in STILL water. Sensor/sonde must be in moving water for accurate measurement. At least 1 ft per sec (30cm per sec). Use stirrer attachment, or raise-lower sonde the necessary amount during measurement. During this period the D.O. reading will increase to a plateau, this is the correct reading. Should be within % of saturation value for that temperature (see D.O. sat table!) Keep sonde cool and wet (wrapped in a wet white towel) to easily check if sensor needs to be recalibrated.
Pre-deployment Calibrate at least 24hrs before deployment. Set up to log at your desired interval (usually every hour on the hour) Leave instrument logging in the water-filled cup in the lab. This is a pre-deployment dataset. Do this again after retrieval for a 24 hr post- deployment dataset. The two should be similar, if not, there were sensor problems that occurred during the deployment.
Lab Calibrate 2 YSI’s. Setup for unattended monitoring (hourly) Leave in lab overnight for pre-deployment data Deploy one at pier for 1 weeks.