Multi-parameter Water-Quality Probes (YSI/Hydrolab)

1. Multi-parameter Water-Quality Probes (YSI/Hydrolab) Lecture 4

2. 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)

3. YSI (Yellow Springs Inc) https://www.ysi.com/ysi/Products

4. YSI sensors

6. HACH - Hydrolab http://www.hydrolab.com/sondes.asp

7. Some Hydrolab sensors

8. 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

9. 2 point calibration Data in this range (interpolated)

10. 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 H2O- saturated air. Most likely to drift over time.

11. 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.

12. 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. stretched

13. 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 80-120% 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.

14. 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.

15. 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.