Multi-parameter Water-Quality
Probes (YSI/Hydrolab)
Lecture 4
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)
YSI (Yellow Springs Inc)
https://www.ysi.com/ysi/Products
YSI sensors
HACH - Hydrolab
http://www.hydrolab.com/sondes.asp
Some Hydrolab sensors
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 2point
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 H2Osaturated 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 80120% 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 postdeployment 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.