Technology Evaluation

A Technical Comparison of Multi Parameter Water Quality Sondes

A multi parameter water quality sonde is an economical way of collecting real time water quality data for groundwater, industrial discharges, stormwater, and surface water monitoring.There are many options available and a lot of it depends on your intended use. However, many of the features are standard and easily comparable between vendors. Here, I intend to compare YSI, HACH, ISCO, and In-Situ multi parameter sondes.

YSI

HACH

ISCO

In-situ

Parameters:

The variety of parameters available vary depending on the sonde. However, all of the four brands of sondes offer the basic parameters of Dissolved Oxygen, pH, Conductivity, and ORP.

Dissolved Oxygen

Sensor	Range	Resolution	Accuracy
YSI ROX*	0-50mg/L	0.01mg/L	0 to 20 mg/L: ± 0.1 mg/L or 1% of reading, whichever is greater; 20 to 50 mg/L: ± 15% of reading
HACH LDO*	0-60mg/L	0.01mg/L	±0.1mg/L @ < 8mg/L, ±0.2mg/L @ > 8mg/L, ±10% reading >20mg/L
ISCO HDO*	0-20mg/L	0.01mg/L	±0.2mg/L
In-Situ RDO*	0-8mg/L 8-20mg/L 20-50mg/L	Not found	±0.1mg/L ±0.2mg/L ±10%

* All versions of Optical Dissolved Oxygen

pH

Sensor	Range	Resolution	Accuracy
YSI	0 to 14 units	0.01 units	± 0.2 unit
HACH	0 to 14 units	0.01 units	± 0.2 unit
ISCO	0 to 14 units	0.01 units	± 0.2 unit
In-Situ	0 to 12 units	Not found	±0.1 unit

Conductivity

Sensor	Range	Resolution	Accuracy
YSI	0 to 100 mS/cm	0.001 to 0.1 mS/cm (range dependent)	± 0.5% of reading + 0.001 mS/cm
HACH	0 to 100 mS/cm	Not found	± 0.5% of reading + 0.001 mS/cm
ISCO	0 to 100 mS/cm	0.1 μS/cm (0 - 999.9) 1 μS/cm (1000 to 9,999) 10 μS/cm (10,000 to 99,990)	±1% of reading ± 0.001 mS/cm
In-Situ	Low: 0.005 to 20 mS/cm High: .15 to 112 mS/cm	Not found	Low: ±0.5% or 0.002 mS/cm High: ±0.5% + 0.002 mS/cm

Oxidation Reduction Potential

Sensor	Range	Resolution	Accuracy
YSI	-999 to +999 mV	0.1 mV	± 20 mV
HACH	-999 to 999 mV	1.0mV	± 20 mV
ISCO	-999 to 999 mV	1.0mV	± 20 mV
In-Situ	±1400 mV	Not found	±5 mV

It is important to note that the accuracy of each parameter is influenced by the quality of the calibration standard and adherence to calibration procedures. Specific calibration procedures can be found in each sonde’s user manual.

In addition to the four basic parameters, each sonde offers these additional parameters.

* YSI offers: Ammonia/Ammonium, Blue Green Algae, BOD, CDOM, Chloride, chlorophyll, Depth, Free Chlorine, Level, Nitrate, Oil/Hydrocarbon, Photosynthetic Active Radiation, Resistivity, Rhodamine, Salinity, Temperature, Total Dissolved Solids, Turbidity

* HACH offers: Chlorophyll, Blue Green Algae, Total Dissolved Gas, Rhodamine, Photosynthetic Active Radiation, Temperature, Turbidity, Depth, Ammonium, Nitrate, Chloride

* ISCO offers: Depth, Salinity, Total Dissolved Solids, Turbidity

* In-Situ offers: Barometric Pressure, Salinity, Total Dissolved Solids, Level/Pressure, Temperature, Turbidity, Ammonium, Nitrate, Chloride

Other details to consider include weight, power supply, maintenance, and data interface.

Detail	YSI	HACH	ISCO	In-Situ
Weight	3.4lbs	7.4lbs	5.2lbs	4.2lbs
Power Supply	4 alkaline C-cells with detachable battery cover	8 alkaline C-cells	12 VDC Supplied by connected sampler or flow meter,or USB connection to computer	2 alkaline D-cells
Maintenance	Field serviceable. Probes can be calibrated and/or changed in the field	Can be calibrated in the field but must be returned to manufacturing if you need to change or reconfigure the probes.	Field serviceable. Probes can be calibrated and/or changed in the field	Field serviceable. Probes can be calibrated and/or changed in the field

Data Interface:

Sonde	Type of data interface	Function	Pros/Cons	Picture
YSI	Handheld unit, Multi Parameter Display System	Display and record data	No need for laptop in the field, Ecowatch software, easy to use interface	*
HACH	Handheld unit, Surveyor Field Unit	Display and record data	No need for laptop in the field, waterproof, rechargeable batteries (which can be a pro or con)	*
ISCO	No handheld, must be connected to laptop or sampler	Display and record data	Eliminates the need for a handheld device, only as rugged as the laptop	*
In-Situ	Handheld unit, Rugged Reader	Display and record data	No need for laptop in the field, Rugged design, protected from dust, rain, and accidental submersion, Microsoft Windows Operating System	*

Additional Information:

Although these four brands are very comparable, YSI has recently launched it’s new EXO platform that incorporate a combination of advanced features that are unique to YSI.  “Smart probes” allow users to calibrate multiple probes during a single calibration. Furthermore, since calibrations are stored on the probe, instead of the sonde, these probes can be swapped out without having to do a recalibration. This can help to decrease errors, as well as save on the amount of calibration standard used.

“Smart ports” is another unique feature that automatically recognizes probes/sensors. It also utilizes wet-mateable connectors. This allows for sensor swaps in wet conditions.

The anti-fouling accessories and internal power also allow for continuous deployment of sondes.  The EXO2 incorporates a central port that accepts a special anti-fouling wiper that cleans all the probes that are attached to the sonde, instead of the usual individual wipers. This is a benefit because probes with individual wipers can be problematic due to the potential for the o ring on the wiper shaft to fail.  

The EXO handheld is a portable weatherproof interface for the EXO sondes that also comes with a number of unique features.  These features include GPS, temperature-compensated barometer, wet-mate wireless connector, Bluetooth communications, and 2 GB of storage.  Besides the handheld, the EXO sonde has multiple data outputs.  The sonde can be outfitted with a DCP signal output adapter, usb adapter, or via Bluetooth technology.

Water quality multiparameter sondes are a useful tool when immediate data is required. All of the sondes that are on the market are comparable in it’s abilities so the user’s needs and budget should be the deciding factor. Although other sources or manufacturers of multiparameter sondes are comparable in certain aspects, the YSI EXO sondes incorporate all of the features listed above in one package. Also, the bluetooth capability gives these new sondes added value.