YSI Offers A Hand-Held Multiparameter Instrument For Spot Sampling And Profiling Of Waters

A hand-held multiparameter digital system facilitates spot sampling for monitoring groundwater, reservoirs, receiving streams and other waters.
YSI Offers A Hand-Held Multiparameter Instrument For Spot Sampling And Profiling Of Waters
The ProDSS meter incorporates multiple sensors in a single probe.

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Water utilities often need to look upstream at conditions in their source water; wastewater agencies sometimes need to explore conditions in waters downstream of their discharge.

These investigations require instruments that are accurate and portable and stand up to the harsh realities of life in the field. YSI, a Xylem brand, now offers a multiparameter hand-held meter designed to meet those needs.

The ProDSS (Digital Sampling System) instrument puts capability for multiple measurements in one lightweight hand-held device. It uses smart sensors that can measure up to 17 parameters, and it has a one-cable design for user convenience.

It is suited for applications including groundwater and reservoir sampling, lake and watershed studies, and wastewater treatment plant receiving water testing. Laura St. Pierre, a senior product manager in water-quality systems with YSI, talked about the technology in an interview with Treatment Plant Operator.

TPO: What need was YSI aiming to fulfill with this offering?

St. Pierre: Typically, utilities doing surface water- or groundwater-quality studies need five main parameters: temperature, dissolved oxygen, pH, conductivity and ORP. We’ve always had compact instruments for sampling those five. However, many utilities also need to measure turbidity and sometimes depth. We now provide that capability in a compact instrument. We always could measure those parameters and then some on our larger systems, but those really are not ideal for spot sampling. They are larger and better suited for continuous deployment. The ProDSS, being much lighter and more portable, is especially suited for spot sampling.

TPO: What specific attributes make this device suitable for use in the field?

St. Pierre: It’s designed to stand up to harsh conditions. The rubber-over-molded case with metal, military-spec connectors is IP-67 waterproof and drop-rated to 1 meter. It has a color display and a backlit keypad so it can be used in any lighting condition. It uses a rechargeable lithium-ion battery that lasts about 20 hours. Users can easily get their sampling day in without using alkaline batteries and having to throw them away. The sensors are durable for field use with laser-welded titanium bodies.

TPO: What are the advantages of the smart sensor technology?

St. Pierre: The sensors analyze the signal coming from the sensor head and process it into measurement data, then digitally send that data up the cable to the hand-held unit. That yields very accurate measurements. It also allows us to use cable lengths up to 100 meters for applications such as reservoir and lake management studies. The sensors are also digitally recognized by the instrument as soon as they are plugged in. That makes it easy to set up. It also shortens the time from box to field: Users don’t have to go in and enable parameters or turn measurement units on. Calibration data stays with the sensor so the sensor doesn’t have to be reconfigured every time it’s plugged into the unit.

TPO: How many sensors can be used simultaneously?

St. Pierre: There are four sensor ports, so users can measure with any combination of four sensors at a time. We also offer ammonium, nitrate and chloride sensors as options. The sensor data enables other calculated parameters. For example, the conductivity/temperature sensor also calculates specific conductance, salinity and total dissolved solids [TDS].

The cable can be ordered with or without depth sensing, which does not occupy a sensor port. The depth measurement uses the barometer in the hand-held unit to compensate for atmospheric pressure. That results in highly accurate depth measurements without the need for a vent tube that comes up the cable and back-vents the pressure transducer to the atmosphere. This high-accuracy sensor helps users know exactly the depth at which they are taking their DO, pH, turbidity and other measurements.

TPO: What is the idea behind the one-cable configuration of this device?

St. Pierre: We have four sensors on the cable assembly that goes into the water. The one-cable design, in which all the sensors connect to one cable going to the hand-held unit, means users don’t have to take multiple instruments or instruments with multiple cables and separate probes into the field. It’s a lot easier and faster to measure with one instrument.

TPO: What can users do with the measurement data they collect with the instrument?

St. Pierre: They can easily download the data to a PC by way of a USB port on the instrument. Or they can back it up directly to a USB stick. They just connect a USB stick, click “Back Up Data” and all the data is sent to the USB stick as a CSV file.

TPO: What measurement methods do the smart sensors use?

St. Pierre: We use a combination of optical and electrochemical sensors. The DO and turbidity probes are optical. The pH, ORP, ammonium, nitrate and chloride probes are ion-selective electrodes [ISEs]. The conductivity probe is a standard 4 nickel conductivity cell, and the depth probe is a pressure transducer.

TPO: Does this device provide any mapping capability?

St. Pierre: Yes — utilities can order it with GPS capability. That allows users to log coordinates with the measurement data so they can map it later. Our KorDSS data management software with geomapping capability is included with the instrument.

TPO: What is required for calibration to sustain measurement accuracy?

St. Pierre: Users should calibrate this unit just as they would any other water-quality sampling instrument. Optical sensors hold their calibration longer than ISEs, so for example the turbidity and DO sensors will hold their calibration longer than the pH, ammonium or nitrate sensors. We recommend verifying the calibration regularly to determine how often calibration is needed. New, clean sensors require less frequent calibration than aging or dirty ISEs.

TPO: What maintenance does the device require?

St. Pierre: It needs to be kept clean and be well rinsed after use. The only regular maintenance is to change the DO sensing cap about once every 18 months. Other than that, it’s just a matter of keeping the battery charged. It can be recharged through a PC, through an AC wall outlet or with an external portable power pack of the type used for cellphones.   


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