Water quality monitoring using a telemetry data logger

Recently a municipal water department made use of a water quality data logger to record dissolved oxygen (DO) concentrations in several ponds and slow-moving rivers to determine the health of aquatic life. If DO concentrations in these water sources become too low, fish and other organisms will face significant risk, especially in stagnant environments. Since DO levels are strongly affected by temperature and are lower in the summer, the customer wanted to take early measures to help protect fish from dying off this season.

Effective municipal water monitoring commonly requires sample collection, and the Environmental Protection Agency (EPA) has specified that the department needs to take a water sample every week in each of its bodies of water that are at risk of low DO levels. The department's technician wanted a remote telemetry data logger to transmit data and alarms but found that leading manufacturers didn't offer models for environmental monitoring.

The department deployed three GSM/GPRS data loggers as a low-cost remote monitoring solution. These rugged field telemetry devices are designed for rapid deployment at a low cost. Each data logger has a single analog 4-20mA input with up to 8 channels to interface with many types of hydrometric sensors. The technician connected each logger to a depth/level pressure sensor and a dissolved oxygen/temperature sensor. With this setup, Channel 1 of each logger records water level, while Channel 2 logs % Sat (Saturation) and Temperature.

At each remote site a data logger has been installed into a fiberglass cabinet with the connected sensors fitted into a GRP 100 mm sq. box section stilling-tube enclosure. This enabled easy riverside installation. For added protection the loggers have a rugged construction, which can withstand temporary submersion, sealed to an IP68 rating.

Fitted with a socket for the external antenna, the devices automatically transmit all data via their GPRS communications, operating as remote outstations. Data capture is performed using the manufacturer's telemetry server — accessible via the internet. Now the department head receives all the data on his desktop PC every Monday morning along with text message warnings whenever preset DO levels are too low. Meanwhile, each device's internal lithium battery pack is field- replaceable and only needs to be changed once every 5 years (with an option for an external lead acid cell). This is particularly effective when combined with low-cost GPRS ‘always-on' protocols.

Each logger's storage capacity holds 29,760 16-bit readings, and the oldest data is overwritten when full. This secure data storage in flash memory eliminates data loss if the battery should fail, and the loggers give advance notice of this with their low-battery alarm. The technician only needs to travel out to the loggers when it's time to collect the water samples.

If especially low DO levels are present in any given body of water, the onsite data logger will alarm users so that preventative measures can be undertaken such as installing aeration equipment and removing excess algae. For effective environmental monitoring, the technician also connected a water sampler to each logger. Each week when the data logger's sampler trigger alarm activates, the water sampler fills up a vial and caps it for later retrieval and lab analysis.

Free software is included with the loggers for setup and control, available in versions for both Windows (98, 2000, XP, Vista or 7) and Windows Mobile (3, 5 or 6). Users set up the data loggers, configured recording rates & alarms, and graphed data for all channels. Operators can also activate a control output on alarm, configure & test telemetry modems, export data to CSV or XML format files and more.

The data loggers have already lowered the department's operating costs by logging every water value and automatically sending data directly to a desktop — they're safely left to log even under hostile conditions. This remote monitoring solution was well within the organization's budget and the remote telemetry capability now saves the organization the time and money otherwise spent sending someone out to collect the logger's readings. In the future if the technician wants to utilize smart sensors, the loggers also have an option for an SDI-12 compatible multi-channel expansion port.

Source: Water Technology

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• Monitors
• Water Safety Plan