Jan 15, 2007

Right on the Stick

Early this year, Horner APG, an industrial controls manufacturer and system integrator, had a customer that needed a cost-effective remote monitoring system for water and wastewater treatment facilities. Horner took on this challenge with traditional analytical equipment but found it could not meet desired performance and cost goals.

In April 2006, Horner learned about AquaSensors’ DataStick technology and quickly saw the potential for reducing cost and improving measurement performance. With the DataStick, Horner saw that one low-cost PLC with an integrated HMI could be used to support a full network of analytical measurements, pumps and valves needed for the measurement skid.

The new system eliminated more expensive PLC equipment, peripheral current loop cards and cut power supply requirements in half. Without the need for current loops and power cables, wiring and DIN rail terminal requirements were reduced by 70%. Because the system did not require intermediate analyzer controllers, panel space was cut to almost nothing.

Traditional solution doesn’t meet the need

Horner built its original skid system in a 6- x 2-ft cabinet with NEMA 4x access doors. The upper compartment of this cabinet housed panel space for four analyzer boxes required with traditional analytical measurements, space for an HMI, a PLC, current loop modules and paper reporting equipment. The lower compartment of the cabinet housed the pump and associated pipes needed to draw process water to the analytical sensors. The cabinet also needed a barrier to protect the electronics from the measurement compartment, adding cost.

In May 2006, Horner purchased five DataStick systems to measure pH, ORP, dissolved oxygen, low-range conductivity and high-range conductivity. Within a short time, Horner APG had used an industry standard protocol to integrate all five measurements into its controller, complete with analytical monitoring and process flow control. Trending graphs were added for each measurement to show history. Using an industry standard communications protocol made it possible to develop a completely customized interface that specifically met the needs of Horner’s customers.

The measurement technology

Each DataStick body is a universal analytical system that can be configured to measure pH, ORP, conductivity, resistivity, dissolved oxygen, dissolved ozone, turbidity, suspended solids or chlorine by simply plugging in a factory calibrated sensor head to the front end. Each is installed directly in process with standard mounting hardware for continuous monitoring and is connected to control computers through a single network cable for direct measurement, calibration, configuration and diagnostics.

Intermediate instrument analyzers and transmitters are not needed. The unit is available with a variety of industry standard protocols that allow the system integrator to customize a single interface for measurement and control from any location. This eliminates the need to open skid cabinets to perform sensor calibrations or current loop scaling with individual analyzers that may have different menu navigation systems. It can be configured to communicate with most computer networks through a family of communications adapters that can be plugged into the back end of the equipment.

Horner selected Modbus RTU for communications between its XLe controller and a series of five DataSticks. The equipment is mounted directly into a process pipe and the Horner XLe controller is mounted into a small 10- x 8-in. NEMA4X enclosure that also contains a power supply and wire termination. Pumps are controlled at the base of the process chamber. This controller can then be networked to transmit the data remotely and allow remote access for calibration, configuration, diagnostics and process control so that site maintenance trips can be made less frequently.

In addition to reducing integrated system cost by cutting labor in half and reducing the complexity of cable and enclosure space, it reduces maintenance and calibration requirements and improves measurement performance. Calibration data is maintained in the sensor head, and sensor heads can be transferred to any system without requiring a new calibration. This allows the user the choice of calibrating in process or in the lab. Integrators that would prefer to treat the analytical measurement point as just another device on the network can schedule plug-in sensor head replacements and avoid the chemistry altogether.

Performance and ease of customization

Horner found the DataStick architecture improves measurement performance because of the close coupling between the sensor head and the communications gateway. Twenty-four-bit data is maintained throughout the system, and environmental noise and signal reduction is not a factor.

Replacement analytical sensor heads for the units are less than half the cost of traditional cabled sensors. Cost of ownership is further reduced because less field time is required for calibration and maintenance.
Phil Horner, president of Horner APG, sees a system that can meet almost any set of requirements for a customer.

“For customers who cannot afford to go down, a redundant backup controller can be installed. Alarm conditions can trigger text messages to be sent to operators, wireless data links can simplify remote site connections, and memory capabilities are sophisticated enough to record data trends, event capture and diagnostics for multiple sensors.”
With the flexibility of the DataStick setup, Horner can offer the customer a choice of display and navigation capabilities from a monochrome 8-line display to an 12-in. color touch screen for up to 20 analytical measurement points.
The good news for the end customer is that options are simple to build at affordable prices with excellent system reliability and remote diagnostic capability. Horner will be promoting this solution under the name of SmartMon Water, which provides monitoring, data logging and alarm programming in a single ready-to-use package.

Implications for the broader market

Horner sees the DataStick as a product that simplifies system integration and makes it possible to provide process measurement and control directly to the municipal or industrial plant.

To date, system integrators have used the unit with great success and have begun to exhibit these systems at international trade shows. When used together, these new plug-and-play analytical products and combined HMI/PLC products change the dynamics of process instrumentation by enabling the end user to take control of analytical measurement directly.

About the author

Bruce Bathurst is president of AquaSensors. He can be reached at 262/255-4459 or by e-mail at [email protected].