Videographic recorder increases efficiency

By replacing a six-pen paper chart recorder at its 210-million-gallon Loudonville Reservoir with a solid-state videographic recorder, the Albany, N.Y., Department of Water and Water Supply gained a new dimension in data availability and flexibility while eliminating the most annoying aspects of data collection.

The recorder monitors and records six channels of chlorination data at the three-basin reservoir that forms a major part of Albany’s gravity-fed water system. The system, which serves more than 100,000 people, includes two surface water impoundments totalling 12.1 billion usable gallons, as well as a 32-mgd filtration plant the reservoir for finished drinking water. The Albany Water Department operates strictly on revenue collected from water sales, without recourse to tax revenue, so efficiency and budget accountability are critical.

SYSTEM OVERVIEW

The system is fed entirely by gravity and receives its water supply from two reservoirs located in the Heldeberg Mountains, approximately 22 miles southwest of the city. The Alcove Reservoir holds 13.5 billion gallons at an elevation of 618 feet, while the Basic Reservoir holds 716 million gallons at an elevation of 946.5 feet.

Water is delivered to the city through a single supply conduit consisting of 54,000 feet of 48-inch diameter cast iron pipe.

Albany, at an elevation of approximately 200 feet, normally receives its water from the Feura Bush filtration plant. If the city is consuming more water than the plant is producing, or if the plant and associated mains are shut down for repair, water flows by gravity from the Loudonville Reservoir, located high above the north end of the city.

At a top elevation of 353.5 feet, the reservoir serves as a balancing reservoir, holding excess capacity when plant output exceeds consumption and supplying pure water when demand is high. Because it is below the filtration plant, yet above the city, gravity allows water to flow to or from the reservoir without pumping. If an emergency necessitated shutting down the raw water line or the line from the filtration plant, the reservoir could supply the city for approximately eight days.

MONITORING THE RESERVOIR

The Loudonville Reservoir consists of three open concrete basins. “Because they are open to the atmosphere, the water tends to lose chlorine over time,” says Mark Hood, water department engineer. Consequently, in 1988, the city installed a chlorination system that monitors and automatically re-chlorinates water when it leaves, bringing it back up to a specified level that will assure its purity.

The paper chart recorder was originally installed to measure water flow rate in or out, chlorine dosage and chlorine residual. These three parameters were recorded for two pipes – from basin A and combined basins B and C – with the recorder’s six pens.

But, there were problems. “It turned out that having the graphs down at the plant didn’t do any good when you were up here trying to view a problem, make adjustments or see what transpired over time,” Hood says. “And the resolution on the chart wasn’t very good, and pulling all the paper out to review it was annoying. Sometimes, paper would hang up or a pen’ would run out of ink, and we wouldn’t have a chart.” To improve the operation, Hood replaced the paper chart recorder with the Angus Electronics VGR4 unit. The entire unit fit into a standard DIN – size panel cutout, making it possible to display data in formats that include view trend text, bargraph, and alarm history. A choice of graphic elements and 16 different background colors makes it possible to customize formats, which can then be printed exactly as they appear on the screen.

“It’s very simple to review,” Hood says. “Unless there is an alarm, our instrumentation technician just stops by every morning, scans what has happened over the past 24 hours and makes adjustments if necessary. If there has been an alarm, it’s easy for him to view what was occurring when the alarm took place. The recorder also keeps numerical data, which we had to interpret off the paper with the chart recorder. Now, with the information on a disk, we can post-process it at the filtration plant or in my office.”

A standard 3-1/2-inch disk holds data for approximately one month at the collection rates in use. Two different rates are used: once a minute during normal operation and every 30 seconds during an alarm, to give finer resolution and more data.

Effective chart speeds are 100 mm per hour under normal conditions and 1,000 mm per hour under alarm conditions.