Small Scale SCADA

Cloud-based technology provides sophisticated yet affordable system monitoring and control for a small California water company.
Small Scale SCADA
SCADA display showing a normal hypochlorite level.

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How can a small water company set up a SCADA system that provides and stores information to support intelligent decisions and control the water system without breaking the budget?

I faced that question two and a half years ago when asked to take over as facilities manager of Gill Creek Mutual Water Company, serving about 86 homes near Geyserville, Calif., when the current managers retired. Having served as a volunteer assistant manager and on the board of directors, I knew the company faced some challenges but had some positive qualities.

On one hand, maintenance and repairs ate up 32 to 45 percent of the budget, our electricity costs were high because we were unable to sync with our utility’s time-of-day rate schedule, and we often depended on customers to tell us when we had a problem such as no water or water overflowing a tank.

On the other hand, we had ample water storage capacity, good-quality groundwater, and a good relationship with regulators and customers. We needed a way to monitor the system and control the equipment.

A traditional SCADA system would have cost $100,000 to set up, and more to maintain and administer — clearly beyond our budget. I called my brother Paul at XiO, specializing in cloud-based automation. He said his company could collect information about our company, store it in the cloud, and use it to make decisions to help control our pumping, ultimately saving us money.

While most of the cost of traditional SCADA is in hardware and software, a cloud-based system is stored on servers shared with other users, and the costs are also shared. Today, we have a cloud-based control system that runs all our equipment and tells me more about our fairly complex water company than I could have imagined. Our total SCADA system has cost less than $25,000.

Each morning when I check our system from a laptop, a smartphone or an iPad, I see that the pumps filled our tanks before electric rates went up at 8:30 a.m. If our system uses more water than expected during the day, the system decides when to run the pumps to avoid peak rates. Also in place is an alarm system that can email maintenance people to report minor anomalies or phone me at any hour if immediate action is needed.

Getting started: communication

We needed to link our three locations: the wells, the pumphouse with contact tank and the hilltop tank reservoir. For years we had used five dedicated phone lines to communicate on/off information between the pumps and tanks. Floats in the tanks directed the pumps to start and stop. One phone line was hooked to an auto-dialer that was less than reliable in sending accurate alarms. The usual replacement for a phone line is to use radios that work with the SCADA system and use serial modems, which means extra costs with every hardware or software change.

Paul recommended a fairly new technology — reliable and low-cost IP radios, which are used to provide Internet access in rural areas. These smart 900 MHz radios establish a local area network (LAN), but we needed line-of-sight.

My first job was to establish radio contact between the pumps and wells. After using GPS to identify four possible transmitter/receiver locations, we plugged the data into Google Earth and found that we had line-of-sight down a canyon if we could locate one of the pumphouse radios on a hill above the pumphouse. We could then run a cable 150 feet to the pumphouse, which would contain most of our control equipment.

We bolted the radios to 1 1/2-inch galvanized pipe and secured them with guy wires. (If we had been confident that the radio network would perform as well as it finally did, we would have used telescoping towers to make maintenance easier for the two radios that stand 30 feet above the ground.) The wells were in direct line-of-sight from the pumphouse, so that hookup was easy.

System monitoring

Phase one was to monitor the system without changing the controls to see what was happening daily. We installed pressure transducers to measure the water level in the upper tank, the intermediate surge (contact) tank and the two wells. The well transducers hang from stainless steel cables two feet above the submersible pumps, but the tank transducers are at the bottom, outside the tanks, connected to the tanks by narrow rodent-resistant tubing.

The transducer, in a PVC housing (Figure 2), sends the signal via a cable to our module in a watertight box (a field-installable unit, or FIU) fastened to the radio tower. The transducers measure the depth of water above the sensor, and the FIU converts that signal to feet and inches. We can measure changes of less than 1/8 inch over the 15-foot tank height. Since we had 110 VAC power at the upper tank, we just plugged in, but since the module and radio together use less than 10 watts, we could have used a solar supply.

We also installed electronic pulse generators on our McCrometer flowmeters at the wells and at the output of our lift pumps, and tied them into the nearby FIUs. Our last monitoring station was in the chlorination room. We rebuilt a free chlorine monitor (Hach CL-17) and plugged it into the FIU in the pump house, and also began reading the level of sodium hypochlorite in a 40-gallon mix drum using a noncontact gauge.

Then we hooked up the system to the Internet using a cellular modem that plugged directly into the Soft-I/O module. There is only one control component inside the FIU. We can now watch our system from any laptop, iPad or smartphone.

What we learned from monitoring surprised us:

Our wells were in good condition after 40 years. The well-level sensors told us that even after the pumps ran for several hours, the water level dropped only 16 feet, leaving at least 66 feet of water over the pumps. Recovery after pumping took only minutes.

For years, the floats in our 84,000-gallon upper tank were only allowing 5,000 gallons of outflow before the pumps ran to refill the tank — the result of an error in how the floats were set.
Both well pumps typically ran together to keep up with the 30 hp lift pump, causing the well pumps to cycle frequently while the lift pump was running. The well pumps seemed to fight each other, and the resulting flow rate was barely higher than if the faster well pump had run alone. We found that one well pump could do the job without cycling, saving significant energy and wear on both pumps. For long pump runs, we could turn on the second well pump to finish the cycle without shutting down the lift pump.

Since all of our pumps started at random times during the day depending on float height, we often paid the highest electric rates. In summer, about half our energy cost came from pumping about 30 percent of the water.

The sodium hypochlorite mix level dropped slowly even when the well pumps were not running. A couple of bad check valves created a vacuum in the pipeline from the wells when water drained back into the well. That sucked chlorine through the metering pump(s) and allowed an extra gallon or so of disinfectant to be drawn into the well pipe each day. This was easily rectified and did not cause a hazard, but we would not have known about it without the controls.

By constantly monitoring the electricity used by each pump, we found that the newer well pump cost us about 50 percent more per 1,000 gallons than the older pump. We also know that one of our lift pumps is much less efficient than we thought.

Several times per month, a flaw in the old startup routine would abruptly stop the lift pumps before the slow-closing Bermad valve shut down. The resulting “hammer” subjected the pipes to damage, and the alternate lift pump often failed to start automatically after the other pump stopped, causing the system to run out of water.

If one of the lift pumps failed to start, the lift pump would shut down and the entire system would lock up until an operator went on site to reset the pumps. During that time, the main tank was heading to empty.

Cloud system startup

We had found a number of areas needing fairly simple fixes. Now it was time to turn the system over to the new controls. The goal is to provide uninterrupted service to the community, so we maintained the ability to run all pumps manually if necessary.

We connected the well pumps so that either could run separately or both could run together to keep the intermediate (contact) tank supplied with water for the lift pumps. This independent operation caused a bit of a problem: Because the flow rate varies greatly depending upon which pump (or pumps) are running, the amount of sodium hypochlorite needed varies similarly. In addition, the only operational flowmeters were nearly a mile from the pumphouse at the wells.

We were saved by the LAN, which makes the combined flow rates of the two wells readily available at the pumphouse. Within seconds of a well pump starting, the signal from the McCrometer flowmeters at the wells and a flow switch in the disinfection room allow the local Soft-I/O module to calculate how much sodium hypochlorite the metering pump(s) should inject into the pipe to the intermediate (contact) tank. A Hach CL-17 downstream of the intermediate tank tells us the free chlorine level as water is pumped to the main reservoir up the hill.

We set up the 30 hp lift pumps to follow certain priorities:

1. Keep the tanks full regardless of electrical costs during high-fire-danger times.

2. Pump water when electrical rates are lowest, if practical.

3. If one lift pump fails to start, or stops during its normal run, trigger an alarm so that the other pump automatically starts and keeps the tanks full.

Alarms are also sent:

  • If the level of available sodium hypochlorite is getting low
  • If the chlorine analyzer shows a high or low free chlorine reading
  • If water levels are either higher or lower than a setpoint in any tank
  • If any pump fails to start or maintain flow
  • If the cloud servers lose contact with one of the sites

Results

By taking advantage of off-peak electricity, we reduced our electric bill by about 25 percent. Some savings came from running the more efficient pump preferentially. Several times we detected system leaks very quickly, resulting in a tight system in which we billed about 99 percent of the water pumped.

More than once, we detected when an operator forgot to fill the sodium hypochlorite tank. We were able to see the outage graphically and refill the drum before untreated water was pumped into the system. Since the cloud-based monitoring system has been active, we have had no out-of-water events.

I have become accustomed to picking up my smartphone or going to my desk and in a minute knowing that all is well on the system. Every event the SCADA system has recorded in the past year is stored in the cloud and is available, without taking up space on a local computer.

The bottom line is that the cloud-based SCADA system helps us anticipate problems rather than react, and thus our maintenance and repair costs have dropped dramatically. Looking at our energy savings and the reduction in emergency service calls, I can say we have made our small water district a better organization. It has certainly made my life easier! A link to a cloud-based SCADA system is at http://my.soft-io.com/demo.

ABOUT THE AUTHOR

Peter Sagues is facilities manager of Gill Creek Mutual Water Co. in Geyserville, Calif.



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