Imagine for a minute - a water or wastewater system without any communication at all. Technically, you could design this system. The instruments and the controls work together, with no interface. Lots of programming in those PLCs with if/then instructions. A completely automated system, without any communication at all. It just takes care of itself. Sounds a little bit like a dream come true.
But how would you know if it works? The only way that you would know if it was working would be to look at your water coming out of your tap in a clean water system, or the quality of your effluent coming from the wastewater system. And then when something did go wrong, there's two problems: one, it's too late to do anything about the water or wastewater that already been through the system, and two, where do you start troubleshooting?
Stop the madness! A big part of any water and wastewater system is getting information from it. To do this, we have to have a form of communication coming from the equipment - basically, we need a way to talk to our system. There are different ways to do this, but here are a few of the most common.
But how would you know if it works? The only way that you would know if it was working would be to look at your water coming out of your tap in a clean water system, or the quality of your effluent coming from the wastewater system. And then when something did go wrong, there's two problems: one, it's too late to do anything about the water or wastewater that already been through the system, and two, where do you start troubleshooting?
Stop the madness! A big part of any water and wastewater system is getting information from it. To do this, we have to have a form of communication coming from the equipment - basically, we need a way to talk to our system. There are different ways to do this, but here are a few of the most common.
- Local lights. It's basic, but a local light, whether it's a beacon light on top of a control panel or an indicator light in a MCC, is letting us know that something is happening in your system. These local lights work really well - if someone is there and paying attention to it.
- Dialers. A lot of times a dialer is the next step up from a beacon light. A dialer requires a dedicated phone line. It takes the readings from sensors and relays that you have in the control panel, and translates them into messages. It is programmed to call you with a prerecorded message when certain conditions are reached, like a high level or low temperature. The specificity of the prerecorded message depends on how many channels the dialer has. You can have anywhere from 4 channels (which would have 4 prerecorded messages) to hundreds (hundreds of prerecorded messages). Often, a 4 channel dialer that is serving multiple sites will have common alarms, like "Lift Station 1 Common Alarm" that calls when any of the alarm conditions are reached. The dialers with hundreds of channels are often used in as "master" dialers in SCADA systems that use a different form of communication between sites.
- Modems. Modems require phone lines, too, but they're sending data through the phone line to the master site. The master site has a PLC that takes all the information received through the modems and displays it, via an HMI, touchscreen or computer. Modem can be pretty sensitive to "noise" on phone lines, and older phone lines can cause communication problems in these systems. Additionally, newer phone lines can be more reliable but often come at a higher cost.
- Cellular/Satellite. Cellular and satellite systems work in similar ways, so I've grouped them together. Controllers with the communication abilities are placed at remote sites, and communicate either via a cellular network or a satellite network to a third party. The third party has a predesigned SCADA software that is accessible from a internet browser. These systems are prepackaged, and have an ongoing fee (monthly or annually) to be able to access the SCADA system. Additionally, you are reliant on the maintenance of the third party SCADA system. If there is a problem, our ability to troubleshoot and fix the system is limited to your equipment - we can't fix or troubleshoot the third party equipment. The place for this kind of system is often in a difficult to reach location that doesn't have line of site with another site.
- Radios. Radios provide wireless communication, and increasingly are becoming more powerful. The industrial radios that we use in water and wastewater systems are industrial strength that offer communication over large distances. There are both licensed and unlicensed radios. Unlicensed radios do not require and FCC license and work really well for many smaller systems. For longer distances that require more power, licensed radios are a great solution. Contrary to Marshall Mather's quote that "the FCC won't let me be me", getting and maintaining a FCC license is not a big deal. There is an initial license coordination fee, and the license needs to be renewed every 10 years for a small fee. While there are companies that will handle the renewal for you, it is definitely something that can be completed by the system itself.
- Fiber optic lines. Fiber optic lines can transfer a lot of information very quickly, and don't require very expensive equipment on either side - just a fiber optic switch. Laying fiber lines is expensive, and it requires a physical line between each site. This often makes it feasible for water and wastewater treatment plants, but untenable for communicating between remote sites like wells and lift stations.
