A Guide to Remote Control Applications
According to PBS, one of the earliest examples of remote control was in 1898 for a radio-controlled boat developed by Nikola Tesla. In recent years, we gained the ability to use smart phones to remote control anything from a digital video recorder to a pump. Just last month NASA's Curiosity, a remote-controlled rover, landed on Mars and will be used by scientists to determine if the atmosphere can support life. Remote control has introduced simplicity, convenience and versatility to our everyday lives.
In this article we will share some of the common and unique ways Mission customers utilize the output capabilities of the M110 and M800 RTUs for remote control. The hardware used for remote control includes the on-board output relays and/or the optional analog outputs in conjunction with the digital and analog inputs.
The three output relays can be commanded automatically or paged manually from your web portal. Common applications that utilize the output relays include:
Remote, auxiliary and emergency pumps
Controlling pumps is the number one way in which the output relays are used. Emergency pumps can be manually turned on from the user portal. With the optional Tank and Well system automatic control of pumps is based on the level of a tank. A remote pump can be controlled based on a digital input with the digital intertie option. For example, a remote, upstream station can be inhibited from pumping temporarily in the event of a high level.
There are several approaches that customers can take when it comes to control valves. If the level at a master lift station indicates a near full condition an output relay can be used to divert flow from upstream stations to a secondary lift station. In a Tank and Well control system, users sometimes connect the third to a control valve connected to a neighboring water system.
In a previous newsletter article we described a remote water sales tracking solution. In that case commercial construction and irrigation companies are issued an electronic key to self-refill their tanker trucks at a strategically placed Mission system. When the key is scanned, a relay is used to open the water valve.
While the Mission system is not a life safety solution, some customers use an output relay to turn on a security light. For example, if a digital input is wired to a gate digital intertie can be enabled to automatically turn a light on when the gate opens.
Manufacturers of stand-by generators recommend that they be exercised periodically. An output relay can be used to start and stop the generator. If the generator is also monitored by a digital input a notification can be sent when it runs.
Apply the one second pulse command from the "Commands" menu.
Additional built-in features are available for use with the output relays. The one second pulse command (pictured above) can be used to reset a PLC or a motor overload upon error. The overload must have an electrical reset option in order to work properly with the output relays. The positive feedback feature can be implemented to confirm the operation of a device controlled by a relay. For example, if a pump is called to run but the HOA switch is set to off, you will receive a "call-to-run fail-to-run" alarm.
The analog output board drives devices that have a provision for 4-20 mA control. Using this variable output signal users can remotely adjust the dosing rate of a chlorine pump or the position of a valve between its minimum and maximum states. Analog intertie, used with the analog output board, allows the master RTU to replicate an analog value to a remote RTU. For example, if the level is high at one station you may want to increase the speed of a variable speed pump at another.
With any control system it is important to remember that all equipment is subject to failure. We strongly recommend taking precautions and implementing redundancy during the design phase in order to develop a safe and reliable system. The "Best Practices for Control Applications" document contains tips and recommendations for fault tolerance, equipment life, and energy savings.
Share your remote control applications with us by sending an email to firstname.lastname@example.org.