Taking batteries out of the cost equation for wirelesshart networks – oilman – the magazine for leaders in american energy

Used to monitor the operating conditions and health of industrial equipment from engines to motors, pumps, valves, and compressors, wireless instrumentation is often used in conjunction with control systems as well as for predictive and preventative maintenance programs.

However, with hundreds – even thousands – of these devices at a single plant site, the cost and resources to replace batteries 6-8 times over the lifetime of each unit can often exceed the initial investment several times over. In addition, it places an unwanted burden on maintenance personnel while also increasing risk of injury when replacing batteries in units located in remote or hazardous areas.

This dramatic extension of battery life is not the result of more advanced, longer-lasting power sources, but rather a careful, microsecond-by-microsecond analysis of the unit’s power consumption along with clever engineering to keep that usage to an absolute minimum.

For an industry in which battery replacement is an accepted consequence of installing wireless sensor networks, removing the need for this task entirely from the equation significantly reduces the lifetime operational costs. It also removes one of the primary barriers to broader implementation for many process facilities.

Most instruments provide a warning when battery power is low. When this occurs, personnel proactively replace the battery before it runs out completely. In addition, there are logistical advantages to replacing batteries of similar age in nearby instruments at the same time.

If you don’t change out batteries proactively, you run some risk. You could get a low battery warning from a neighboring unit a day after you leave the area. So, there can be some benefit to replacing all the batteries in an area and that means extra batteries. But that is another problem that is eliminated altogether with a lifetime battery solution.

However, most network communication is not as predictable and can go from dormant to large spikes in power consumption every time a signal is sent or received. When, and how much power varies, but the more frequently information is transmitted or received from the network, the more power that is burned.

Making judgments about power consumption is incredibly difficult. It is not just a light bulb burning the same power second after second. It is extremely dynamic and can spike to a thousand times more consumption in one microsecond than the next.

Some manufacturers specify battery lifetimes using readings every 32 or 64 seconds in an attempt to provide a reasonable battery life. For our equipment, which monitors the operating conditions of engines, motors, pumps, valves, and compressors, a more ideal repetition rate is every 4 seconds.

This underscores the reason that Adaptive Wireless Solutions, a manufacturer of wireless instruments, has invented new techniques to minimize power consumption and increase battery life to the full life of the instrument. As if to prove the point, the wireless instruments come with built-in batteries that are not replaceable. Replacing a unit with a fully warranted new one is preferable to buying and throwing away batteries on an old unit.

To do this, advanced software and hardware was used to allow product designers to examine the power consumption of its wireless instruments on a sub-microsecond-by-microsecond basis. This provided invaluable insight, identifying areas in which power could be better conserved.

The truth is that most instrument manufacturers can’t provide real numbers on power consumption and battery life, because they just don’t know the answer. At Adaptive they chose to investigate all power usage, and look for accumulative efficiencies in every facet of the device operation.

Among the technologies implemented was a unique software architecture that not only turns the unit on and off automatically when not transmitting or receiving, but also turns the inherent processing on and off as well and does so very rapidly with minimum wasted time. This approach to energy conservation is similar to cars that conserve gas by shutting the engine off at traffic stops or during extended idling.

To keep this connection to an absolute minimum, Adaptive Wireless also re-designed its instruments to be separated into two parts: the end node (with highly accurate sensors at the read point) and the central controller, which contains the WSN antenna.

In this two-tier architecture, the central controller alone communicates with the WirelessHART network. Up to 8 end nodes can then be connected to the central controller using a Bluetooth Low Energy (BLE) radio link. This reduces the consumption from WirelessHART traffic to as little as 1/8 th what it normally would have been.

In many cases, wireless instruments are used in hazardous environments and so are certified as intrinsically safe (IS) or explosion-proof (XP). Given the environment in these plants, there can be a benefit to eliminating the need for plant personnel to spend hours installing replacement batteries – not to mention eliminating travel back-and-forth to the site.

The logistics of moving people in and out of the field is a safety concern for many process industries. These are areas where workers are exposed to hazardous materials and gases. When you don’t have to send someone to the field, you have made a gain. That should not be minimized.