The addition of RFID tags in the widely used pneumatic-tube system in hospitals has dramatically improved system performance without re-build.
There are times when trying to keep a very old system and its underlying management concept operational seems almost hopeless. Think of your favorite PC, operating system, or application from a decade or more ago and the effort it takes to maintain operation. At the same time, there are occasions when a modern technology upgrade can make a system—which has become clogged under the weight of its success—perform like a bigger, better system at modest cost and effort, and no new construction. Such is the case with the addition of RFID tags to pneumatic-tube routing systems.
These days, as email and the web have greatly diminished the need for physical mail in so many situations, it’s important to remember that there are many real-world scenarios where a tangible, physical object must be sent, and bits won’t substitute for it. That’s the case in hospitals where various patient samples—fluids and tissue—must go to different labs and medications need to be sent from in-house pharmacy to patient. To solve this problem, pneumatic tubes—which accept and transport canisters called carriers from a sending station to a distant, selectable receiving station—are used (Figure 1).
Figure 1 The carrier tubes are extremely rugged yet have a simple, easy-locking door latch. They are six inches (15 cm) in diameter and about 13 inches (33 cm) long; longer carriers would need larger-radius tube curves, costing about $125 each. Source: NetBankStore
The earliest and simplest systems used a physical hub-and-spoke network topology. The user put the load in the carrier, added an address label, placed the loaded carrier into the tube, closed the door, and pushed the “go” button. Compressed air would route the carrier to a central sorting location where someone looked at the destination label, placed the carrier in appropriate outgoing tube, and send it on its way. While the activity in the hub could be hectic, from a user’s perspective, the system worked and was a critical part of an efficient hospital.
The alternative of using couriers, even within a building, was slow, inefficient, clogged hallways, and was dependent on available personnel. Eventually, automated routing hubs were developed which read the carrier and directed it to the destination tube.
It’s interesting that before these systems were used for hospitals, they were used for postal mail in cities such as London and New York. The references have some fascinating historical information along with amazing photos. Note that there are also point-to-point pneumatic-tube systems often used at bank drive-up windows to handle customers from lanes which are not adjacent to the building itself. These use the carrier and tube principle, but have none of the addressing or routing issues, as they are dedicated, fixed-route, point-to-point systems rather than spoke and hub.
The use of tubes for mail became obsolete for many reasons; it was a long time ago, even before email slashed the volume of paper mail. However, the role of the pneumatic tube system in hospitals, where there is no viable alternative, has gone the opposite way and its success became its biggest problem. As medical and pharmaceutical technologies advanced, the number of patient tests performed has skyrocketed; moreover, patient samples or medications needing quick transport have also jumped.
System traffic overloaded the tubes, and adding more tubes is either too costly or impossible; it’s like adding more highway lanes in a crowded area (Figure 2). Worse, if a carrier got stuck for whatever reason, it would block lanes of the tube system; if it got misrouted, the consequences could be worse.
Figure 2 This very small portion of the recently upgraded system at the University of Pennsylvania Medical School highlights the overall complexity of the tubes running within hospital walls or routing centers. Source: Hospital of the University of Pennsylvania
That’s’ where modern electronic technology has reinvented the pneumatic-tube system to do more and do it better without adding more tubes. In addition to paper labels indicating the destination address—needed only for personal convenience and backup—or barcode slips to be inserted into the carrier, the newest systems use RFID technology to label each carrier. The user at the sending station enters the address code on the touchscreen keypad, and the tube-management system links that address code with an RFID tag, which is permanently attached to that carrier (Figure 3).
Figure 3 The user station of a modern system is an excellent model of a functional, focused, minimalistic and unambiguous user interface. Source: Swisslog Healthcare
From that point on, the system is totally automated. As the carriers speed along at between 15 and 20 mph (20 to 30 km/hr), they are continuously tracked and routed via switching nodes on the best available path to the recipient.
The system management does more than just direct each carrier on its journey. It checks that it’s going where it should be going (problems do occur, but rarely), identifies traffic jams due to a stuck carrier (again, surprisingly rarely) and continuously monitors and manages traffic flow, waits, and queue sizes, and even ensures that enough empty carriers are returned to each station based on use patterns. Many systems even have a provision for rushing critical items such as blood to an operating room via a “priority” carrier coding, allowing these carriers to supersede other ones in the routing plan and travel path.
These systems are complicated networks and have many parallels to electronic communication systems. The system at Stanford University Hospital has 124 stations (every nursing unit has its own); 141 transfer units (akin to routers); 99 inter-zone connectors; and 29 blowers. Maximum travel time for a carrier over the many thousands of feet between sender and receiver is under three minutes in most cases, even during peak-traffic periods. The analysis of traffic, waits, queues, and other parameters is as quantitative as it is for many electronic networks (Figure 4). A large system can be handling hundreds of these carriers per hour, which doesn’t sound like much until you realize that average travel-time and wait for arrival is not the key, but maximum wait (delay) is what counts.
Figure 4 Traffic analysis for these systems is very similar to analysis of electronic-communication links; the graphs show system loading versus queue size from two perspectives. Source: Telecom Pneumatic Tube Systems
Even without the upgrade and benefits of RFID tags, these pneumatic-tube systems were in no danger of being obsolete, as there is no viable alternative to their function, until Star Trek-like transporters and replicators become available. Given that reality, it’s interesting to see how the addition of RFID tags to the carriers in these systems has enabled building a superstructure that has improved system performance, throughout, reliability and other critical specifications even as the system load factor has also increased. You might even call it a true IoT success story.
Have you ever been involved in a system design where adding more sensors at modest cost enabled much-enhanced system management and performance? Was it difficult to convince those paying for the R&D effort or the actual installation to add these sensors? Did the eventual benefits go beyond what you anticipated, or did they fall short of the goals?
This article was originally published on Planet Analog.
Bill Schweber is an electronics engineer who has written three textbooks on electronic communications systems, as well as hundreds of technical articles, opinion columns, and product features. In past roles, he worked as a technical website manager for multiple EE Times sites and as both Executive Editor and Analog Editor at EDN. At Analog Devices, he was in marketing communications; as a result, he has been on both sides of the technical PR function, presenting company products, stories, and messages to the media and also as the recipient of these. Prior to the marcom role at Analog, Bill was Associate Editor of its respected technical journal, and also worked in its product marketing and applications engineering groups. Before those roles, he was at Instron Corp., doing hands-on analog- and power-circuit design and systems integration for materials-testing machine controls. He has a BSEE from Columbia University and an MSEE from the University of Massachusetts, is a Registered Professional Engineer, and holds an Advanced Class amateur radio license. He has also planned, written, and presented online courses on a variety of engineering topics, including MOSFET basics, ADC selection, and driving LEDs.