When it comes to medical device projects, one of the key issues is the lifespan of the machine. As a result, I’m always surprised that engineers consider using conventional memory devices, such as USB sticks and camera cards in a design.

Let’s say you are working on a fluid removal instrument that is going to be available on the market in eighteen months time. You need to build in a memory device to ensure that the machine is used for a limited amount of time, to meet the compliance requirements. After this period, the device needs to be withdrawn from use and re-sterilised. Sitting at your drawing board, metaphorically speaking, you design in a USB stick, produced by a commercial manufacturer. In eighteen months time, just as the machine is about to be mass produced your colleague in purchasing contacts the USB manufacturer to place an order. He or she receives the unwelcome news that they need to place a final order now, because the USB stick is end of line and they have already stopped making them.

This is a typical scenario. You see, according to Moore’s law, outlined by Intel founder Gordon Moore in 1965, computer chips double their output every eighteen months. This law can be applied, roughly, across most products in the IT world. As a result, in order to maintain their position in the consumer market, memory manufacturers need to increase the capacity of their devices massively on a regular basis. So, that cheap and nifty 64MB memory-stick you sourced isn’t going to be available when you go to market. Instead, you will be offered the 6GB model, which will cost a small fortune but offer over ninety times the memory you need for your fluid removal machine (and even at 64MB you were over specifying to future proof the instrument). 

The only solution is to source a rugged, industrial, memory token that offers the necessary sterilisation capability you need for compliance and the lifespan required to make sure you can still order spares in twenty years time. Typical applications for this kind of portable memory products include limit-use, calibration, data upload, firmware updates, data transfer, data logging, user authentication and access control.

Calibration allows the user to automatically upload parameters from a token to another device to eliminate manual errors. One existing application applies this to a heart monitor with a single use balloon catheter. Each catheter is precisely calibrated before use, using a token, which saves time, reduces implementation cost and eliminates errors.

Limit use allows the tokens to monitor how many times the device has been used and for how long, as in our fluid removal machine earlier on. Another example can be found in a DNA analysis system that uses disposable gel cartridges. Here, the token activates the equipment, monitors the usage and notifies the device once the cartridge has reached the limit of its lifetime and needs to be replaced.

The memory tokens and receptacles supplied by Nexus are manufactured in the US by Datakey Electronics. They have been in UK applications for over twenty years and are already used across the globe by customers including St. Jude Medical, General Dynamics, Cisco Systems, Raytheon, Siemens, Tyco Healthcare, Gilbarco, several governments and many other multi-national corporations.

So, my advice would be; conventional memory – forget it. If the device still needs to be on the market in twenty years time, or even five, you need to go down the specialised, rugged route. 

This article was published in Medical Device Technology - March / April 2009