Making sense out of buying sensors

While there are many technologies promising to hold the key to future success in manufacturing medical devices, they are only now coming to the forefront. These include things like nanotechnology, bio-absorption, smart materials and more. Industry figures indicate that today's $100 billion market is poised to triple in the next few years. The pressure is on the industry to design better, faster, cheaper products now – a demand that seems at times virtually impossible.

However, there are things that can be done to make existing and future designs more reliable, multifunctional, affordable and easier to manufacture. The relatively low- technology sensor offers promise for refreshing current and future designs.

New technologies, designs and manufacturing techniques have come together to create fresh methods of incorporating multiple sensing technologies into medical devices. Imagine the ability to sense two, three, or more parameters without adding to the cost, weight, or size of a device.

For as many parameters that need sensing, there are ways in which to sense them. This list of parameters includes: current, force, humidity, flow, infrared, liquid level, load, pressure, position, temperature, turbidity and ultrasound.

There are actuating, controlling and monitoring devices such as: flexible or rigid heaters, thermostats, indicators, instruments and recorders. All of these require sealed, limit, pushbutton, key, relay, toggle or rocker switches, either singly or in combination.

Upgrading a current device's sensing performance may be accomplished through some simple redesign that adds little cost and offers the promise of streamlining current manufacturing. The key to getting the job done correctly is choosing a vendor who not only supplies the right sensor technology, but also fulfills needs for service, medical industry requirements, innovation, performance and regulatory expertise.

Let's say your current design senses only temperature. By adding sensing for flow and humidity, this device would be the only one in its class to sense all three parameters. There are three ways to obtain and utilize these sensors:

1. Buy three sensors from three vendors. Next, calibrate, mount and test the final assembly yourself in your own manufacturing plant.

2. Buy three sensors from three vendors. Then hire a contract house to assemble them on a pc board, calibrate and test them, and then have them send the sensors back to you.

3. Buy three sensors from one vendor. Single source programs incorporate intelligence into the chip and harmonize communications protocols to eliminate multiple communications platforms. Next, they test, calibrate and ship a combination sensor with a connector that is plug-and-play, a module ready for installation in your device.

Intelligence includes, though is not limited to, data transformation, signal filtering or conditioning, analog-to-digital conversions, self- diagnostics, control logic, memory and bus communications compatibility.

Medical device designers purchasing their sensors using step one or step two should be cautious. They may be shortchanging their designs, adding cost, adding weight, complicating design and production cycles and diluting a possible competitive advantage by delaying FDA clearance. The following paragraphs detail the pros and cons of each of these methods.

Three sensors from three vendors.

Most sensor companies tend to specialize in one or two "measurands," typically designing and manufacturing pressure sensors or humidity sensors. It's thought that these vendors are temperature sensor experts, so the purchaser will be getting the best temperature sensor available at the lowest price. After all, that's their specialty. A disadvantage to this method is that three sensors bought from three different vendors may not be able to communicate with each other. If that's the case, the disparity will need to be dealt with at either the controller or at the motherboard.

Sourcing from three vendors who ship you the sensors means that you also have the responsibility of testing, calibrating and mounting individual sensors into the subsystem. This scheme involves multiple sources and divided responsibility for overall quality, delivery and reliability. Although perceived expertise and price may, at first glance, be appealing, there may be communications protocol and assembly work to perform later.

Three sensors, three vendors, one contract-manufacturing house.

The second choice is to source three sensors from three separate measurand suppliers. The separate suppliers ship the sensors directly to a contract manufacturer for testing, calibrating and mounting. The benefit here is that this precludes the need to perform these tasks in–house. You receive a complete, inspected subassembly ready for final installation.

A disadvantage is that a fourth vendor has been added to the mix. There is another project to manage, another company to qualify, certify, trace, supervise and pay. Besides having more entities that require communication and supervision, adding vendors tends to protract schedules, increase QA checks and cause other delays in shipping, paperwork and so on. You may still have communications protocol issues with divided responsibility for overall quality, delivery and reliability.

Three sensors from one supplier who handles the whole project.

The third choice is to acquire all three sensors from one vendor. At first glance this may appear more costly and carry more risks. Also, you may not obtain a high-level of operational and manufacturing experience from those companies focusing on just one or two sensor types. Your management may consider using multiple sensor vendors to avoid price hikes or stock-outs.

However, choosing a single vendor specializing in multiple sensor technology can make life simpler in many ways. First, it eliminates costs and time involved when using multiple vendors. Many manufacturers are undergoing severe vendor reduction programs, so reducing sensor vendor count can be a big plus. This not only saves time, but it also saves the company money and scores points with your Procurement Department.

Second, there are many advantages to having multiple measurand capabilities on a single chip. Having just one communications protocol eliminates the need to accommodate disparate communications. It can eliminate possible signal rationalization needed for device control. A single communications protocol means that the three sensors act in concert, giving the device a new level of sophistication without adding cost.

A single chip is more reliable because there are fewer connections. Assembly is simplified since fewer connections mean less soldering and testing. A single connector on a combination sensor delivers plug- and-play capability. A single combo sensor can be hermetically sealed to provide moisture resistance, which is almost impossible to do using discrete sensors. A combination sensor may use less power than three separate sensors and deliver multiple sensing ranges, also providing a less complicated layout.

Third, the sensor supplier can mount them to a PC board, calibrate them and add intelligence, diagnostics, and communications capabiliity. They also perform final testing on the unified sensor subsystem before shipping it to you. This purchasing method means that the supplier is a single sensor subsystem source completely responsible for its overall quality, delivery and reliability.

Fourth, forging a relationship with a single full-service supplier can help with the next generation of designs. In addition to helping quickly upgrade sensing performance of the existing design, having a supplier with depth, innovation and experience will prove invaluable.

Having such a partnership, along with their trust, respect and knowledge of your short and long-range goals for designs will enable the supplier to contribute a great deal to the next generation of medical devices. Such a relationship also fosters collaboration among your other vendors, suppliers and associates. This relationship can also provide valuable, critical outside expert perspectives.

Dan Dixon is Product Manager for medical sensor products of the Honeywell Sensing & Control Medical Business, Minneapolis, MN.

www.honeywell.com/medical