As previously discussed, the world of linear position sensors is pretty diverse. There are many types of linear sensors available in many different form factors, employing many different technologies, and coming in at many different price points. For the sake of discussion, let’s imagine you’re shopping for a linear position sensor, and you’ve decidedon a form factor. You’ve settled on a position sensor that will be externally mounted on your machine. And you don’t really care much about the “under the hood” technology; you just care that the sensor does what it’s supposed to do when it’s installed. Now, let’s further assume that you find a couple of different sensors that you think will do the job, and the only difference is the cost. It makes sense to choose the lowest cost option, right? Well, maybe not.
A Tale of Two Technologies
Some low-cost linear position sensors – resistive linear potentiometers spring to mind – employ technology that relies on mechanical contact to operate. In the case of resistive potentiometers, or linear pots as they’re often referred to, this mechanical contact takes the form of a mechanical wiper sliding along a resistive element. The changing resistance causes the output to change. It’s a pretty simple device, it works fairly well right out of the box, and the purchase cost is often fairly low. But, that reliance on mechanical contact limits the effective useful life of a linear pot. As with anything mechanical, it’s eventually going to wear out and fail. How it fails, and how soon it fails, depends on the application. The failure could happen all at once, or the sensor’s performance could degrade over time until it becomes completely unusable. So before you choose that lowest-cost option, you might ask yourself some very important questions:
- In the case of a complete failure: How much is going to cost me when this sensor fails? How much production time am I going to lose while waiting for the sensor to be replaced?
- In the case of gradual performance degradation: How badly is my production process going to suffer as the sensor’s performance degrades? Am I unknowingly making bad parts because my position feedback is getting flaky?
So it’s pretty clear that the initial purchase cost of the sensor is not the only cost to be considered. Ultimately, the costs associated with downtime, part replacement, and bad parts could far outweigh any cost saving on the on the initial purchase. This is what you might call the true cost of low-cost.
The good news is there are other sensor technologies that do not rely on mechanical contact, and therefore aren’t prone to this type of mechanical failure and/or performance degradation.
The even better news is that there are linear position sensors that use non-contact sensing technology, but cost the same as, or very close to the same as, many of those failure prone contact-based products. There are even non-contact products that duplicate the form factor of typical resistive linear pots.
Better technology at the same price? In the end, the choice is pretty easy.