The Case of the Rusty Sensor

The Case of the Rusty Sensor

By Charles Fisher,

VP of Sales RESCO Electronics

The Problem

Several years back, I was contacted by one of our customers that needed a temperature sensor for a deionized (DI) water tank.  Although we have helped this customer engineer several different sensors over the years, RESCO had not been involved in this design.  Our customer is a Fortune 50 medical equipment manufacturer in the in vitro diagnostics market and this sensor is part of one of their blood analyzers.

After about a year of supplying the assembly with no apparent problems, I was contacted by a manufacturing engineer at the customer to discuss a major issue that had occurred. Apparently rust was appearing in the water and they were able to trace it back to the sensor assembly.  The manufacturer of the sensor assembly suggested changing to a different version of sensor but when we tried the result was still the same.  After extensive testing by our customer, they determined that the UV light being used in the tank was causing a breakdown in the integrity of plating on the sensor and causing it to rust.  Unfortunately, the original sensor manufacturer was unable or unwilling to offer any suggestions to address the issue.

The Solution

Since the late 1970’s, RESCO has been partners with a leading thermistor and temperature sensing company.  Together we had supported multiple customers, including this one, in both the medical and aerospace sectors.  Working with the engineering teams across our two organizations we were able to come up with a solution.

First, the team engineered a tubular housing for the sensor that has sufficient thermal properties to get the precise readings that were required while being able to withstand the environment caused by the UV light.  Our customer required that the housing on the new sensor use the same coating as used on the original sensor to avoid costly chemistry re-validation testing.  For added reliability, a second thermistor was added to the probe at a very small incremental cost.

The Secondary Problem

Together with our customer and partner, we had resolved the engineering issue.  The next problem was that the proposed solution was going to add significant cost to our customer’s instrument at a time when every dollar was being scrutinized.  Unfortunately, we could find no shortcuts or modifications to the design that would meet both the original cost and the system requirements.


However, we did find a solution, not by reducing the cost of the sensor but by increasing it!  Yes, I know this sounds crazy, but what we did was look at the manufacturing process to install the sensor assembly in the DI water tank.  We found that our customer was going through a series of time-consuming modifications to the tank to install the original sensor.  To reduce these installation costs, we worked with our partner to modify the design of the sensor assembly to simplify its installation.  The redesign was a success and now installation is much simpler and less costly.  The manufacturing cost savings were far greater than the additional cost of the new sensor assembly, making the solution a significant win for our customer.

The Conclusion

This was an interesting and unique challenge for our team.  Finding a solution that met both the technical requirements and didn’t raise the overall cost of our customer’s instrument took a collaborative effort. By leveraging our partnership with our partner we were able to solve this issue.  That said, an even greater value comes from using these partnerships early in the design cycle so that pitfalls can be reduced and redesign costs avoided.

This same customer has recently launched a new platform that is using temperature sensing solutions from RESCO and our partner.  During the engineering prototype testing, there were some engineering challenges that came to light due to the environment the sensor is located in.  By leveraging the partnership among the customer, RESCO and our supplier, we were able to resolve these issues during design. As a result, we kept these issues from ever making it to market and avoided costs associated with instrument downtime and field replacements.


This article originally published on the blog portion of RESCO’s website. For more informative articles, navigate to the blog tab at www