The accuracy, time response, and repeatability of an IV/blood warmer varied enough from unit to unit that it caused performance and validation failures. When accuracy is a primary concern, time response and repeatability are sometimes overlooked. Temperature sensing for blood warming is critical because the FDA says blood cannot exceed 41C without damage. Each warming unit must quickly apply exact heat when necessary, but not overheat it.

Improvements to the sensor included a slightly smaller casing that allowed placing it against the inside tip of the sensor case. This generated a for more consistent time response, one customer goal.

After dissecting the original temperature sensor, engineers with heater and sensor manufacturer Minco Inc. in Minneapolis (minco.com) determined the problem's root causes were design flaws and assembly inconsistencies. For example, sensors were not consistently positioned in the units which affected time response from unit to unit.

Engineers at the OEM for the warmer and Minco designed a sensor that improved on its internal construction and casing so it provides consistent and quick response while meeting repeatability needs. The final solution includes a 100-ohm platinum RTD (resistance temperature detector) for control, as well as a 50K-ohm thermistor for over-temperature protection. The sensor case was also redesigned for easy and repeatable installation.