"Measuring relative humidity is not an exact science," says Joseph Puglisi, product manager for Gefran Coreci
. "By principle, no RH sensor can be exactly identical to another RH sensor, even if they were made under similar conditions." The company's S6000, however, has an integrated microprocessor (ASIC) which is said to "correct" the difference between two sensors. "That characteristic enables the user to replace the sensitive element without needing to return the whole device for recalibration," explains Mr. Puglisi. "The calibration of the S6000, which is independent of the transmitter whose main role is to amplify the signal, consists in the linearization of the sensor performances and provides a consistent output of 0-1 V, device by device," he adds.
The company says its objective in designing the S6000 was to create a miniaturized microchip to reduce noise caused by the thermal inertia of the transmitter and to improve metrological characteristics. "We then decided to focus our research and development effort on the specifications and the different functions which would be realized by the ASIC such as input and output signals, consumption, frequency, etc.," explains Mr. Puglisi. "The development took 2 years of work in partnership with a company specialized in ASIC development. One ASIC is now calibrated with one sensor, apart from any other electronic treatment."
The product, according to the company, takes a different approach than those offered by its competitors. "Our competitors do not have an ASIC associated individually with the sensor," explains Mr. Puglisi. "They are seeking interchangeability by replacing only the sensitive element, which is less expensive since the cost of the microprocessor is avoided. But, it is also less accurate since RH sensors are not identical." The difference in accuracy, according to Mr. Puglisi, is +/-2.5 percent RH with the S6000 sensor compared to the +/5 percent RH after replacement.
The company said designing the sensor module with a microprocessor was a challenge. "After the prototypes were realized and tested, we faced the challenge of setting up a calibration procedure which could be used for high-volume productions. Because each relative humidity sensor is different, each ASIC must be electronically programmed separately," explains Mr. Puglisi. The company overcame the challenge by developing its own control and testing program, and it also purchased highly accurate calibration chambers to establish the calibration points.