Lucky number four!
The new RTD PW series is the response of IST AG to growing demand for high-precision platinum temperature sensors. The four-wire design is located directly on the chip to enable F0.15-class measurements up to +600 degrees Celsius with very low hysteresis.12 Sep 2018
Established in 1991, Innovative Sensor Technology (IST) AG is part of the Endress+Hauser Gruppe and is headquartered in the Swiss Canton of St. Gallen. The sensor specialist with its team of approximately 400 staff is dedicated to meeting customers' specific needs and specifications. The latest product of this dedication is the RTD PW series for high-precision measurements, which meets the escalating demand for highly accurate platinum temperature sensors.
Four-wire designs have proven particularly suitable for the desired level of precision because they can effectively suppress wire resistances and their temperature influences. They also offer various options for positioning the reference point. In the case of sensors with two wires, the four-lead extension is typically placed at the wire end - the extension point forming the reference point. However, this design can lead to measurement inaccuracies, for example due to possible thermal stresses when using different wire materials or due to minor position changes. Furthermore, the alternative method of attaching the extensions directly to the welding pads has proven to be less than optimal. Covering the welding points (glob top) to reduce strain can lead to mechanical tension, which can result in drift, particularly due to the installation of the sensor. IST AG has therefore scrutinized this problem afresh and developed a new sensor that is specially designed for the needs of high-precision measurements that have to exhibit long-term stability. On this new four-wire RTD, the reference points are inside the sensor chip. The splitting onto four extended wires already occurs in the meander area, away from the glob top. Here, as in the rest of the meander area, only high-purity thin-film platinum is used. This is designed to suppress the contact resistance in this area and minimize the influence of mechanical stress due to or on the glob top. The continuation of the four extended wires with pure platinum wire is designed to ensure minimal material variation from the chip side, thus enabling high long-term stability and the suppression of thermal stress.
Innovative Sensor Technology - IST AG (9642 Ebnat-Kappel, Switzerland)
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