FAQ (Frequently Asked Questions)
Resistance Thermometer Sensor
What is the cause when a resistance value defect or disconnection of a resistance thermometer sensor occurs?
1. A sheathed resistance thermometer sensor which seemed robust with excellent strength has been used to calibrate another sensor. Calibration was implemented after one year. As a result, the resistance value was outside the allowance and there was a partial disconnection.
The resistance element section of a resistance thermometer sensor is extremely delicate structurally. The ceramic insulator has a coil shape platinum wire of tens of micrometers inside and excessive vibration and impact may change the resistance value and cause disconnection in an extreme case.
In the relevant case, a metal fitting was directly installed to the sheath of the sensor for calibration with a machine screw. As a result, the sheath surface had obvious hollows and scratches and it was judged that the use condition was improper. When we asked about how the sheath was used, we found out that the sheath was placed hitting a desk and handled roughly. We judged the resistance value defect and disconnection occurred because of that.
Improper use conditions cause the sheathed resistance thermometer sensor resistance value defect and disconnection in most cases. If sheathed resistance thermometer sensors are handled in the same way as sheathed thermocouples, an excessive load will be applied to the tip of the resistance element and an abnormality will occur. Excessive vibration/impact is strictly prohibited.
Photo: Sheath Tip Scratch
Photo: Enlarged X-ray Photo of Resistance Element Disconnection
2. A delivered sheathed resistance thermometer sensor was disconnected on installation by a customer. We took it back and inspected it and we found that the sensor was fastened with a double bite type joint attached to the tip of the element. That was a completely wrong use method of the sheathed resistance thermometer sensor.
Since the temperature sensing part of a sheathed resistance thermometer sensor has a resistance element inside, outer force must not be applied to the part in the same way as the previous case example. The photo of the sensor fastened is shown.
Photo: Sheath Tip Part
Furthermore, we removed the joint and ferrule cut into the sheath and took a photo of the disconnected part with an enlarged X-ray apparatus. Obviously the sheath was deformed, the ceramic resistance element was cracked and the element wire was disconnected.
Photo: Element Disconnection Part
As above, sheathed resistance thermometer sensors are easily disconnected with a wrong use method. The only countermeasures are understanding the structure of sheathed resistance thermometer sensors and using the sensors correctly. Our instruction manual has the description below and we expect users and designers to read the instruction manuals.
Temperature Sensor Instruction Manual Extract
Technical Data
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