I am using NTC Thermistor bought from Mitsubishi (http://www.mmc.co.jp/adv/dev/english/contents/thermistor/lead/cn_ch.html). The sensor is made by increasing the length or the sensor wire from 30 mm to 320 mm by soldering 2 teflon wire. The sensor is then inserted into a 30 mm aluminium tube and encapsulated using sylgard 160(http://www.dowcorning.com/applications/search/products/details.aspx?prod=02356368&type=prod) silicone elastomer kit.
The wire are then heat sleeved. The sensor along with its 30 mm tube and 60 mm of its wire is then place in a water bath whose temperature varies from 10 to 4 deg c. This sensor is used to control a compressor which in-turn cools the water bath till it reaches 4 deg C
The issue is that after a fortnight or so the water bath turns into ice since the compressor does not stop. On inspecting the temperature sensor resistance it is found that it gets stuck at one particular value. After this the sensor was removed from the circuit board connection and the water bath. The sensor is kept at room temperature for a day or two and the sensor starts showing correct readings. This has happened 5 times in 3 different machines. Every time a sensor which has gone faulty shows a different reading when the resistance is stuck but always returns back to normal after a few days.
This issue has caused a lot of our machines to malfunction and we have bought 5000 such sensors. Guys please give me some suggestions and tell me if more information is required.
The wire are then heat sleeved. The sensor along with its 30 mm tube and 60 mm of its wire is then place in a water bath whose temperature varies from 10 to 4 deg c. This sensor is used to control a compressor which in-turn cools the water bath till it reaches 4 deg C
The issue is that after a fortnight or so the water bath turns into ice since the compressor does not stop. On inspecting the temperature sensor resistance it is found that it gets stuck at one particular value. After this the sensor was removed from the circuit board connection and the water bath. The sensor is kept at room temperature for a day or two and the sensor starts showing correct readings. This has happened 5 times in 3 different machines. Every time a sensor which has gone faulty shows a different reading when the resistance is stuck but always returns back to normal after a few days.
This issue has caused a lot of our machines to malfunction and we have bought 5000 such sensors. Guys please give me some suggestions and tell me if more information is required.
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