Problem with RJ45_DS18B20 sensor

I bought EmonPi and a RJ45/DS18B20 sensor. I don’t know what is happening with the measurement results.
Sometimes I have from t1 input correct temperature (21-22Cd), but sometimes there is 85:

Please help - can the sensor be damaged?
kind regards Michal

Rather annoyingly, the sensor library indicates a fault by displaying 85°C, depending on application that could be hard to recognize as a fault if that temp is within the normal working range.

In your case this is obviously a fault, but since it is the only error indicator there is no further info than there’s a fault, It could just be a simple bad connection that occasionally gets disturbed so check everything is tight and give things a gentle wiggle to see if you can get it to fault to order. A good place to start is the cable entry to the rj45 plug.

I have had the same problem - in my case cured by crimping the plug again, then filling the cable entry with hot glue to act as a strain relief.

85°C is the initial value in the sensor’s memory when it is powered up. When the sensor is commanded to convert (read) the temperature, that value of 85°C is overwritten. Your sketch should then read the correct value stored in the memory.
But if there is a bad connection and the command to convert the temperature fails, when your sketch reads the memory, it reads 85°C.

(Why Dallas chose 85°C, which is a valid temperature within the operating range, I cannot imagine.)