I have a Parsivel and I save its data using a cr1000 by SDI-12 protocol two-wire method. It was working fine for a long time but suddenly the data measured was NaN. I thought that the sensor was wrong but when I connected the Parsivelto a PC by an RS-485 protocol I could see the sensor and it is ok. Any idea why the SDI-12 is not working? From a terminal emulator, in transparent mode, I just get SDI12 Failure.
Perhaps there is some sort of hardware fault. Have you checked the cable from the datalogger to the sensor? Does it work OK with a voltmeter to buzz through the lines?
Have you tried a different Control port on the CR1000 to see if the original port has been damaged?
If you have another CR1000, could you try that instead?
Can you be sure that the the Parsivel SDI-12 and RS485 use the same hardware internally?
Some thoughts to look at.