Decagon 5TE

Hi, I already use Decagon 5TE (with Arduino Mega2560),
But I want to add new one to my system, I mean my system requires 2 decagon at the same time, but I did not do it because of the SDI-12 protocol,
Can you help me please?

It would help a lot if you had posted links to the sensor your talking about and also describe/post the code your using now to read the sensor you already have.
A quick look at the SDI-12 spec says it can address up to 62 separate sensors on a single bus and Google shows there are at least two libraries written for Arduino to support sdi-12 and both of these seem to support multiple sensors.

Sensor Manual
Sensor SDI manual
Official SDI-12 Spec
Arduino library 1
Arduino library 2

Thank you for your interest, but I have already examined all of these sheets,
Yes, they says that it is possible usşng multiple 5TE sensors but although I done exactly what they describe, there is no multiple sensor data, the result is only : 0 , which come from these sensors.
If you have information about this sensor, can you give me detailed information please?

Thank you for your interest, but I have already examined all of these sheets,
Yes, they says that it is possible usşng multiple 5TE sensors but although I done exactly what they describe,

That’s more than me as I have only glossed over them . What have you done?
I would assume you need to first connect the sensors individually to set unique addresses instead of the default address zero if your using them on the same pin.
One library might not need this as it states you need to connect each device on a separate pin the other library seems to support multiple sensors on the same pin.