DC402 Turning off alarms on unused second input

There is no way to "turn off" an unused input on a DC402. If you leave the terminals open you will get error messages. 

Connect a simulated sensor to the unused input to clear the errors. Use a resistor on 11-12 to simulate the temp sensor, 1000 ohms for PT1000, 100 Ohms for PT100. Simulate the same type temperature sensor that the other channel is using. 

Use a resistance to simulate the cell that gives a conductivity reading within the range, usually 1000 ohms between 14-15 will work. Once you have connected the resistors the input the errors will clear.