Noise system docs

Lockin connection scheme

Lockin frequency mode:

          |-----> AUX OUT 1: Magnetic field DC
          |
Lockin ---|<----- SIG IN: Voltage input 
          |
          |-----> AUX OUT 2: Bias voltage

Lockin field mode:

    
          |-----> SIG OUT: Magnetic field AC + DC 
          |
Lockin ---|<----- SIG IN: Voltage input 
          |
          |-----> AUX OUT 2: Bias voltage