National Instruments SCXI -1125 用户手册

© National Instruments Corporation

The value of the bias resistor should be between 100 k

Ω and 1 MΩ .  An 

added DC offset voltage results, due to input bias current flowing through 
the bias resistor. For example, with a 1 M

Ω bias resistor and the specified 

maximum input bias current of 1 nA, you have a maximum added input 
offset voltage of ±1 mV in addition to the initial offset voltage.

Since only the AC signal is of interest when AC-coupling, you can choose 
to remove the DC offset in software by using a simple highpass filter.

Pins A2, A4, A8, C2, C4, C6, and C8 on the front signal connector are not isolated 

and do not have the same protection circuitry as the positive and negative analog input pairs 
discussed in the 

 section. Hooking up external signals to these pins can 

damage the SCXI-1125 module.

The front signal connector is a special 32-pin DIN C male front connector 
used for connecting analog input signals, including the CJC, to the analog 
circuitry of the SCXI-1125. This connection allows access to the eight 
differential analog input signals. The positive terminal is AIx + and the 
negative terminal AIx –. A missing pin exists between two consecutive 
input channels to meet the UL spacing requirements for high voltage 
signals. CJ TEMP is the signal connection used by the cold-junction 
channel on the SCXI-1125. The signals on pins A6, A8, C6, and C8 are 
reserved for serial communication. The +5 V signal and CHS GND signals 
are used as the power supply and ground signals for the CJC sensor and 
other circuitry on the terminal block. The pin assignments for the 
SCXI-1125 front signal connection are shown in Table 2-1.

Do not make signal connections to pins A2, A4, A6, A8, C2, C4, C6, or C8 on the 

front signal connector. Connecting external signals to these pins can damage the 
SCXI-1125 Module.