Solution
According to the the
PXIe-4300 Specifications Manual , the input impedance will be different depending on whether the device is on or off. This is due to protection and signal conditioning circuitry that is only active when the device is on.
When on, the PXIe-4300 has over 1 GΩ input impedance between AI+ and COM, and between AI- and COM. As shown in Figure 1 below.
Figure 1: NI PXIe-4300 Input Impedance with no Terminal Block The TB-4300 is a non attenuating feed-through terminal block. It has no effect on the input impedance of the device, as shown in Figure 2 below.
Figure 2: NI PXIe-4300 Input Impedance with TB-4300 Terminal Block
The TB-4300B is an attenuating terminal that has a 1.2 MΩ impedance between the AI+ and AI- pins as shown in Figure 3 below. This terminal block has no effect on the impedance of the NI PXIe-4300 impedance between AI+ and COM or AI- and COM.
Figure 3: NI PXIe-4300 Input Impedance with TB-4300B Terminal Block