Analog inputs

The Spectrum module is equipped with fully differential analog input terminals. These inputs are labeled as Vin+ and Vin- and appear as a pair for each differential channel (see also Wiring panel overview). In order to maintain a high input impedance, neither terminal is internally connected to the device ground or any other reference voltage. Therefore, it is the responsibility of the user to ensure that the input signal is biased in such a way that the common-mode input voltage range requirement is satisfied. If the input signal is truly isolated and therefore has no common-mode reference voltage, then the Vin- terminal can be connected to a ground terminal with a jumper wire to ensure common-mode range compliance.

The voltage inputs have true bipolar input capability. Firstly, this means the inputs Vin+ and Vin- can vary both positively and negatively relative to one another. Secondly, it also means the absolute voltage of either input can vary above or below the system ground voltage, provided it remains within the common-mode input range.

The inputs are designed to accept differential signals. If a single-ended signal is to be measured, it should be connected to the Vin+ terminal and the Vin- terminal must be externally connected to ground by the user.

The inputs have four selectable input signal ranges. The ranges are ±200 mV, ±1000 mV, ±5000 mV, and ±10,000 mV. Best practice is to select the smallest input range that will capture the expected full-scale range of the measured signal.