Chapter 3 Signal Connections© National Instruments Corporation 3-5 AT-MIO-16 User ManualConnection of analog input signals to the AT-MIO-16 depends on the configuration of theAT-MIO-16 analog input circuitry and the type of input signal source. The different AT-MIO-16configurations use the AT-MIO-16 instrumentation amplifier in different ways. Figure 3-2shows a diagram of the AT-MIO-16 instrumentation amplifier.-InstrumentationAmplifier-MeasuredVoltageVm = [V in + -V in-] * GainV in- VmVin+++Figure 3-2. AT-MIO-16 Instrumentation AmplifierThe AT-MIO-16 instrumentation amplifier applies gain, common-mode voltage rejection, andhigh-input impedance to the analog input signals connected to the AT-MIO-16 board. Signalsare routed to the positive and negative inputs of the instrumentation amplifier through inputmultiplexers on the AT-MIO-16. The instrumentation amplifier converts two input signals to asignal that is the difference between the two input signals multiplied by the gain setting of theamplifier. The amplifier output voltage is referenced to the AT-MIO-16 ground. TheAT-MIO-16 ADC measures this output voltage when it performs A/D conversions.All signals must be referenced to ground somewhere, either at the source device or at theAT-MIO-16. If you have a floating source, you must use a ground-referenced input connectionat the AT-MIO-16. If you have a grounded source, you must use a nonreferenced inputconnection at the AT-MIO-16.Types of Signal SourcesWhen configuring the input mode of the AT-MIO-16 and making signal connections, you mustfirst determine whether the signal source is floating or ground referenced. These two types ofsignals are described in the following sections.
