Data acquisition input modules receive signals from devices such as sensors and often provide voltage and current excitation along with signal conditioning for subsequent analog-to-digital conversion. They plug into backplanes or motherboards, or interface directly with computer buses. Some data acquisition input modules receive AC and DC voltages, AC and DC currents, charges from piezoelectric elements, or frequency inputs. Other devices receive signals from accelerometers, thermocouples, thermistors, resistance temperature detectors (RTDs), strain gauges, linear rotary differential transformers (LVDTs), and rotary variable differential transformers (RVDTs). Encoders, tachometers, timers, relays, and switches can also provide inputs for data acquisition input modules. Optional features include random access memory (RAM), data storage, and configurable application software for real time graphing and mathematical or statistical functions.