Linear variable differential transformer (LVDT) and rotary variable differential transformer (RVDT) signal conditioners are devices that translate the linear or rotary movement of a ferromagnetic armature into an AC voltage that is proportional to the armature position. LVDT and RVDT signal conditioners receive AC or DC currents or AC or DC voltages as input signals. They excite a transducer according to defined parameters for voltage and frequency. A variable gain differential amplifier receives the resulting signal, which is then coupled to a synchronous detector, multi-step filter, analog-to-digital converter, and micro-controller. Some LVDT and RVDT signal conditioners have voltage or current outputs that power or activate the sensor that provides the input signals. Other devices use a sampling frequency to convert analog signals to digital values.
LVDT and RVDT signal conditioners are available in a variety of device configurations. Data acquisition computer boards plug into backplanes or motherboards, or interface directly with a computer bus. Input modules accept signals from sensors, timers, switches, amplifiers, and transistors for use in larger data acquisition system. Output modules produce amplified, conditioned, or digitized signals. LVDT and RVDT signal conditioners with combined input/output (I/O) modules are also available. Some devices include signal isolators, bridge conditioners, multiplexers, analog-to-digital converters, or digital-to-analog converters. Others provide frequency converters, voltage converters, frequency-to-voltage converters, and voltage-to-frequency converters. Charge, current loop, and current-to-voltage converters are also available.
LVDT and RVDT signal conditioners vary in terms of filter and amplifier specifications. Devices that include signal filters block or decrease (attenuate) unwanted frequencies or signal wave characteristics. Integral filters allow some signal frequencies to pass while attenuating others. Integral amplifiers multiply a signal to the matching scale of the input device. Since amplifier gains or multiplication factors may be greater than one or only fractional, programmable gain amplifiers are also available. These devices allow users to make adjustments from a local interface such as a front panel, or from a computer interface, touch screen, or remote handheld device. Some LVDT and RVDT signal conditioners are programmable, networkable, web-enabled, or bundled with application software for controlling or monitoring data acquisition or signal conditioning from a supervisory or host computer.
There are several form factors for LVDT and RVDT signal conditioners. Some devices mount on integrated circuits (ICs), standard DIN rails, or printed circuit boards (PCBs) that attach to enclosures or plug into computer backplanes. Others bolt into walls, cabinets, enclosures, or panels. Rack-mounted units fit inside a standard 19” telecommunications rack. Modular styles include stackable units that dock in bays, slots, or boxes. Benchtop or freestanding LVDT and RVDT signal conditioners often feature full casings or cabinets and integral interfaces.
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