Bridge conditioners are instruments that provide excitation and support for strain gages, Wheatstone bridges, load cells and sensors. They also include circuitry for signal conditioning, amplification, and processing. Bridge conditioners provide four-way galvanic isolation between their input, output, excitation, and power supply circuits. Electrical isolation breaks the galvanic path between the input and output signals. Physical wiring between the input and output is not required. Normally, the input is transferred to the output by converting it to an optical or magnetic signal that is reconstructed on the output. In this way, bridge conditioners prevent unwanted signals from traveling along the input line. 

Bridge conditioners receive three types of inputs: signal inputs, sensor inputs, and inputs from special devices. Signal inputs include DC voltage, DC current, AC voltage, and AC current. They also include frequency and charge, signals that often require filtering and amplification. In terms of sensors, current loop converters receive inputs from accelerometers, thermocouples, thermistors, and resistance temperature detectors (RTDs). They also receive inputs from strain gauges, many of which use a Wheatstone bridge, and from both linear and rotary variable differential transformers (LVDTs and RVDTs). Inputs from special devices include not only signals from encoders, but also signal per cycle counts from counters or tachometers. Timers, clocks, relays, and switches can also provided special inputs to bridge conditioners.

There are several filter architectures for bridge conditioners. Analog filters are designed with resistors and capacitors and are used in applications with low noise requirements. Digital filters are designed with solid-state components and include both finite impulse response (FIR) and infinite impulse response (IIR) filters. Filter functions are often programmable and may include anti-alias features that correct the signal misrepresentation that occurs during slow sampling. Low pass and high pass filters block or attenuate signals at frequencies above or below a specified cutoff frequency. Band pass filters block or attenuate signals at frequencies outside of the low pass and high pass cutoff frequencies. Band stop frequencies block only a portion of the frequency spectrum while all-pass filters allow all frequencies to pass.  

Bridge conditioners provide several types of outputs. Some devices provide variable levels of voltage or current, or output frequencies or pulse signals. Other devices provide timer, counter, relay, and resistance outputs. Bridge conditioners that include integral amplifiers vary in terms of programmable gain, gain range, maximum output, and bandwidth. Amplifier gain, the factor by which the input signal is multiplied, can be adjusted from a touch screen, a front panel display, or a computer monitor. Some advanced bridge conditioners include application software for real-time monitoring and mathematical and statistical functions. Bridge conditioners that interface to computers use a variety of communications protocols, including Ethernet, DeviceNet, and IEEE 1394.


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