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Bridge Excitation

Last Modified: April 19, 2018

Bridge-based sensors require a constant voltage to power the bridge. Bridge signal conditioners typically include a voltage source. While there is no standard voltage level that is recognized industry wide, excitation voltage levels of around 3 V and 10 V are common.

Excitation sources can suffer from stability and accuracy issues. To compensate, ratiometric devices constantly measure the actual excitation voltage and use it, rather than an intended excitation value, when scaling data.

Remote Sensing

If the bridge circuit is located away from the signal conditioner and excitation source, a possible source of error is voltage drops caused by resistance in the wires that connect the excitation voltage to the bridge. Therefore, some signal conditioners include a feature called remote sensing to compensate for this error. There are two common methods of remote sensing.

With feedback remote sensing, you connect extra sense wires to the point where the excitation voltage wires connect to the bridge circuit. The extra sense wires serve to regulate the excitation supply, to compensate for lead losses, and to deliver the needed voltage at the bridge.

An alternative remote sensing scheme uses a separate measurement channel to measure directly the excitation voltage delivered across the bridge. Because the measurement channel leads carry very little current, the lead resistance has negligible effect on the measurement. You then can use the measured excitation voltage in the voltage-to-strain conversion to compensate for lead losses.

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