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MarsBravo

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Suppose a Wheatstone bridge with four equal active strain sensors (350 ohm each).

The output nodes are connected to a high impedance instrumentation amplifier, so no current draw from there. The bridge is placed at consiberable distance from the exitation voltage source (and the amplifier), so the length of the extension cable (with all four wires) must be accounted for in such a way that it adds to the total resistance of the bridge but not to the sensitive part (the bridge). It will reduce the sensivity of the bridge, but in a small way.

Can the bridge and the extension cable resistors considered as three resistors in series (the bridge resistance measured from the exitation source is still 350 ohm!), or has one take into account the split of resistors within the bridge (dividing the exitation current) as the extension cable resistors 'serves' both branches?

In the attachment, the difference in the formula is in red. CF is the calibration factor, CF' is the adjusted CF. Which formula is right?

The output nodes are connected to a high impedance instrumentation amplifier, so no current draw from there. The bridge is placed at consiberable distance from the exitation voltage source (and the amplifier), so the length of the extension cable (with all four wires) must be accounted for in such a way that it adds to the total resistance of the bridge but not to the sensitive part (the bridge). It will reduce the sensivity of the bridge, but in a small way.

Can the bridge and the extension cable resistors considered as three resistors in series (the bridge resistance measured from the exitation source is still 350 ohm!), or has one take into account the split of resistors within the bridge (dividing the exitation current) as the extension cable resistors 'serves' both branches?

In the attachment, the difference in the formula is in red. CF is the calibration factor, CF' is the adjusted CF. Which formula is right?