Errors and Precautions in Using Bridge Circuits

ERRORS IN BRIDGES:

Study of the different bridge circuits in this topic was made under idealized conditions. Assumption was made that the bridge consists of lumped impedance units connected only by the wires used in the circuit connecting the elements. This is far from truth. The reason is that idealized conditions can be valid if the frequency is low, the impedances under consideration are low. and that the expected accuracy is not high. Practically some factors like stray couplings between bridge arms etc, modify the balance conditions making the balance impracticable or wrong balance condition. The following are the factors causing errors in bridges:

1. Stray conductance effects, due to imperfect insulation. 

2. Mutual inductance effects due to magnetic coupling between various components of the bridge.

3. Stray capacitance effects, due to electrostatic fields between conductors at different potentials. 

4. Residuals in components for example the presence of small magnitudes of series inductance or shunt capacitance in non-reactive resistors.

PRECAUTIONS FOR REDUCING ERRORS:

The following precautions may be taken to avoid errors :

1. High quality components must be used for the elements of the bridge.

2. The layout of the bridge must be made to avoid interaction of the bridge arms.

3. The sensitivity of the bridge must be more.

4. The bridge components and other pieces must be mounted on insulation stands to prevent stray conductance effects.

5. Presence of large conducting masses near the bridge arms must be avoided to prevent eddy current effects.

6. Residual error can be avoided by identifying the nature, evaluating them and compensating them.

7. Wave filters that eliminate the unwanted harmonics from the source or tuned detectors in place of headphones may be used to avoid the difficulty of frequency and wave form errors.