Bridge excitation voltage and gauge self-heating

What is calculated?

The bridge signal grows in proportion to the excitation, but the heat generated in the gauge grows with its square. In a full bridge each gauge sees half the excitation, so P_DMS = U_B²/(4R). Whether the heat is removed depends on the power density referred to the grid area together with the object's thermal conductivity. Keil's example: 5 V on 120 Ω gives 52 mW and 21 mA per gauge, on 350 Ω only 18 mW and 7 mA.

Equations

P = U²/R (Keil Gl. 2.40)

P_DMS = U_B²/(4R) (Keil Gl. 2.41)

Leistungsdichte = P_DMS / (l_g · b_g)

U_B,max = √(4·R·p_zul·A)

Step by step

1. Enter grid dimensions and resistance from the datasheet.
2. Choose the power-density guideline by material and type of measurement.
3. Set the excitation so the power density stays below the guideline; reduce it markedly for plastics, wood or stacked rosettes.

Typical mistake

Applying the full excitation instead of U_B/2 to a single gauge, or confusing grid area with carrier area.

Application and limits

Setting the amplifier excitation, choosing between 120 Ω and 350 Ω gauges and assessing warm-up behaviour (zero drift after switch-on).

Guidelines apply to well-bonded foil gauges on flat surfaces; stacked rosettes and quarter bridges with completion resistors inside the instrument need separate consideration.

Technical basis

Keil, Dehnungsmessstreifen, 2nd ed. 2017, sec. 2.8 electrical loading capacity, eqs. (2.39)–(2.41) and guidelines per [2.8.3].

The source supports the equation structure and worked examples; this calculator does not replace calibration of the measuring chain.

Frequently asked questions

In the same cluster

• Strain-gauge basic equation: resistance change from strain and gauge factor
• Transverse sensitivity: correction for two perpendicular gauges
• Temperature response: apparent strain of a gauge under temperature change
• Wheatstone bridge: output voltage of the unbalanced bridge
• Basic strain-gauge bridge equation: signal from four strains
• Quarter, half and full bridge: bridge factor and signal

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