MethodWhat is calculated?
A high-value resistor across one arm lowers its resistance and unbalances the balanced bridge reproducibly – the whole measuring chain can be checked without mechanical load. Keil's example: 0.5 mV/V on a 120 Ω bridge needs a 60 kΩ shunt per eq. 8.7; exactly 59.94 kΩ.
Equations
R_K = R_N·R/(R_N+R) (Keil Gl. 8.1)
U_M = ½U_B·R/(2R_N+R) (Keil Gl. 8.5)
U_M/U_B ≈ R/(4R_N) ⇒ R_N = U_B·R/(4U_M) (Keil Gl. 8.6, 8.7)
ε_sim = −4·(U_M/U_B)/k
LimitsAssumptions and typical mistake
Applies to the balanced bridge with constant excitation; lead resistance between shunt and arm alters the signal slightly at DC and considerably at high carrier frequency.
Placing the shunt across the whole half bridge instead of one arm, or interpreting the negative sign of the simulated signal as a fault.
InputsWhat you enter – and where the values come from
- Arm resistance R (gauge) [Ω]
- Resistance of the bridge arm the shunt is placed across – for a self-installed gauge its nominal resistance (120 or 350 Ω), for a finished transducer the resistance of one bridge arm per datasheet. Source: gauge package or transducer datasheet.
- Desired calibration signal U_M/U_B [mV/V]
- Desired test signal in millivolts of output per volt of excitation (mV/V). A shunt is a known resistor connected temporarily in parallel with one bridge arm to electrically simulate a defined load. Source: your chosen test point near rated output or the shunt-calibration value in the transducer certificate.
- Gauge factor k
- The gauge factor is the sensitivity of the strain gauge: it states how much the electrical resistance changes when the gauge is stretched (ΔR/R = k·ε). Without it no strain can be computed from an electrical signal. Source: printed on every gauge package or in the manufacturer datasheet, typically 2.0 to 2.1 for constantan foil gauges; valid at room temperature. The same value must be set in the amplifier.
- Excitation U_B [V]
- The bridge excitation is the DC or AC voltage with which the amplifier supplies the bridge circuit. The signal is proportional to it – which is why signals are usually stated as a ratio in mV/V and the excitation is only needed for the absolute signal voltage. Source: amplifier setting, usually 2.5 V, 5 V or 10 V; the upper limit is set by gauge self-heating (see the excitation calculator).
ContextWhat this calculator is for
Checking and reproducing the calibration of force transducers and load cells in situ, function checks of remote measuring points, scaling of data-acquisition systems.
What comes next
- Enter the arm resistance and the desired calibration signal (e.g. transducer rated output).
- Pick the closest E-series resistor to the exact value and back-calculate the actual signal.
- Switch the shunt in at the transducer where possible; mind capacitive cable asymmetry at 5 kHz carrier frequency.
SourceTechnical basis
Keil, Dehnungsmessstreifen, 2nd ed. 2017, sec. 8.7.3 shunt calibration, eqs. (8.1)–(8.7), fig. 8.7.
The source supports the equation structure and worked examples; this calculator does not replace calibration of the measuring chain.
FAQFrequently asked questions
Does the shunt replace a force calibration?
No, it only reproduces an electrical signal; the signal ↔ quantity relation must be established once with a reference standard.
Why a negative signal?
The parallel resistor reduces the arm resistance like a compression of the gauge.
What accuracy does the shunt need?
At least the target calibration accuracy, typically 0.01 to 0.1 %, with a low temperature coefficient.
In the same cluster
All strain-gauge calculators