User's Guide

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Binsfeld Engineering Inc. | 231-334-4383 www.binsfeld.com 869610-9_A2 Pg. 42

Shunt Calibration

The more common method is to perform a shunt calibration. This

method takes into account deviations in the setup from the strain gage to

the transmitter, but unlike a deadweight calibration, none of the

deviations in the physical parameters.

The easiest way to conduct a shunt calibration is by enabling one of the

reference shunt resistors on-board the TX20K. An internal precision

resistor is placed in parallel with one arm of the bridge to simulate a

precise strain value. As stated earlier, Reference 1 simulates 100

microstrain (µe) and Reference 2 simulates 500 µe when using a 350

Ω

strain gage with a Gage Factor of 2.0. Alternatively, precision resistors

can be placed in parallel with one arm of the bridge to simulate a torque

load. The Tech Info section on our website (www.binsfeld.com) has a

helpful Torque Strain Calculator to assist in determining the strain a

given resistor value simulates. The equation relating strain and shunt

resistance is shown below:

Legend of Terms

Shunt Calibration Resistance (kΩ)

Gage Resistance (Ω)

Number of Active Gages

Gage Factor

Strain (µe)

In the example from Steps 1 & 2, the Full Scale Torque is 4,901 ft-lb and

the RX20K output has been scaled so that 10 V corresponds to a torque

load of 5,000 ft-lb by setting the System Gain to 3920. This was

determined by multiplying the Transmitter Gain of 4000 (±500 µe range)

by the Scale Factor (Z) that was calculated to be 0.9802.

First, determine what the system output should be when applying the

shunt resistance. In this case, Reference 1 (100 µe) is a good choice

(20% of Full Scale). To calculate the calibrated output of the system,

use the equation below:

= ───────

(N)(GF)(ε)