1. Transducers based on strain gauges
(SG) based force transducers
are widely used and offer reliable
operation even in unfavorable ambient conditions. The mechanical installation has already been dealt with in the article on 'Installation of force transducers
'. Here, we want to address the electrical connection
Strain gauge based sensors use the so-called Wheatstone bridge
. This bridge circuit comprises four resistors
connected as shown below:
It is essential that all strain gauge sensors are fed with an adequate supply voltage or bridge excitation voltage Ub
This excitation voltage Ub
is provided by the amplifier systems. Typical values range between
2.5 and 10 V
. The right value for your force transducer can be found in the data sheet; see 'Operating range of the excitation voltage'.
The above circuit diagram shows that four leads
are sufficient to operate a Wheatstone bridge. Two leads supply the sensor with electric voltage, the other two leads feed the amplifier with the measuring voltage.
The reference excitation voltage is the supply voltage with which the sensors were supplied during determination of the technical data.
The operating range of the excitation voltage is the bridge excitation voltage at which your force transducer can be operated while complying with the technical specifications.
With the bridge excitation voltage exceeding the specified limit, the strain gauges and other resistors in the force transducer heat up excessively so that individual parameters (sensitivity, temperature coefficient of the sensitivity) will change. When the operating range of the excitation voltage is not exceeded, these changes can be neglected in experimental and production applications.
The lower limit of the excitation voltage range results from experimental data: tests at 'zero' excitation voltage cannot be carried through.
With high-precision measurements (reference measuring chains), it is generally recommended to choose the bridge excitation voltage given in the sensor's calibration certificate. It is even more advisable to have the measuring chain, i.e. the transducer and the electronics, calibrated together as a system.