You need a Microlink 594 unit when monitoring strain gauge bridges or balanced bridges such as pressure transducers, using a Microlink 700 USB unit or Microlink 85x Ethernet/Internet unit. This strain gauge box sits next to the Microlink and provides screw terminals allowing the signals to be permanently wired.
Strain gauges need an external excitation voltage to supply sufficient current to keep all the bridge circuits energised. Four sets of 16 screw terminals give + and - excitation and + and - signals for each of 16 bridges. Two 1 kOhm termination resistors are mounted in half bridge configuration whilst high quality 350 and 120 Ohm resistors can be provided for the completion of quarter bridges. The analogue-to-digital converter on the Microlink is suitable for direct measurement of voltage imbalance, provided you choose a high resolution.
When a bridge input is selected the software automatically monitors excitation voltage and performs the bridge calculation to produce a reading in microstrain. You can set a zero reference level and monitor changes relative to that level.
With the 594 unit you can configure individual channels to accept any one of the following inputs.
voltage input quarter bridge single strain gauge half bridge tensile + compressive strain gauge half bridge normal + transverse strain gauge full bridge 2 tensile + 2 compressive gauges full bridge 2 normal + 2 transverse gauges full bridge tensile normal + compressive normal + tensile transverse + compressive transverse gauge
The 594 unit, costs £180. To buy on-line go to Windmill Software's data acquisition catalogue: strain. For more on strain gauges and strain measurement see the Windmill Data Acquisition Intelligence site.