CR6-micro-bridge-program

Repository for my work with a Campbell Scientific CR6 data logger with LoggerNet, for a micro-bridge logging and demonstration kit.

This program is designed for a micro-bridge demonstration project. It is designed to collect data from the following sensors and for the following purposes:

5 foil strain gauges, each forming a quarter of a full-bridge. The strain is measured using 4WFBS350 full-bridge terminal input modules.

Strain gauges 1-4 are placed symmetrically on the 4 pillars of the micro-bridge, and are used like a mass/weight reading to determine the centre of mass/load of the bridge.

Strain gauge 5 is placed on the underside of the bridge as a way to convert the strain to a mass/weight with calibration.

1 tri-axis accelerometer, reading only the z-axis currently due to availability of universal terminals on the CR6.

Accelerometer is used to measure bridge vibrations.

1 Tfmini Plus LiDAR sensor. It uses the UART serial and digital communication protocol.

LiDAR is used to measure the distance from the ground up to the underside of the bridge, to measure bridge deflections.

This project does come with the following issues:

The LiDAR sensor is limited by its resolution of only 1cm.

The centre of mass result is certainly not accurate. With the current bridge and set-up, the changes in strain for the 4 pillar strain gauges is too insensitive to loading the bridge.

These gauges also appear to read/produce quite a bit of noise which destabilises the result of determining the centre, especially after zeroing the strain.

The sensitivity to noise is somewhat combated by taking the average reading of the strain over some less frequent interval than the scan rate.

The averaging involves a trade-off between response time and sensitivity to noise:

The slower the scan rate the less sentitive the calculation of the centre is to noise, but the response time to update the centre is decreased.

Similar noise issue are present with the mass/weight strain reading, resulting in an unstable value.