Manual reading gauges

A manual reading gauge is read on site, by eye or with a calliper, with no power supply, no battery and no maintenance. It is the oldest form of monitoring and, in many cases, the most relevant: when the measuring point is accessible and a monthly or quarterly visit is enough, it provides exactly the same information as a wireless sensor, for a fraction of the cost.

Choosing according to the phenomenon observed

The movement to be measured determines the choice of instrument. For a crack opening in a single plane, a G1-type gauge is enough. If the crack slides as well as opens, a 2-axis instrument is needed, able to read opening and shear simultaneously. An offset between two parts of a structure is a matter of misalignment, a wall leaning out of plumb a matter of tilt, and a beam under load a matter of deflection. Each calls for a different gauge geometry, and installing the wrong instrument means precisely measuring the wrong thing.

Mechanical or digital

Mechanical gauges are bonded or screwed in place in a few minutes and stay in position for the whole observation period. Their resolution ranges from 0.1 mm to 0.05 mm depending on the model, which covers the vast majority of building defects.

The digital crackmeter meets a different need. Only the mounting plates remain on the structure; the measuring device itself moves from one point to the next. A single instrument can thus monitor dozens of cracks to 0.01 mm, making it the tool of choice for experts instrumenting several points on the same site.

A reading is only worth something if it is kept

A single measurement tells you nothing. It is the series that reveals whether a crack is worsening, stabilising or simply following seasonal cycles. The Saugnac app archives every reading, automatically reads the value of G1 gauges from a photo, and produces the trend charts that go into the report. It is supplied with the instruments.

When to choose remote monitoring

Manual reading reaches its limits in three situations: a hard-to-reach point, a high measuring frequency, or an alert threshold that must be monitored continuously. Wireless sensors then take over, and the two approaches work very well together on the same structure.