Purpose

The CMD system is used to monitor the opening and closing of a surface crack as well as relative lateral movement between the two sides of the crack as a function of time.

Principle

With the CMD (Crack Monitoring Device), a three-point rosette, in the shape of an equilateral triangle with 50-mm side lengths, is bonded to the surface. Two of the rosette points are positioned parallel to the crack, and the third one is positioned on the opposite side of the crack approximately half the distance to the base line.
CMD_1
Temperature and moisture related movements, measured between points A and B, together with crack movement measurements between points A and C as well as between points B and C are transformed mathematically into the opening or closing of the crack and into the relative lateral movement of the two sides of the crack.

The measurements are made manually with the CMD-200 using a caliper, or they can be made electronically with the CMD-300 using displacement sensors (LVDTs). The CMD-300 also has the option for remote monitoring from the office by means of a GSM cellular phone modem. The purchaser supplies the SIM card.