Aluminothermic Welds (Cadweld®) / AL-40

The secret: a 0,01µΩ resolution

The electrical resistance value of a good exothermic weld is about ten micro ohms, and the difference between a good and a bad weld can be as low as one micro ohm. In order to be able to measure this difference, the accuracy and resolution of the tool used are very important. In addition, these joints are welded in the field, and so the tool must be portable and easy to use .The AL-40 is alone in this category.

A unique probe

The AL-40 is equipped with a probe designed specifically for exothermic welds. It uses the four-points measuring method. This technique consists of injecting a known current through two current contacts and then measuring the voltage with the help of two voltage contacts placed in between. The current is read as well to eliminate the contact-resistance factor. The instrument is also equipped with a microprocessor that eliminates offsets and parasite voltages. Thanks to its unique filtering system, the AL-40 can be used in the presence of intense magnetic fields.

Quick and easy measuring

The measuring is done automatically when the probe is pressed against the weld. Once the AL-40 has detected the presence of the four contacts, the result is displayed instantly. Additional measurements can be made by lifting the probe and pressing it back against the weld.

The relative mode

A relative measuring mode ("REL" Key) allows the user to compare the difference between a reference measurement and the ones obtained during the quality control. The refined voltage measuring system of the AL-40 enables it to use very low injection currents (up to 5 Amps), which presents many advantages:

-it works on batteries; so it is lightweight and handy
-the low injection current allows the use of very fine contact points (see image on the left)
-waterproof and shock resistant, it is suitable either for laboratory or field applications
-Its liquid crystal display with backlight allows the use of the AL-40 in weak lighting conditions.

Quality control of exothermic joints

The quality of energy and grounding networks joints is of prime importance for the companies who produce or use high power electric energy (power plants, substations, railways, aluminium foundries, etc). A bad quality joint causes a decay of the network's performance that soon translates into excessive maintenance. The traditional method of checking welded electrical connection used to be visual inspection, but this method is now considered ineffective because many factors   can escape notice. Oxidation of conductors, insufficient preheating temperature or traces of humidity can all result in a solid, good- looking weld the resistance value of which is still too high.