**2. Measurements in welding processes**

Automatic welding is affected by disturbances in the production parameters and welding conditions. Variations in components' position and dimensions, weld joint misalignment, oil in the surface and other improprieties in materials, instability in welding wire speed, and shielding gas flow are examples of disturbances. However, by adding measuring systems, the control system may have a better performance when disturbances are found. For this purpose, the disturbances and affected variables must be measured or estimated online, to counteract the effects of the disturbances through the control actions. These variables can be different in each process type or change your significance in the process. Some variables can be measured directly from the welding power source or using indirect measuring techniques, and others need to be estimated from measured variables. This last group includes the weld bead depth or penetration.

In welding processes, the variables can be classified depending on whether they can be measured or modified and if these actions can be done online or offline. Responding to this classification, the variables in welding processes can be divided into five basic groups [8]:


An example of variables and groups for the constant voltage GMAW orbital process is shown in **Figure 1**, and some measurement techniques are described in the following sections.

> communications. The communication interface usually implements a serial protocol or digital and analogical inputs and outputs to obtain or send information from an external supervisory control system (computer, programmable logic controller, and robotic system, among others). This interface can be used to synchronize work between power sources and robotic systems, other machines, control levels, or factory management. The welding variables, as voltage, electric current, and wire feed speed, can be measured and modified using this interface. Some commonly used standard network protocols are RS-232, RS-485, Modbus (RTU, TCP, or UDP), CAN Bus, DeviceNet, Field Bus, and Ethernet. Other companies define their protocol such as the Arclink developed by Lincoln Electric and SpeedNet by Fronius. The communication protocol can be "open" or "proprietary." In the first case, the user can communicate his control system directly with the power source using the communication protocol description. In the second case, he needs to buy and use proprietary software or hardware. The implementation of protocols used in

*Variables and classification groups to conventional constant voltage gas metal arc welding (GMAW) process*

**Figure 1.**

**81**

*(adapted from [8]).*

*Online Measurements in Welding Processes DOI: http://dx.doi.org/10.5772/intechopen.91771*

### **2.1 Measurement of welding variables**

The most common measurement variables in welding are related to the power supplied to the process by the unit of material length or area, and most are defined or measured by the power source. In conventional arc welding processes, these variables are *electric voltage*, *intensity of electric current* (also called simply *amperage* or *welding current*), and *wire feed speed* in processes with material addition. The parameters to control the waveform of voltage or electric current in the advanced arc welding process are important also. Other variables can be necessary to define and know, as *gas flow*, *pre-gas time* and *post-gas time*, *source impedance*, and time or position when the arc is open and closed (*arc status*). In laser welding processes, *laser power*, *pulse rate*, *focal distance*, and *spot size* are important too.

The modern welding power sources have one or various microcontrollers or microprocessors to control source operations, data acquisition, and
