How infrared cameras (IR) help in condition monitoring (CM)
A thermographic camera (Infrared imaging or thermal camera) uses infrared radiation to detect objects.
Infrared imaging plays an essential function in predictive maintenance. The cameras monitor plant machinery or equipment to create thermal images that reveal hot spots. These hot spots help detect future malfunctions, overheating, machinery or facilities damage, and personnel injury. Repairs or maintenance can be performed at the safest and most cost-efficient time.
An essential condition for the safe operation of any electrical installation is the correct equipment selection. The maintenance of such equipment must follow established parameters in terms of heating evacuation in all operating modes and the current conducting parts that connect them. Heat transfer is also carried out in electrical installations from warm to cold areas in three ways: through conduction, convection, and radiation.
Thermal imaging system / infrared camera
Every object emits infrared energy, which is referred to as a heat signature. This infrared energy is measured and detected by an infrared camera (IR) or thermal imager. The camera converts this infrared data into an electronic image representing the object's apparent surface temperature under measurement. A thermal imager has an optical system that focuses infrared energy onto a special detector chip (sensor array) consisting of thousands of grid-arranged detector pixels. An electronic signal is produced when each pixel in the sensor array reacts to the infrared energy focused on it. The camera processing unit takes the signal from each pixel and applies a mathematical algorithm to create a colour map (thermograph) of the apparent temperature of the object under measurement. Each temperature value is assigned a different colour, and a matrix of colour is produced. This matrix is sent to the camera's memory unit, which displays the object's thermography (thermal image), as shown in Figure 1.
Figure 1: Thermal imaging system (infrared camera)
Infrared camera CM applications scenario
By detecting anomalies often invisible to the naked eye, thermography allows corrective action to be taken before costly system failures occur. There are endless use cases for thermal imaging cameras in the predictive maintenance area; some of them are electrical & mechanical maintenance, utilities, and energy loss. Below are a few of the challenges faced in the industrial application scenario.
Low voltage inspections: Electrical inspections require infrared cameras. Loose electrical connections increase current resistance leading to an increase in temperature. As a result, components may fail, resulting in unplanned outages and injuries. Furthermore, the efficiency of an electrical grid decreases before failure; thus, energy is lost by generating heat, leading to unnecessary losses, as shown below.
High voltage inspections: Infrared cameras are routinely used to monitor power transformers. Temperatures of cooling fins and high voltage connections may be compared so that remedial action can be done before significant problems arise. Circuit breakers, switchers, and high-voltage power lines are among the other high-voltage installations that are checked with an infrared camera. The infrared imaging will identify potential issue regions, as seen in the figure below.
Mechanical maintenance: Most manufacturing industries consist of critical static and rotating equipment that serves as the backbone of operations, such as motors, starters, conveyors, assembly systems etc. Thermographic data complements vibration studies in mechanical equipment monitoring.
Figure 2(a): Poor connection and internal damage (b)internal fuse damage
Figure 3(a): Incorrectly secured connection (b)Inspection of high voltage power lines
Figure 4(a): Suspected roller (b)Overheated motor
Integration of infrared thermography with condition monitoring
For fault detection using an infrared thermal imaging camera, an IR monitoring scanning algorithm is shown below for the overall equipment scan process. The IR scan is a part of an integrated condition monitoring system using other technologies for comprehensive condition monitoring.
As appropriate, the scan process for the machine or equipment can be configured at predetermined time intervals. Once the scan process begins, it compares thermal images of a defined target to the baseline image of the equipment to spot thermal anomalies in the system. If no deviation is found, the rescan process begins after a time interval determined by the user. If an anomaly is spotted during the scan process, it will proceed to the next phase to evaluate the problem utilising IR thermal imaging software. The diagnosis process begins with identifying the nature of the problem; once found, the problem is compared to the priority set by the maintenance planner in the importance and alarm list. If the problem is drastic and inadequate, it generates an IR report for the effective area of the target object with all necessary temperature gradient details and thermal patterns for detailed investigation and repair to the maintenance planner for necessary corrective action during this diagnostic phase.
Figure 5: IR monitoring scan process for the equipment
Figure 6: Typical components of the thermal imaging system used in condition monitoring
If the nature of the problem is not a high priority, it is added to the waiting stack for rescanning. If an anomaly is found but the problem is not identified, it will investigate further, employing vibration and ultrasonic testing of the equipment.