Application of infrared thermal imaging technology in equipment maintenance

Heat is often an early sign of equipment damage or malfunction, making it a key performance parameter monitored in a predictive maintenance (PDM) program. Technicians performing infrared thermography predictive maintenance regularly check the temperature of key equipment, so they can track the equipment's operating status over time and quickly discover abnormal readings for further inspection. By monitoring equipment performance and scheduling maintenance when needed, the possibility of unplanned downtime due to equipment failure can be reduced, maintenance expenses and equipment repair costs can be reduced, the life of equipment assets can be extended, and maintenance effectiveness and production capacity can be maximized.

Principle of infrared thermal imaging technology

In 1800, British astronomer William Herschel used a spectroscopic prism to decompose sunlight into monochromatic light from red to purple, and measured the thermal effects of different colors of light in turn. He found that when the mercury thermometer was moved to the dark area beyond the boundary of red light, where the human eye could not see any light, the temperature was higher than that in the red light area. Repeated experiments proved that there is indeed a kind of "heat line" invisible to the human eye outside the red light, which was later called "infrared light", or "infrared radiation". Any object in nature, as long as the temperature is higher than absolute zero (-273.15℃), will emit energy in a very wide wavelength range in the form of electromagnetic radiation, generating electromagnetic waves (radiant energy).

The wavelength band where infrared rays penetrate the atmosphere better is usually called the "atmospheric window". Infrared thermal imaging detection technology uses the so-called "atmospheric window". The short-wave window is between 1 and 5 μm, while the long-wave window is between 8 and 14 μm.

From Planck's law, we can know that the higher the temperature of an object, the more its peak radiation energy tends to the short-wave direction. Therefore, infrared thermal imagers, especially those used for building inspection, usually work in the long-wave band of 8-14μm. The temperature range of infrared inspection for buildings is generally between -20-100℃.

Infrared thermal imager is a new type of photoelectric detection equipment, which can instantly visualize the thermal information of the target surface and quickly locate faults. With the help of professional analysis software, it can also perform analysis to complete building energy conservation, safety inspection and electrical preventive maintenance.

A thermal imager consists of two basic parts: the optics and the detector. The optics focus the infrared radiation emitted by an object onto the detector, which converts the incoming radiation into electrical signals that are then processed into a visible image, or thermal map (see Figure 1).

Introduction to Predictive Maintenance of Equipment

Infrared thermal imaging cameras are the first line of defense in a predictive maintenance program. Technicians can quickly measure and compare the thermal signature of each piece of equipment on their inspection route without interrupting equipment operations.

If the temperature is significantly different from previous readings, other maintenance techniques (vibration analysis, motor circuit analysis, airborne ultrasonic analysis, and lubricant analysis, etc.) can be used to investigate the cause of the problem and decide on the next course of action.

For best results, integrate all of your maintenance technologies into the same computer system so they share the same equipment lists, historical data, reports and work orders. By correlating infrared data with data from other technologies, the actual health of all your machines can be reported in a consolidated format. [page]

Predictive maintenance process of infrared thermal imaging equipment

1. Start with an existing equipment inventory from a computerized maintenance management system (CMMS) or other inventory management tool.

2. Discard components that are not suitable for infrared measurement.

3. Check maintenance and production records. Prioritize key equipment that is prone to failure or often causes production problems.

4. Use a database or spreadsheet program to group critical equipment together by area or function and divide them into roughly 2-3 hour inspection blocks.

5. Be careful when using thermal imagers to obtain baseline images of each critical piece of equipment: On some equipment, you may want to capture multiple thermal images of critical components or subsystems on a regular basis.

6. Download the reference image into the software and document your inspection route with location name, inspection description, emissivity, and RTC and alarm values ​​if desired.

7. When it is time to do your next inspection, if your thermal imager supports data upload, simply load the previous inspection images into the imager and follow the on-screen prompts.

Application Introduction

Motor detection

There are many parts in the motor, and there are many places and reasons for failure. The following problems can be found by infrared thermal imager.

(1) Electrical wiring (electrical junction box housing)

Problem: Overheating of the terminal blocks.

Possible causes: loose connection, oxidation and corrosion of terminal blocks, over-tight connection.

Recommended Action: Reconnect or replace the terminal block.

Problem: Cable overheating.

Possible causes: unbalanced voltage or overload.

Recommended Action: Use a multimeter, clamp meter, or power quality analyzer to confirm the specific cause.

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(2) Temperature distribution of motor housing

Problem: The temperature in some areas of the housing is too high.

Possible reasons: The internal iron core or winding is short-circuited due to aging or damage of the insulation layer.

Recommended Action: Remove the housing for inspection.

Problem: The overall temperature of the shell is too high

Possible cause: Insufficient air flow causing cooling failure.

Recommended action: If the downtime is short, clean only the motor air inlet grille; and schedule a thorough motor cleaning at the next planned downtime.

(3) Bearings and couplings connected to the motor

Problem: The temperature of bearings and couplings is too high.

Possible causes: poor lubrication or misaligned shaft.

Recommended actions: Check lubrication or adjust the shaft.

Transformer testing

The transformer box heats up due to oil pipeline blockage, eddy current loss, internal abnormalities, poor core insulation, etc. The detection of the transformer box by the infrared thermal imager can keep the transformer box at a normal temperature at all times and avoid damage to the transformer due to excessive temperature.

Capacitor cabinet

Capacitors are mainly used for reactive power compensation or phase shifting in power supply systems, and are installed in large quantities in power distribution systems at all levels. In industries with high power loads (such as petrochemicals, metallurgy, papermaking, and automobiles), capacitor cabinets are the most common electrical equipment in workshops, and the frequency of their failures is relatively high; once a capacitor fails, it will affect the quality of power supply at the least, and in severe cases it will cause an explosion, leading to a production stoppage accident. The energy loss (dielectric loss) caused by the dielectric inside the capacitor or the dielectric of the electrical insulation near the current-carrying conductor under the action of AC voltage, even in normal conditions, the dielectric inside the equipment and the insulating dielectric around the conductor will also have dielectric loss and heat under the action of AC voltage. When the insulation performance of the insulating medium is defective, it will cause the dielectric loss to increase, the capacitance value to increase, and the dielectric loss heat power to increase, thereby causing the operating temperature of the equipment to increase.

According to DL/T 664 "Guidelines for the Application of Infrared Diagnostic Technology for Energized Equipment", the abnormal thermal image characteristics of coupling capacitors are obvious overall or local heating, the maximum allowable temperature rise is 1.5°C (film-paper type), and the allowable temperature difference of the same type is 0.5°C (film-paper type).

Conveyor belts and pulleys

Rubber conveyor belts are the most widely used, but rubber is prone to aging and breaking due to long-term friction or heat transfer from overheated bearings. In severe cases, it can cause production accidents such as shutdowns. Infrared thermal imagers can detect hidden faults in the early stages of overheating and aging of rubber conveyor belts in a timely manner to avoid accident losses.

There are two friction forces on the rubber conveyor belt: one is the static friction with the object on the conveyor belt. If the object and the conveyor belt move relative to each other, the static friction will turn into dynamic friction; the other is the static friction with the drive shaft. If the conveyor belt ages, it will also turn into dynamic friction with the bearing. The dynamic friction generates more heat for the drive belt than the static friction. Rubber is a material that is easily aged by high temperature. If it is exposed to high temperature for a long time, the rubber will be damaged and broken. In addition, due to the unbalanced placement of the items on the conveyor belt, the conveyor belt tilts to one side, which will also increase the pressure between the rubber conveyor belt and the drive shaft on one side, causing local overheating of the rubber belt.