When a control cabinet becomes too warm, the problem often does not become apparent immediately. The system initially runs normally, individual components appear to work reliably, and yet after several hours of operation, faults, shutdowns or unexplained error messages occur. This is particularly critical for power supplies, frequency inverters, PLC components, relays, fuses, communication modules and electronic control systems.
A one-time temperature measurement with a handheld instrument is often not sufficient in such cases. What matters is not only the temperature at a specific moment, but the temperature profile over several hours or days. This is exactly where a temperature data logger is useful: It continuously records the control cabinet temperature and makes it visible when temperature peaks occur, how strongly the control cabinet heats up during production and whether fans, filters or cooling units are working sufficiently.
This article explains when temperature monitoring in a control cabinet is useful, how to use a data logger correctly, what measurement duration is practical and what should be considered when positioning, evaluating and assessing the measured values.
Table of contents
- Basics: Why control cabinet temperature is so important
- When is a data logger useful in the control cabinet?
- Typical causes of excessive control cabinet temperatures
- Ideal placement of the data logger in the control cabinet
- Measurement duration: Why several days are often better than a snapshot
- Detecting temperature peaks during production times
- Influence of fans, filters and cooling units
- Limit values and evaluation of measurement results
- Considering temperature and humidity together
- Documentation and evaluation of measurement data
- Table: Typical measuring points and what they indicate
- Practical example: Sporadic system shutdown due to temperature rise
- Which measuring instruments / products are suitable?
- Conclusion: Temperature profiles show more than individual measurements
- FAQ: Frequently asked questions about control cabinet temperature and data loggers
Basics: Why control cabinet temperature is so important
A control cabinet protects electrical and electronic components from external influences. At the same time, heat is generated inside. Power supplies, frequency inverters, transformers, contactors, relays, PLC modules, fuses and communication modules generate power losses during operation. The higher the load, the more the control cabinet can heat up.
Excessive temperatures have a direct impact on the service life and reliability of many components. Electronic components age faster, power supplies may go into power limitation, frequency inverters may issue thermal warnings, and relays or terminals may be subjected to greater stress. Sporadic faults in control systems or communication modules can also be encouraged by unfavorable temperature conditions.
It is particularly problematic that the temperature inside the control cabinet is not constant. It depends on the ambient temperature, machine load, solar radiation, ventilation, filter condition, installation position of the control cabinet and operating time. A control cabinet that appears inconspicuous in the morning can become significantly too warm in the afternoon or after several hours of full-load operation.
A reliable assessment is therefore only possible if the temperature is observed over a sufficiently long period of time. This is exactly what temperature data loggers are used for.
When is a data logger useful in the control cabinet?
A data logger is useful whenever temperature problems are not permanently visible or only occur under certain operating conditions. This particularly applies to systems that only run under full load at certain times, machines with changing production cycles or control cabinets in areas with strongly fluctuating ambient temperatures.
Typical indications include sporadic system shutdowns, recurring error messages, thermal warnings on frequency inverters, power supply failures, communication interruptions, unexplained PLC faults or components that become noticeably warm. A measurement can also be useful after modifications to the control cabinet, retrofitting additional loads or replacing fans and cooling units.
The major advantage of a data logger is that it objectively documents the temperature profile. Instead of merely assuming whether the control cabinet becomes too warm, a traceable measurement record is created. This shows when the temperature rises, how high the peak values are and whether the temperature drops sufficiently again after load changes.
This is particularly valuable for troubleshooting, because the measured values can be compared with operating times, production cycles, shift operation, machine load or fault messages.
Typical causes of excessive control cabinet temperatures
An increased control cabinet temperature rarely occurs without a reason. The cause is often a combination of high power dissipation, insufficient air circulation and unfavorable ambient conditions. A typical case is a control cabinet that was originally adequately dimensioned but was later expanded with additional components.
Dirty filter mats are also a common cause. If fans are running but the filters are clogged, the warm air is no longer removed sufficiently. From the outside, the control cabinet often appears inconspicuous, while heat builds up inside.
Other causes can include defective control cabinet fans, incorrectly installed fans, unfavorable air routing, blocked ventilation openings, direct sunlight, excessive ambient temperature, missing control cabinet cooling or excessive packing density inside the control cabinet.
The position of heat sources also plays a role. Frequency inverters, power supplies and transformers often generate significantly more heat than terminal strips or relays. If sensitive control components are mounted directly above such heat sources, the local temperature can be significantly higher than in other areas of the control cabinet.
Ideal placement of the data logger in the control cabinet
The placement of the data logger determines how meaningful the measurement is. If the logger is mounted in a favorable position with good air movement, critical temperature peaks may be missed. If it is attached directly to a warm component, it may measure the surface temperature of that component rather than the air temperature inside the control cabinet.
For monitoring the internal temperature of the control cabinet, the data logger should be positioned so that it records the actual air temperature in the relevant area. In practice, the upper area of the control cabinet is often of interest because warm air rises and temperature peaks can form there. In addition, a measurement near sensitive components can be useful, for example near PLC modules, power supplies or communication modules.
In larger control cabinets or cabinet systems, a single measuring point is often not sufficient. In such cases, it may be useful to use several loggers or multi-channel measuring systems. This makes it possible to detect temperature differences between upper and lower areas, between power supply and control area or between warm power components and sensitive electronics.
It is important that the logger is securely fastened, does not touch any live parts and does not interfere with operation, ventilation or wiring. Work inside the control cabinet may only be carried out by qualified personnel and in accordance with the applicable safety rules.
Measurement duration: Why several days are often better than a snapshot
A short measurement over a few minutes only shows the condition at exactly that moment. For many temperature problems, this is not enough. Critical temperatures often only occur after several hours of production operation, when components, the control cabinet housing and the surrounding environment have fully warmed up.
A useful measurement duration depends on the system. For continuously running systems, a measurement over 24 to 72 hours can already provide important information. For systems with changing production cycles, weekend operation or strongly fluctuating load, a measurement over several days or a complete working week can be significantly more meaningful.
What matters is that the measurement captures typical operating states. These include start-up phases, full-load operation, downtimes, shift changes, cleaning phases and, where applicable, higher ambient temperatures in the afternoon. If measurements are only taken during a quiet phase, the result may be too optimistic.
The data logger should therefore be configured so that the measurement interval and memory capacity match the planned measurement duration. For many applications, measurement intervals of one to five minutes are practical. For very rapid temperature changes, a shorter interval may be useful; for long-term monitoring, a longer interval may be sufficient.
Detecting temperature peaks during production times
Many control cabinet problems are not caused by a permanently excessive temperature, but by recurring temperature peaks. These can occur when several drives are running simultaneously, a frequency inverter is heavily loaded over a longer period of time or the ambient temperature rises during production.
A data logger makes such peaks visible. The evaluation then shows whether the temperature rises slowly, whether it drops again after production ends or whether it continues to increase throughout the day. This profile is particularly important for troubleshooting.
If, for example, the temperature rises significantly every day from 1 p.m. onwards, this may indicate a combination of machine load, hall temperature and insufficient ventilation. If the temperature rises immediately after a specific machine is started, the focus is more likely to be on the power dissipation of this system or the associated control cabinet area.
It is important not to look at temperature data in isolation. A comparison with operating data, shift times, fault messages, frequency inverter warnings, maintenance events or production logs is helpful.
Influence of fans, filters and cooling units
Fans, filter fans, heat exchangers and control cabinet cooling units are intended to prevent heat from building up inside the control cabinet. Their effect can be checked well with a data logger. Measurements before and after maintenance work in particular can show whether a cleaned filter, a replaced fan or a newly adjusted cooling unit actually provides an improvement.
A typical sign of poor air circulation is a slow, steady temperature rise over several hours. If the temperature does not drop despite running fans or only drops significantly after production ends, the cooling system should be examined more closely.
Dirty filters are particularly critical because their performance gradually deteriorates. The system initially continues to run, but the temperature reserve in the control cabinet decreases. On hot days or under high machine load, failures can then suddenly occur.
For cooling units, it should not only be checked whether the unit is running, but also whether the setpoint temperature is appropriate, whether condensate is drained properly, whether air paths are clear and whether the cooling capacity matches the power dissipation in the control cabinet.
Limit values and evaluation of measurement results
When evaluating the control cabinet temperature, no general limit values should be used without considering the installed components. The decisive factor is the permissible operating conditions of the respective devices. Manufacturer specifications regarding ambient temperature, derating, installation position and minimum distances must be taken into account.
A power supply, a frequency inverter or a PLC module can have different temperature limits depending on its design. It must also be considered that the temperature at the measuring point is not necessarily the same as the temperature directly at the hottest component.
In practice, not only the maximum value is important, but also the duration of the load. A short peak may be evaluated differently from several hours of thermal load close to the permissible limit. Recurring high temperatures can significantly shorten the service life of components.
The evaluation should therefore answer at least three questions: How high is the maximum temperature? How long does the temperature remain elevated? And does the temperature increase always occur in connection with certain operating states?
Considering temperature and humidity together
In many control cabinets, not only temperature is relevant, but also humidity. High humidity, condensation or dew point problems can lead to corrosion, creepage currents, insulation problems and contact faults. This is particularly critical for control cabinets in outdoor areas, unheated halls, washing systems, cooling areas or systems with large temperature fluctuations.
If a control cabinet heats up during the day and cools down significantly at night, moisture may condense. In such cases, a pure temperature data logger may not be sufficient. A combined temperature and humidity data logger can show whether, in addition to thermal stress, there is also a humidity problem.
Considering temperature and relative humidity together helps to better assess condensation risks. This is particularly important if corrosion, fogged inspection windows, damp filter mats or sporadic insulation faults have already been noticed.
In the case of permanent humidity problems, the control cabinet seal, cable glands, heating, ventilation, pressure compensation and environmental influences should also be checked in addition to the measurement.
Documentation and evaluation of measurement data
The benefit of a data logger mainly comes from the subsequent evaluation. The measurement data should therefore not only be stored, but also properly documented. This includes the measurement period, measurement interval, exact position of the logger, operating state of the system, environmental situation and special events during the measurement.
A graphical representation of the temperature profile is particularly helpful. It shows at a glance whether the temperature remains stable, rises slowly, fluctuates cyclically or suddenly forms peaks. In combination with shift times or production logs, causes can often be narrowed down much more quickly.
For maintenance and servicing, it is useful to compare measurements before and after a measure. If, for example, a filter is cleaned or a fan is replaced, a second measurement can show whether the temperature actually remains lower.
In the case of recurring problems, regular temperature recording can help detect changes at an early stage. This turns a one-time troubleshooting measure into a preventive maintenance approach.
Table: Typical measuring points and what they indicate
| Measuring point in the control cabinet | What becomes visible? | Typical application |
|---|---|---|
| Upper interior area | Heat build-up due to rising warm air | General evaluation of the internal control cabinet temperature |
| Near the power supply | Thermal load on the power supply | Troubleshooting voltage drops or power supply failures |
| Near the frequency inverter | Temperature rise during motor load and full-load operation | Analysis of thermal warnings or inverter shutdowns |
| Near PLC / control system | Ambient temperature of sensitive electronics | Troubleshooting communication errors or sporadic control problems |
| Air inlet | Temperature of incoming air | Evaluation of filter fans and ambient influence |
| Air outlet | Heating of the discharged air | Checking ventilation effectiveness |
| Cooling unit area | Effect of active cooling | Checking setpoint, operating behavior and cooling capacity |
| Outside of the control cabinet | Influence of the ambient temperature | Comparison between internal and external temperature |
Practical example: Sporadic system shutdown due to temperature rise
In a production system, sporadic shutdowns have been occurring for several weeks. The fault does not occur every day and initially cannot be reproduced during maintenance. The system fault memory contains indications of communication problems and occasional warnings on a frequency inverter. During a brief check in the morning, the control cabinet appears inconspicuous.
Since the fault occurs mainly during longer production runs, a temperature data logger is installed in the upper area of the control cabinet. A second measuring point is placed near the PLC module. The measurement runs over five working days so that different load conditions and shift times are recorded.
The evaluation shows a clear pattern: During the first few hours, the temperature remains stable. After several hours of full-load operation, however, the temperature in the upper area of the control cabinet rises significantly. Especially on days with high hall temperatures, the control cabinet reaches critical values. Shortly afterwards, the known faults occur.
During the subsequent inspection, it is found that the filter mats are heavily soiled and one fan is only operating with limited performance. After cleaning the filters, replacing the fan and carrying out another measurement, the temperature remains significantly lower. The sporadic shutdowns no longer occur.
Which measuring instruments / products are suitable?
Compact temperature data loggers that can store measured values over several hours or days are suitable for temporary monitoring of control cabinet temperature. One example is the testo 174T mini temperature data logger. It is particularly suitable for simple temperature recordings when a compact logger is to be placed directly inside the control cabinet.
If relative humidity is also to be considered in addition to temperature, combined temperature and humidity data loggers are useful. A suitable overview is provided in the category humidity data loggers. Such devices are helpful when condensation, moisture or dew point problems are suspected inside the control cabinet.
For more extensive measurement tasks, multiple measured variables or longer recordings, multifunction measuring instruments as data loggers may also be considered. They are suitable when temperature, current, voltage, humidity or other signals need to be documented in addition.
A general overview of suitable devices can be found in the category temperature data loggers. Which device is suitable depends on the measurement duration, measuring range, memory requirements, number of measuring points, desired evaluation and environmental conditions inside the control cabinet.
Conclusion: Temperature profiles show more than individual measurements
An excessively high control cabinet temperature can cause failures that at first glance are not clearly related to heat. Sporadic faults, thermal warnings, power supply failures or communication problems in particular often cannot be reliably assessed with a snapshot measurement.
A temperature data logger makes the time profile visible. It shows whether the control cabinet only becomes too warm after several hours of operation, whether temperature peaks are related to production times and whether fans, filters or cooling units are working sufficiently.
In practice, it is crucial to position the logger correctly, measure over a sufficiently long period of time and compare the data with operating states. This allows thermal problems to be detected, documented and corrected in a more targeted manner.
FAQ: Frequently asked questions about control cabinet temperature and data loggers
Why should the temperature in the control cabinet be monitored?
Excessive temperatures can shorten the service life of electrical and electronic components and lead to faults, failures or thermal shutdowns.
When is a data logger useful in the control cabinet?
A data logger is useful when temperature problems only occur temporarily, for example during full load, on warm days or after several hours of production operation.
Is a one-time temperature measurement sufficient?
A single measurement can be helpful for an initial assessment. However, for troubleshooting sporadic problems, recording over several hours or days is significantly more meaningful.
Where should a temperature data logger be placed in the control cabinet?
The upper area of the control cabinet is often of interest because warm air rises. In addition, a measurement near sensitive components such as PLC, power supply or frequency inverter can be useful.
How long should the control cabinet temperature be recorded?
The measurement duration should capture typical operating states. In many cases, 24 to 72 hours are useful. With changing load, a complete working week may be better.
Which measurement interval is useful?
For many applications, measurement intervals of one to five minutes are practical. For rapid temperature changes, a shorter interval may be required.
What causes a control cabinet to become too warm?
Common causes include high power dissipation, dirty filters, defective fans, blocked air paths, high ambient temperature, direct sunlight or excessive packing density.
How can you tell whether there is a fan or filter problem?
A steady temperature rise despite the system running can indicate poor air circulation. Measurements before and after filter cleaning or fan replacement show whether the situation has improved.
Should humidity also be measured in the control cabinet?
Yes, if condensation, corrosion, humid environments or large temperature changes play a role. In that case, a combined temperature and humidity data logger is useful.
What limit temperature applies in the control cabinet?
There is no general value for all control cabinets. The permissible operating conditions of the installed components and the manufacturer specifications are decisive.
Can a data logger remain permanently in the control cabinet?
This is possible depending on the device and application. For permanent monitoring, memory, battery, interfaces, alarm function and environmental conditions should be selected appropriately.
Who is allowed to install a data logger in the control cabinet?
Work inside the control cabinet may only be carried out by qualified personnel. The logger must be securely fastened and must not interfere with live parts, ventilation or wiring.
What is the benefit of evaluating the data as a diagram?
A diagram shows temperature rises, peaks and cooling phases much better than individual numerical values. This makes it easier to identify correlations with production times or faults.
Can a data logger help with sporadic system faults?
Yes. If faults are related to rising temperature, the data logger can make the temporal correlation visible and significantly simplify troubleshooting.