Understanding the Total Cost of Sensor Ownership (TCO) in Industrial Applications

When selecting a humidity sensor for industrial applications, the initial purchase price is often the primary focus. However, understanding the total cost of ownership (TCO) is essential, as hidden costs like calibration, maintenance, and sensor lifespan significantly impact budgets over time. This article explains how these factors influence TCO and why high-quality sensors with minimal maintenance requirements provide lasting value in industries where precise humidity control is critical, such as pharmaceuticals, food production, and meteorology.

1. The Real Cost: Beyond the Purchase Price

The upfront cost of a sensor is just the beginning. Total Cost of Ownership (TCO) not only includes the initial purchase price but also installation, calibration, maintenance, downtime, and replacement expenses. Sensors that initially appear cheaper can incur higher costs over time due to frequent calibrations and adjustments, unexpected failures and increased maintenance efforts.

Example: A permanently installed probe is more cost-effective compared to a replaceable probe, but it comes with certain disadvantages in terms of calibration, maintenance and downtime.

If uninterrupted operation is crucial, a replaceable probe offers significant advantages, as it allows for quick replacement with a ready-to-use probe, resulting in minimal downtime. Additionally, the replaceable probe can be easily removed for on-site adjustment or sent to the Rotronic service center.

In contrast, a permanently installed probe requires full disassembly from the installation if it needs to be sent for servicing, leading to longer downtime and more effort to reinstall.

2. Calibration and Adjustment: Managing Recurring Costs

Humidity sensors naturally drift over time, especially in industrial environments with extreme temperatures, high humidity, airborne contaminants, or chemical exposure. This drift affects measurement accuracy, potentially leading to poor climate control, product defects, regulatory non-compliance, and increased energy consumption.

Regular calibration is essential to ensure accurate readings and consistent process quality. The required calibration interval depends on several factors, including measurement accuracy requirements, sensor type, environmental conditions (e.g., temperature fluctuations and contaminant exposure), and industry regulations. This makes calibration highly application specific and there is no universal rule on how often it should be performed.

However, each calibration incurs costs such as technician labor, calibration equipment, and potential downtime during sensor adjustment or replacement. Therefore, it is crucial to define how much drift is acceptable to maintain process stability. Based on sensor drift behavior and the cost of each calibration, the most suitable sensor can be selected.

Example

When choosing between polymer sensor A with an accuracy of ±0.8 %rh and polymer sensor B with an accuracy of ±2 %rh, assuming that both experience the same drift over the same timeframe, sensor B will require twice as many calibrations and adjustments to stay within acceptable limits.

There is also a difference in the type of sensor material used. For example: thin-film sensor C is compared with polymer sensor B, with the same accuracy of +/-2 %. If both sensors are exposed to the same contamination, the thin-film sensor drifts away faster than the polymer sensor.

High-quality sensors offer greater stability and drift resistance, reducing calibration frequency and lowering long-term operational costs.

3. Maintenance: Unforeseeable or Scheduled Costs

Humidity sensors require regular maintenance to ensure accurate measurements and long-term functionality. Depending on the environment, sensors may accumulate contaminants such as dust, solvents, or chemical residues, which can affect performance. Factors like temperature fluctuations, air velocity, and improper installation (e.g., exposure to direct radiation or airflow distortions) can also contribute to sensor degradation.

Maintenance costs fall into two categories:

• Scheduled maintenance: Routine cleaning, protective cap replacement, preventive inspections, or adjustment s. If a sensor's readings deviate significantly beyond acceptable tolerances, adjustment is required to restore accuracy, either on site or at a service center.
• Unforeseeable maintenance: Unexpected failures requiring troubleshooting or component replacements.

Scheduled maintenance can be optimized by selecting the right sensor filter for the specific application. A filter can protect the sensor from physical particles, while others shield it from chemical contaminants or water droplets. Choosing the right filter is crucial to ensure the optimal functioning and longevity of the sensor.

While unexpected failures cannot always be avoided, several strategies help minimize risks:

• Choosing sensors with protective features such as potted electronics and coatings.
• Redundant sensor installations in critical applications prevent downtime by allowing immediate replacement.
• Regular condition checks, including visual inspections and reference sensor comparisons, help detect issues early and ensure reliable operation.

Neglecting maintenance can lead to inaccurate readings, increased downtime, and premature sensor failure. High-quality sensors that have been designed to resist contaminants and offer stable performance reduce both planned and unplanned maintenance, optimizing long-term costs.

4. Sensor Lifespan: Maximizing Long-Term Value

The lifespan of a humidity sensor is influenced by its durability, environmental exposure, and operational conditions. While some sensors can last for over a decade in controlled environments, those exposed to extreme conditions – such as high humidity, aggressive chemicals, or mechanical stress – may require more frequent replacements.

Key factors affecting sensor lifespan:

• Sensor durability: High-quality materials and protective coatings extend longevity.
• Environmental exposure: Harsh chemicals, condensation, and high temperatures accelerate wear.
• Measurement stability: Sensors with minimal drift require fewer replacements over time.

All Rotronic HC2A-S probes are potted to ensure reliable operation of the electronics. Additionally, specific variants include protective coatings, which improve resistance against dust, sea salt, fungicides, and pesticides, ensuring better long-term stability and robustness against environmental influences.

Choosing sensors with an extended lifespan minimizes replacement costs and reduces overall TCO. Investing in robust, long-lasting technology ensures stable performance and cost efficiency throughout the sensor’s operational life.

Conclusion: Smart investments for Long-Term Savings

Selecting a humidity sensor based solely on its purchase price can be misleading. The Total Cost of Ownership (TCO) extends far beyond the initial investment, encompassing calibration, maintenance, and sensor lifespan, all of which significantly impact long-term costs.

Regular calibration ensures measurement accuracy but adds recurring expenses, while maintenance – whether scheduled or unforeseen – can contribute to operational downtime and increased labor costs. Additionally, sensor lifespan plays a crucial role in determining replacement frequency, with high-quality, durable sensors significantly reducing long-term expenditures.

Investing in stable, low-maintenance sensors minimizes disruptions, optimizes efficiency, and enhances overall cost-effectiveness. By choosing reliable, long-lasting solutions like those from Rotronic, industries can maintain accurate humidity control, reduce operational risks, and achieve sustainable cost savings.

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