Sensor Readings and Accuracy

Accurate sensor readings are essential for effective environmental monitoring and preservation, ensuring that the data you collect reflects the true conditions in your spaces.

Table of Contents

• Sensor Readings
• Sensor Accuracy
• Device Age
• Calibration
• Accuracy Ranges and Standard Deviations
• Measuring Data
• Testing Device Accuracy
• Illuminance Sensor Accuracy
• Additional Resources

Sensor Readings

The frequency of readings—and especially transmissions—significantly impacts battery life. Different data loggers operate in various ways: some take readings every 5 minutes, average them over 6 readings, and then record the average every 30 minutes, while others capture and transmit a single point-in-time reading.

Each approach has its advantages and disadvantages. If you require a quick response to changing conditions, a more frequent reading interval may be suitable. Conversely, if the data logger is placed in a stable environment and your focus is on long-term trends, a longer interval may suffice. By default, Conserv Smart Collection Sensors (SCSs) transmit messages every 15 to 20 minutes depending on which device you have.

Generally, a reading interval of 10 to 30 minutes is recommended for collections.

Sensor Accuracy

If you have imported data loggers such as HOBOs or PEM2s that also monitor your collection environment, they may show different temperature or relative humidity (RH) readings than your Conserv Smart Collection Sensors (SCSs). If this occurs, there are a few things you should consider.

Device Age

Over time, devices may experience a decline in accuracy, known as "drift." If your devices are more than a few years old and have not been updated or calibrated, this could explain discrepancies in readings. Conserv offers a three-year guarantee on SCSs, and if a decline in accuracy is detected, Conserv provides replacements at no additional cost.

Calibration

All devices need regular calibration to keep their reading accuracy on point. When you receive your Conserv sensors, you can trust that they've been calibrated and tested right before they're shipped to you. Over time, recalibration is necessary for any device, even Conserv sensors. This is why we regularly monitor their accuracy for you, and will send you newly calibrated devices as soon as we notice a difference, or when they reach a lifespan that indicates recalibration is required. If you're not sure when your non-Conserv devices were last calibrated, you might want to consider sending them off for calibration and testing.

All devices require regular calibration to maintain accurate readings. When you receive your SCSs, you can trust that they have been calibrated and tested just before shipment. Over time, recalibration becomes necessary for any device, including SCSs. That is why Conserv sends newly calibrated replacements if any unusual changes are detected or when they reach the end of their subscription cycle. If you are unsure when your own data loggers were last calibrated, it may be time to send them for testing and recalibration.

Accuracy Ranges and Standard Deviations

Every device has a manufacturer-specified accuracy range, which can vary depending on the company and several factors. The same applies to SCSs. As a result, SCSs may display different readings compared to devices from other companies due to these differing accuracy ranges. In some cases, the deviations may even occur in different directions. It is important to know the accuracy ranges for all of your devices. For Conserv’s accuracy ranges, see Technical Details and Specifications.

Measuring Data

Temperature readings are generally accurate across manufacturers, but deviations are more common in RH measurements. Digital sensors for RH readings rely on electrical properties of the sensor material, like capacitive or resistive elements. Two sensors that use different measurement technologies may also yield slightly different results.

If you notice RH discrepancies, refer to this article for a deeper dive into RH variations.

Testing Device Accuracy

You can test your device's accuracy in-house using saturated salt solutions, which create specific RH conditions in small enclosures. You can compare the device readings versus the RH that you created. Refer to AIC instructions for guidance.

Illuminance Sensor Accuracy

The following SCSs were tested for accuracy using a known reference meter. Conserv conducted tests on SCS-3-4 and SCS-3-5 to verify the accuracy of illuminance readings with the full lens package. A recently calibrated Elsec 765, widely accepted in cultural heritage preservation, served as the benchmark. To eliminate any external light variables, testing was done in a dark room.

The illuminance test setup used an LED illuminator covering the full visible light spectrum, positioned 40 cm from the sensor with perpendicular input to the lens. Eight different SCSs were tested at four different lux levels (2000, 800, 500, and 300), each compared twice against the Elsec 765.

The UV test setup involved exposing a calibrated reference UV meter and SCSs to a calibrated illuminator irradiating at a wavelength of 365nm. The illuminator provided a consistent UV source at a fixed height. An Extech UV 510 with a recent calibration certificate was used as the comparison reference for UV measurements.

Additional Resources

Conserv is committed to providing accurate, real-time data. If you notice significant discrepancies between your Conserv sensors and other devices that are not explained in this article, please open a support ticket.

In 2024, Conserv’s VP of Customer Experience, preventive conservator Melissa King, co-hosted a webinar, C2C Care Webinar, with facilities expert Chris Cameron. Conserv strongly recommends that you watch the section that begins around minute 25:45 where Melissa goes into detail about how to compare sensors.