Calibrating Querx Sensors

May 12, 2022

Blog: Calibrating Querx Sensors | egnite Smart Sensors

When calibrating a device, its measurements are compared to an exceptionally precise reference device.

ISO- or DAkkS-Calibration

Querx network sensors are factory calibrated, however, a certificate is not provided. egnite optionally offers ISO- or DAkkS-calibration certificates. Whether or not you require this depends on the way you intend to use Querx.

On the one hand, using a calibrated device offers you the certainty that the measured value is actually as close to the real value as you require it to be and as the data sheet claims. Of course, it would also suffice to periodically compare the measurements taken by Querx to a reference device’s results. Or even simpler, just dip a connected waterproof cable sensor into ice-water and then into boiling water. If the values are approximately 0.0 °C and 100.0 °C, this might be sufficient for your applications. There is nothing wrong with this approach.

Keep in mind, though, that this method only works with Querx PT models. Please do not try it with Querx TH or THP models, since their sensors are not suited to being submerged in liquids.

Should you, on the other hand, be under the obligation to provide proof that certain temperature ranges are constantly maintained, e.g. when storing frozen food or medicine, things look quite different. The legislators, your customers or your internal quality assurance may require a traceable calibration.

What “traceable calibration” means for a DAkkS-calibration: Traceable to a standard set by a state institution. A calibration laboratory compares the values measured by its devices to those set by the standard and documents the deviations. The values measured by Querx are in turn compared to the values of the laboratory’s devices and the deviations are once again documented. This ensures that the deviations of a Querx sensor are actually traceable to a standard set by a state institution.

The less expensive ISO-calibration, also known as factory calibration, uses standards that are subject to regular test equipment monitoring. Traceability to national standards, as with DAkkS-calibration, is not given, though. In many cases, however, ISO calibration is sufficient.

Calibration Points

At which temperatures the deviations are determined also depends on the application. If Querx is to be used to ensure that a freezer’s temperature does not exceed -18 °C, it makes sense to calibrate the device at this particular temperature. A limit value can usually be exceeded for a certain time before the frozen goods are harmed. In order to ensure that Querx can also measure higher temperatures accurately, the calibration is, for example, repeated at +20 °C. The accuracy of measurements between -18 °C and +20 °C will then be sufficient for most applications. Pt100- and Pt1000-sensors in particular, are very linear over a wide temperature range. When measuring wider ranges, it might be necessary to include a calibration point at the middle of the range. In our example this would mean a further calibration at +1 °C.

Calibrating Measuring Device and Sensor

In contrast to the Querx TH and THP models, which combine the measurement electronics and sensor into one unit, in the case of the Querx PT models these are two distinct units. Both of them play a role for the accuracy of the measured values. Thus, it is recommended to always calibrate both components together. In general, however, there is the possibility of calibrating Querx PT or Querx WLAN PT and the selected temperature sensors separately, especially when choosing DAkkS-certified calibration.

Calibration Intervals

One question that is frequently asked concerns how soon the calibration process is to be repeated. This primarily depends on the device’s and sensor’s long-term stability, which in turn depend on the intended application. Frequent changes between high and low temperatures or high and low humidities cause changes in the material. Continuous use in high temperatures or high humidity can equally influence the measurements’ long-term stability. Additionally, it has been observed, that certain changes to materials decrease with increasing age.

In essence, this means that the calibration interval needs to be decided upon by the user themselves. egnite recommends scheduling the second calibration one year after the first. Should no notable changes emerge, the interval can then be extended to two or three years, provided the application conditions remain the same.

Calibration by egnite

egnite offers ISO- and DAkkS-calibration for temperature and humidity by an accredited laboratory. The easiest way to order the calibration is together with Querx. Please specify the number of calibration points and their values. The laboratory is able to calibrate Querx TH and THP in the following ranges: Temperature from 10 to 70°C and relative humidity from 40 to 90% at 20 to 23°C and 10 to 90% at 40°C. For Querx PT an extended range from -20 to 660°C is available.

For a later recalibration, you can send us the device. We just need the device and, in the case of Querx PT, the sensor as well. We do not need power supply, cables or other accessories. Prior to handover to the laboratory, we will check for proper functioning and reset the configuration to the factory settings. Therefore, please save your configuration as described in the manual. An adjustment is not provided in the process. If we detect major deviations of the sensor, we can replace it after consultation with you for a small fee.

After about 10 working days you will get the device back. You will receive the certificate by email in the form of a PDF document. You will also receive the DAkkS certificate as an original paper copy with the device.

Calibration of the air pressure for Querx THP is not available at this time, unfortunately. However, you can easily purchase a Querx network sensor and hand it over to a laboratory of your choice for calibration.