Calibrating Querx Network Sensors

Blog: Calibrating Querx Network Sensors | egnite Smart Sensors

When calibrating a device, its measurements are compared to an exceptionally precise reference device. The device that is calibrated is not intended to be adjusted in this process.

DAkkS-Calibration

egnite offers the Querx network sensors with the option of calibration certified by the German Accreditation Body (DAkkS). 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 in this context is “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.

Other manufacturers and laboratories offer the cheaper mode of ISO-calibration. This uses standards that undergo a periodical process of inspection equipment monitoring. This approach does not ensure traceability to a state standard, as the DAkkS-calibration does. However, in many cases an ISO-calibration will suffice.

egnite only offers DAkkS-calibration from an accredited laboratory. If you do not require this, you can, of course, optionally purchase a Querx network sensor and have it calibrated by a laboratory near you.

Calibration Points

The application dictates the temperatures at which a device’s measurement deviations are determined. 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, however, 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.

When ordering a calibrated Querx sensor you will need to specify the number of calibration points and the temperatures at which the sensor is to be calibrated.

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, 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.

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