The one-piece design of the TAD and TD families eliminates ingress.
Using ifm’s thin film technology, the TAD family of instruments are designed with two embedded sensing elements that self-detect and warn if any signal drift is occurring.
Drift, when the measured temperature is not the actual process temperature, is caused by thermal (e.g., temperature shocks) and mechanical (e.g., pressure spikes) stresses. All temperature instruments experience drift to one degree or another. The dual element technology uses a positive resistance RTD and a negative resistance NTC element. These two different measurement technologies react to temperature changes in opposite directions. This allows the instrument’s micro controller to measure the differential between the two independent systems. Any deviation between the two measurements indicate that drift is occurring.
Rather than identifying instrument drift during a normal calibration verification, the dual element construction signals drift as soon as it occurs. This improves machine reliability, but more importantly, does not allow suspect product out of your manufacturing plant.
This technology is great for applications where redundant process temperature measurement would be used like:
Maintenance of critical temperatures is required during product pasteurization to ensure bacteria are killed before the product leaves your plant. What if your temperature instrument could continuously monitor itself for drift, even in between calibration periods?
The TAD family of sensors uses a dual RTD design that immediately signals when a drift occurs. This guarantees product safety without waiting until the next scheduled instrument calibration.
Food and Beverage applications require periodic wash down with caustics, acids and water to ensure sanitary conditions. These cleaning cycles subject instruments to high thermal shock. Temperature drift often occurs with head transmitter assemblies under these harsh environments. What if you could eliminate the primary issues associated with temperature instrument drift?
The integrated RTD element and one-piece design eliminates ingress which is a primary contributor to instrument drift.
Via IO-Link, the TAD family can provide:
Q. What is meant by "drift?"
A. Drift is a term used to indicate any time the value measured by the instrument differs from the actual value of the process. It is caused by mechanical stresses, such as pressure spikes or vibration, and thermal stresses, such as big changes in temperature over a short time span, and corrosion due to moisture ingress. All temperature instruments drift over their life span.
Q. How is drift typically detected?
A. In critical applications, where drift of 0.5 °C or less is important, it is necessary to take steps to minimize the effect of drift. Traditional steps are shown in the image below.
Q. How does the continuous drift monitoring of the TAD provide a safer process than regular calibration verification alone?
A. Traditional calibration verification can only guarantee the sensor’s accuracy at the time of the verification. If, at any point, the sensor starts to drift, it will not be detected until the next verification period. The TAD will detect the drift as it occurs. With this immediate drift detection, it might be possible to reduce regular calibration verification, while still providing security for product safety.
Using IO-Link communication, the measured value can be used in the PLC for process control. Additionally, the individual values of the PT and NTC can be documented in the user’s quality system for verification of proper process performance.
Q. The TAD sensors do not have pushbuttons. How do I change the measuring scale or the drift warning and alarm limits?
A. LR Device (QA0011) is ifm’s software to configure sensors. It can be used with a USB (E30390) cable connected to a laptop. Sensors can also be configured remotely using IO-Link.
Q. How do I calculate the accuracy of the TAD sensors? The datasheet makes it seem complicated.
A. The TAD is ifm’s most accurate temperature instrument. Since it is a one-piece design and calibrated at the factory as the complete system, calculating the accuracy is easy. The datasheet calls out:
± 0.2 (-10...130°C); ± 0.3 (130...140°C); ± 0.3 ± 0.1% MS (-25...-10/140...160°C); (probe completely inserted into the measured medium up to the sealing chamfer)
Restated in table form:
These values are achieved when the probe of the TAD is fully immersed in the medium.