Technical Datasheet
Technical Datasheet for Pressure Connector Options
In many real-world applications, temperatures are variable, and the pressure output changes with temperature. Datasheets often specify a percentage of full scale per degree Celsius (%FS/°C). Over a wide operating temperature range, this value often becomes the largest contributor to accuracy, typically 1-2%, which is ten times the pressure error at a single temperature. The ADROIT6000 addresses this challenge by creating a digital map of pressure over temperature, reducing the error to less than 0.1% FS. However, there is another pitfall. In applications, the temperature is not only variable but often dynamic. If the pressure and temperature elements are not at the same temperature, an error of about 0.2% per °C difference can occur. In a rapidly changing temperature situation, this error can be dramatic. This is often mitigated by mounting the temperature element near the pressure element. However, the only complete solution is to use the technique employed in the ADROIT6000, where temperature measurement is taken from the same resistors that also measure pressure.
There is always a time delay between a change in input and a change in output.
When measuring with a speed approaching the response time, it is possible to generate very large errors. Therefore, it is important to wait long enough for a change to allow the output to catch up before taking a measurement. There are several factors that contribute to the response time of a system and increase the overall delay in the system’s output. Fortunately, piezo-resistive sensor elements are very fast (in the range of 100 microseconds). In fact, they are so much faster than other parts of the system that they can usually be ignored. The signal conditioning electronics are variable but in the range of 1 to 100 milliseconds. Possibly even more variable than the electronics is the installation, where a narrow and long pressure connection, depending on the medium, can limit the change to many seconds. When fast measurements are needed, wide, short connections are required. Non-compressible fluids transmit pressure very quickly, whereas gases, especially low-pressure gases, may take some time to transmit pressure to a device. The ADROIT6000 bypasses this problem in two ways. First, the electronics are fast with a 1 ms response time to a pressure change. Second, the device is small and can operate at high temperatures, allowing it to be installed close to the pressure source, thus minimizing delays due to the transmission of a pressure wave through a connecting tube. Another advantage is the reduction in installation costs for expensive pressure connection tubes.
Apart from temperature and time, both of which can be mitigated through an understanding of these issues and careful sensor installation, there are several underlying sources of error that can only be managed by the sensor manufacturer themselves. The most important of these is thermal hysteresis. Thermal hysteresis is the difference in the output signal at a given temperature, depending on whether this temperature was reached from a previously warmer or colder temperature. This makes correction impossible, even with the most sophisticated supporting electronics. It increases the more extreme the temperature the sensor is exposed to. A sensor in a laboratory changing from 20°C to 25°C will exhibit very little thermal hysteresis, but a sensor in an engine compartment under arctic conditions changing from -40°C to 125°C will have a much larger value. The ADROIT6000 has been developed with techniques to minimize thermal hysteresis. These include the choice of construction materials, the reduction of oil volume, and several details of mechanical design. By employing these techniques, thermal hysteresis can be reduced to about 0.1% for a compensated temperature range of -40 to 125°C. In digitally compensated sensors, thermal hysteresis is the largest contributor to the Total Error Band (TEB) specified in the datasheets and explains why sensor performance deteriorates over a larger operating temperature range.
After thermal hysteresis, long-term stability is the second largest source of error. Similar to thermal hysteresis and because it is variable over time, it is impossible to compensate for it with electronics. Keeping these errors small is only possible through careful mechanical design of the pressure measurement module within the pressure sensor. The ADROIT6000 uses high-precision machined metal parts, stable silicon measurement elements, and low-energy yet highly penetrating welds. All these factors contribute to creating extremely stable measurement modules. Typical stability values in the first year are 0.05%, and the sensors become more stable with age.
In some applications, regular recalibration is necessary to confirm accuracy. The performance of the ADROIT6000 can be measured with standard calibration devices such as the multifunctional calibrator DPI620 Genii from Druck. If adjustments are needed, Druck has developed a user-friendly interface and an app that complements the ADROIT6000. After entering the zero and voltage data into the app, a single button press adjusts the sensor accordingly. Even without a calibration device, the app allows for zero adjustment.
These features create a product with the highest performance, offering long-lasting reliability and effectiveness even in the harshest environments.
