Why High Temperature Affects Pressure Sensor Accuracy

When selecting a right pressure sensor, it is important to understand the high temperature that will occur during actual use. If the measurement technique in use have no sufficient temperature compensation, it is most likely to cause serious errors and other risks. That is why the end users of pressure sensors need to know in advance the temperatures expected in their own specific application. There are two values need to be considered, that is medium temperature and ambient temperature. Both of these values are important. The medium temperature is the temperature at which the pressure port of the pressure sensor is exposed. The ambient temperature is the value produced in the environment surrounding the application and ultimately affects the electrical connection. The definition of the two values are different and their effects on pressure sensors are different.

• Why temperature is an important factor for pressure sensor accuracy

1. The materials used in the pressure sensor will show a certain temperature dependence. Therefore, measurement accuracy of the pressure sensor also varies with temperature. Therefore, zero offset and span error related to temperature will occur. For example, if the pressure sensor stressed a pressure of 10 bar at 25 ℃ and then the same pressure value is stressed for a second time at 100 ℃, different measurements value will be obtained. For users who only use the output data of the pressure sensor, it means that when the temperature compensation itself is still insufficient, excellent accuracy are practically useless.
2. In addition to avoiding serious measurement errors, the mechanical function of the measuring instrument depends on the existing temperature. The main influence objects are the components of the pressure sensor, such as electrical connections and cables for transmitting measured values. The cable socket and the cable itself can melt and even catch fire.
3. In addition to measurement accuracy, temperature also has an impact on the operational safety of pressure sensors. Fortunately, users do not have to bear these risks because the pressure sensors can be optimized for different temperature conditions. A way is temperature compensation, on the other hand additional cooling elements can be used, especially heat-resistant materials.

• Two forms of temperature compensation for pressure sensor

1. Passive compensation. Temperature-dependent resistance in the Wheatstone bridge is activated.
2. Active compensation (polynomial compensation). When the temperature inside the heating cabinet rises, the various pressures will approach. Then compare these values to the values in the calibration standard. Then input the temperature coefficient determined by above into the electronic equipment of the pressure sensor so that the temperature error in actual operation can be compensated actively. Active temperature compensation is still the preferred method because it gives the most accurate results.

On the other hand, temperature compensation itself has its limitations. As mentioned earlier, temperature does not only affect the pressure sensor accuracy. The mechanical components of the measuring unit are also affected at temperatures above 150 ℃. At these temperatures, the contact and adhesion become loose and the pressure sensor itself is damaged. If expected that there will be an abnormally high medium temperature, additional cooling elements are required to ensure proper functioning of the pressure sensor.

• Cooling element for very high medium temperature

In order to protect the pressure sensor from high temperature, four variants can be used depending on the application and the temperature involved.

• Variants A: the medium temperature is about 150℃

In this variant, the heat sink elements are integrated between the measuring unit of the pressure sensor and the amplifier. This is an operation that separates the electronic device from the actual application so that they are not damaged by high temperatures.

• Variants B: the medium temperature is higher than 150℃

If the medium is very hot, screw in the cooling element in front of the pressure port of the pressure sensor. For example, you can screw in the heat sink from both sides. Therefore, now the pressure port is only in contact with the cooling medium. These forward-connected heat sinks have no effect on the pressure sensor accuracy at all. However, if the medium is very hot steam, use a siphon as the cooling element.

• Variants C: Extremely high medium temperature (up to 250℃)

When the medium temperature is extremely high, a forward isolation system with cooling section can be used. However, the size of this variant is quite large and has a negative impact on the pressure sensor accuracy.

• Variants D: Special case for the heating cabinet or climate chamber

When the ambient temperature is as high as 150℃ and pressure measurement is required in the heating cabinet, the electronic equipment of the pressure sensor cannot be exposed to these temperatures which will cause damage. In this case, only the measuring unit (with pressure port and stainless steel housing) is located inside the cabinet, which is connected to the remote electronics outside the cabinet (also in the stainless steel housing) via a high temperature FEP cable.

In summary, the accuracy of the pressure sensor is affected by temperature conditions. The temperature acting on the pressure port can be compensated passively or actively so that the pressure sensor meets the accuracy requirements within the expected temperature range. In addition, the influence of the ambient temperature on the mechanical components of the measuring instrument must also be considered. It can also be controlled using front cooling elements and heat resistant materials. Therefore, users should always rely on the comprehensive recommendations provided by the manufacturer and ensure that the pressure sensors used are optimized for their specific application.
The most trouble-free way is to use the high temperature pressure sensor directly. High temperature pressure sensor produced by ATO can measure the medium with temperatures up to 300 ℃ and contain heat sinks, which can satisfy the pressure measurement in high temperature medium.