Understand the effect of temperature on pressure sensors

Operating temperature range is pressure sensor

The "Operational" or "Environmental" temperature range means that the lowest and highest temperature transmitter bodies will be exposed during operation. For example, -20 to + 80 ° C is the standard operating pressure range for standard pressure transmitters. If the transmitter case temperature falls outside of this range, the output signal can show extreme drift or the transmitter can stop operating completely. Even relatively short exposures outside the specified range can cause permanent damage. This is why it is important to verify the extreme environment of each application in order to select an appropriate pressure sensor.

Other factors may affect the operating temperature of the transmitter. If the transmitter body is made of metal and the temperature or heat medium is measured, heat will also be applied to the transmitter by this method. For example, this can allow a transmitter rated current to operate at least -20 ambient in a colder environment, which will "heat up" through heat transfer from the process medium.

Another factor to consider is the cable. Many cable materials become stiff and fragile. Exposure to extreme cold can cause cable insulation to crack if bent in extremely cold environments.

Storage temperature

It is usually also provided when storing temperature. In most cases, the storage range is wider than the operating temperature range. Electronic circuits are usually not susceptible to operation when the temperature is too high. The rated storage temperature specification may actually be less than the operating temperature range if the manufacturer includes launch packaging and testing to simulate shipping. For example, a bubble wrap may drop more than 100 OC (212OF).

Medium temperature

The temperature range of the media is another important indicator to consider when selecting a pressure transmitter. The temperature of the media directly affects the overall performance and accuracy of the pressure sensor's readings. Care must be taken to select the transmitter and media temperature range that is greater than the expected minimum and maximum media temperatures. Temperature metrics that exceed the media can cause significant errors or complete instrument failure.

A typical medium temperature range is specified as -30 to + 100 °C. However, many transmitters are available with significantly high temperature media specifications and many options for handling media extreme temperatures. These include a built-in cooling and metal fin element that reaches the pressure sensor before providing convective cooling for the medium. A siphon can be used to measure the pressure of high pressure steam. Even higher temperature ranges are available with a diaphragm seal and capillary. Diaphragm seals when measuring the pressure of a high temperature medium are often used. The seal's function is to isolate the media from the transmitter and capillary, which can be several feet long, and provide isolation from extreme temperatures.

Temperature compensation range

A "compensated temperature range" specification is typically set in most cases. The compensation temperature is a range in which the internal circuit of the sensor is designed to limit the temperature error to a prescribed level. For example, a pressure transmitter can have a temperature range of -30 to +100 °C medium. The compensated temperature range can be limited to -0 to +80 °C, where the temperature error will be no greater than, say 0.2% of the span is within this range, varying every 10 degrees Celsius. The temperature error of the external compensation range will be significantly greater. As a rule of thumb, the compensation range outside the temperature error (but still below the maximum medium temperature) can be up to three times the compensation range calibration temperature

Finally, the calibration temperature is also defined in the specification. This is the transmitter exposed to temperature during the calibration process during manufacturing and used as a starting point for calculating the error within the "compensated pressure range" described above. Some of the pressure transmitter manufacturers offer calibration temperatures for special application options. For example, a pressure transmitter has been calibrated to a standard temperature of 15-25oC. No additional temperature error is introduced if the transmitter is operating within this range. If the application is said to be at a constant temperature of 80 ° C, the transmitter can be factory calibrated at this higher temperature. This provides users with improved transmitter performance in high temperature applications.