Examine the pressure application and determine the maximum pressure that the transmitter will see.

Consider the following values:

1. The normal operating pressure range, low and high.

2. The maximum abnormal operating pressure range, low and high.

3. The maximum safe overpressure range (burst or damage limits).

4. Peak and frequency of pressure pulses.

The low limit of pressure must be considered if the transmitter can be damaged by vacuum and could be exposed to vacuum. Users should also pay attention to the hydrotest pressure associated with the line, though this does not tend to be a problem. Also, if the sensor is directly exposed to high temperature, the pressure rating will be limited by that temperature. Exposure to abnormal events (such as water hammer) must also be taken into account.

Once the pressure limits are determined, it is good practice to allow a 20% safety factor. If there is an overpressure or safety device, the pressure rating of the pressure transmitter can be at the trip setting of the overpressure device.

Over-rating a transmitter can negatively impact its range and sensitivity. These two parameters have a direct correlation to the accuracy of the measurement. The installation of a pressure snubber or dampener could alleviate the need for the safety factor, as we'll discuss later.

Select a transmitter with the operating pressures at 50-75% of the calibrated range. This assumes that there are not many expected upsets that could cause large swings in pressure. If there are large swings (widening the range) due to process conditions, installing a second transmitter to handle the additional range should be considered.

Consider both the process temperature range and the ambient temperature range. The process temperature range represents the normal and abnormal temperatures the transducer will be exposed to via the process. The ambient temperature range gives the amount of temperature error to allow for without degrading performance outside the limits set by the application.