Choosing the correct pressure range for a [sensor](https://www.ampheo.com/c/sensors) is critical. An incorrectly selected range can lead to measurement inaccuracies, sensor damage, and increased costs.

The selection process is a balance of four key factors: the expected operating pressure, the required accuracy, the need for overpressure protection, and the type of pressure being measured.

Here is a step-by-step guide to making the right choice.

**Step 1: Understand Your Pressure Environment**
First, you must define the pressure you need to measure with precision.

**1. Determine the Normal Operating Pressure (OP):**

* What is the typical, expected pressure during normal system operation?
* Example: A water pump normally operates at 60 PSI.

**2. Determine the Maximum and Minimum Pressure:**

* Maximum Pressure (Pmax): What is the highest pressure the system could see during normal operation, including small surges or fluctuations? (This is different from overpressure).
* Minimum Pressure (Pmin): What is the lowest pressure (or highest vacuum) the system could see during normal operation?
* Example: The water pump might see brief surges up to 70 PSI and a minimum pressure of 5 PSI when off.

**3. Identify Overpressure Conditions:**

* What is the absolute maximum pressure the sensor might be exposed to without failing? This is often due to fault conditions like a blocked line, a stuck valve, or a compressor malfunction.
* Example: If a valve fails, the pump could deadhead and generate up to 150 PSI.
* The sensor must survive this pressure without damage. This is its Proof Pressure or Overpressure rating.

**4. Confirm the Pressure Type:**

* Gauge Pressure (PSIG / barG): Pressure relative to atmospheric pressure. (e.g., tire pressure).
* Absolute Pressure (PSIA / barA): Pressure relative to a perfect vacuum. (e.g., atmospheric pressure for weather, vacuum systems).
* Differential Pressure: The difference between two pressures. (e.g., [filter](https://www.onzuu.com/category/filters) monitoring, flow measurement).
* Sealed Gauge Pressure: Similar to gauge pressure but referenced to a fixed atmospheric pressure, not the current one.

**Step 2: Apply the "Rule of Thumb" for Optimal Accuracy**
The golden rule for selecting the range based on accuracy is:

Choose a sensor where the Normal Operating Pressure is between 60% and 80% of the sensor's full scale.

**Why this rule?**

* Maximizes Resolution and Accuracy: Most [sensors](https://www.ampheoelec.de/c/sensors) are most accurate in the middle two-thirds of their range. Using a 0-100 PSI sensor to measure 5 PSI will be very inaccurate because you're only using 5% of its range.
* Provides Headroom: It gives you buffer room for those normal surges and fluctuations without pegging the sensor at its maximum value.

**Example Calculation:**

* Your Normal Operating Pressure (OP) is 60 PSI.
* 60 PSI / 0.8 = 75 PSI
* 60 PSI / 0.6 = 100 PSI
* Ideal Sensor Range: A sensor with a full-scale range between 75 PSI and 100 PSI (e.g., a 0-100 PSI sensor) would be perfect.

**Step 3: Verify Overpressure Protection**
Once you have a candidate range (e.g., 0-100 PSI), you must check the sensor's datasheet for its Proof Pressure and Burst Pressure ratings.

* Proof Pressure: The maximum pressure that can be applied without causing a permanent shift in the sensor's calibration specifications. It should be higher than your fault condition pressure (150 PSI in our example).
* Burst Pressure: The maximum pressure that causes the sensor's mechanical structure to fail physically. This is the absolute limit.

In our example: A 0-100 PSI sensor must have a Proof Pressure rating of at least 150 PSI. If it doesn't, you need to choose a sensor with a higher range (e.g., 0-200 PSI) that can handle the overpressure, even though it will be slightly less accurate at your 60 PSI operating point. Safety and durability trump accuracy.

**Step 4: Consider the Complete Picture**
Finally, factor in these additional considerations:

* Cost and Availability: Standard ranges (0-100 PSI, 0-300 PSI, 0-1000 PSI) are cheaper and more readily available than custom ranges.
* Output Signal: Ensure the output signal (e.g., 4-20mA, 0-5V, 0-10V) is compatible with your data acquisition system. A 4-20mA signal is often preferred as it is less susceptible to noise over long distances and indicates a fault if the signal falls below 4mA.
* Media Compatibility: The wetted materials of the sensor (e.g., stainless steel, ceramic) must be compatible with the medium you are measuring (water, air, oil, aggressive chemicals).

**Summary: A Practical Checklist**
1. Define Pressures: List your Operating (OP), Max (Pmax), Min (Pmin), and Overpressure values.
2. Calculate Ideal Range: Use the 60-80% rule: OP / 0.8 <= Full Scale Range <= OP / 0.6.
3. Check Proof Pressure: Ensure the sensor's Proof Pressure rating exceeds your maximum overpressure fault condition.
4. Confirm Type & Media: Double-check you've selected the correct pressure type (Gauge, Absolute, Differential) and that the wetted materials are compatible.
5. Check the Output: Verify the electrical output (e.g., 4-20mA) works with your system.

**Final Example Selection:**

* Need: Measure water pressure, OP = 60 PSI, Pmax = 70 PSI, Overpressure = 150 PSI.
* Ideal Range from Rule: 0-100 PSI.
* Check Datasheet: Find a 0-100 PSI Gauge [Pressure sensor](https://www.onzuu.com/category/pressure-sensors-transducers) with a Proof Pressure of >150 PSI (e.g., 200 PSI) and 316L Stainless Steel wetted parts.
* Result: This sensor will be accurate, safe, and reliable for the application.