Choosing a Low-Pressure Transducer for Critical Environments

This article was originally published on July 5, 2022, and updated on November 4, 2024.

Critical environments like cleanrooms, data centers, laboratories, hospital operating rooms, isolation rooms and other controlled spaces must adhere to strict environmental guidelines requiring close pressure monitoring. To ensure these areas are not compromised, your pressure-measuring instruments must be highly accurate, reliable and compliant with these very specific requirements. Choosing the wrong instrument can result in equipment damage, worker injury or incorrect measurements.

As the product manager who oversees the low-pressure sensor product line at Ashcroft, I understand the complexities of these environments and am often asked for guidance on selecting sensors for critical applications such as these. 

In this article, you will learn some factors to consider when choosing a low-pressure transducer for critical environments, so you’ll know you’re getting the proper equipment for your process. You will also be directed to additional resources that can help answer other common questions about this topic.   

Factors to Consider When Selecting Low-Pressure Transducers for Critical Environments

When selecting the appropriate pressure transducer for a cleanroom or any other critical environment, there are several key factors to consider to ensure optimal performance and safety. 

Assessing Pressure Sensor Accuracy and Performance

The effectiveness of your system relies heavily on the accuracy of your pressure sensor. To calculate the accuracy of a pressure sensor, there are a couple of methods to consider:

1. Best-fit-straight-line (BFSL) method. This is a statistically derived approach that some manufacturers use to express sensor accuracy. It works by minimizing the error between a straight line and the actual curve measurement without passing through the curve's endpoints. 
   
   The BFSL method does not include zero and span setting errors, which can each be as much as ±1.00%. This discrepancy could require onsite calibration by the installer to ensure the transducer functions within the desired accuracy parameters. For example, if your pressure sensor uses the BFSL method, your ±0.25% accuracy specification might actually be ±1.25% to ±2.25% accuracy.
   
   
2. Terminal point method. This method for calculating a sensor's accuracy draws a straight line from the actual zero point to the actual full-scale value endpoint. Since the terminal point is based on the curve's endpoints, it is considered a more accurate representation of the sensor's non-linearity.
   
   The Ashcroft® uses its own TruAccuracy™ specification, which is exclusively based on terminal point methodology. This specification already accounts for zero and span setting errors, meaning the unit is ready for installation without the need for additional calibration adjustments. Using the TruAccuracy™ standard, the Ashcroft® CXLdp, DXLdp, and GXLdp Pressure Transducers all boast a ±0.25% of span accuracy right out of the box. 

Ensuring Repeatability, Reliability, and Durability

The classification of cleanroom environments is governed by various regulations set by the International Standards Organization (ISO), which demands the utmost precision and reliability from the systems and components used.

Ashcroft’s differential pressure transducers use patented Silicon Capacitive MEMS Sensor (SI-GLAS™) technology to meet the strict requirements of critical room applications. This technology features an ultra-thin crystal diaphragm for consistent and stable sensor performance, ensuring accurate, long-lasting, and reliable pressure measurements. The sensor also has no glues or organic materials, preventing drift or wear over time and further enhancing its durability and reliability.

How Ashcroft® Si-Glas™ Technology works

The silicon MEMS sensor used in Ashcroft® ultra-low-pressure transducers features a variable capacitance design and a glass-clad silicon chip. This Si-Glas™ technology combines the high sensitivity of a variable capacitance transducer with the repeatable performance of a micro-machined, single-crystal silicon diaphragm.

The sensor is constructed from metals and glass that are molecularly bonded to silicon, eliminating the use of epoxies or other organic materials that could lead to drift or mechanical degradation over time. The silicon diaphragm is highly elastic, providing exceptional repeatability, stability, and the ability to measure pressure ranges as low as 0 to 0.10 in. H₂O. It can also withstand high static pressures up to 25 psi.

Figure 1. SI-GLASS™ Sensor 

Considerations for Validation and Calibration

Instruments used in critical rooms must undergo routine validations to confirm they are functioning at optimal levels. This procedure can be expensive and time-consuming, and it will assess whether sensor recalibration is needed.

To verify accuracy, technicians must detach the electrical cables and pressure sensor connections, which increases the complexity and time needed to ensure the system's precision. If recalibration is necessary, the system will be taken offline while the instrument is transported to a different location for calibration before being reinstalled.

An in-place calibration option makes accuracy checks and adjustments easier.

To facilitate these accuracy checks without disrupting your entire system, Ashcroft provides an "in-place" calibration tool called the Ashcroft® SpoolCal™ Actuator.  This "actuator valve" links to a master testing device to verify the current process pressure and enable calibration adjustments if needed - all without interfering with the process connections.

With the optional SpoolCal™ calibration valve, the cleanroom operator and their service partners can make important measurements and adjustments directly on the transducers in no time:

• Connection of a master test instrument to verify the current measured value
• Calibration and adjustment of the DP transducer

The SpoolCal™ Actuator is an option that is available for the Ashcroft® DXLdp and GXLdp Pressure Transducers. 

Figure 2. Ashcroft® GXLdp with optional SpoolCal™ Actuator Valve. 

Ready to learn more?

With a better understanding of the key factors in selecting the appropriate pressure transducer for low-pressure critical environments, you can now explore the best solution for your specific application. Keeping these factors in mind can help ensure that you avoid problems and keep your process running with reliable and accurate pressure measurements.

For your reference, I have compiled some relevant articles on pressure transducers that you may find useful.

• Si-Glass Silicon Capacitive MEMS Technology
• Product Review: MEMS Pressure Transducer Sensor Technology
• How Does Media Temperature Affect Pressure Transducer Performance?
• Product Review: GXLdp Differential Pressure Transducer
• How Accurate Are Your HVAC System’s Pressure Instruments?

And if you’d like to learn more about critical environment applications, download our guide: