Engineers required a precise and reliable pressure measurement solution for a test chamber used with dangerous gases. The process operates at a low pressure, slightly below one atmosphere, where inaccurate readings or sensor failure could pose a significant safety risk. The final solution involved replacing a standard gauge transmitter with a highly configurable industrial transmitter specified with an absolute pressure range and features designed for hazardous environments.
- Application: Low-pressure monitoring and control in a hazardous gas test chamber.
- Challenge: Selecting the correct pressure reference (absolute vs. gauge) and a specific, narrow pressure range to ensure safety and measurement resolution.
- Measurement Parameters: An operational range of 650 to 800 Torr, with a standard chamber pressure of 750 Torr.
- Solution: A DMP 331 series pressure transmitter configured with a custom 0.8 to 1.2 bar absolute range and the optional ATEX/IECEx intrinsic safety certification.
Engineers in a facility conducting low-pressure tests on hazardous gases faced a critical measurement challenge that impacted both process accuracy and operational safety. The application involved maintaining a precise pressure within a sealed test chamber, typically operating around 750 Torr. The primary concern was preventing over-pressurization, which could lead to catastrophic failure when working with volatile media. The engineering team had previously used industrial pressure transmitters with a 0 to 0.1 bar gauge pressure range, but these units had failed, likely due to damage sustained during periodic deep vacuum cycles used for chamber leak testing. This failure, combined with ambiguity in the readings near atmospheric pressure, prompted a search for a more suitable and robust solution.
The core of the problem lay in the selection of the pressure reference. A gauge pressure sensor measures pressure relative to the ambient atmospheric pressure, which can fluctuate. For a process operating so close to atmospheric pressure, this created inconsistent and confusing data. The key was to shift from a gauge reference to an absolute pressure reference, which measures against a perfect vacuum. This provides a true, unambiguous pressure reading, essential for the repeatability and safety of the tests. The solution was an industrial pressure transmitter from the DMP 331 series, specifically configured to address the unique demands of the application. The modular design of this transmitter series allows for customer-specific versions, making it an ideal choice.
A custom pressure range of 0.8 to 1.2 bar absolute (approximately 600 to 900 Torr) was specified. This tailored scaling focuses the entire 4-20mA signal output across the narrow operational window, providing significantly higher resolution and more precise control over the chamber environment.
Furthermore, to mitigate the risk of sensor damage during leak tests, the user instituted a procedure to isolate the transmitter using a ball valve during deep vacuum pulls, a best practice for protecting oil-filled sensor diaphragms.
DMP 331 Near-Atmospheric Pressure Transmitter
- SKU ID: s1-dmp331-0017
- Pressure Range: 0.8 to 1.2 bar (600 to 900 Torr)
- Range Type: Absolute (0 to +P)
- Output Signal: 4-20mA, ATEX / IECEx IS, (2 wire)
- Accuracy: 0.5% ranges (11-12bit resolution)
- Electrical Connection: DIN43650A plug IP65
- Process Connection: 1/4 NPT male
- Process Connector Material: Stainless steel 316L
- Diaphragm Material: Stainless steel 316L
- Media Exposed Seals: FKM