A customer required a pressure monitoring solution for flammable solvent storage tanks, a challenging application due to the combination of a low bi-directional pressure range, a hazardous area classification, aggressive chemical media, and the need for a certified safety instrumented system (SIS). The solution involved providing a highly specialised pressure transmitter tailored to these specific operational and safety parameters.
- Application: Nitrogen blanketing pressure control in flammable solvent storage tanks.
- Challenge: The instrumentation needed to be intrinsically safe for a Zone 0 environment, compatible with corrosive solvents like Acetone and Iso Propyl Alcohol, measure a low -100 to +100 mbar range, and be certified for use in a SIL2 safety loop.
- Solution: An all-welded, stainless steel industrial pressure transmitter with dual ATEX/IECEx and SIL2 certification.
The customer’s application was the measurement of nitrogen pressure within a storage tank containing a mixture of flammable solvents, including Acetone, Iso Propyl Alcohol, and N-Butyl Acetate. This process, known as nitrogen blanketing or tank padding, involves maintaining a low-pressure layer of inert nitrogen gas above the liquid surface. This prevents the ingress of atmospheric oxygen, thereby creating a non-flammable atmosphere inside the tank and reducing solvent evaporation.
For this system to operate safely and effectively, a very low-range, bi-directional gauge pressure measurement from -100 to +100 millibar was required to carefully control the nitrogen blanket.
The critical challenges for this application were threefold. Firstly, because the tanks contained highly flammable solvents, the area was classified as Zone 0, mandating the use of intrinsically safe (Ex ia) instrumentation. Secondly, the standard FKM elastomer seals typically used in pressure transmitters were chemically incompatible with the specified solvents, which would cause them to swell, crack, and ultimately fail. Thirdly, the entire pressure monitoring function was part of a safety-instrumented system requiring instrumentation with a Safety Integrity Level (SIL) rating of 2.
The proposed solution was the DMP331 series industrial pressure transmitter, configured specifically to meet the demanding requirements. A model with a -100 to +100 mbar bi-directional range was selected to provide precise control over the nitrogen blanket.
The key to solving the chemical compatibility issue was the selection of an all-welded process connection. This construction feature hermetically seals the stainless steel 316L diaphragm directly to the G1/2 EN837 male process fitting. By creating a seamless, all-metal wetted parts assembly, it completely eliminates the need for any elastomer seals to be in contact with the aggressive solvents, ensuring long-term stability and sensor integrity. The use of 316L stainless steel for all wetted parts provides robust resistance against the specified chemicals.
To address the hazardous area and functional safety requirements, the transmitter was specified with a 2-wire 4-20mA output that combines both ATEX/IECEx intrinsic safety certification for Zone 0 (II 1G Ex ia IIC T4 Ga) and SIL2 certification according to IEC 61508. This dual certification is a significant advantage, as it ensures the device is suitable for the most critical hazardous locations while also meeting the reliability and failure-rate criteria for a safety loop.
The modular design of the DMP331 series was instrumental in providing this tailored solution. It allowed for the combination of the specific low bi-directional pressure range with the highly specialised all-welded construction and dual safety certifications. Although different electrical connections were discussed, the final configuration utilised a standard DIN 43650A plug, which provides a reliable IP65-rated connection suitable for industrial environments.
DMP 331 Intrinsically Safe/SIL2 Certified Bi-Directional Range Pressure Transmitter
- SKU ID: s1-dmp331-0018
- Part No: 110-S100-ES-5-100-200-2-000
- Pressure Range: -100 to +100 mbar
- Range Type: Bi-directional Gauge (-P to +P)
- Output Signal: 4-20mA, ATEX / IECEx IS, SIL2 (2 wire)
- Accuracy: 0.5% ranges (11-12bit resolution)
- Electrical Connection: DIN43650A plug IP65
- Process Connection: G1/2 EN837 male
- Process Connector Material: Stainless steel 316L
- Diaphragm Material: Stainless steel 316L
- Media Exposed Seals: Welded