Electronic Pressure Measurement: AMETEK USG Model 1536 Stainless Steel Semiconductor Pressure Gauges

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DESCRIPTION

AMETEK USG Model 1536
Stainless Steel Pressure Gauge for
Semiconductor Industry

AMETEK U.S. Gauge Model 1536 pressure gauges are designed and manufactured for gas distribution equipment used in semiconductor manufacturing. These 2 inch, all stain- less steel gauges are clean room produced, nitrogen purged, and double bagged.

These instruments are compatible with many toxic and corrosive gases. Welded face seal connections provide a threadless pressure seal and virtually eliminate a major source of contamination. Also available in NPT connections.

The Model 1536 is available in pressure ranges from 0 to 30 inches Hg VAC, to 0 to 4000 psi. This precision gauge incorporates rugged case construction with pressure relief.

FEATURES

• Cleaning for UHP gas applications exceeding ANSI B40.100 specifications 
• Ra: 10 μinch (0.25 μm) finish on face seal connections 
• Helium leak tested to con rm leakage rates of less than 10-9 scc/sec. 
• All stainless steel (Type 316L) internal surfaces for corrosion resistance 
• Large, easy-to-read dial graduations 
• Handles wide variety of exotic gases 
• Available with welded face seal fittings, or NPT connection 
• Assembled and packaged in Class 10 clean room 
• Low mount or center back connections

SPECIFICATIONS

Close-up of
VCR connection

• Size: 2 inch diameter
• Case: Drawn stainless steel polished with pressure relief Ring and Window: One piece, threaded polycarbonate Pointer: Aluminum, black finish.
• Dial: Aluminum, white background with black markings Bourdon Tube: Type 316L stainless steel.
• Connection: Type 316L stainless steel, low mount or center back mount, male or female face seal  fitting, or 1/4 inch male NPT – connectors are shipped with protective plastic caps.
• Surface Finish:
• Face seal connections: Ra: 10 μinch (0.25 μm) 1/4 inch NPT connections: 32 Ra.
• Ranges: 30 inches Hg vacuum to 4000 psi, single or dual scale, see ordering information.
• Overpressure: 130% of span maximum Working Temperature:
• Ambient: -40°F (-40°C) to 149°F (65°C) Fluid: Maximum 212°F (100°C) Accuracy:
• ±1% of span.
• Scales: psi, bar, kg/cm2, KPa, MPa (single or dual scale) inches Hg (for vacuum range, compound and vacuum gauges only).

Understanding Hydrostatic Pressure

Pressure measurement is an inferential way to determine the height of a column of liquid in a vessel in process control. The vertical height of the fluid is directly proportional to the pressure at the bottom of the column, meaning the amount of pressure at the bottom of the column, due to gravity, relies on a constant to indicate a measurement. Regardless of whether the vessel is shaped like a funnel, a tube, a rectangle, or a concave polygon, the relationship between the height of the column and the accumulated fluid pressure is constant. Weight density depends on the liquid being measured, but the same method is used to determine the pressure.

A common method for measuring hydrostatic pressure is a simple gauge. The gauge is installed at the bottom of a vessel containing a column of liquid and returns a measurement in force per unit area units, such as PSI. Gauges can also be calibrated to return measurement in units representing the height of liquid since the linear relationship between the liquid height and the pressure. The particular density of a liquid allows for a calculation of specific gravity, which expresses how dense the liquid is when compared to water. Calculating the level or depth of a column of milk in a food and beverage industry storage vessel requires the hydrostatic pressure and the density of the milk. With these values, along with some constants, the depth of the liquid can be calculated.

The liquid depth measurement can be combined with known dimensions of the holding vessel to calculate the volume of liquid in the container. One measurement is made and combined with a host of constants to determine liquid volume. The density of the liquid must be constant in order for this method to be effective. Density variation would render the hydrostatic pressure measurement unreliable, so the method is best applied to operations where the liquid density is known and constant.

Interestingly, changes in liquid density will have no effect on measurement of liquid mass as opposed to volume as long as the area of the vessel being used to store the liquid remains constant. If a liquid inside a vessel that’s partially full were to experience a temperature increase, resulting in an expansion of volume with correspondingly lower density, the transmitter will be able to still calculate the exact mass of the liquid since the increase in the physical amount of liquid is proportional to a decrease in the liquid’s density. The intersecting relationships between the process variables in hydrostatic pressure measurement demonstrate both the flexibility of process instrumentation and how consistently reliable measurements depend on a number of process related factors.

For more information on any type of pressure instrumentation, visit Ives Equipment at http://www.ivesequipment.com or call 877-768-1600.

Diaphragm Seals: Critical Isolation and Protection for Your Process Instruments

Diaphragm Seal courtesy of
AMETEK U.S. Gauge

Diaphragm seals play a critical role in protecting items like pressure switches, gauges, and transmitters from the fluid being evaluated by the sensor. The seal is a flexible membrane which both seals and isolates an enclosure. Pressure crosses the barrier without inhibition, but the material being contained does not. Typical materials composing diaphragm seals are elastomers, with rubbers being the prime substance in both general and specialty purposes.

In the operating principle of the diaphragm seal, the chamber between the diaphragm and the instrument is filled with system fluid, allowing for the transfer of pressure from the process media to the sensor being protected. The seals are attached to the process by threaded, open flange, sanitary, or other forms of connection.  The seals can also be known as ‘chemical seals’ or ‘gauge guards’. Stainless steel, Carpenter 20, Hastelloy, Monel, Inconel, and titanium are used in high pressure environments, and some materials are known to work better when paired with certain chemicals.

Diagram of diaphragm seal
(courtesy of Wikipedia)

Sanitary processes, such as food and pharmaceuticals, use diaphragm seals to prevent against the accumulation of process fluid in pressure ports. If such a buildup were to occur, such as milk invading a pressure port on a pressure gauge and spoiling, the quality and purity of the fluid in the process may be compromised. Extremely pure process fluids, like ultra-pure water, could be contaminated by the metal surface of a process sensor. Pneumatic systems rely on the elimination of even the smallest pressure fluctuations, and diaphragm seals prevent those by ensuring the separation of the process materials from the sensors.

Diaphragm seals protect the sensors
on pressure switches like this
United Electric Controls model.

Despite their protective function and reliability, there are some potential complications related to diaphragm seals. Devices are now built to address and counter many potential issues related to process monitoring involving diaphragm seals. Products seek to eliminate any and all “dead space,” allow for continuous process flow, and are self-cleaning thanks to continuous flow design. Some high pressure seals come equipped with anti-clogging features, accomplished by the elimination of internal cavities while protecting gauges. Multi-purpose seals reduce temperature influence and improve instrument performance while pinpointing and diffusing areas of high stress. These pre-emptive measures result in longer instrument life-cycles and improve performance while ensuring protection from corrosion. The seals’ ability to protect both process quality and their own vitality make them essential components of process control.

For more information on diaphragm seals, visit Ives Equipment at http://www.ivesequipment.com or call (877) 768-1600.