P571 Application Notes

General Description

The SMD P571 Pressure Sensor is a family of monolithic stainless steel-bodied pressure sensors with a proprietary thin-film technology strain gauge applied, capable of producing a linear, analog voltage output in response to loadings of 100psi to 15,000psi depending on the model chosen.

Physical Considerations

Mounting: These sensors are designed to be butt-welded using Electron Beam or other suitable welding technology to a structure or appropriate pressure fitting with their open side toward the pressure to be monitored. It is strongly suggested that a “weld chill” or other heat sinking mechanism be used during the welding process so as to ensure the temperature of the gauged area does not exceed 250° C.

Loading: Gaseous or fluid pressure is to be applied to the open side of the sensor. The configuration of the P940 pressure sensor provides for no inherent overload protection (loading in excess of 200% of rated capacity) therefore provisions should be designed into the system to preclude excessive pressure and damage to the sensor. “Burst Pressure” for these devices is rated at a minimum of 400% of full pressure specified.

Wiring: Wire leads of various material, length, and color per customer request are a common option however adequate forms of strain relieving should be provided in the assembly design.

Electrical Considerations

As seen in the schematic drawing, 4 resistive elements are created by proprietary thin film technology in a Wheatstone Bridge configuration and adjoining areas of strain concentration. The application of a pressure force to the sensor causes an electrical imbalance between the resistive elements and produces an output voltage (typically in millivolts) that is linear and proportionate to the pressure applied. Less than the maximum excitation voltage may be used however the resulting output will be reduced proportionately. A “5 wire” option is available wherein the “‐ excite” leads are not connected and made available separately to aid in refining the “zero balance” or no-load output. Small resistances may be added to either side of the bridge circuit to achieve the desired effect. Also available as an option is the inclusion of a 1K ohm “RTD” useful in monitoring the temperature at the sensor substrate.

Environment Concerns & Precautions

While the thin film technology is itself immune to normal humidity levels, care must be taken to avoid condensing moisture and direct water exposure. The P571 is very stable over time and temperature. Due to the nature of the thin film technology, care in handling should be observed and no damage be allowed to occur especially in the area of the thin-film strain gauges. During handling and assembly procedures anti‐static discharge practices should be observed.

 

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