Pressure Sensor
Frequently Asked Questions

Categories

    Technology [1-2]

  1. What is Krystal Bond Technology?
  2. What is unique about this technology in comparison to other technologies?
  3. Common Pressure Sensor Terminology [3-8]

  4. What are the current pressure ranges offered?
  5. What pressure units are sensors calibrated to?
  6. I want to measure the level of water. How do I convert feet to PSI?
  7. Can pressure sensors and transducers utilizing Krystal Bond Technology measure from vacuum to positive pressure?
  8. What is the difference between a pressure sensor, pressure transducer, pressure transmitter, pressure switch, and digital pressure gauge?
  9. What is the media compatibility of pressure products?
  10. Mechanical Inforomation [9-10]

  11. What type of mechanical interfaces are offered for the pressure/process port / connection?
  12. What type of electrical interfaces are offered?
  13. Electrical Information [11-14]

  14. Can pressure sensors and transducers operate with an unregulated power supply?
  15. How do I wire or connect my pressure sensor?
  16. What are the advantages/disadvantages of each electrical output type?
  17. Are pressure sensors and transducers able to withstand electrical interferences, such as EMI/RFI, transient, and ESD?
  18. Product Offering [15-21]

  19. What third party approvals are available for pressure sensors, transducers and transmitters?
  20. Are pressure transducers and transmitters approved for Canadian markets?
  21. What is meant by "panel mount" pressure sensor?
  22. For OEM customers, are custom, embedded pressure sensor designs?
  23. What does long-term stability mean? How does it affect the measurements?
  24. Are zero & span adjustments available on AST pressure transmitters?
  25. Are pressure sensor sub-assemblies available for customers to value add in house?
  26. Contact US [22-23]

  27. What is the best way for me to contact AST with regards to my sensor needs?
  28. What is the return policy?

Answers

1) What is Krystal Bond Technology?

Krystal Bond Technology is a diffusion process developed by AST to inorganically bond micro-machined semiconductor strain gages to metallic diaphragms in the presence of high temperatures.

Krystal Bond Technology offers two distinct advantages:

  • Customers get the sensitivity of MEMS silicon based piezo resistive gages, which can be more than 10 times higher than the sensitivity of other technologies. The combination of high performance strain gauges and Krystal Bond Technology result in a gauge factor of 140 with low operating strain. (Operating stain is typically 275 microstrain @ 100% pressure!)
  • Pressure sensors, with Krystal Bond Technology, offer high electrical isolation (up to 1000VDC), low pressure & thermal hysteresis (<0.05% of FS), high frequency response. (High frequency response = fast response to changes in pressure, < 1mSec)
  • Krystal Bond Technology can be used with a wide range of materials, such as Stainless Steels, Inconel, Hastelloy, and Titanium.
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2) What is unique about this technology in comparison to other technologies?

In addition to the advantages mentioned above, the combination of Krystal Bondô Technology with high quality metallic, one-piece diaphragms offer many advantages that other technologies can not deliver:

  • Excellent long-term stability (<0.25% of FS per year)
  • High temperature operation (Media temps up to 250įC)
  • No leak paths (Most products have a one-piece sensor element with No O-rings, process connection welds, or fluid filled cavities)
  • High cyclic life ( >100,000,000 Full Pressure Cycles)
  • High overload and burst pressure capabilities for safe operation even in extreme conditions.
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3) What are the current pressure ranges offered?

Absolute Pressure: 0-15, 0-30, 0-50, 0-100, 0-300 PSIa

Gauge Pressure: 0-1 thru 0-60,000 PSIG (0-0.0689 thru 0-4000 BAR)

Sealed Gauge Pressure: 0-100 thru 0-60,000 PSIs (0-7 thru 0-4000 BAR)

Differential Pressure: 0-0.18 thru 0-5,000 PSId (0-12.5millibar thru 0-350 BAR)

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4) What pressure units are sensors calibrated to?

  • PSI (pounds per square inch)
  • BAR (1 BAR = 14.504 PSI)
  • Kg/cm2 (1 Kg/cm2 = 14.223 psi)
  • Inches of H2O (1 ďH2O = 0.0361 Psi. Also, 1.0 psi = 27.68 ď of H2O)
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5) I want to measure the level of water. How do I convert feet to PSI?

  • 1 foot of water = 12 inches H2O
  • 12 inches H2O = 0.4335 PSI
  • Multiply 0.4335 by the height [in feet] of the measuring range
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6) Can pressure sensors and transducers utilizing Krystal Bond Technology measure from vacuum to positive pressure?

Yes, Krystal Bond Technology can be used in this type of application. AST refers to this as a Compound pressure sensor. A compound presure sensor is a gauge or sealed gauge sensor that is calibrated to emulate an absolute range. For example:

0-100 PSIA sensor = -14.7 to 85 PSIg sensor

or

0-7 BARa sensor = -1 to 6 Barg sensor

This option offers the ability to measure in PSIg ranges below 0 PSIg, avoiding the errors of absolute sensors that are seen during changes in daily barometric pressure or changes in altitude.

Locations where this is particularly useful are:

  • refrigeration (separation and compressor)
  • suction compressors
  • reciprocating compressors
  • pressure spike/transients monitoring in pipes and pipelines
  • water pumps (especially where the pumps are made in used in different altitudes)
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7) What is the difference between a pressure sensor, pressure transducer, pressure transmitter, pressure switch, and digital pressure gauge?

Please note that these terms are often interchanged without regard to the meaning below, and that the exact definitions may differ from source to source. AST uses these general definitions.

  • Pressure Sensors
    Millivolt (mV) output signal (also a general term for all pressure types); a device that measures pressure. The millivolt output signal can typically be used ten (10) to (20) feet away from the electronics without significant signal loss.
  • Pressure Transducers
    High level voltage or frequency output signal including 0.5 to 4.5V ratiometric (output signal is proportional to the supply) and 1-5V. These output signals should be used within twenty (20) feet of the electronics.
  • Pressure Transmitters
    Current output signal, i.e. 4-20mA (4 to 20mA); the current is measured on the device, rather than the voltage; all AST pressure transmitters are two wire devices (red for supply. black for the ground). 4-20mA pressure transmitters offer good electrical noise immunity (EMI/RFI).
  • Pressure Switches
    A pressure sensing device that has contacts at set points to open or close a circuit.
  • Digital Pressure Gauges
    Pressure measurement with a display; digital pressure gauges originated as battery powered gauges, but now feature output signals as well.
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8) What is the media compatibility of pressure sensors?

Below is a small chart that shows some of the wetted materials for pressure sensors and the media most commonly designated for each one. The chart is a guideline and can not factor all application variables. If you have a question about media compatibility, call us for some advise (thatís what weíre here for!) and weíll provide our input into your material selection.

  • 17-4 PH Stainless Steel
    Hydraulic fluid, Air (nitrogen, oxygen, etc), Natural Gas, Freon, Paint, Steam, Plastic Molding, Diesel Fuel, CO2
  • 316 L Stainless Steel
    Hydrogen*, chlorinated water, ammonia refrigerants, Petroleum products (crude or processed)
    *Only Krystal Bondô Technology
  • Inconel
    High H2S content gas, Salt Water / Sea Water, High Temperature liquids and gases
  • Titanium
    Medical, Aerospace
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9) What type of mechanical interfaces are offered for the pressure/process port / connection?

AST offers wide selection of threads. If you do not see your desired thread here, please contact us. There is a good possibility that an option is already designed, yet not published on our website or literature. Some threads are more common than others (such as 1/4"-18 male NPT, ASTís most common thread) and will have shorter lead times and wider availability.

NPT (National Pipe Thread)
This is the most common thread family for ASTís pressure products.

  • 1/8-27" NPT, both Male and Female* (rated up to 10,000 psi)
    *ASTís 1/8"-27 Female NPT is only offered in a the Panel Mount style preferred by most of ASTís 1/8"-27 Female NPT users. Please click here for more info on ASTís innovative Panel Mount design.
  • 1/4-18" NPT, both Male and Female (rated up to 10,000 psi)
  • 1/2-14" NPT, both Male and Female (rated up to 5,000 psi)

SAE (Society of Automotive Engineers) and UNF (Unified Fine) Threads
Great choice for pressure ranges up to 25,000 psi

  • 3/8"-24 UNF, a.k.a. SAE 3 (Limited availability)
  • 7/16"-20 UNF, a.k.a. SAE 4 (Female available with flare seating and internal Schraeder Depressor Pin)
  • 9/16"-18 UNF, a.k.a. SAE 6
  • 9/16"-18 UNF with 37į Flare, a.k.a. AN6 (Most commonly available for pressure 10,000 PSI and above.)

Metric Threads

  • M12*1.5 Male (Very limited availability)
  • M14*1.5 Male
  • M16*1.5 Female (To be used with a metal dual cone seal. For extremely high pressures only 40,000 and above)
  • M18*1.0 (Very limited availability)
  • M20*1.5

Other

  • 1/8" BSPP (British Standard Pipe Parallel) Male (Up to 15,000 psi)
  • 1/4" BSPP Male (Up to 15,000 psi)
  • G 1/4 Male (DIN 3852, Part 2, Type E, to be used with DIN 3869 ring seal.)
  • 1/4 VCR Male (Often electro polished for use with high purity systems.)
  • F250C Female Autoclave (With seating for a metal cone seal. For pressures from 20,000 to 40,000 psi)
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10) What type of electrical interfaces are offered?

AST offers a wide variety of options for connecting the electrical end of your pressure sensors. Below are some of the more common options. If you do not see the desired electrical connection in this list, there is a good possibility that AST already offers it on one of our custom requirements, or can offer a compatible alternative connection.

Note: AST can install a Stainless Steel Conduit fitting onto the electrical end of almost any AST product with a cable selected as the electrical connection.

  • Cable options for Non-submersible sensors:
    24 AWG cable in 2 ft, 4 ft, 6 ft, & 10 ft
  • Cable options for Submersible sensors:
    22 AWG cable in 6 ft, 10 ft, 15 ft, 20 ft, 25 ft, 35 ft, 40 ft, 50 ft, 75 ft, 100 ft, 150 ft
  • Various In-line Connectors (Molex, Deustch, Amp/Tyco, Packard/Delphi) attached to the end of the cable
  • Packard/Delphi Metripack 150 series, 3-pin Connector (Common Automotive Connector, Mates with AST p/n A04391)
  • Hirschmann 43650 Forms A, and C
  • M12x1 Eurofast
  • Bendix: 6 Pin MIL-C-26482 (REF. MS 3113)

Please visit our Wiring and Installation Page for availability on each product and wiring: Wiring

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11) Can pressure sensors and transducers operate with an unregulated power supply?

Please refer to the following chart:

Output
Unregulated Supply (10-28V or 10-30V)
Regulated Supply, typically 5.0VDC
Regulated Supply, 5.0VDC
5mV/V, 10mV/V, or 20mV/V
 
X
 
0.5-4.5VDC Ratiometric
 
 
X
1-5V, 1-6V, 0-5V, 0-10V
X
 
 
4-20mA (Loop Power)
X
 
 

All non-ratiometric pressure transducers and transmitters can operate from an unregulated power supply between 10 and 32VDC. For 4-20mA, it is important to have sufficient supply to maintain the minimum compliance voltage of 9V while driving long cable lengths. Ratiometric units must be supplied with regulated power supply, usually 5V.

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12) How do I wire or connect my pressure sensor or transducer?

Please view our wiring diagrams for both wire and connector electrical connections in our Wiring Section. Back to top

13) What are the advantages/disadvantages of each electrical output type?

Please review the following pdf document for electrical output information:

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14) Are pressure sensors and transducers able to withstand electrical interferences, such as EMI/RFI, transient, and ESD?

Some of AST's pressure products are designed to stand high levels of electrical interference such as EMI/RFI, electrical transients and ESD. These products are called "stand-alone" products. Radiated susceptibility up to 100V/m, transients to +/- 2kV and ESD levels of 8kV are standard features of a stand-alone product and comply with EN50082-2. To see which sensors meet CE EN61326, view our Products Page.

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15) What third party approvals are available for pressure sensors, transducers and transmitters?

AST currently offers a variety of third party approvals from agencies such as UL, ABS [type approval], ABSA [CRN], and CSA [ATEX pending] agency approvals for on and offshore applications.

Please view the following PDF for a listing of agency approvals:

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16) Are pressure transducers and transmitters approved for Canadian markets?

AST offers a full line of CSA certified pressure sensors and transducers for hazardous areas and a Single Seal marking.

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17) What is meant by "panel mount" pressure sensor?

A panel mount is a unique design that replaces the traditional sensors and bulk head fitting with a single design. This allow the media to be kept outside the panel box while maintaining maximum safety of the system. Existing uses include gas cabinets, pump controls, natural gas flow control and refrigeration/HVAC. Please view our AST4200 Panel Mount Pressure Sensor as well as a detailed Panel Mount Pressure Sensor Application Note.

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18) For OEM customers, are custom, embedded pressure sensor designs?

Custom pressure sensors can be designed in either threaded or unthreaded miniature packages for embedding in manifolds and valves. To learn more, visit: Custom Pressure Sensors.

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19) What does long-term stability mean? How does it affect the measurements?

Long-term stability is normally associated with the change in zero offset due to aging of component and relaxation of the metallic diaphragm over a period of time. It normally causes the zero reading to go high or low over time. Independent tests carried out on AST's products have shown this number to be <.25% under the influence of temperature and pressure cycling for 1500hrs.

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20) Are zero & span adjustments available on AST pressure transmitters?

AST4310 andAST4410 pressure transmitters zero and span adjustments are legacy products for AST. With a very robust pressure sensor, the drift common to other technologies requires adjustment in the field. The sensor diaphragm thickness as well as advanced sensor and controller electronics have vastly reduced the need for adjustable transmitters.

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21) Are pressure sensor sub-assemblies available for customers to value add in house?

Yes, AST can supply either compensated or uncompensated front-end sub-assemblies. Electrical interface is by means of the Molex connector, flex strip or hook-up wires.

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22) What is the best way for me to contact AST with regards to my sensor needs?

The best method for prompt response is to visit the Contact Us web page. You may also call/fax our offices in NJ (Phone: 973-448-1901; Fax: 973-448-1905) or your local factory trained sales representative (please see Sales Representatives and Distributors section).

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23) What is the return policy?

Warranty Workmanship - AST, Inc. pressure sensors and transmitters have a limited one-year warranty to the original purchaser. AST will replace or repair, free of charge, any defective pressure transmitter. This warranty does not apply to any units that have been modified; misused, neglected or installed where the application exceeds published ratings. AST's pressure sensors are made with pride in New Jersey, USA. If in the area please feel free to stop by for a visit!

Complete Warranty Statement (PDF)

Installation/Applications - The purchaser is responsible for media compatibility, functional adequacy, and correct installation of the transmitter.

Request an RMA number

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