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Figure 1: CS10 with -70 to +70mBar pressure range

Core Sensors offers a variety of high quality bi-directional pressure transducers for use in low pressure vapor recovery operations. Unlike a unidirectional pressure transducer that can measure pressures from zero to a defined positive pressure (i.e. 0 to 70mBar), bi-directional pressure transducers measure both positive and negative pressure (i.e. -70mBar to +70mBar).

Bi-directional pressure transducers are commonly found in Vapor Recovery Units (VRU’s) which monitor and recover light hydrocarbon vapors that collect at the top of oil and gas storage tanks. The positive end of the pressure transducers measurement range is used to monitor the increase in vapor pressure at the top of the storage tank and the negative end of the measurement range is used to monitor the suction when recovering the vapors from the tank. Recovering these vapors reduces the potential impact on the environment since they are not being vented or flared and also presents financial savings for a company by converting the collected vapors into a liquid state which can then be added back into the storage tanks.

Other applications to consider bi-directional pressure transducers include:

  • Landfill Gas Recovery
  • Digester Gas Recovery
  • Casinghead Pressure Reduction

Core Sensors utilizes 316L SS wetted material in the manufacturing process to allow for a wide media compatibility. Custom configurations are available including a Hastelloy C276 diaphragm material for added corrosion resistance.

Since bi-directional pressure transducers are very low pressure, it is important that the proper venting techniques are followed. Not properly venting the transducer can result in incorrect/inconsistent pressure readings and a reduction in expected lifespan of the equipment. Core Sensors uses two different venting methods depending on your electrical termination choice:

  • Transducers with cable connections have a vent tube that runs the length of the cable and exits the cable jacket with the rest of the conductors. Terminate the vent tube in a clean and dry area, preferably a weatherproof enclosure, to prevent moisture ingress.
  • Transducers with connectors have a vent hole on or near the connector instead of a vent tube. The exact location of the vent hole depends on the electrical connector being used. A PTFE patch is used internally over the vent hole to prevent moisture ingress. It is important to install the sensor in an area where minimal moisture will make contact with the sensors electrical connector.
Common pressure ranges include:

  • Calibrated Measurement Range
  • -70mBar to +70mBar
  • -150mBar to +150mBar
  • -350mBar to +350mBar
  • -1050mBar to +1050mBar
  • Equivalent PSI Range
  • ~ -1.015 to +1.015 PSI
  • ~ -2.175 to +2.175 PSI
  • ~ -5.076 to +5.076 PSI
  • ~ -15.228 to +15.228 PSI

Recommended Products

For applications where hazardous area approvals are not required, we recommend the CS10 Industrial Pressure Transducer. Figure 1 above shows a CS10 transducer with a +/-70mBar bi-directional pressure range, 4-20mA output signal, 1/4″ MNPT mechanical interface and a 1/2″ MNPT conduit fitting with integral cable. Visit the CS10 product page here for more information.

Core Sensors is preparing to release new hazardous area approved transducers manufactured in the USA. Hazardous area approvals will include CSA Class I, Division 1 Intrinsically Safe and Class 1, Division 2 Non-Incendive. Stay tuned to this post and core-sensors.com for release date information.

For more information, call us today at (862) 245-2673 to discuss your application with a knowledgeable Core sales representative.

The post <b>Bi-Directional Pressure Transducers for Vapor Recovery</b> appeared first on Core Sensors.

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Core Sensors by Jason Casler - 3w ago
Sensor Selection

I know my application but I am not sure which sensor is best for me. Where do I start?

 Sensors are offered with a variety of mechanical, electrical, and approval options. Below are few tips for narrowing down the sensor selection for your application:

  • Confirm the environment of the sensor (is the sensor in a hazardous location, are there environmental conditions to account for, etc.). Understanding the approvals and certifications required can quickly filter the types of sensors available and make the decision easier.
  • Are there space limitations such as an enclosure?
  • Is the output signal predetermined by an existing set up or is it open to options? What types of supply voltages are available to power the sensor?
  • Are there mechanical installation preferences for installing the sensor, such as a specific threaded process connection?
  • Are there any special material requirements for the sensor in terms of compatibility with the liquid or gas being measured? For example, if water is being measured, what type of water? Is it chlorinated, tap water, or salt water? If measuring oil and gas pressure, is there hydrogen sulfide and at what concentration? If the sensor is going to be submerged, what are all of the materials that it will come into contact with?

These bullets are not intended to intimidate, but rather guide to the best solution.  We understand sensor selection can be confusing with all the different varieties available. Please call us at 862-245-2673. A sales specialist will go over your requirements and walk you through the ideal sensor configuration.

How do I purchase sensors from Core Sensors?

Core Sensors accepts all major credit cards. Credit cards are charged at the time of order shipment. We also offer Net 30 day payment terms for qualified accounts. Visit our How To Buy section for more information.

Core Sensors Options

What electrical connection options are available?

Core Sensors offers a variety of electrical terminations to fit just about any installation. Standard configurations include integral cable, connector or inline connector.  Customers can choose from connectors such as DIN 43650-A and C, M12x1, Packard Metripack 150, 6-Pin Bendix, Deutsch DT04 3 Pin and 4 Pin and others. Certain product families have a limited selection of options due to hazardous certifications and design limitations. Wire-to-cable connectors are available in-line installed directly at the sensor for retrofit applications. Custom configurations are available upon request.

Can I buy mating connectors and mating cable assemblies with my sensor?

Absolutely! We offer both standard and customizable field wireable mating connectors and cable assemblies. Click here to learn more about the accessories that we offer for our sensors.

Do you offer oxygen cleaned products?

Yes! The presence of certain flammable liquids or particles when combined with gases such as Oxygen can create problems for systems. We offer oxygen cleaning on most products, where the sensor is cleaned, inspected and double bagged to ensure operation in environments with Oxygen in contact with the process connection. Visit our Oxygen Cleaned Pressure Sensors application page for more information.

Can your products be used in hydrogen applications?

Yes! The sensor technology and sensor material play a crucial role in the survivability of the sensor in hydrogen applications. Our sales team has extensive knowledge and application experience to properly assist you with the correct sensor configuration. Visit our Hydrogen Pressure Sensor application page to learn more.

Do you offer low-powered pressure sensors that operate from a 3V power supply

With the increased popularity of IoT and remote monitoring applications, lower current consumption and sensors operating from lower voltage power supplies has increased. Core Sensors manufactures a variety of low-powered pressure transducers that operating from a 3VDC power supply and produces a 0.5-2.5V output signal. While millivolt output pressure sensors are available, this is amplified from the traditional millivolt signal, giving greater calibration capabilities through a digital ASIC as well as more signal for users to use in the field. Contact Core Sensors to learn more about the output signal and your application.

Technical Support

How do I wire my pressure sensor?

Click here to view and download our standard wiring diagrams. Wire color and pin designations can also be found directly on the sensors label. If you have a new requirement that you do not see listed, please contact the factory to receive a quotation for non-standard requirements.

I ordered the wrong pressure range. Can my sensor be re-ranged?

No, the pressure range and output signal are factory set and cannot be re-ranged after sealing up the sensor for shipment. A new sensor needs to be purchased with the correct pressure range indicated.

I am not getting an output signal out of my pressure sensor. What should I do?

Here are a few troubleshooting steps that can be performed at the customer site to potentially diagnose an issue:

  • Ensure the sensor is wired correctly. Color and pin designations can be found on the label of the sensor and can be downloaded here. While most output signals are protected from incorrect wiring, it is possible to cause damage with certain output signals. Check the sensor is wired as outlined.
  • Ensure the correct excitation voltage is being used and is reaching the sensor. Excitation voltage requirements can be found on the sensors label as well as on the datasheet of the model family. For long distance transmissions, ensure enough supply voltage is reaching the sensor.
  • To isolate any issues with other equipment, measure the output signal at zero pressure using an independent multimeter and power supply.

If at any time you are uncomfortable or uncertain on how to perform these tests, please call us at 862-245-2673 and we will be happy to walk you through the appropriate steps.

I need to return a sensor for evaluation. Where do I start?

Any item returned to Core Sensors must first be issued a Return Material Authorization (RMA) number. Click here for more information.

Application Knowledge

What is the difference between gauge, sealed gauge and absolute pressure?

Gauge – Gauge pressure refers to pressure measurements in relation to atmospheric pressure. A gauge pressure sensor has either a vent hole or vent tube that allows the back side of the sensors diaphragm (internal to the sensors housing) to see the same atmospheric pressure as the pressure port side of the diaphragm. This is why gauge sensors read zero pressure when the port is open to atmospheric pressure. Gauge pressure reference is commonly used in low pressure applications as changes in barometric pressure from weather or altitude changes can have a considerable effect on the output of the sensor.

Sealed Gauge – Sealed gauge refers to a sensor that has atmospheric pressure sealed on the inside of the sensors housing. There are no vent holes or vent tubes. The atmospheric pressure sealed inside the sensor is determined at the time of welding. Sealed gauge reference is common in high pressure applications where changes in atmospheric pressure have a negligible effect on the output of the sensor. Customers may also consider a sealed gauge reference in applications where a lot of moisture or high pressure washdowns occur.

Absolute – Absolute pressure refers to pressure measurements in relation to a full vacuum. For example, if an absolute pressure sensor is held open to the air then the sensor will read the actual barometric pressure at that location. Therefore, absolute pressure sensors are affected by altitude changes and other barometric changes.

What is the difference between compound and absolute pressure?

Compound sensors are very similar to absolute sensors in that they both measure a vacuum. The difference is how the vacuum is displayed by the sensor.

In a compound pressure sensor, the sensor is zero referenced to atmospheric pressure. When measuring a vacuum, a compound pressure sensor will display a negative number. For example, a 10 PSI vacuum would display as “-10 PSI” with a compound pressure sensor.

In an absolute pressure sensor, the sensor is zero referenced to a full vacuum. When measuring a vacuum, an absolute pressure sensor will display a positive number. Using the same example as the compound pressure sensor above, a 10 PSI vacuum would display as “10 PSI” with an absolute pressure sensor.

What is a compound pressure transducer and how do I calculate the output signal?

A compound pressure transducer has an offset “zero” output signal such that the baseline signal measures a full vacuum pressure range of -14.7 PSI (or -1 bar). Typically this is offered for gauge and some sealed gauge pressure sensors and transducers. Applications include compression equipment and HVAC/R.

Here are two examples of how to properly calculate the output signal points on a compound pressure sensor. The same steps can be used to calculate the expected set points on non-compound sensors as well.

Example 1: -14.7 to 20 PSI pressure range with 4-20mA output signal:

The first step is to calculate the mA (milliamps) per PSI value.

  • Calculate the full span of the pressure range: 14.7 + 20 = 34.7 PSI
  • Calculate the full span of the output signal: 20 – 4 = 16mA
  • 16mA / 34.7 PSI = 0.4611 mA/PSI

Next, we need to calculate the output signal at zero pressure. We do this by taking 14.7 PSI and multiplying by 0.4611 mA/PSI. We use 14.7 because the sensors zero pressure output is 14.7 PSI above 4mA:

  • 14.7 PSI X 0.4611 = 6.778 mA

Finally, we need to add in 4mA for the offset of the output signal. This is required since the output signal of the sensor starts at 4mA and not 0mA:

6.778mA + 4mA = 10.778mA

The results of the above calculations are as follows:

4mA = -14.7 PSI

10.778mA = 0 PSI

20mA = 20 PSI

Example 2: -14.7 to 50 PSI pressure range with 1-5V output signal:

The first step is to calculate the volts per PSI value.

  • Calculate the full span of the pressure range: 14.7 + 50 = 64.7 PSI
  • Calculate the full span of the output signal: 5 – 1 = 4V
  • 4V / 64.7 PSI = 0.0618 V/PSI

Next, we need to calculate the output signal at zero pressure. We do this by taking 14.7 PSI and multiplying by 0.0618 V/PSI. We use 14.7 because the sensors zero pressure output is 14.7 PSI above 1 Volt:

  • 14.7 PSI X 0.0618 V/PSI = 0.908 V

Finally, we need to add in 1 volt for the offset of the output signal. This is required since the output signal of the sensor starts at 1 volt and not 0 volts:

0.908V + 1V = 1.908V

The results of the above calculations are as follows:

1V = -14.7 PSI

1.908V = 0 PSI

5V = 50 PSI

What is a bi-directional pressure sensor?

Bi-directional pressure sensors measure both positive and negative pressure. The zero point on a bi-directional pressure sensor is the mid-point of the applicable output signal such as 12mA on a 4-20mA output signal. For example, a customer can choose to have a 10 PSI bi-directional pressure range with a 4-20mA output signal. This sensor would have the following set points:

4mA = -10 PSI

12mA = 0 PSI

20mA = 10 PSI

A bi-directional pressure sensor is ideal for applications such as vapor recovery. The positive end of the pressure transducers measurement range is used to monitor the increase in vapor pressure at the top of the storage tank and the negative end of the measurement range is used to monitor the suction when recovering the vapors from the tank.

What is a snubber?

A snubber, also sometimes referred to as a restrictor plug, is designed to slow down the process media as it enters the pressure sensors port. This is important in applications where pressure transients are common such as hydraulics and water pumps. These pressure transients can exceed the rating of the sensors diaphragm and, at a minimum, cause permanent shifts in the sensors output. Snubbers can also mechanically filter out the signal spikes of the hammering effect. The delay of the output signal can prevent pumps and panels from premature on/off functions, increasing the life of the equipment. Core Sensors welds an internal stainless steel snubber in the pressure port to avoid any leak paths or additional length considerations that come with external threaded on snubbers.

The post <b>Frequently Asked Questions</b> appeared first on Core Sensors.

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