The Differences Between Capacitive & Piezoresistive Pressure Sensors

Posted by Seta Davidian on Oct 19, 2020 8:41:49 AM

This is a guest blog post reproduced with permission from ES Systems, a specialist in high quality pressure sensors for a variety of applications.

The majority of the pressure sensors currently installed in the field are based on MEMS technology and utilize either piezoresistive or capacitive measurement principle. In this article, we will be discussing their main differences and we will be highlighting the advantages of each.

How Piezoresistive Technology Works

The term piezoresistive is composed by the Greek word “piezo” (meaning squeeze or press) and resist. In piezoresistive sensors, four resistors are placed on a silicon diaphragm in order to measure the result of strain or physical pressure applied upon them. Any perceptible change in resistance is being converted, through a Wheatstone bridge circuit into an output voltage. The piezoresistive pressure measurement principle is one of the firstly developed in MEMS technology and it was developed many years before the capacitive one. As a result, it is most commonly used. Due to their widespread and low production cost, piezoresistive pressure sensors are widely used in consumer electronics and the automotive industry, as well as in household appliances.

diagram illustrating how a Piezoresistive sensor works

 

Capacitive Technology Measurement Principle

Two parallel and electrically isolated conducting plates are needed to ensure that a capacitive pressure sensor operates efficiently. The bottom plate is fixed while the top one is sensitive to pressure changes. When pressure is applied, the top plate (or membrane) bends and a capacitance Δ is created. This variation in capacitance is then translated to an electrical signal where it can be read and conditioned by an ASIC or microcontroller.

diagram illustrating how a capacitive sensor works

 

Technology Comparison, Piezoresistive Vs. Capacitive

In comparison to piezoresistive sensors, capacitive pressure sensors offer many advantages. Even though they may require more complex signal conditioning circuits and calibration algorithms, they have higher accuracy and lower total error band. Moreover, capacitive pressure sensors have low power consumption since there is no DC current flowing through the sensor element due to its nature. Thus, very low power sensing systems, can be designed and implemented that require only a small bias to the circuit by an external reader, making them ideal for remote or implanted medical applications. The table below summarizes the pros and cons of the MEMS capacitive pressure sensors with respect to the piezoresistive ones.

Pros Cons
Burst & proof pressure Calibration complexity
Accuracy, total error band Production cost
Power consumption  
Long term stability  

 

 

Typical MEMS capacitive schematic and layout representation

MEMS capacitive pressure sensors also offer excellent long-term stability. This is a design attribute. As illustrated above, a typical MEMS capacitive pressure sensor element features two sense and two reference capacitors. The reference capacitors are not sensitive to pressure variations. The pressure calculation is performed using the following algorithm.

Long term stability is mainly affected by the aging of the sensing elements and therefore the drift in measurement accuracy over time.

Due to the layout of capacitive dies, the sense and reference capacitors are exposed to the same environment. That means that they are exposed to the same conditions and stimuli that cause aging to the sensors and therefore long-term drift. Since the sense and reference capacitors are exposed to the same conditions and are manufactured using the same materials and procedures, they also age with the same rate. Therefore, utilizing the pressure calculation algorithm and the layout of the MEMS die, the long-term drift effect is minimized and therefore an excellent long-term stability is achieved.

Last but not least, the major advantage of MEMS capacitive technology over piezoresistive is the overpressure tolerance (proof pressure and burst pressure). Due to their design, MEMS capacitive sensors can withstand up to 100x the rated pressure. This happens due to the fact that the sensor architecture consists of a fixed bottom plate and a suspended membrane which deforms with pressure. When overpressure is applied the deformation reaches the bottom membrane and inevitably stops without breaking. At the same time due to the distance traveled and the stresses exerted there are no plastic deformations. This translates into an unaffected sensor performance after the release of the overpressure.

Is capacitive technology ideal for overpressure?

As explained above, whenever overpressure is applied to automation equipment, conventional pressure sensors could get damaged. For that reason, sensors based on silicon capacitive process technology could be used. Understanding the advantages of capacitive technology and the various ways it can be applied to pressure sensors is important and could lead to increased productivity and lower maintenance costs. ES Systems has designed pressure sensors with capacitive technology that can offer high performance and precision along with great efficiency and reliability at a competitive cost.

Are capacitive sensors ideal for medical applications?

Medical applications can be enhanced by MEMS capacitive pressure sensors, as they could provide very high accuracy and long-term stability. More specifically, they are extremely tolerant of overpressure, making them suitable for use in applications where measurement safety is critical and sensor repair is not an option.

The cutting-edge MEMS capacitive technology can be applied in demanding environments regarding absolute, gauge, relative, or differential pressure measurements. For this reason, ES Systems offers three families of high-end capacitive pressure sensors for those needing superior accuracy. These families are:

  • ESCP-MIS1, designed to sustain high measurement quality in harsh environments and media. Available now.
  • ESCP-BMS1, ideal for industrial, medical and HVAC applications that require high accuracy and low total error band. Available early December 2020.
ESCP MIS1 header ESCP BMS1 header new
ESCP-MIS1 ESCP-BMS1

 

Want to chat more about pressure sensors? Get in touch to tell us what you need!

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Topics: Pressure Sensors

ME78X/ME79X Ceramic Pressure Sensors Updated Data Sheets

Posted by Seta Davidian on Sep 25, 2020 10:04:22 AM

Servoflo is pleased to announce updated data sheets for the ME78X and ME79X ceramic pressure sensors from Metallux. These state-of-the-art ceramic pressure sensors have excellent accuracy and versatility for those users designing a pressure transducer or embedding a sensor in a pump, valve or other part of a pressure control system. A notable change is new designs for both the ME78X and ME79X will use an SSOP14 package rather than the previous DFN package.

me78x ceramic pressure sensorThe ME78X are a flush diaphragm, piezoresistive sensor with signal conditioning electronics embedded into the ceramic to provide a 0.5 to 4.5V ratiometric output or I2C output with pressure & temperature information. Calibration can be done in bar (0.5 to 600 bar) or psi (7.5 to 8500 psi). Furthermore, the sensor is available in a variety of configurations including absolute, gauge or sealed gauge. Accuracy choices include high accuracy, standard accuracy, no temperature compensation, or uncalibrated & uncompensated. The ME78X provides incredible versatility for users. The most updated information on the ME78X can be found here.

me790-headerME79X are monolithic piezoresistive ceramic pressure sensors. The Wheatstone bridge is screen-printed directly on one side of the ceramic cell by means of thick film technology and signal conditioning electronics generate 0.5 - 4.5V ratiometric output. Pressure and temperature calibration are done electronically with the on-board ASIC and can be performed in bar (3 to 400 bar) or in psi (50 to 5000 psi).

Electronics provide offset and span correction when the temperature changes. Aging detection is constantly performed. This new method guarantees good precision and long-term stability. The most recent data sheet includes a new mechanical configuration where springs are used for contacts. This innovative methods eliminates the need for soldering, increasing assembly speed, as well as improving ease of assembly resulting in lower overall costs. This mechanical configuration has been tested and validated in the automotive field for many years. Get the most recent information on the ME79X here.

You may notice that the ME78X is flush with a smooth side exposed to the pressure media and the ME79X are monolithic with a small indentation in the middle exposed to the media. Why choose one or the other? If a customer is making an absolute or sealed gauge sensor, then flush mount is ideal as they have a fixed reference. 

Both the ME78X and ME79X have excellent chemical resistance due to the AI2O3 ceramic, making them suitable for nearly all aggressive media.

Do you want to learn more about ceramic pressure sensors? Our e-book is a great place to start!

Download Our Ceramic Pressure Sensor Guide

Data sheet links:

ME78X

ME79X

 

Topics: Ceramic Pressure Sensors, Pressure Sensors

Why Use Servoflo for Board Level Pressure Sensors

Posted by Seta Davidian on Jun 16, 2020 10:02:31 AM

Users of pressure sensors enjoy a broad selection of models and manufacturers from which to choose. While detailed specifications of individual models are easy to come by, it often helps to understand more about the overall supplier. The following blog post compares board-level pressure sensors from Servoflo and other providers of pressure sensors.

Advantages of Servoflo

At Servoflo, we distribute a broad range of pressure sensors from leading manufacturers, including Fujikura, TE Connectivity, Merit Sensors, Silicon Microstructures and many more. Our sensor products meet the board-level pressure measurement requirements across different price and performance points for pressure ranges from 2-inch water column (WC) to several thousand psi for applications in the medical, HVAC, and industrial industries.

By partnering with us, our customers benefit from our:

Individualized Customer Service

We focus on providing individual attention to meet the unique needs of our customers rather than locking them into a single family of standard products that feature unnecessary features at additional costs. Additionally, some of our suppliers provide customers with the opportunity to produce modified sensor designs that fit their specific applications in very low volumes with little to no price premium or expensive upfront investment. This level of customer service and customizing is not available from many large providers (both distributors & large manufacturers).

Greater Flexibility and Added Benefits

In many cases, pressure is not the only parameter requiring measurement. Other critical parameters that may require monitoring include mass flow, humidity, and temperature. We consider all of these factors and more when curating our product selection to offer solutions that meet a broader range of applications at competitive prices. In addition, we can provide benefits like inventory management, stocking, responsiveness, and easy access to technical support like we do.

Sample Overview of Fujikura Sensors

al4-headerFujikura’s AL4 pressure sensor is a low-pressure sensor with digital output. It consists of a silicon piezoresistive pressure sensing chip combined with a signal conditioning integrated circuit. This sensor amplifies the low-level signal from the sensing chip, applies temperature compensation and calibration, and converts it to digital data in proportion to the applied pressure. Highlighted features of this sensor include: 

  • Gauge: positive, negative, or bi-directional
  • Differential: new feature now available!
  • Pressure Ranges: 0–1 kPa (.145 psi) to 0–10 kPa (1.45 psi), depending on model
  • Pressure Media: non-corrosive gases
  • Supply Voltage (constant voltage): 5 +/-0.25 VDC, 3.3 VDC, or 3.0 VDC
  • Accuracy: +/-1.5% FS
  • Ports: dual barbed
  • Size: 11.36 mm x 10.32 mm x 10.32 mm SMT package

Typical uses include battery-operated devices, medical equipment, industrial pneumatic devices, and various consumer devices.

Overview of Silicon Microstructures Sensors

sm933x-headerMEMS pressure transducer technology and CMOS mixed-signal processing come together in the SM9333/SM9336 ultra-low differential pressure sensor. These sensors offer digital, fully conditioned, and multi-order pressure and temperature-compensated sensing. The highlighted features of this model include: 

  • Pressure Range: 125 Pa to 250 Pa differential
  • Digital Interface: 16 bit I2C
  • Compensated Temperature Range: -20° C to 85° C
  • Total Accuracy: +1% full-scale
  • Insensitivity to mounting orientation
  • Robust JEDEC SOIC (16 package with a dual vertical porting option)

Quality Sensors From Servoflo

The above highlighted products are 2 examples of our extensive product offering. We have many more product options that fit a wide variety of needs. High-quality products, individualized customer service, product design flexibility, and a variety of added benefits make Servoflo the better choice for board-level pressure sensors. Contact us to learn more about our board-level pressure sensor solutions or request a quote for our products from one of our experts.

 

Topics: Pressure Sensors

Additional Solutions From Servoflo’s Mass Flow Sensors

Posted by David Ezekiel on Feb 6, 2020 9:28:14 AM

Companies across a range of different industries use mass flow sensing technologies to meet specific application requirements in a variety of applications. Here, the team at Servoflo provides a few examples of the advantages of mass flow sensors in machines and mechanisms being designed today.

Solutions for Servoflo’s FS6122 Bi-Directional Medical Respiratory Sensor

fs6122-header

In the medical industry, mass flow sensors play a key role in the functionality of respiratory monitoring equipment, such as CPAP or anesthesia delivery systems and other types of medical equipment. For example, the Servoflo FS6122 Bi-Directional Medical Respiratory Sensor has been especially designed for suitability in medical applications. It is an energy-saving, fast-responding sensor that can measure mass flow rate in the range of -250 to 250 SLPM (standard litres per minute). This bi-directional sensor also has a unique additional feature of an optional humidity sensor, giving users even more environmental measurement capability.

Some typical flow sensor applications in the medical industry include:

· Air mattresses and cushions

· Anesthesia equipment

· Asthma detection products

· Biological chamber air circulation devices

· Drug delivery solutions

· Endoscopes

· Gamma knives

· Infusion pumps

· Oxygen concentrators and conservers

· Other oxygen therapy tools

· Respirator and breath detection machines (especially for cases of sleep apnea)

· Smart oxygen homecare cylinders

· Spirometers

· Veterinary machines and tools

Solutions for Servoflo’s FS5001B MEMS Mass Flow Sensor

Other mass flow sensors from Servoflo have exceptional operational capabilities for industrial and electrical applications, among many others. For instance, the FS5001B MEMS Mass Flow Sensor has the following key attributes:

· An effective operational range anywhere from 0 to 200 SCCM (standard cubic centimeters per minutes) up to 0-1000 SCCM

· An exceptionally quick response time of 10 milliseconds

· A pressure rating that can go up to 5 bar (72 psi)

· A small form factor of 48.5 x 48.5 x 18.5 mm

· Accurate readings within a range of ±2.0%, in addition to a ±0.5% range for full scale readings

· Outputs that include linear analog from 0.5 to 4.5 volts, digital RS232, or I2C

Additional Applications of Mass Flow Sensors

Mass flow sensors are highly versatile. For instance, most car engines use mass air flow sensors to inject the correct mix of fuel and air into the engine’s combustion chambers. Mass flow sensors also allow welders that use oxy-fuel equipment to work safely.

The following list includes several examples of common use cases for mass flow sensors:

· Medical: specifically the FS6122 Bi-Directional Medical Respiratory Sensor

· Electronics

· HVAC Engineering: particularly for variable air volume (or VAV) systems, cleanroom management, and refrigerant monitoring

· Industrial: for use in process gas monitors, gas mixing solutions, and welding gas controls, among many other applications

· Food and Beverage: for oven flow monitors, food freshening solutions, and even food packaging

Servoflo’s High Quality Mass Flow Sensors

Mass flow sensors are critical for organizations that run the gamut of commercial and industrial sectors. High quality mass flow sensors lead to better products, durable applications, and benefits for all.

At Servoflo, our expertly trained and dedicated professionals are committed to providing only the best mass flow sensor solutions for our customers. To learn more about our sensor products, request a free quote today.

Topics: Mass Flow Sensors, Sensor Solution

Pressure Sensors for the Medical Industry

Posted by Seta Davidian on Dec 4, 2019 1:05:40 PM

In the medical industry, board level pressure sensors are commonly used in patient monitoring equipment. When used in treatment equipment, such as drug delivery systems or respiratory devices, they can act as monitors that trigger upon reaching a preset threshold and tell the control units to continue, change, or cease treatment.

image003 (1)

Servoflo has worked with Fortune 500 major medical equipment manufacturers by providing pressure sensors and other environmental sensors in applications such as:

 
  • Respirators and breath detection equipment
  • O2 concentrators and conservers
  • Deep vein thrombosis treatment
  • Infusion pumps
  • Inflatable mattresses
  • Blood pressure measurement

Pressure Sensors for Respirators and Breath Detection Equipment

Our pressure sensors for respirator and breath detection equipment generally monitor low-pressure conditions. They come in a variety of gauge or differential models, digital or analog outputs, and supply voltages. A good example of a pressure sensor is the AL4 Series.  The AL4 has various pressure ranges as low as 0-1 kPa (0.145 psi) with a digital output. What makes the AL4 special is that it has a high overpressure of 15 psi.

 Check out the industry page to review our wide selection of respirator and breath detection equipment pressure sensors.

Pressure Sensors and Oxygen Sensors for O2 Concentrators and Conservers

Oxygen concentrators take in air, filter out impurities and other gases, and deliver pure oxygen to patients who require oxygen therapy, such as ones undergoing surgery or treatment for lung disease. Due to their critical function, these machines require highly accurate and consistent pressure sensors that can ensure precise and accurate control over treatment.oxygen-concentrator-header (1)

There are two applications for pressure sensors. The first is breath detection, similar to the respirator application described above. The second is to monitor the pressure in the oxygen line, which typically runs between 30-40 psi.

In this pressure range, there are many choices for sensors. Because there are so many options to choose from, Servoflo can help narrow down the choices for you by helping you choose a sensor based on your exact requirements. This way, you will not pick a sensor that is neither not accurate enough nor too accurate (& higher cost) for your application.

We also offer oxygen sensors that monitor the oxygen percentages delivered to the patient. Check out the product page to more about our selection of pressure sensors and oxygen sensors for O2 concentrators and conservers.

Pressure Sensors for Deep Vein Thrombosis Treatment

Deep vein thrombosis, also referred to as DVT, occurs when a blood clot develops in a vein located deep within the body. Pneumatic compression devices can prevent DVT or facilitate treatment by promoting circulation and lymphatic drainage. Typical pressures run about 5 psi.

Our pressure sensors for deep vein thrombosis treatment equipment feature a variety of specifications, including in regard to outputs, pressure ranges, and accuracy levels, to ensure that individualized DVT treatments occur as expected. Check out the product page to more about our selection of deep vein thrombosis pressure sensors.

Infusion Pumps

Medical professionals use infusion pumps in hospitals, medical offices, nursing homes, and private residences to deliver vital fluids, such as nutrients, medication, or saline, to a patient’s body. These machines need accurate pressure sensors to maintain a controlled flow. The pressure sensors are used to monitor the pump’s backpressure to ensure that the pump is working correctly.

infusion-pump-2 (1)Our infusion pump pressure sensors meet a variety of pressure range demands. The sensors are temperature-compensated and have chips that provide data for smart infusion pump equipment. Check out the product page to more about our selection of infusion pump pressure sensors.

Inflatable Mattresses

Medical inflatable mattresses have more specialized functions than traditional inflatable mattresses. They enhance circulation to prevent soreness, stress, or decreased blood flow while providing support and comfort. Patients use medical inflatable mattresses during extended periods of bed rest to reduce the risk of skin shearing and pressure sores. Different varieties of these mattresses need pressure sensors, typically 3 psi and below, to prevent air loss or replenish lost air.

Our line of sensors facilitates the maintenance of stable, comfortable pressure levels and monitor the mattress’s fluid conditions to protect the patient. Check out the product page to more about our selection of inflatable mattress pressure sensors.

Blood Pressure Measurement

Blood pressure measurement is one of the main applications of medical pressure sensors. The sensors allow for non-invasive measurement of blood pressure, providing insight into a patient’s condition during routine appointments, extended hospital stays, and medical treatments. The pressure sensors are used in electronic blood pressure equipment (not the traditional mechanical units used in a doctor’s office).

Our pressure sensors come in a variety of power requirement, display, pressure threshold, and size options. We have pressure sensors designed specifically for blood pressure instrumentation. The models include the AP3/AG3NIBP. This is a standard sensor specially calibrated  for +/- 3 mm of mercury. Check out the product page to more about our selection of blood pressure sensors.

Contact Servoflo for Your Medical Pressure Sensor Needs Today

Pressure sensors serve an important role in many medical applications. As such, it’s crucial to choose high-quality sensors that exactly suit the nature and requirements of the application. To learn more about our pressure sensors, contact us today. For assistance choosing one for your application, download our eBook or request a quote.

 

Topics: Pressure Sensors

Why Humidity Measurement is Essential to the Success of an Industrial Process

Posted by Seta Davidian on Dec 3, 2019 1:21:33 PM

Moisture, whether in liquid or gaseous form, is one of several process variables that industry professionals must measure, monitor, and control. In industrial applications, moisture levels—i.e., humidity—can significantly impact the lifespan of the process equipment, the quality of the end product, and the overall performance of the process operation. Mitigating these potential consequences of moisture in industrial processes necessitates understanding its fundamentals.

The following blog post provides an overview of moisture, outlining its unique properties and why measuring its levels in industrial processes is important.

Fundamentals of Moisture

Like with temperature, pressure, and fluid flow, project managers and equipment operators must account for moisture when planning and performing a process operation. However, unlike these other variables, moisture offers the following challenges:

  1. In dynamic processes, it is more difficult to accurately and consistently measure.
  2. It serves as a contaminant that often results in more severe damage to process equipment, end products, and industrial processes.

These two qualities underline the importance of acquiring a comprehensive understanding of moisture to control its presence in industrial processes more effectively.

Why Measure Moisture?

humidity-group-newMoisture exists naturally in industrial gases and the surrounding environment. Within controlled industrial settings, industry professionals generally consider this moisture as an undesirable contaminant as it significantly impacts the quality and consistency of a process. If left unchecked, excess moisture causes condensation, corrosion, and contamination, which may result in:

  • Penetration of the vast majority of surfaces, resulting in corrosion and/or loss of integrity
  • Interference with test results, potentially rendering them useless
  • Reduction in product quality
  • Damage to process tubing
  • Formation of ice in process equipment (at low temperatures)
  • Premature failure and wear of process equipment
  • Unexpected reactions between process substances such as chemicals or gases 

With these consequences in mind, industry professionals often implement protocols that accurately measure moisture levels to control or eliminate moisture as needed. Measuring and managing moisture allows them to:

  • Minimize the amount of damage experienced by process equipment
  • Increase the quality and consistency of end products
  • Reduce energy usage and related costs
  • Lower overall operational costs

Altogether, the above advantages of measuring moisture levels in process operations allow companies to better meet contractual obligations, often resulting in greater customer satisfaction, enhanced brand reputation, and higher profits.

Contact Servoflo for Your Moisture Measurement Needs

At Servoflo, we understand how critical moisture levels are to the success of a project. Our broad selection of humidity sensors and other sensing tools facilitates the accurate measurement of moisture in processes regardless of the industry or application. For design engineers or original equipment manufacturers (OEMs), we offer a variety of durable, reliable, and versatile elements suitable for use in moisture or humidity measurement instrumentation, including:

To learn more about our sensor offerings, contact us today. If you need assistance choosing one for your next equipment build, request a quote. One of our knowledgeable team members will be glad to assist you with any concerns that you may have. 

Topics: Humidity Sensors

Important Details to Know When Selecting a Ceramic Pressure Sensor

Posted by Seta Davidian on Jan 11, 2019 1:29:55 PM

Ceramic pressure sensors are utilized in a variety of ways across numerous industries – but not all sensors are created equal. While all serve the function of measuring the pressure of liquids and gases, their applications range as far as measuring oil levels in the automotive industry to supporting life-saving medical devices.

Cover imageCeramic sensors can operate in harsh environments with extreme pressure and temperature factors at play due to their robust, stable, and cost-efficient nature. They are also valuable in applications where harsh chemicals may be present. As such, ceramic pressure sensors often present the best solution for difficult measuring applications. Many types of ceramic pressure sensors exist to address a broad range of challenges in numerous industries.

Types of Ceramic Sensors

Servoflo offers a wide range of ceramic pressure sensors that can used to measure pressure rates or fluid levels. From full transducer packages to smart metering systems, our range of ceramic sensors provide solutions for every potential application.

Flush Mount vs. Monolithic

Flush mount sensors are flat, smooth, and feature no dead volume of media pressure. Monolithic sensors, on the other hand, have an indentation in the side that is exposed to the pressure media. Flush mount solutions from Servoflo offer a wider range of pressure tolerances, from 0.5 bar to as high as 600 bar.

Which sensor you choose will be determined by your application requirements, as flush and monolithic mounts each have strengths in different areas. For example, a flush mount would be ideal if sealed gauge or absolute sensors are required by the application, while monolithic sensors are often ideal for a range of industrial automation or process control applications.

Piezoresistive vs. Capacitive

Servoflo's Metallux line of ceramic pressure sensors are, either piezoresistive or capacitive by nature. Both are resistant to corrosion and compatible with a wide array of environmental conditions and suitable for various industrial, automotive, or medical applications.

Capacitive sensors are often preferred for applications that feature high overpressure values but also require accurate low pressure measurement or high resolution measurements.

Differential Pressure Sensors

me800-headerThe ME800 ceramic differential pressure sensors measure differential pressure using a single sensor rather than two. This saves on cost and improves accuracy by narrowing down the possibility of error. Should errors occur, a single sensor makes them easier to pinpoint, which helps you to repair, replace, or recalibrate equipment quickly and limit costly downtime.

Amplified vs. Unamplified

If you'd prefer to calibrate and amplify your own sensors, we offer sensors with a millivolt of output that provide a blank slate for your design. This option gives you the freedom to amplify your own transducer signal and allows you to maintain control over both pressure range and output frequency.

For users who don’t require advanced customization or are simply seeking a standardized solution, we also have calibrated, temperature-compensated sensor models that are amplified and ready for use. We can provide ratiometric, non-ratiometric, current loop, and I2C sensors that integrate directly into existing systems and provide a wide range of sensitivity suitable for myriad applications.

Ratiometric vs. Non-Ratiometric

Amplified units consist of ratiometric and non-ratiometric sensors. Which of these two models will be appropriate depends largely on the voltage requirements of the application. Generally, lower voltage applications (0.5V to 4.5V) should choose a ratiometric sensor, while applications that use 12V or more should use a non-ratiometric sensor.

Choosing the incorrect solution for your voltage requirements will impact the reliability of digital conversion readouts.

Ceramic Pressure Sensor Sizes

9-mm-header-1Servoflo's sensors come in a variety of sizes, ranging from 9 mm (model ME900) in diameter up to 32.4 mm in diameter. The 9 mm sensor is an exciting addition to the Servoflo line of pressure sensors because it provides an ideal solution for small spaces and applications which otherwise may have been too constrictive for simple installation. The 9 mm solution comes pre-calibrated and pre-amplified, so customers must only add a cable to begin using it.

Ceramic Pressure Sensor Solutions from Servoflo

Choosing the proper ceramic pressure sensor solution can be an intimidating process—especially when your application requires precise readings. It’s often best to consult with a sensor expert in advance of your purchase to make sure you get the ideal solution for your needs.

For more information and deeper insights, please download our eBook: Ceramic Pressure Sensors 101.

Ceramic-Pressure-3D

Download Our Ceramic Pressure Sensor Guide

Topics: Ceramic Pressure Sensors

How to Select a Humidity Sensor

Posted by Seta Davidian on Dec 13, 2018 8:47:37 AM

Humidity sensors are an important piece of equipment in the medical, automotive, HVAC, and food production industries, among others. Any industrial facility that requires a controlled atmosphere requires a properly functioning humidity sensor. Whether your requirements for maintaining or reducing humidity levels are for safety, function, environmental control, or comfort, it's important that you choose the most appropriate sensor for the job.

Choosing a Humidity Sensor

head-digital-humidity-elements

By knowing what questions to ask when choosing a proper humidity sensor for your situation, you can ensure successful operation and longer life for your equipment. The first step is to know your budget and assess your needs. Some of the factors to consider here include:

  • Size, accuracy, and interchangeability
  • Long-term stability needs
  • Repeatability requirements
  • Required resistances of the sensor to any chemicals or contaminants it will be exposed to

It is also important to understand the different types of humidity sensors available to choose from.

  • Resistive humidity sensors measure an electrical change that can be caused by a conductive substance. These systems use electrodes and AC excitation voltage to produce a data value for relative humidity.
  • Thermal conductivity humidity sensors measure absolute humidity. They do this by calculating the difference in the conductivity of dry air compared to air that contains water vapor. These sensors use thermistor elements to form a bridge circuit and measure the difference in resistance.

Selecting the Right Humidity Sensor for Your Application

Choosing the most appropriate humidity sensor for your application can help ensure the cost-effectiveness and success of your project.

  • Accuracy

The first aspect you should examine is the level of accuracy you need.  The more accurate the sensor needs to be, the higher the cost will be.

  • Interchangeability

Cost can also be affected by the interchangeability of the sensor, which may cause vibration and lead to additional costs for calibration. 

  • Condensation

If condensation is present, you may also need to factor in the cost of condensation resistant filters.

  • Packaging

Package type can impact cost savings if you choose a combined humidity and temperature sensor instead of two separate sensors. 

  • Power

Power consumption will have overarching long-term effect on costs.

Different applications will have additional considerations that must be reviewed.  Industrial applications have to consider the environment of the system and whether or not the sensor is resistant to chemicals or contaminants. For example, healthcare applications often require precise conditions and accurate, repeatable measurements, as well as the ability to maintain a clean environment. Similarly, humidity sensors are critical in HVAC and transportation applications to prevent excess moisture that fosters bacteria and mold growth. 

Other Important Considerations

When considering the purchase of a humidity sensor, there are a few logistical concerns that also need to be reviewed. Ask the following questions to help you narrow down the proper solution and provider: 

  • What are the lead times of the supplier and will you get your parts in time?
  • Does the supplier have a location close enough to provide in-person consultations and to deliver your product, or will the distance increase the lead time?
  • Do you have second source requirements in the event of a supply chain issue?
  • Can the supplier make a product unique to your specs or will they try to retrofit an existing product?
  • Are they willing to share data and guarantee their accuracy with a warranty and service policy?
  • Do they stand behind their products with technical support?
  • How does the price compare to the rest of the market when you look at the component, consultations, and long-term service provided?

Humidity Monitoring Solutions from Servoflo

As you can see, there are many factors to take into consideration when selecting a humidity sensor.  Not only do you need to make sure you’ve selected the right one for your application, but you also need to make sure that you select the right company.

Servoflo has been providing sensor solutions to a broad range of industries and applications for nearly 20 years. To learn more about what it takes to select the best humidity sensor for your project, check out our eBook here.

Humidity-Sensor-Guide

Download Our Humidity Sensor Selection Guide

Topics: Humidity Sensors

Humidity Sensors: Capacitive vs. Resistive

Posted by Seta Davidian on Oct 25, 2018 3:17:57 PM

Servoflo distributes a variety of capacitive and resistive humidity sensors for medical, HVAC, instrumentation, critical containment and other applications.  Some situations need precise and highly accuracy relative humidity (rH) measurement to maintain narrow, specific environmental conditions while others have a broad temperature range with wider tolerance ranges for rH measurement. This blog post explains the differences between capacitive and resistive relative humidity sensors and why to choose one type over the other.

humidity sensor

Capacitive Sensors

Humidity and dew sensors, also called hygrometers, are necessary when consistent environmental conditions are required to be maintained.  A capacitive humidity sensor is so named because it uses capacitive measurement, which relies on electrical capacitance. These are a common type of humidity sensors.

The capacitive sensor is composed of two metal plates, or electrodes, separated by a thin layer of non-conductive polymer film.  The film attracts moisture from the air and when the moisture makes contact with the metal plates it creates a voltage change.  The output voltage measurement is captured and can be displayed via an analog dial, output into another system, or converted into a digital reading that indicates the amount of moisture in the air.

The capacitive sensor is contained in a hygrometer to measure relative humidity. The sensor is one part of the system that also contains a probe, cable, electronics, and an output signal.  Together they function to accurately measure the entire humidity range from 0% to 100%.

Resistive Sensors

Resistive sensors work on a similar principle to capacitive sensors, where electrical change is measured to produce a value for relative humidity. However, the mechanism in this system is different. Although resistive sensors use a hygroscopic (moisture-absorbing) material similar to the capacitive system, the difference is that the measurement is of the resistance change in the material rather than the capacitance. 

In this case, the output voltage has an inverse exponential relationship to relative humidity. As with capacitive sensors, the data regarding the output voltage can be captured, stored, or converted. These sensors use cost-effective, scalable dielectrophoresis, in which a free-standing structure is created to house pre-patterned electrodes that are separated by a single crystalline zinc oxide nanowire (ZnO NWs).

The benefit of a resistive sensor is the high surface-volume ratio, which allows it to measure humidity changes in the environment up to 90% relative humidity at room temperature. These systems do have limitations, and as such are not optimal for measuring values below 5% RH.  Applications that favor a resistive sensor include automotive, smart food packaging, and relative humidity sensor networks.

Selecting a Humidity Sensor

Although the capacitive sensor and resistive sensor have the same goal in measuring humidity, they differ in their methods.  Capacitive sensors are considered to be more accurate and stable while producing repeatable results—however, their cost can be prohibitive, making them more suitable for medical type applications where precision is paramount.  The less expensive resistive sensors are more practical for situations where frequent measurements are taken that do not require extremely precise data.

For more detailed information about selecting a humidity sensor and the applications and industries these are frequently used in, download our eBook.  You can check out our full line of digital humidity sensors on our website here

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Download Our Humidity Sensor Selection Guide

Topics: Humidity Sensors

Why Use Ceramic Pressure Sensors

Posted by Seta Davidian on Jun 12, 2018 1:31:07 PM

Industry professionals employ pressure sensors in a variety of applications, ranging from aerospace to oil and gas to utilities. In many cases, they are subjected to harsh operating and environmental conditions, such as high pressures, corrosive compounds, and temperature extremes. For use in these circumstances, ceramic pressure sensors are a suitable option.

Pressure sensors are often employed to handle extreme conditions such as high pressures, corrosive atmospheres, and high temperature processes. Ceramic pressure sensors are an ideal alternative to conventional oil-filled pressure sensors under such circumstances.

Because of their unique construction and ceramic’s chemically inert nature, ceramic pressure sensors can withstand harsh atmospheric conditions without sacrificing performance. Robust, reliable, and washable, they are a durable and cost-effective solution to a variety of demanding applications.

The following blog post provides an overview of ceramic pressure sensors, outlining the benefits, types available, and applications.

Benefits of Ceramic Pressure Sensors

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Ceramic pressure sensors offer several benefits, including:

  • Greater strength and durability. Compared to their stainless steel counterparts, sensing diaphragms made of ceramic are 10x stronger. This quality results in greater durability and longevity. Ceramic’s superior resistance to abrasion further enhances these characteristics.
  • Lower cost. Ceramic diaphragms are less expensive to manufacture than stainless steel ones. This quality, coupled with longer service life, can result in significantly lower equipment costs.
  • Better corrosion and chemical resistance. Ceramic is chemically inert and corrosion resistant, making it highly compatible with most process materials.
  • Smaller environmental risk. Ceramic sensors do not contain oil, reducing their risk of negatively impacting the surrounding environment due to fluid leaks.
  • Higher temperature and pressure operating capacities. Ceramic is capable of withstanding greater pressures and temperatures than stainless steel. It also displays a broader range of sensitivity, with the ability to simultaneously measure low pressure while withstanding high overpressure.

The above qualities, among others, make ceramic pressure sensors well-suited for applications with harsh environments. Even when exposed to high pressures, extreme temperatures, corrosive compounds, or high levels of shock and vibration, they provide consistent and reliable performance.

Ceramic pressure sensors have many advantages over traditional stainless steel counterparts. Perhaps most importantly, they are significantly stronger than oil-filled diaphragms. Similarly, they can withstand high operating temperatures and pressures without losing sensitivity at low pressure values. They tolerate relatively high over pressures as well.

Since ceramic sensors do not rely on oil, the diaphragm can be thicker, and it does not carry the risk of a leak that could compromise an entire batch of sensors. Because they are sturdier, ceramic pressure sensors will not deviate from their calibrated setting even after multiple operating cycles, thus minimizing the risk of sensor drift. All these features make ceramic pressure sensors ideal for a large number of industrial applications, particularly if accuracy, dynamic range, and corrosion resistance are critical requirements.

Types of Ceramic Pressure Sensors

Ceramic pressure sensors are available in a wide range of designs, each suited for use in particular applications. Some of the most common ceramic pressure sensor variations include:

Flush Mount vs. Monolithic Sensors

The key difference between flush mount and monolithic ceramic pressure sensors lies in the surface design. While flush mount sensors provide a flat surface for exposure to the pressure media, monolithic sensors feature an indentation in the exposed side of the sensors. As flush mount sensors maintain a fixed reference, they are generally used for applications that require absolute or sealed gauge sensing.

Piezoresistive vs. Capacitive Sensors

Ceramic pressure sensors employ either piezoresistive or capacitive means to measure pressure. Piezoresistive sensors measure the changes in electrical current in direct correlation to changes in pressure on the diaphragm. Capacitive sensors measure pressure displacement by analyzing the difference in electrical frequency between two sensors. The latter type is preferable for applications that require measurement of low-pressure values under high overpressure conditions.

Amplified vs. Unamplified Sensors

Pressure sensors come with several amplification options—including ratiometric, non-radiometric, current loop, and I2C—each of which can be calibrated as needed. For users who wish to perform their own amplification and calibration, unamplified ceramic sensors are also available.

Ratiometric vs. Non-Ratiometric Sensors

Ratiometric sensors take into account the power supply when converting sensor output, allowing for more accurate measurement without the interference of power supply variation. Non-ratiometric sensors are used when the measurements are against an absolute reference and not affected by fluctuation of the power source.

When to Use Ceramic Pressure Sensors

me501-flush-mountCeramic pressure sensors are suited to a wide variety of industries. In the automotive industry, for example, they are often used to measure oil levels. Within the transportation industry, they are used to maintain hydraulic systems (which benefit from greater water resistance) and control emissions (where greater resistance to heat and corrosion may be necessary). They are also used to measure the flow rate of the working fluid in water reservoirs, waste water treatment plants, and other chemical processing plants.

Due to their superior resistance to corrosion, high pressures, and extreme temperatures, ceramic pressure sensors find use in a variety of industrial applications with harsh environmental and operating conditions. Typical industries that employ these devices include:

  • Automotive instrumentation
  • Chemical
  • Food and beverage 
  • Heavy manufacturing
  • HVAC
  • Oil and gas
  • Water and wastewater treatment  

The high strength of ceramic sensors makes them ideally suited for applications that feature a large number of pressure cycles. Because of ceramic’s chemically non-reactive nature, they can be used in HVAC systems to measure refrigerant levels and for flow measurement in the oil and gas industry. They are also inert enough for used in food and beverage industry to monitor ingredient flow.

High-Quality Ceramic Pressure Sensors From Servoflo

For decades, Servoflo has served industry with quality pressure sensor support, optimization, and system design services. With customers from every major industry, ranging from aerospace to waste management, we have the knowledge and experience to provide ceramic pressure sensors that suit any requirement.

For the last 30 years, Servoflo has offered technical support, product optimization, and system design services to users of pressure sensors in every major industry. Trusted by companies of every size, our pressure sensors can handle difficult applications with accuracy and efficiency.

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In particular, our ceramic sensors offer unmatched quality and reliability in industries ranging from aerospace to waste management. Regardless of your demands, Servoflo can help you meet any requirement.

If you’d like to learn more about Servoflo’s ceramic pressure sensors or discover how they can improve your business, download our “Ceramic Pressure Sensors 101: Why, When, and Where to Use Them” eBook today.

Topics: Ceramic Pressure Sensors, Sensor Solution