Pressure & Oxygen Sensors in Oxygen Concentrators

Posted by Seta Davidian on Jan 7, 2016 10:51:57 AM

An oxygen concentrator is a medical device to deliver oxygen to a patient. A typical concentrator consists of a compressor, absorption columns with air filters, circuitry, a product tank and regulator. Oxygen concentrators differ from machines delivering compressed oxygen from tanks filled at a separate location. Instead, an oxygen concentrator takes standard room air, filters out the nitrogen and other gases, leaving oxygen to be delivered to the patient.

The block diagram shows a design of a typical oxygen concentrator. Pressure and oxygen sensors are used at various points to ensure proper creation and delivery of oxygen. For example, a pressure sensor is used at the product tank to measure the tank's level and to ensure there is proper flow moving into the regulator.



Often times there is also a pressure sensor between the regulator and outlet oxygen. A stationary oxygen concentrator may use a pressure sensor in the 50 kPa rap-ag-sensors-ad.jpgange to detect a kink in the tubing. (See AP2/AG2 analog pressure sensor or AP3/AG3 pressure sensor with threshold detection). For portable oxygen concentrators, a pressure sensor in the 1 kPa range is used to detect inhalation which then controls the regulator. Here, it is important to use a pressure sensor that is sensitive enough to detect the low flow rate of breathing but can also withstand high overpressures. The AL4 is a good option meeting this requirement.

oxygen-sensor-element-single.pngFinally, and perhaps most obviously, an oxygen sensor can be installed to sense the oxygen percentage of the air being delivered to the patient. The oxygen sensor allows the designer to create alarms and set points for the filtering portion of the concentrator.

The abundance of sensing technology has allows for the development of more flexible medical equipment with more features and functionality. This description of oxygen concentrators is one example of where the evolution of technology has created better health for all.

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Topics: Pressure Sensors, Oxygen Sensors

Oxygen Sensors - How They Work & Where Are They Used

Posted by Seta Davidian on Dec 10, 2015 2:06:44 PM

Oxygen measurement is critical in a wide range of applications. From ensuring enough oxygen exists for life sustainability and development, to monitoring harmful and dangerous gases, oxygen sensing can be found in medical equipment, HVAC systems, industrial processing, instrumentation, and the new exciting field of additive layer manufacturing with metals and alloys.

oxygen sensorThe oxygen sensors offered by Servoflo are a zirconium-based sensor. The sensing element is heated to more than 350°C which allows oxygen molecules to penetrate the sensing chamber. A voltage is applied to pump the oxygen out of the chamber. The measurement current produced is proportional to the quantity of oxygen molecules pumped away. 

Key advantages of the zirconium-based approach include:

  • Long-term stability with minimal drift
  • The operating lifetime of the sensor is greater than 4 years
  • Temperature operation up to 300°C
  • Ambient pressure has no effect on oxygen measurement, eliminating the need for pressure compensation

Stand-alone oxygen sensors with a raw signal output are available. Users have to take the sensor signal and provide compensation and amplification. Alternatively, Servoflo is offering signal conditioned sensor modules with either an analog or digital signal output, the FXC-MLxx or FCX-MCxx Series.fcx-ml.png

The FXC-ML or FXC-MC has the following features:

  • Can be configured for flow (force air into the sensor) or diffusion operation (sitting open-ended)
  • Configurable for analog output or digital output
  • Sensor head and connecting cable can be configured for 200°C
  • Measurement ranges include 0.1-25% and 0.2-95% O2
  • Accuracy of ±0.5% FS
  • High quality Swiss manufacturing
  • Standard off the shelf modules can be easily customized to meet your specific requirements
0.1 to 25% O2 0.1 to 25% or .2 to 95% O2
24VDC supply 24VDC Supply
4-20 mA output (logarithmic) Linear analog of 0-10V, 0-20 mA, 4-20 mA included. Digital outputs available.
Learn more about FXC-MLxx Learn more about the FCX-MCxx

A wonderful aspect of these products is the ability for customization of many features. Here are some examples of customized versions of the FCX-ML/MC oxygen sensor modules:

CO2 incubators/cell culturing: The customer required I2C only for an output, and a sensor head to withstand 200°C while the cable and sensor head connector needed to withstand 180°C. 

Critical containment and ventilated small animal enclosures: A customer required an RS485 output with DIN41612 for rack mounting.

Additive layer manufacturing with metals and alloys: 3D printing with metals and alloys is a new, growing field. The quality of the finished part is directly proportional to the oxygen concentration (the lower the better, ideally >1%). Special cable terminations were provided to prevent EMC issues.

Additional examples of customization are shown in the image below.

oxygen sensor customization

Should I use the oxygen sensor element only or buy a packaged solution? The answer is, it depends. A packaged solution such as the FCX-ML or MC is great for users who need to find a quick solution to evaluate the oxygen sensor without having to create electronics and circuitry. If a user has in-house expertise to compensate the raw signal, provide the electronics and desired packaging, then purchasing the sensor alone is a viable option. The packaged solution is great for those with limited resources to develop electronics and need help with packaging and design. Here, you can let Servoflo solve your sensor integration issues for you.

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Topics: Oxygen Sensors

Key Advantages of New Ultra Low Pressure Sensors

Posted by Seta Davidian on Oct 22, 2015 9:56:21 AM

ultra low pressure sensorsContinuous improvement in MEMS pressure die has allowed for the development of ultra low pressure sensors in small packages. Fully calibrated and compensated, these pressure sensors can measure as low as 0.07 psi (5 mbar), and come in gauge or differential packages with an I2C output.

Previous solutions for measuring low pressure include large, bulky packages that are high in cost, large in size, and a cost prohibitive price for high volume applications. This new generation of ultra low pressure sensors provides the following key advantages:

  • High working and burst pressures
  • Long-term stability over time
  • Wide temperature compensation
  • Simplified system calibration
  • Interchangeability of sensors
  • Low voltage supply
  • Insensitive to mounting orientation

These important features have opened up new applications in many areas, including:

  • Medical - respirators, sleep apnea, and more
  • HVAC - VAV controls, portable devices, and critical containment such as cleanrooms, fume hoods and biological safety cabinets
  • Pneumatic devices and other industrial controls
  • Consumer applications
  • Transducer development

Here are some examples of ultra low pressure sensors now available.

SM9543 - Differential pressure sensor wtih ranges as low as±0.07 psi (±5 mbar), I2C interface, 3 - 3.6V power supply, accuracy of ±1.5% full-scale. JEDEC SOIC-16 package (about 10 mm x 10 mm). Temperature compensated from -5°C to +65°C. Burst pressure of 3 psi.

SM9541 - Similar to SM9543 with slightly higher pressure ranges from 0.14 psi up to 2 psi. Gauge and differential available. Burst pressure varies with calibration range from 3 psi up to 15 psi.

AL4 - Gauge pressure sensor for 0-20 mbar (0-2 kPa) up to 100 mbar (10 kPa). I2C interface, supply voltage options of 3V, 3.3V, 5V.±1.5% accuracy. High load pressure of 100 kPa. Size of 11.36 mm x 10.32 mm. Modified calibration ranges available.

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Topics: Pressure Sensors

Pressure Unit Conversion Tool

Posted by Seta Davidian on Oct 19, 2015 1:03:24 PM

This is self-explanatory...Bookmark it for quick reference!

Courtesy of



Topics: Pressure Sensors

How to Measure Negative Pressure Using a Gauge Pressure Sensor

Posted by Seta Davidian on Sep 29, 2015 11:55:33 AM

For many negative pressure or vacuum pressure applications, 2 types of pressure sensors are available: gauge sensors or absolute pressure sensors. The reference pressure is the differentiating factor between these 2 types of sensors. The diagram below illustrates how the different methodologies work.

measuring negative pressure using a gauge pressure sensor

Absolute pressure sensors reference a vacuum, or zero pressure, and their full-scale pressure range is atmospheric pressure, which is about 14.7 psi at sea level (see item A). Hence, users have the capability of measuring up to negative 14.7 psi range of pressure.

SM9541 dual port gauge pressure sensorIn the case of a gauge sensor,  either a single port or dual port model can be used. In the case of a dual port gauge sensor, the "lower pressure" port measures the negative or vacuum pressure (B). By accessing the "lower pressure" port, the user is mimicking applying a positive pressure to the higher pressure port as in pressure range (C). The advantage of using a gauge sensor is if the user wants to measure a vacuum smaller than the full vacuum range 14.7 psi, such as -3 psi, using a lower range focusing on the negative pressure range is more appropriate. This way, by using a smaller full-scale range pressure sensor, the user captures the the full-range of the vacuum pressure measurements, thus obtaining more resolution and more design flexibility. For a single port gauge sensor, the single port is vented to atmosphere.

For example, if a user is trying to measure the inhalation pressure in a respiratory application, the pressure range would be no more than 0.6 psi. If an absolute pressure sensor is used, only 4% of the pressure range would be used, hence wasting 96% of the sensor's calibrated range. By using a gauge sensor such as the SM9541 Series, the user can capitalize on higher resolution and measure smaller negative pressure ranges.

Examples of classic applications where negative pressure measurements are needed include negative wound pressure therapy, breathing applications, pump control/performance monitoring, HVAC applications such as filter monitoring and pressurized rooms such as cleanrooms and isolation rooms.

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Review gauge pressure sensors under 4" of water

Review gauge pressure sensors between 4" of water & 3 psi

Topics: Pressure Sensors

Next Generation Sensor Signal Conditioning IC: ZSSC415X With Analog Output

Posted by Seta Davidian on Sep 21, 2015 11:53:00 AM

zssc4151-headerThe  ZSSC415X SSIC family is the newest offering to help users simplify sensor design, reduce external components,  minimize board space, and provide a faster migration to production. This sensor signal conditioning IC is ideal for those using pressure sensors, strain gauges, and RTD temperature sensors.

Key features include:

  • Capable of measuring full resistive bridge sensors and internal or external temperature sensors with analog output
  • Overvoltage reverse battery protection of +/-40V, making the ZSSC415X one of the most robust sensor signal conditioners available
  • Small QFN24 package with option for TSSOP14
  • Large sensor offset correction using digital zooming with 17-18 bit resolution
  • AEC-Q100 qualified and with extended diagnostics to allow for ASILB, an automotive safety standard
  • Robust EMC performance

Typical applications include but are not limited to: automotive applications including power steering, fluid level measurement, emission control and industrial applications such as factory automation, machine tools, bulk material storage.

ZMDI SSIC solutions are designed to specifically enable sensors to become more energy efficient. A wide variety of SSIC solutions are available to help users create efficiently optimized sensor solutions for medical, automotive, HVAC, industrial and intelligent sensor networking. The block diagram is below.

zssc4150-block-diagramWe have worked with ZMDI for many years and have always been impressed with their high level of support and superior technical expertise. We hope you think so too!

Learn more about the ZSSC415X

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Topics: Sensor Signal Conditioning

1 Sensor Measures Pressure, Humidity & Temperature!

Posted by Seta Davidian on Aug 19, 2015 11:09:00 AM

pressure humidity temperature sensorSensors are rapidly changing with increased functionality in MEMs technologies.  The new MS8607-02BA01 exemplifies how new technology is creating amazing new sensors.

The MS8607 measures pressure, humidity and temperature in a small QFN package measuring only 5 mm3 x 3 mm3 x 1 mm3. Inside this small package is a piezoresistive sensor providing pressure and temperature and a capacitive-type sensor for measuring relative humidity.  The measured signals are converted into a 24-bit digital value for pressure and temperature and a 12-bit digital value for relative humidity measurement.

The sensor requires 8 pads for operation, uses I2C communication and operates with a very low 1.8 to 3.6  supply voltage. With an operating pressure range of 10 to 2000 mbar, it has a pressure accuracy of ±2.0 mBar and pressure resolution of 0.016 mBar. For humidity, the measuring range is 0-100% rH with an accuracy of ±3% rH and a resolution of 0.04% rH. Finally, for temperature, the operating range is -40°C to +85°C with a temperature accuracy of ±2°C and resolution of 0.01°C.

The MS8607 is ideal for applications in the consumer and industrial marketplace, including smartphones, tablets, printers, HVAC applications, weather stations, home appliances, humidifiers and much more.

Learn more about the MS8607.

Get budgetary pricing for the MS8607 and other barometric pressure sensors offered by Servoflo.

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Topics: Humidity Sensors, Barometric Pressure Sensors

Why We Love the HTU20/21 Humidity Sensor Chips

Posted by Seta Davidian on Aug 4, 2015 12:40:35 PM

digital humidity sensor with PTFE filterThe HTU20/21 are tiny humidity and temperature sensors in a 3 mm x 3 mm x 0.9 mm DFN package. This tiny sensor packs a punch due to its:

  • Humidity operating range of 0-100%
  • Temperature range of -40°C to +125°C
  • Supply voltage of 0.3 to 3.6 VDC
  • Optional PTFE filter (F) option (shown in image on right)
  • No calibration required in standard conditions, allowing for full interchangeability
  • Instantaneous desaturation after long periods in saturation phase

Every sensor is individually calibrated and tested. The lot ID is printed on the sensor and an electronic ID is stored in the chip. Resolution can be changed by command from 8/12 bit up to 12/14 bit. A fast response time of 2 ms (using 8 bit resolution) up to 14 ms (using 12 bit resolution) gives designers flexibility in managing their humidity measurement.

HTU21D digital humidity sensor without filterFor temperature measurement, the accuracy is ±0.3°C at 25°C. The resolution is 0.01°C at 14 bit resolution and 0.04°C at 12 bit resolution.

The HTU20 has an accuracy of ±5% from 20-80% rH while the HTU21 has an accuracy of ±3% in that same humidity range. There are 2 output choices in each family: The P version has a pwm output while the D version has I2C. 

Best of all, the price of the HTU humidity sensors is extremely competitive. At 5,000 pieces, the price is between $1.46 to $1.95 each depending on the model.

Applications for the HTU20/21 family include medical, home appliances, printers, humidifiers, smart phones/tablets, indoor air quality and more.

Get the complete specification for HTU20/21.

Is this not the humidity sensor you are looking for? Then check out our complete line of analog and digital humidity sensors and transducers. We also have a product & pricing guide for your review.

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Topics: Humidity Sensors

Using a Restrictor to Pump Microliters Per Minute

Posted by Seta Davidian on Aug 3, 2015 9:41:00 AM

This blog post provides a summary of the application note: A Guideline for Operating Micropumps at Low Flow Rates.

mp6 piezo diaphragm micropumpThe Bartels mp6 micropump is a piezoresistive diaphragm micropump targeting flow rates up to 7 millileters per minute (ml/min) for liquids and 18 ml/min for gases with no backpressure and 600 mbar maximum pressure at no flow. Users can adjust the pumping rate by modifying the amplitude and frequency. 

To achieve low flow rates, the user should lower the amplitude. The consequence of doing this without a restrictor is that the generated pressure levels are also lowered which may be unsuitable. A minor pressure raise could also cause clogging since the maximum backpressure is too low to overcome. When a restrictor is applied (preferably to the pump exit), the flow rate is reduced by the fluidic resistance. That means with the maximum amplitude and optimal frequency, the flow rate is only as high as the restrictor allows. The pressure generation of the pump is the same as without the restrictor. (see the chart below).

flow rate with restrictor

The restrictor can be a short piece of narrow tubing (capillary) for a simple application or a precision orifice with an exact inner dimension. The application note focuses primarily on using capillaries as the user can adjust the flow rate by changing the length. Orifices come in preset dimensions - diameter and length - and it may not be possible to find the correct orifice for a specific flow rate.

Calculating the correct restrictor can be done by treating the pump as an electrical circuit, calculating the internal fluidic resistance of the pump, adding the restrictor as a resistor and applying the law of Hagen-Poiseuille to determine the resistance. The maximum flow rate is dependent on the total resistance of this system. Detailed steps are available in the application notes.

Once the restictor is finally set, it is then possible to vary the flow rate by changing the amplitude from the new restricted max flow to zero. The full range of the amplitude allows smaller flow rate steps with voltage changes than with the unrestricted pump. See the calculation results in the example below based on an mp6 pumping water.

how to pump microliters per min 

Possible capillary material includes PEEK tubing and polyimide (PI) tubing which is available in a wide variety of diameters and is readily available from many suppliers. PEEK and PI material are resistant to a wide variety of pumping media.

Download the complete application note

Visit the mp6  micropump specification page

Micropump Product & Pricing Guide

Topics: Micropumps

Understanding Ceramic Pressure Sensor Models

Posted by Seta Davidian on Jul 29, 2015 9:25:44 AM

ceramic-group-pressure-headCeramic pressure sensors by Metallux of Switzerland are high quality, high performing sensors for harsh environments and/or higher pressures (models up to 800 bar). With various models including piezo-resistive, ceramic capacitive, monolithic, flush-mount, compensated, unamplified and more, a user reviewing ceramic pressure sensors may want some help understanding the various options.


Piezo-Resistive Versus Capacitive: At a high level, Metallux ceramic pressure sensors are either piezo-resistive or capacitive pressure sensors. Why choose one over the other? Capacitive sensors are used when the pressure sensors must withstand high overpressures. In addition, capacitive models such as the ME550 (shown right) are very good at measuring low pressure down to 60 mbar. Both capacitive and piezo-resistive have similar chemical resistance and media compatibility.

me75xFlush Mount Versus Monolithic: In a flush mount sensor such as the ME77X Series, the sensor side exposed to the pressure media is flat and smooth. A monolithic sensor such as the ME75X has an indentation in the center of the exposed side. 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. Flush mount also come in lower (0.5 bar) and higher pressures (up to 600 bar). Flush mount ceramic sensors also have no dead volume of the pressure media.

Amplified or Unamplified: Another choice in ceramic pressure sensors involves whether or not to choose an amplified, calibrated sensor (ME75X, ME78X, ME790) or an unamplified model (ME501, ME504, etc). The choice depends on the users' requirements. For customers who do not have the capacity to amplify the signal and wanted a completely calibrated and temperature compensated sensor, Metallux offers many models with either a ratiometric, non-ratiometric, current loop, or I2C. The integrated signal conditioning lets users start using the sensors quickly. A user who is perhaps designing their own transducer will likely consider purchasing an unamplified model. Then, these users who typically have the experienced needed, can create a customized signal conditioning design based on their specific application requirements. 

Physical Size: Not all Metallux ceramic pressure sensors are the same size! The largest is the ME509 at 32.4 mm in diameter. The smallest is me ME657 at 12.85 mm in diameter. Many models are 18 mm in diameter.

Ceramic pressure sensors are a great choice if you are looking for higher pressures (up to 800 bar) in a harsh or wet environment. Gauge, sealed gauge and absolute models are also available. Strong chemical resistance due to the user of the AI2O3 ceramic lets users expose the sensors to a wide variety of environmental factors. Typical applications for Metallux ceramic pressure sensors include transducer development, tank level monitoring, process control and industrial automation.

We hope you found this blog post to be useful! Please feel free to reach out to us at with questions or comments. We welcome your feedback.

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Topics: Ceramic Pressure Sensors, Pressure Sensors

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