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

See all ZMDI Sensor Signal Conditioning IC's

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.

Download Barometric  Product & Pricing Guide

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.

Download Humidity  Product & Pricing Guide


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.

Download the metallux-family-tree here.

Download Ceramic Pressure Sensor Product & Pricing Guide

Topics: Ceramic Pressure Sensors, Pressure Sensors

Why Choose Fujikura Pressure Sensors Over Freescale?

Posted by Seta Davidian on Mar 23, 2015 10:12:00 AM

pressure sensorsIn the world of pressure sensors, users have a broad range of manufacturers and part numbers to choose from. Although detailed specifications on individual parts are easy to come by, we thought it would be nice to provide a comparison between the new AP/AG pressure sensors from Fujikura to various Freescale sensors, including the MPXV7025, MP3V5050(V)/MPX(V)5050(v), MPX(V)5100, and MPX5500. The following summary provides details on how Fujikura pressure sensors offer higher performance and more flexibility for users.

  • More input voltage flexibility: All Fujikura AP/AG sensors come in a 3V, 3.3V or 5V supply. The Freescale sensors models listed above come in some but not all supply voltages.
  • Pressure range choices: With a broad selection of ranges from +/-100 kPa up to 1000 kPa, Fujikura offers many more choices.
  • Customization: In addition, Fujikura is willing to offer custom calibration and custom outputs in quantities that are normally too small for other manufacturers.
  • Accuracy: Fujikura offers +/-1.5% full scale accuracy versus +/-2.5% or +/-5% for Freescale pressure sensors.
  • Additional models with threshold detection (AP3/AG3) or digital outputs (AP4/AG4) 
  • Lower supply current: Freescale sensors require a 10 mA supply current. Fujikura, on the other hand, has a supply current of 3 mA for the 5V supply and 2 mA for the 3V and 3.3V supply versions.

Fujikura's stocking distributor (yes, Servoflo) has over 30 years experience selling and providing technical support for Fujikura pressure sensors.

Typical applications for these parts include sleep apnea, oxygen conservers, blood pressure measurement, ventilators, industrial applications and more.

Our experience over the last 30 years selling Fujikura have shown that these pressure sensors are high quality yet cost-effective for customers. The ability to easily customize sensors for customers' specific needs is a powerful consideration when comparing pressure sensors. We are proud of our relationship with Fujikura and look forward to showing you why!

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Topics: Pressure Sensors

mp6 Micropump in Medical Device for Fast Detection of Hospital Germs

Posted by Seta Davidian on Sep 15, 2014 12:57:00 PM
mp6 micropump medical

The mp6 micropumps from Bartels Mikrotechnik GmbH are suitable for pumping liquids and gases for a variety of different applications. Here we are highlighting the use of the mp6 in a germ detection device used in hospitals.

Bartels and the Austrian Gesundheits-Cluster Oberösterreich worked together with the project goal being the automation of "Genspeed", a medical system for fast diagnosis of hospital germs of Greiner Bio-One International AG. The newly developed on-spot instant diagnosis device "Genspeed R2" is able to verify the existence of different infectious germs - including, among others, antibiotic-resistant bacteria such as MRSA at the human body - from different samples within 75 minutes.

mp6 micropumpTechnological core elements of the device are a microfluidic-chip and a miniaturized automated dispensing system based on the mp6 micropumps. Different reagents can be disposed with microliter accuracy into the inlet opening of the microfluidic chip. The controlled liquid volumes are precisely applied in the correct succession with testing results shown on a computer screen. This method delivers results much faster than the traditional diagnosis chain of sending a sample to a laboratory. This is a perfect example of the capability of microfluidics in respect to optimization of standard processes, reduction of waiting times - and therefore costs - as well as improving patient treatment response times. This system uses 3 mp6 pumps and 1 mp6-oem controller.

Learn more about the mp6 micropump and also try our product & pricing guide for micropumps.

Micropump Product & Pricing Guide





Topics: Micropumps

Why We Do Not Take Online Orders for Pressure Sensors

Posted by Seta Davidian on Aug 26, 2014 10:11:00 AM

pressure sensors

On our Servoflo website, you have likely noticed limited online ordering of pressure sensors. Even though we have a huge offering of pressure sensors from 0.1” to several thousand psi, there are specific reasons why we do not have an online store and parametric search for sensors.

Complexity of pressure sensor part numbers – Have you ever searched for a sensor and become completely overwhelmed figuring out the correct part number to order? Have you ever ordered a part and then realized after your purchase you made a mistake, and then had to order a different part?

Stock – have you had difficulty finding stock of a particular part, and then spent an afternoon browsing, clicking, and sorting through part numbers and manufacturers?

In short, trying to buy pressure sensors online can be a time consuming, frustrating experience. The sheer combination of permutations and combinations of part numbers make for nightmare scenarios for both purchasers and webmasters.

OK, so now after spending an afternoon browsing you may be completely confused by what you saw where. Now that you have come across various pressure sensors options (such as amplified versus unamplified), you may be wondering, what type of pressure sensor do I really need? What does this accuracy spec mean on this datasheet versus this accuracy spec from a different manufacturer? I need a specific package but I don’t see it…Let us show you how to get you out of this mess.

Just the other day, we received a telephone call from a potential customer. After 30 seconds of listening to the customer explain his application, David Ezekiel, our Vice President said, “I know exactly what you need, let me send you the detailed part information.” The customer was very appreciative and thankful for being put in the right direction. We knew how to answer his question because we had experience in his application combined with our vast knowledge of pressure sensors.

So, after you “Google” to find a pressure sensor supplier the next step is to “Servoflo it!”. Find the right sensor for YOUR application quickly and easily by either calling us at 781-862-9572 or emailing your specification through our sensor selector tool

Servoflo It!

Topics: Pressure Sensors

Sensors Expo 2014 Update

Posted by Seta Davidian on Jul 18, 2014 12:41:00 PM

UPDATE! Here is a short video clip of our booth and the products we showed! Thanks to Randy Frank at Design World for the video.


From June 25 to June 26, 2014, Servoflo exhibited at the Sensors Expo show in Chicago. We had a great time and thought it would be fun to share a couple of pictures of our booth.Servoflo Booth

The show was well attended, and booth traffic was busy on both days. We met many new customers interested in a wide variety of our products. Applications ranged from industrial, consumer, medical and more. It was interesting to see how many people traveled to come to the show, which also had many educational sessions. 

20140625 115510 resized 600

We enjoyed exhibiting next to our supplier ZMDI (a supplier of signal conditioning IC's, LED drivers, and power management IC's). Their special pink popcorn giveaway was very popular with booth visitors.

We hope to see you at next year's Sensors Show which will be held June 9 - 11 in Long Beach, California.

You can check out the official Sensors Expo highlights reel here.

(Above image is David Ezekiel of Servoflo providing visitors with sensing solutions!)

Topics: Sensors Expo, Pressure Sensors

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