Key Considerations for Flow Sensor Measurement

Posted by Seta Davidian on Mar 7, 2018 3:05:32 PM

To obtain accurate, precise flow measurements, it’s critical to select the proper MEMS mass flow sensor for the specific application at hand. When choosing a flow sensor, accuracy, sensitivity, and size should all be kept in mind, along with a range of other key factors.

Flow sensors play a crucial role in many different applications and industries, such as chemical and semiconductor manufacturing, medical device manufacturing, and natural gas metering.

fs1015cl.jpgThermal mass flow sensors, in particular, offer numerous advantages, including:

  • Small size
  • Fast response time
  • Low power consumption
  • High sensitivity to low flow rates

Operating independently of density, pressure, and viscosity, these devices generally consist of upstream and downstream temperature sensors and a heater located between them.

When selecting a MEMS thermal flow sensor, the following measurement considerations should be kept in mind: mass flow rate vs. volumetric flow rate, mechanical flow channel diameter vs. flow rate, and the nominal operating flow rate of the products.

Mass Flow Rate vs. Volumetric Flow Rate

MEMS flow sensing products typically measure the mass flow rate, which is automatically compensated for changes in temperature and pressure. Mass flow rate always is referenced in relation to the standard condition of a specific temperature and pressure.

The reference pressure is typically 101.325 kPa, or 14.5 PSI; the standard temperature may vary, at 0°, 15°, or 20 °C. The manufacturer will specify the conditions in the user manual. The default reference temperature for current Siargo products, for instance, is 20 °C, which can be customized upon request.

Mechanical Flow Channel Diameter vs. Flow Rate

All flow measurement products are packaged with a flow channel to ensure optimal performance; therefore, it’s critical to select the proper flow channel for the desired flow rate measurement.

It’s generally not recommended that users measure a high flow rate in a small channel or a small flow rate in a large channel. Also, the product’s flow channel should not be connected to a different size system channel. However, if there is no option but to alter the flow channel size, the product’s flow channel size should always be smaller than that of the system channel.

Nominal Operating Flow Rate of the Products

Flow sensors normally have about a 20% margin for the specified full-scale flow rate. However, it’s recommended that users select a full-scale flow rate that falls within the application’s maximum flow rate in order to ensure optimal performance and reliability.

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When dealing with low flow rate accuracy, sensor products have a default range of over 100:1, allowing them to meet most applications’ requirements. Most of today’s products do not offer a bidirectional flow rate measurement option, but this can be customized as needed.

Learn More

For further assistance in picking the right flow sensor for your specific application, and to learn about other key considerations to keep in mind during the selection process, download our free eBook, “MEMS Mass Flow Sensor Selection.”

Topics: Mass Flow Sensors

Sensor Design Engineering Services

Posted by Seta Davidian on Sep 26, 2016 11:48:16 AM

gauge.jpgServoflo, a premier supplier of pressure, mass flow, environmental sensors and micropumps,  is pleased to announce expansion of its design engineering services for custom sensor development. The objective is to be a primary resource for customers who require modification or customization of sensors and how they are integrated into product designs. Services include but are not limited to:

  • adding flex to a sensor
  • creating a custom flow path for mass flow sensors
  • adding Wi-Fi or BlueTooth™ capabilities to a sensor
  • adding a display
  • custom packaging enclosures
  • hybrid circuit design

flex.jpgThis one-stop solution provides customers with efficient and reliable design expertise without having to manage multiple vendors as well as streamlining assembly. Purchasing a complete solution saves customers money and time. Often, a bill of materials is reviewed and pressure is put on individual component costs. This strategy neglects the labor needed to inspect, integrate, and test various separate components such as a sensor element, cable, and package. A complete sensor solution can actually reduce overall bill of materials and labor costs. This sensor design strategy is also important for customers who may not have design expertise in these areas.

Specific application examples include:

  • Creation of a pressure gauge with display and enclosure
  • Hybrid circuit design to integrate a pressure sensor and electronics for better protection in a high temperature and high humidity environment
  • Adding a flex cable to a standard board level sensor to eliminate the assembly and testing steps at installation
  • Customized sensor calibration and output to meet a specific customer requirement
  • Design of a special flow path in a mass flow sensor for medical equipment
  • Design custom electronics to create a pressure or mass flow switch (or other environmental sensor)

If you have a special requirement you would like to discuss, please utilize the button below for fastest response.

 Discuss a custom solution

Topics: Pressure Sensors, Ceramic Pressure Sensors, Mass Flow Sensors

Mass Flow Sensors for Anesthesia Machines

Posted by Seta Davidian on Apr 7, 2016 1:23:50 PM

Mass Flow Sensor FS4008General anesthesia machines typically deliver a cocktail of gases to a patient to ensure sedation during surgery. Nitrous oxide (also known as laughing gas) and other gases are mixed with oxygen and delivered to the patient. The buffer area shown in the drawing below is where the combination of nitrous oxide and oxygen is mixed together. Here, the anesthesiologist needs to be aware of the mix of gases that is appropriate to the patient. At times, the combination needs to be adjusted depending on patient requirements.

To control the level of oxygen and nitrous oxide delivered to the buffering section of the anesthesia machine, it is necessary to measure the volume of each gas. In the drawing below, the FS4008 mass flow sensor is shown as a method to measure and monitor the various gas levels. The FS4008 comes in various flow ranges from 0-10 SLPM up to 0-50 SLPM. Available outputs include linear voltage or digital RS232 or RS485, allowing for the FS4008 to be easily integrated into a control system for the various gases. The flow channel diameter is 8 mm, and there are exchangeable mechanical connectors for ease of installation (BSPT thread and one-touch connectors).Slide2.jpg

 

At the delivery location of the gas mixture to the patient, another flow measurement point is needed. Here, the FS6022 mass flow sensor can play an important role in ensuring gases are delivered to the patient and then subsequently exhaled. Because the FS6022 has bi-directional measurement capability, it is ideal for use in the scavenging portion of the anesthesia machine, which expels the used gas from the patient's lungs.  For details about the FS6022, you can also review our blog post: Mass Flow Sensors for Medical Ventilators

In summary, measuring and monitoring mass flow of gases in anesthesia equipment is a critical part of patient comfort and surgery success. Not only is it important to measure the mix of anesthesia gases, it is also vital to measure delivery of the gases to the patient.

You can learn more about mass flow sensors here or download our mass flow product & pricing guide.

Download Mass Flow  Product & Pricing Guide

 

Topics: Mass Flow Sensors

Mass Flow Sensors for Medical Ventilators

Posted by Seta Davidian on Feb 23, 2016 9:39:29 AM

A ventilator uses pressure to blow air or a mix of air and oxygen to a patient. This blog post describes how the FS1015FL (shown on the left below) and FS6022 (shown on the right below) mass flow sensors are used in medical ventilators. These mass flow sensors are members of the new Siargo line which Servoflo is now offering.

mass flow sensor fs1015clmass flow sensor bi-directional bidirectional fs6022 

Both of these mass flow sensors use a MEMs sensor chip based on the calorimetric principle. The chip is packaged in a special way to receive laminar flow. The sensor chip has a micro heater and a pair of sensors upstream and downstream. When gas flow passes over the sensor chip, it brings the heat from upstream to downstream. Mass flow rate is calculated by measuring the temperature differences from the upstream and downstream sensors.

The illustration below shows how the mass flow sensors are installed inside the ventilator. The inlet air and oxygen is mixed and delivered to the buffer and valve. The FS1015CL sensors are calibrated for either 0-100 SLM or 0-150 SLPM. The flow rate of air/oxygen is measured to ensure the correct amount is delivered to the patient. The FS1015 has a 5V supply with a linear voltage output or an I2C interface. Standard ISO 15 mm medical connection is available. 

mass flow sensors in medical ventilators

 

The FS6022 is a mass flow sensor with a bi-directional option. Ranges include up to 250 SLPM or 300 SLPM. Having a standard voltage output, the bi-directional model provides a 2.5 to 5V output for the positive full-scale flow rate and 2.5 to 0 V for the negative flow rate.  Here, the FS6022 is used to monitor the inhalation and exhalation of the patient. 

These sensors can be sterilized in medical liquids.

Review:

We have a recently updated mass flow sensor product & pricing guide which includes these models. 

Download Mass Flow  Product & Pricing Guide

Topics: Mass Flow Sensors